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diff --git a/.gitattributes b/.gitattributes new file mode 100644 index 0000000..6833f05 --- /dev/null +++ b/.gitattributes @@ -0,0 +1,3 @@ +* text=auto +*.txt text +*.md text diff --git a/7981-8.txt b/7981-8.txt new file mode 100644 index 0000000..42ca80e --- /dev/null +++ b/7981-8.txt @@ -0,0 +1,6161 @@ +The Project Gutenberg EBook of Synthetic Tannins, by Georg Grasser + +Copyright laws are changing all over the world. Be sure to check the +copyright laws for your country before downloading or redistributing +this or any other Project Gutenberg eBook. + +This header should be the first thing seen when viewing this Project +Gutenberg file. Please do not remove it. Do not change or edit the +header without written permission. + +Please read the "legal small print," and other information about the +eBook and Project Gutenberg at the bottom of this file. Included is +important information about your specific rights and restrictions in +how the file may be used. You can also find out about how to make a +donation to Project Gutenberg, and how to get involved. + + +**Welcome To The World of Free Plain Vanilla Electronic Texts** + +**eBooks Readable By Both Humans and By Computers, Since 1971** + +*****These eBooks Were Prepared By Thousands of Volunteers!***** + + +Title: Synthetic Tannins + +Author: Georg Grasser + +Release Date: April, 2005 [EBook #7981] +[Yes, we are more than one year ahead of schedule] +[This file was first posted on June 8, 2003] + +Edition: 10 + +Language: English + +Character set encoding: ISO-Latin-1 + +*** START OF THE PROJECT GUTENBERG EBOOK SYNTHETIC TANNINS *** + + + + +Produced by Juliet Sutherland, Thomas Hutchinson, Charles Franks +and the Online Distributed Proofreading Team. + + + + + +SYNTHETIC TANNINS + +THEIR SYNTHESIS, INDUSTRIAL +PRODUCTION AND APPLICATION + + +by +Georg Crasser, Dr. Phil., Ing. +Lecturer in Tanning Chemistry +at the German Technical College, Brunn + + + + + + +AUTHOR'S PREFACE + +Whilst the synthesis of the natural tannins has been successfully +outlined by Emil Fischer, it has been left to the Chemical Industry, +notably the Badische Anilin und Soda-fabrik in +Ludwigshafen-on-the-Rhine, to discover the means of making possible the +production of the synthetic tannins. + +The scientific results of Fischer's researches are to-day common +knowledge, and these, together with questions arising therefrom, will +only be lightly touched upon in the book herewith presented. Even an +attempt at enumerating the present synthetic tannins has so far not been +published, and I have therefore availed myself of the opportunity of +making a brief summary of them. My work at the B.A.S.F. deepened my +insight in this new field; ample opportunity of applying these synthetic +products in practice was given me when, as a result of the war, I was +appointed technical consultant to the Austrian Hide and Leather +Commission, and in this capacity was called upon to act as general +adviser to the trade. The ultimate object of my scientific researches +was then to investigate the chemistry of this particular field, and this +has led me to present a picture, complete as far as it goes, of this +branch of chemical technology. + +The intention of the present volume is to communicate to the reader what +has so far been scientifically evolved and practically applied in this +field. First of all, however, it may illustrate the extreme importance +and the universal applicability of the synthetic tannins in the making +of leather. The modern leather industry cannot, to-day, be without these +important products, but also in those tanneries, where the synthetic +tannins have not so far been regarded as indispensable, their use is +strongly recommended. Just as in the case of the coal-tar dyes, the +synthetic tannins will make us independent of foreign supplies, and thus +keep within our own borders the vast sum of money required in former +days for the purchase of foreign tanning materials. May this book prove +the means of providing an incentive for a still wider application of the +synthetic tannins. + +GRASSER. + +GRAZ, _August_ 1920. + + + + +TRANSLATOR'S PREFACE + +Doctor Grasser hardly needs an introduction to the leather trade of this +country in its scientific aspect, but if one be sought for, none could +serve the purpose better than a translation of the book herewith +presented to the British-speaking public. + +Viewed with curiosity from their start, the synthetic tannins +needed--like many other important discoveries--an extreme emergency for +the purpose of showing their value. The Great War provided the +opportunity of which chemical industry was to avail itself, and to-day +we do not only see synthetic tannins placed upon the market as a +veritable triumph of chemical technology and a creditable triumph of +manufacturing chemistry; we also see their immensely practical qualities +established as a fact, and, as the author aptly remarks, no modern +tanner can to-day dissociate himself from the use of synthetic tannins +for the production of leather in the true sense of this word. There is +no branch of leather-making where synthetic tannins cannot help and +improve processes already established. + +The immense number of substances patented by German manufacturing +chemists for the purpose of producing synthetic tanning materials is +almost staggering. In view of this fact it is doubly pleasing to see +that British chemists have found new ways, and are able to produce +equally good and more varied synthetic tannins than has hitherto been +deemed possible. The originator of these products and his acolytes +must at least share the credit with those who, in spite of the +limitations necessarily set by the former, have been able to find new +and better ways. + +In his book Dr. Grasser gives a short review of the necessary forerunner +of any work upon synthetic tannins: the investigations and syntheses of +the natural tannins. It is certainly to be hoped that we may soon see +such works as those of Fischer's and Freudenberg's, recently published, +translated into English. For the guidance of the reader it may be noted +that a short account of the works of these authors may be found in the +_Journal of the Society of Leather Trades' Chemists_, vol. v. (May +issue); in addition to this some of the matter contained in the chapter +on synthesis of tanning matters appeared in the January 1921 issue of +the _Journal of the American Leather Chemists' Association._ + +In addition to these two sections, the last part of this book deals with +the practical applications of synthetic tannins, and it is hoped that +the tanner will find much valuable information in these pages. The main +outlines of the synthesis of tanning matters should prove of great value +to the chemist engaged in this branch of chemical technology. + +The translator takes great pleasure in the acknowledging the valuable +assistance rendered him by Mr. Robin Bruce Croad, A.R.T.C., F.I.C., and +by Mr. Arthur Harvey. + +F. G. A. ENNA + + + + +CONTENTS + +Introduction: Classification of Synthetic Tannins + +PART I +SECTION I + +The Synthesis of Vegetable Tannins + +1. Tannin +2. Digallic Acid +3. Ellagic Acid +4. Depsides + Carbomethoxylation of Hydroxybenzoic Acids + Chlorides of Carbomethoxyhydroxybenzoic Acids + Preparation of Didepsides + Preparation of Tridepsides + Preparation of Tetradepsides + Tannoid Substances of the Tannin Type + Chart showing the Decomposition of Products of Tannin + + +SECTION II + +Synthesis of Tanning Matters + +1. Aromatic Sulphonic Acids +2. Condensation of Phenols + Condensation of Hydroxybenzene + Condensation of Dihydroxybenzene + Trihydroxy benzene + Polyhydroxybenzenes + Quinone + Phenolic Ethers + Nitro Bodies + Amino Bodies + Aromatic Alcohols + Aromatic Acids +3. Condensation of Naphthalene Derivatives +4. Condensation of the Anthracene Group +5. Di- and Triphenylmethane Groups +6. Summary + +Table + + +SECTION III + +Tanning Effects of Mixtures and Natural Products + +1. Mixture of Phenolsulphonic Acid and Formaldehyde +2. Mixture of Phenolsulphonic Acid and Natural Tannins +3. Tanning Effects of Different Natural Substances + + +SECTION IV + +Methods of Examining Tanning Matters + + + +PART II + +Synthetic Tannins: Their Industrial Production and Application + +A. Condensation of Free Phenolsulphonic Acid +B. Condensation of Partly Neutralised Phenolsulphonic Acid +C. Condensation of Completely Neutralised Phenolsulphonic Acid +D. Condensation of Cresolsulphonic Acid +E. Relative Behaviour of an Alkaline Solution of Bakelite and + Natural Tannins +F. Dicresylmethanedisulphonic Acid (Neradol D) + 1. Neradol D Reactions + 2. Electro-Chemical Behaviour of Neradol D + 3. The Influence of Salts and Acid Contents + on the Tanning Effect of Neradol D + 4. Phlobaphene Solubilising Action of Neradols + 5. Effect of Neradol D on Pelt + 6. Reactions of Neradol D with Iron and Alkalies + 7. Reagents suitable for Demonstrating the + Various Stages of Neradol D Tannage + 8. Combination Tannages with Neradol D + (1) Chrome Neradol D Liquors + (2) Aluminum Salts and Neradol + (3) Fat Neradol D Tannage + 9. Analysis of Leather containing Neradol D + 10. Properties of Leather Tanned with Neradol D + 11. Neradol D, Free from Sulphuric Acid + 12. Neutral Neradol +G. Different Methods of Condensation as Applied to + Phenolsulphonic Acid + 1. Condensation Induced by Heat + 2. Condensation with Sulphur Chloride + 3. Condensation with Phosphorus Compounds + 4. Condensation with Aldehydes + 5. Condensation with Glycerol + +REGISTER OF AUTHORS + +INDEX + + + + +INTRODUCTION + +CLASSIFICATION OF SYNTHETIC TANNINS + +In laying down a definition of "Synthetic Tannins," it is first of all +necessary to clearly define the conception of "tannin." Primarily, +tannins may be considered those substances of vegetable origin which may +be found, as water-soluble bodies, in many plants, exhibiting certain +chemical behaviour, possessing astringent properties and being capable +of converting animal hide into leather. This latter property of the +tannins, that of converting the easily decomposable protein of animal +hide into a permanently conserved substance and imparting to this +well-defined and technically valuable properties, has become the +criterion of the practical consideration of a tannin. It appears that +different substances certainly show the chemical reactions peculiar to +the tannins, and to a certain extent also exhibit astringent character +without, however, possessing the important property peculiar to the +tannins of converting hide into leather. Such substances, in our +present-day terminology, are termed pseudo-tannins (_e.g._, the "tannin" +contained in coffee-beans). Decomposition products of the natural +tannins, to which belong, for instance, gallic acid and the +dihydroxybenzenes, exhibit the well-known reactions of the tannins +(coloration with iron salts), but they cannot be regarded as tannins +from either a technical or a physiological standpoint. + +As regards their chemical constitution, the natural (true) tannins +probably belong to different groups of organic compounds, and with our +present-day scant knowledge of their chemistry, it is impossible to +classify them. One is, however, justified in assuming that both the +natural tannins and the related humic acids are ester-derivatives of +hydroxybenzoic acids. [Footnote: E. Fischer, _Ber._, 1913, 46, 3253.] + +The production of synthetic tannins employs two quite distinct +methods; one is to synthesise the most simple tannin, viz., the +tannic acid contained in galls (tannin), or to build up substances +similar in character to the tannins, from hydroxybenzoic acids. The +other, entirely new way, is to produce chemical substances, which +certainly have nothing in common with the constitution of the natural +tannins, but which behave like true tannins in contact with animal pelt, +and in addition, since they can be manufactured on a commercial scale, +are of practical value. + +Owing to the fact that, until recently, the constitution of tannin has +remained unknown, it is easy to comprehend that the efforts to +synthesise the latter substance, or compounds similar to it, have been +mainly attempted on similar lines. The oldest investigation in this +direction dates from H. Schiff,[Footnote: Liebig's _Ann._, 1873, 43, +170.] who prepared substances similar to tannin by dehydrating +hydroxybenzoic acids. By allowing phosphorus oxychloride to interact +with phenolsulphonic acid, he obtained a well-defined substance +possessing tanning properties, which he considered an esterified +phenolsulphonic acid anhydride, the composition of which he determined +as HO.C_6H_4.SO_2.O.C_6H_4HSO_3. It is, however, probable that this +substance is not homogeneous, but consists of a mixture of higher +condensation products. + +Klepl [Footnote: _Jour. pr. Chem._, 1883, 28, 208.] obtained--by simply +heating _p_-hydroxybenzoic acid--a so-called di- and tridepside, but +this simple method is not applicable to many other hydroxybenzoic acids, +since these are decomposed by the high temperature required to induce +reaction. + +Amongst other attempts to produce condensation products with +characteristics similar to those possessed by the tannins, those by +Gerhardt [Footnote: Liebig's _Ann_, 1853, 87, 159.] and Loewe [Footnote: +_Jahresh. f. Chem._, 1868, 559.] must be especially noted; they treated +gallic acid with phosphorus oxychloride or arsenic acid, and thereby +obtained amorphous compounds, exhibiting the reactions characteristic of +tanning substances. E. Fischer and Freudenberg, [Footnote: Liebig's +_Ann._, 372, 45.] by treating _p_-hydroxybenzoic acid in the same way, +succeeded in obtaining a didepside, and during the last years +practically only these two investigators have demonstrated the syntheses +of these depsides and produced high-molecular polydepsides. + +At the same time researches were instituted with the object of +determining the constitution of tannin, and E. Fischer succeeded in +demonstrating its probable composition as being that of a glucoside +containing 5 molecules of digallic acid per 1 molecule of glucose. + +This last-named class of synthetic tannins--which may be properly termed +"tanning matters" in contradistinction to the true tannins--exhibit very +distinct tanning character when brought in contact with animal hide, but +from the point of view of chemical constitution have nothing in common +with the natural tannins. Not only are they of interest to the industry +from a practical point of view; they have also been examined very +closely from a chemical standpoint. + +It is, however, necessary to differentiate with great exactitude between +the conception of _true tanning effect_ and _pickling effect_ when +considering the action of chemical substances on pelt (i.e., animal +hide, treated with lime, depilated, and the surplus flesh +removed). Whereas any _true tannage_ is characterised by the complete +penetration of the substance and its subsequent fixation by the pelt in +such a way that a thorough soaking and washing will not bring about a +reconversion (of the leather) to the pelt state; _pickling_, on the +other hand, is only characterised by the penetration of the substance in +the pelt and fixation to such an extent that a subsequent washing of the +pickled pelt will bring back the latter to a state closely approximating +that of a true pelt. Simple as such a differentiation appears, there +are still a number of cases occupying a position between the two +referred to, and which we may term _pseudo-tannage_. An example of the +latter is formaldehyde tannage; formaldehyde has for a long time been +employed in histological work for the purpose of hardening animal hide, +by which it is readily absorbed from solution whereby it hardens the +hide without, however, swelling it. A hide which has thus been treated +with formaldehyde absorbs the natural tannins with greater ease; this, +on the one hand, argues the probability of formaldehyde acting as a +pickling agent; on the other hand, it is also one of its characteristics +that it will either in neutral acid, [Footnote: R. Combret, Ger. Pat, +112, 183.] or, still better, in alkaline [Footnote: J. Pullman, +Ger. Pat, 111,408; Griffith, _Lea. Tr. Rev._, 1908.] solution, convert +pelt into leather. In a formaldehyde-tanned leather, however, no trace +of tannin can be detected; and the yield (of leather, based on the pelt +employed), which, from a practical standpoint, is so important, is so +very low that it is hardly possible to speak of it as a tannin in the +ordinary sense of the word. Formaldehyde must, therefore, be termed a +pseudo-tannin. + +The tanning effect of formaldehyde is, according to Thuau, [Footnote: +_Collegium_, 1909, 363, 211.] increased by those salts which bring +about colloidal polymerisation of the formaldehyde, the resultant +compounds being absorbed by the hide fibre. Fahrion considers this to be +a true tannage, and is supported by Nierenstein [Footnote: _Ibid._, +1905, 157, 159.]:-- + + R.NH_2 R.NH-| + +O.C.H. = CH_2 + H_2O + R.NH_2 | R.NH-| + (Hide.) H (Leather.) + +A peculiar combination between true tannage and pickling is to be found +in the tawing process (tannage with potash, alum, and salt), whereby, +firstly, the salt and the acid character of the alum produce a pickling +effect, and secondly, the alum at the same time is hydrolysed, and its +dissociation components partly adsorbed by the hide, thereby effecting +true tannage. This double effect is still more pronounced in the +synthetic tannins which contain colloidal bodies of pronounced tanning +intensity on the one hand, inorganic and organic salts on the other, +which then act as described above. Their real mode of action can only +be explained with the aid of experimental data. The following chapters +will deal with the different behaviour of the various groups of +synthetic tannins. + + + + +PART I +SECTION I + +THE SYNTHESIS OF VEGETABLE TANNINS + + +1. TANNIN + +The first investigations of gall-tannin date from the year 1770, at +which time, however, no exact differentiation between tannin and gallic +acid was made. The first step in this direction was made when +Scheele,[Footnote: Grell's _Chem. Ann._, 1787, 3, I.] in 1787, +discovered gallic acid in fermented gall extract, and in the same year +Kunzemuller [Footnote:_Ibid._, 1787,3,413.] separated gallic acid (or +pyrogallol) as a crystalline body from oak galls. Dize [Footnote: +_Jour. Chim. et Phys._, 1791, 399.] continued the investigations, which +were brought to a conclusion with Deyeux' work [Footnote: _Ann. Chim._, +1793, 17, I.]; both recognised that the substance isolated was not a +single substance, but was a mixture of gallic acid, a green colouring +matter, a rosin (tannin?), and extraneous matter. Proust [Footnote: +_Ibid._, 1799, 25, 225.] was the first to differentiate the crystalline +gallic acid from the amorphous, astringent substance, which latter he +named "Tannin." + +Amongst the numerous subsequent investigations of tannin must be +especially noted the one by Berzelius [Footnote: Pogg,_Ann._, 1827, 10, +257.], who purified the potash salt and decomposed this with sulphuric +acid. Pelouze [Footnote: Liebig's _Ann._, 1843, 47, 358.], later on, +observed the formation of the crystalline gallic acid from tannin, when +the latter is boiled with sulphuric acid; this had already been observed +by J. Liebig.[Footnote: _Ibid._1843, 39, 100.] Both had noticed the +absence of nitrogen. In addition to the methods of preparation of tannin +then in vogue neutral solvents were mainly employed by subsequent +investigators; Pelouze [Footnote: _Jour. Prakt. Chem._, 1834, 2, 301, +and 328.] treated powdered galls with ether containing alcohol and +water, and considered the upper layer to be a solution of gallic acid +and impurities, the bottom layer to contain the pure tannin. + +The EMPIRICAL FORMULA of tannin has also been the subject of much +speculation by the different investigators, the difficulty here being +that of obtaining a pure specimen of the substance free from sugars, and +which could be submitted to elementary analysis. Whereas these early +purified substances were thought to correspond to the formula of +digallic acid (galloylgallic acid), C_14H_10O_9, Fischer and Freudenberg +[Footnote: _Ber._, 1912, 915 and 2709.] were able to show, with +approximate certainty, that the constitution of tannin is that of a +pentadigalloyl glucose. + +Early attempts at _hydrolysing tannin_ gave varying results, some +investigators claiming the presence, and others the absence of +sugars. Here, again, E. Fischer and Freudenberg [Footnote: _Ibid._] were +able to conclusively prove that on hydrolysing tannin with dilute acids, +7.9 per cent. glucose is dissociated, and that hence glucose forms part +of the tannin molecule. Fischer and Freudenberg also determined the +optical activity of pure tannin in water: [Greek: a]_D was found to lie +between +58° and +70°. + +Graham found [Footnote: _Phil. Transact._, 1861, 183.] that the _tannin +molecule_ is of considerable size, since its diffusion velocity is 200 +times less than that of common salt. Paternň [Footnote: +_Zeits. phys. Chem._, 1890, iv. 457.] was the first to determine the +molecular weight of tannin, employing Raoult's method; he found that +tannin in aqueous solution behaves like a colloid and that hence +Raoult's method is not applicable. When, on the other hand, he dissolved +tannin in acetic acid, results concordant with the formula of +C_14H_10O_9, corresponding to a molecular weight of 322, were +obtained. Sabanajew [Footnote: _Ibid._, 1890, v. 192.] later determined +the molecular weight of tannin in aqueous solution as 1104, in acetic +acid solution as 1113-1322, Krafft [Footnote: _Ber._, 1899, 32, 1613.] +as 1587-1626 in aqueous solution. Walden [Footnote: _Ibid._, 1898, +3167.] determined the molecular weight of tannin-schuchardt as +1350-1560, tannin-merck as 753-763, digallic acid as 307-316 (calculated +322). Feist [Footnote: _Chem. Ztg._, 1908, 918.] determined the +molecular weight of tannin as 615 and one of his own preparation as 746, +Turkish tannin as 521 and Chinese tannin as 899. In this connection it +should be noted that the calculated molecular weight of pentagalloyl +glucose, which in E. Fischer's opinion forms a substantial part of the +tannin molecule, is 940, but Fischer also thinks that this compound +possesses a much higher molecular weight. + +STRUCTURE OF TANNIN--The oldest structural formula of tannin is Schiff's +digallic acid formula:--[Footnote 1: _Ber_., 1871, 4, 231.] + + ---------CO.O.---------- + ^ ^ OH + | | | | + HO | | OH HOOC | | OH + V V + OH + +A drawback to the acceptance of this formula is the absence of an +asymmetrical C-atom; the formula, therefore, does not explain the +optical activity exhibited by tannin. Schiff attempted to overcome this +difficulty by adopting a diagonal structural formula, but even when +adopting Clauss' diagonal formula for benzene the optical activity of a +number of other compounds depends upon the existence of the asymmetrical +C-atom. Biginelli [Footnote 2: _Gazz chim. Ital_., 1909, 39, 268.] also +opposed the digallic acid formula, and supported his view by referring +to the arsenic compounds obtained by him on heating arsenic acid and +gallic acid, instead of obtaining digallic acid. Walden, [Footnote 3: +_Ber_., 1898, 31, 3168.] on the other hand, found, on analysing the +digallic acid thus prepared, only slight traces of arsenic and, by the +elementary analysis, obtained figures closely corresponding to those of +digallic acid. + +Bottinger [Footnote 4: _Ibid_., 1884, 17, 1476.] prepared the so-called +_[Greek: b]_-digallic acid by heating ethyl gallate with pyroracemic +acid and sulphuric acid and proposed the so-called ketone-tannin +formula:-- + + HO_____OH ______OH + HO{_____}--------CO--------{______}OH + COOH OH + +Schiff completed this formula by a diagonal, so as to explain the +optical activity observed-- + + HO OH ______OH + HO{_____}--------CO--------{______}OH + COOH OH + [Diagonal bond between HO and COOH on left.] + +The ketone formula was corroborated by Nierenstein, [Footnote: _Ber._ +1905, 38, 3641.] who distilled tannin with zinc dust and obtained +diphenylmethane (smell of benzene) and a crystalline product, +M.P. 7O°-71° C. (M.P. of diphenyl = 71° C.). König and Kostanecki +[Footnote: _Ibid._, 1906, 39, 4027.] sought to find the constitution of +the tannins in the leuco-compounds of the oxyketones, to which catechin +belongs. Nierenstein (see above), however, emphasises that the high +molecular weight and the optical activity speak against the digallic +acid formula, but in favour of this are the following points: (1) the +decomposition of tannin with the formation of gallic acid; (2) the +decomposition of methylotannin with the formation of di- and trimethyl +esters of gallic acid; and (3) the production of diphenylmethane on +distillation with zinc dust. The latter reaction especially illustrates +the analogous formation of fluorene from compounds of the type-- + + --CO.O + ^ ______ ^ + | | | | + | | | | + V V + +Nierenstein gave the name "Tannophor" to the mother-substance of tannin, +phenylbenzoate, C_6H_5-COO-C_6H_5. + +Dekker [Footnote: "De Looistoffen," vol. ii, p. 30 (1908).] was, +however, unable to detect diphenylmethane on distilling with zinc dust, +and did, therefore, not accept Nierenstein's views. In proposing the +formula-- + + O + || + HO ^ _ __C + | | | + | | }O + | | | __OH + | |____|_C_/ \OH + HO V \__/ + OH OH OH + +Dekker [Footnote: _Ber._, 1906, 34, 2497.] was enabled to account for +most of the details in the behaviour of tannin, viz.: (1) the +empirical constitution, C_14H_10O_9; (2) the almost complete +hydrolysis into gallic acid (the dotted line indicates the +decomposition of the molecule into 2 molecules gallic acid by taking +up water); (3) the formation of diphenylmethane as a result of +distillation with zinc dust; and (4) the electrical +non-conductivity. Since tannin on acetylating yields a considerable +amount of triacetylgallic acid, it should, according to Dekker, +contain at least six acetylisable hydroxyls. + +Nierenstein [Footnote: _Chem. Ztg._, 1906, 31, 880.] objected to this +formula on account of its containing seven hydroxyl groups, whereas +Dekker found six, Nierenstein five, and Herzig still fewer hydroxyl +groups. The formula would also favour the conception of tinctorial +properties which could hardly be ascribed to tannin. Lloyd [Footnote: +_Chemical News_, 1908, 97, 133.] proposed a very intricate formula +containing three digallic acid groups joined into one six-ring system, +which would then explain the optical activity; it would, on the other +hand, also require an inactive cis-form. + +Iljin [Footnote: _Jour. of the Russian phys. chem. Soc._, 1908, 39, +470.] prepared two phenylhydrazine derivatives of tannin (C_74 H_58 N_8 +O_30 and C_98 H_82 N_14 O_96) and proposed the formula, C_58 H_40 O_33, +the constitution of which would be-- + + R_1 R_1 + | | + }C--O--O--C{ + | | | + R_2 | R_2 + O + R_1 | R_1 + | | | + }C--O--O--C{ + | | + R_2 R_2 + + where R1= CO C_6 H_2 (OH)_3 + and R2= C_6 H_2 (OH)_2 + +Nierenstein [Footnote: _Ber._, 1905, 38, 3841; 1907, 40, 917; 1908, 41, +77 and 3015; 1909, 42, 1122 and 3552; _Chem. Ztg._, 1907, 31, 72; 1909, +34, 15.] considers tannin to be a mixture of digallic acid and +leucotannin, the latter possessing the formula-- + + + ^-------CH.OH--O----^ OH + | | | | + HO V OH HOOC V OH + OH + +The optical activity of tannin is expressed in this formula and its +probability is corroborated by Nierenstein, who was able to resolve the +acetylated tannin by fractional precipitation into pentacetyl tannin +(M.P. 203°-208° C.) and pentacetyl leucotannin (M.P. 166° C.). By +oxidation, the former is converted into ellagic acid, and on hydrolysis +with dilute sulphuric acid readily yielded gallic acid. Hydrolysis of +the pentacetyl leucotannin, however, yielded gallic aldehyde, and +oxidation yielded purpurotannin (a naphthalene derivative) in addition +to ellagic acid. + +Nierenstein [Footnote: _Ber._, 1910, 43, 628.] also succeeded in +converting tannin into carboethoxytannin, the latter on saponification +yielding crystalline, inactive digallic acid. On acetylating pentacetyl +leucotannin with acetyl chloride a hexacetyl derivative (M.P. 159° C.) +is obtained, the strychnine salt of which is resolved into both of the +active components. This proves the presence of digallic acid and +leucotannin in tannin lev. pur. Schering investigated by Nierenstein. +The latter author [Footnote: Liebig's _Ann._, 1912, 386, 318; 388, 223.] +later considered tannin to be polydigalloylleucodigallic acid anhydride +and the simplest tannin to be a digalloylleucodigallic acid +anhydride. This view, however, would not stand subsequent criticisms, +being in disagreement with the earlier observations of molecular weight +and acidic properties of tannin. Manning [Footnote: _Ibid._, 1912, 34, +918.] believed to have isolated a pentethylester of the pentagalloyl +glucoside from tannin, but this was shown to be the ethyl ester of +gallic acid. + +Feist [Footnote: _Ber._, 1912, 45, 1493.] had arrived at the conclusion +that tannin was a glucose compound, and maintained that tannin from +Turkish galls was a compound of glucogallic acid combined as an ester +with 2 molecules gallic acid. But Fischer and Strauss [Footnote: +_Ibid._, 1912, 45, 3773.] synthetically prepared a glucoside of gallic +acid exhibiting differences from Feist's preparation which were so great +that the latter no longer could be considered a single glucoside of +gallic acid. + +Fischer and Freudenberg [Footnote: _Ibid._, 1912, 45, 2717; 1913, 46, +1127.] subsequently elaborated a method of purifying tannin, and on +investigating the purified substance, arrived at the conclusion that +no other hydroxybenzoic acid than gallic acid was present in +tannin. On repeating Strecker's hydrolysis they obtained 7-8 per cent, +sugar, and hence concluded that 1 molecule of glucose was combined +with about 10 molecules of gallic acid. Owing to the difficulty of +isolating the intermediary hydrolysis products, and the subsequent +impossibility of drawing any conclusions as to the constitution of +tannin, the latter investigators decided to adopt the methods offered +by synthesis. Their basic idea was the absence of carboxylic groups in +tannin, and that hence the total gallic acid must be present in ester +form. These conditions are fulfilled if one views tannin as being an +ester compound of 1 molecule of glucose and 5 molecules of digallic +acid, of similar construction as, for example, pentacetyl +glucose. Fischer and Freudenberg succeeded in preparing the former by +shaking a mixture of finely powdered glucose, chloroform, and +quinoline with an excess of tricarbomethoxygalloyl chloride for +twenty-four hours and precipitating the resulting product with methyl +alcohol; suitably purified, a light amorphous colourless substance was +obtained which proved to be penta-(tricarbomethoxygalloyl) +glucose. Careful saponification with excess alkali in acetone-aqueous +solution at room temperature yielded a tannin very closely resembling +tannin, identified as pentagalloyl glucose. It is doubtful, however, +whether this substance is homogeneous, and it is probably a mixture of +two stereoisomers. + +Fischer and Freudenberg, therefore, further concluded that tannin is +mainly an ester compound of glucose and 5 molecules _m_-digallic +acid. Elucidation on this point offered itself advantageously in +Herzwig's methylotannin, [Footnote: _Ber._, 1905, 38, 989.] which is +obtained by the interaction of diazomethane and tannin. The first step +was then to prepare pentamethyl-_m_-digallic acid + + CH_3.O_______ ______COOH + CH_3.O{_______}--CO.O--{______} + CH_3.O CH_3.O O.CH_3 + +from trimethylgalloyl chloride and the _m-p_-dimethyl ether of gallic +acid; the chloride of this substance, coupled with [Greek: a]- and +[Greek: b]-glucose, yields-- + + _CH.OR + | | + | CH.OR H_______O.CH_3 + | | R=CO{_______}O.CH_3 + O{ CH.OR H O + | | H_____O.CH_3 + | CH CO{_____}O.CH_3 + | | H O.CH_3 + |_CH.OR + + CH_2.OR + + [Illustration: Penta-(pentamethyl-_m_-digalloyl)-glucose.] + +The [Greek: a]- and [Greek: b]-derivatives thus obtained differ in their +behaviour towards polarised light, and are, again, probably mixtures of +two stereoisomers, _i.e._, mixtures of derivatives of [Greek: a]- and +[Greek: b]-glucose. Compared to methylotannin, these preparations +exhibit very close resemblance to the former, from which it may be +concluded that they are closely related to this substance, and probably +possess the same or a very similar structure; the result of the above +experiments has, therefore, brought us at least in close proximity to +the structure of tannin. It must, however, be borne in mind that the +analysis and hydrolysis of tannin does not afford an explanation of the +question as to whether tannin is a compound of glucose and 10, 9, or 11 +molecules of gallic acid; it is also possible, though not probable, that +tannin would contain a polysaccharide instead of glucose +itself. Similarly to sugar, the true glucosides can be coupled with +hydroxybenzoic acids, which is proved by the preparation of +tetra-galloyl-[Greek: a]-methyl glucoside; this substance, also, +exhibits tannoid character. + + +2. DIGALLIC ACID + +Whereas, until recently, tannin had been considered to be gallic acid +anhydride, or digallic acid, closer investigations have revealed that +neither is tannin digallic acid nor is the synthetically prepared +digallic acid identical with tannin. Schiff [Footnote: _Ber._, 1871, +231 and 967.] prepared digallic acid by the interaction of phosphorus +oxychloride and gallic acid, and believed the product obtained to be +identical with tannin; to this latter he first ascribed an ether formula +(I.), later an ester formula (II.)-- + + (OH)_2 (OH)_2 + ¦¦ ¦¦ + C_6H_2---0---C_6H_2 + ¦ ¦ + COOH COOH + (I.) + + (OH)_2 + ¦¦ + C_6H_2(OH)_3--C--O.C_6H_2 + ¦¦ ¦ + O COOH + (II.) + +Froda [Footnote: _Gasz. chim._, 1878, 9.] held that Schiff's +condensation product contained phosphorus or arsenic acid and ascribed +its tanning properties to the latter; according to this investigator, +digallic acid, when completely freed from arsenic acid, does not react +with gelatine or quinine. Biginelli [Footnote: _Ibid._, 1909, 39, +ii. 268 and 283.] did not consider the action of arsenic acid that of a +catalyst, but held that it entered into reaction; according to his +investigations products containing arsenic (C_7H_7O_8As and +C_14H_11O_12As) are obtained when gallic acid is heated with arsenic +acid. + +In his preparation of digallic acid, Iljin [Footnote: +_Jour. f. prakt. Chem._, 1911, 82, 451.] could only obtain gallic acid, +and the ethyl ether of gallic acid showing no characteristics of the +tannins; when, however, he heated gallic acid with arsenic pentoxide, he +obtained bodies exhibiting the reactions given by tannins. + +Bottinger [Foonote: _Ber._, 1884, 1503.] made the first attempt at +synthesising tannin; he heated gallic acid or its ethyl ester with +glyoxylic acid or pyroracemic acid, and obtained a substance of the +composition C_14H_10O_9.2H_2O, which certainly showed some of the +characteristics exhibited by tannin, but which by no means was identical +with the latter. Bottinger's preparation is probably identical with +[Greek: b]-digallic acid, one of two dibasic isomers having the +composition-- + + C_6H_2(OH)_2COOH + | + C_6H(OH)_3COOH + +the other possible isomer having the composition + + C_6H(OH)_3COOH + CO | + C_6H_2(OH)_3 + +Fischer [Footnote: _Ber_., 1908, 41, 2875.] obtained a digallic acid +(M.P. 275°-280° C) by coupling tricarbomethoxygalloyl chloride with +dicarbomethoxygallic acid. + +Nierenstein [Footnote: _Ibid_., 1910, 43, 628.] obtained, from the +carbethoxy compound of tannin, a crystalline, optically active digallic +acid, M.P. 268°-270° C. The pentacetate of this substance, obtained by +reduction and acetylisation, yielded hexacetylleucotannin. A +pentamethyldigallic acid methyl ester of the composition + + ((O.CH_3)_3)C_6H_2----COO-----C_6H_2((OCH_3)_2)COO.CH_3 + +was obtained by Mauthner [Footnote: _Jour. f. prakt. Chem_., 1911, 84, +140.] from the chloride of trimethylgallic acid and the methyl ester of +the acid from the glucoside of syringin; on saponification with caustic +potash the former compound yielded trimethylgallic acid and syringic +acid. + +Fischer [Footnote: _Ber_., 1913, 46, 1116.] synthesised the so-called +_m_-digallic acid by coupling tricarbomethoxygalloyl chloride with +carbonylgallic acid and subsequent splitting off of CO_2. The +_m_-digallic acid appears as rather thick, colourless, microscopic +needles containing about 16 per cent. water of crystallisation, +M.P. 271° C. They are slightly soluble in cold, soluble in hot water, +and very soluble in methyl and ethyl alcohols. Their aqueous solution +gives dark blue coloration with ferric chloride, and precipitates +gelatine and quinine. + +Fischer and his students [Footnote 5: _Ibid_., 1912, 45, 915, 2709; +1913, 46, 1116.] prepared quite a number of digallic acid derivatives, +amongst which are the following:-- + + Pentamethyl-_m_-digallic acid methyl ester, C_20H_22O_9. + Pentacetyl-_m_-digallic acid, C_24H_20O_14. + Pentamethyl-_m_-digallic acid, C_19H_20O_9. + Pentamethyl-_m_-digalloyl chloride, C_19H_19O_8Cl. + Pentamethyl-_p_-digallic acid, C_19H_20O_9. + Pentamethyl-_p_-digallic acid methyl ester, C_20H_22O_9. + +Hydrolysis of digallic acid yields gallic acid; oxidation, on the other +hand, ellagic acid and luteic acid (Luteo Säure), which can be separated +by shaking with pyridine. The reduction of digallic acid yields, by +different methods, the same reduction compound, [Footnote: Nierenstein, +Abderhalden's "Handb. d. biochem. Arbeitsm.," vi. 154.] viz., the +racemic leucodigallic acid, which differs from digallic acid by being +devoid of any tannoid properties; the latter distinction may be ascribed +to the transformation of the tannophor group--CO.O--, to the +tannoid-inactive group CH(OH)--O--. + +The successful resolving of racemic leucodigallic acid into both of its +optically active components can only be brought about through the _d_- +or _l_-hexacarbethoxyleucodigallic acid on introducing the latter into a +1 per cent. pyridine solution and heating to 45°-50° C., whereby the +_d_- or _l_-acid is formed accompanied by a strong evolution of carbon +dioxide. + +Hydrolysis of leucogallic acid yields gallic acid and gallic aldehyde; +oxidation by means of hydrogen peroxide yields ellagic acid and luteic +acid, and oxidation with potassium persulphate and sulphuric acid, in +acetic acid solution, yields purpurotannin (see below) [Footnote: +Liebig's _Ann_., 1912, 386, 318.]. + +Another distinct difference between digallic acid and leucodigallic acid +is the fact that the formaldehyde condensation product of the former +resembles gallic acid, whereas that of the latter resembles tannin; it +is therefore probable that the leucodigallic acid part of the tannin +molecule imparts this characteristic property to tannin. + + ---CO.O--- + ^ ^ + | | | | + HO V OH COOH V OH + OH OH + [Illustration: Digallic Acid becomes...] + + ---CO.O--- + ^ ^ OH + | | | | + HO V OH COOH V OH + OH OH + [Illustration: Luteic Acid becomes...] + + ---CO.O--- + ^ ^ OH + | | | | + HO V --O.CO-- V OH + OH OH + [Illustration: Ellagic Acid becomes...] + + COOH COOH + ^ _______ ^ + | | | | + HO V ---O--- V OH + OH OH + [Illustration: Purpuro Tannin.] + + +3. Ellagic Acid + +Ellagic acid was discovered in 1831 by Braconnot, who named it "acide +ellagique." Its presence in the vegetable kingdom was not quite +comprehended for some time, and Nierenstein [Footnote: _Chem. Ztg._, +1909, 87.] was the first to prepare this substance from algarobilla, +dividivi, oak bark, pomegranate, myrabolarms, and valonea. The acid is +obtained by precipitating it with water from a hot alcoholic extraction +of the plants referred to, and recrystallising the precipitate from hot +alcohol. Another method of preparation consists in boiling the +disintegrated plants with dilute hydrochloric acid, washing the residue, +and extracting with hot alcohol, from which the acid will then +crystallise. According to Lowe, [Footnote: _Zeits. f. analyt. Chem._, +1875, 35.] it may be obtained from dividivi, an aqueous extract of +which is heated to 110° C. in a tube closed at both ends, when +crystalline ellagic acid is deposited. Heinemann [Footnote: Ger. Pat., +137,033 and 137,934.] obtained ellagic acid by simply boiling +repeatedly aqueous tannin solutions. + +Lowe [Footnote: _Jour. f. prakt. Chem._, 1868, 103, 464.] first +synthesised ellagic acid by heating gallic acid with arsenic acid or +silver oxide. Herzig [Footnote: _Monatshefte fur Chemie_, 1908, 29, +263.] states that ellagic acid is deposited when air is conducted +through a mixture of the ethyl or methyl ester of gallic acid and +ammonia. Perkin [Footnote: _Proc. Chem. Soc._, 1905, 21, 212.] obtained +a substance very similar to ellagic acid by electrolysis of gallic acid +in sulphuric acid solution; on oxidising gallic acid in concentrated +sulphuric acid solution, Perkin and Nierenstein [Footnote: _Ibid._, +1905, 21, 185.] obtained flavellagic acid. Ellagic acid is also +obtained by heating luteic acid in a 10 per cent. soda solution. + +Ellagic acid thus prepared crystallises with 2 molecules of water as +yellow micro-crystalline rhombic prisms or prismatic needles. The +crystals lose this water when heated to 100° C., and it is possible that +it is water of constitution, in which case the substance would be +hexoxydiphenylcarboxylic acid, and the substance left after drying at +100° C., the dilactone.[Footnote: _Arch. d. Pharm_., 1907, 244, 575.] +Ellagic acid is slightly soluble in water, alcohol, and ether, but is +easily soluble in caustic potash. With concentrated nitric acid the +product assumes a red colour, which appears to be due to the presence of +impurities; ellagic acid is commercially known as "alizarin yellow." + +The constitution of ellagic acid was uncertain for a long time, and +different structural formulae were proposed which more or less +corresponded to its properties. The most satisfactory structural formula +was proposed by Graebe--[Footnote: _Chem. Ztg_., 1903, 129.] + + ---CO.O--- + ^ -------- ^ OH + | | | | + HO V --O.CO-- V OH + OH + +This would represent a tetroxydiphenylmethylolide. + +The probability of the correctness of this formula is supported +by the possibility of the following derivatives: monomethylellagic +acid, C'14H'6O'7(O.CH'3); dimethylellagic acid, +C'14H'4O'6(O.CH'3)'2; tetramethylellagic acid, C'14H'2O'4(O.CH'3)'4; +phenylhydrazinellagic acid, C'14H'6O'8.N'2H'3C'6H'5. + +By the electrolytic reduction of ellagic acid, hexoxydiphenyl, +(OH)'3C'6H'2-C'6H'2(OH)'3, is obtained; the ordinary +methods of reduction yield leucoellagic acid, C'14H'10O'8, which +crystallises in small sharp needles, melting with decomposition +at 294°-295° C. Leucoellagic acid is soluble in ethyl and methyl +alcohols, and in glacial acetic acid, insoluble in chloroform, +benzene, toluene, carbon tetrachloride, and petrol ether; it +gives a bluish-green colour with ferric chloride which quickly +turns black. Leucoellagic acid is soluble in alkalies, the +solution assuming a deep-red coloration; it reduces silver +nitrate in the cold, but is not adsorbed by mordanted cotton +cloth, in which respect it differs from ellagic acid.[Footnote: Liebig's +_Ann_., 1912, 394, 249. + +ELLAGITANNIC ACID, C'26H'28'O'10-3H'2O, is closely related to ellagic +acid; the former consists of faintly yellow needles, M.P. 329°-336°C. +It is soluble in water, precipitates gelatine, and is adsorbed by hide +powder. It occurs with gallic acid, tannin, and ellagic acid in +dividivi, myrabolams, algarobilla, and chestnut wood extracts. + +Other bodies of this class include:-- + +METELLAGIC ACID, Cl_4H_6O_5, derived from methoxybenzoic acid, and +recrystallised from acetic acid, forms small crystalline needles, +M.P. 273°-276° C., and yields fluorene on distillation with zinc dust. + + ----CO.O---- + ^ ---------- ^ + | | | | + V ---O.CO--- V + OH + +FLAVELLAGIC ACID, C_14H_6O_9, is obtained by the oxidation of gallic +acid with concentrated sulphuric acid and potassium persulphate. It +crystallises from pyridine in prismatic needles melting above 360° +C. Distillation with zinc dust yields fluorene (see above)-- + + ----CO.O---- + ^ ---------- ^ OH + | | | | + HO V ---O.CO--- V OH + OH OH + +By heating ellagic acid for three-quarters of an hour at 185° C. with +concentrated sulphuric acid, ceruleo-ellagic acid (dioxyellagic acid), +C_14H_6O_10, is formed as yellowish needles, M.P. 360° C., which are but +little soluble in the usual solvents. The acid is slightly soluble in +strong caustic soda solution, the colour of the solution, on diluting, +changing to green and blue. + +LUTEIC ACID (Luteo Saure, pentoxybiphenylmethylolide carboxylic +acid),C_14H_8O_9, occurs, in addition to ellagic acid, in myrabolams-- +[Footnote: _Ber_., 1909, 42, 353.] + + ----CO.O---- + ^ ---------- ^ OH + | | | | + HO V OH HOOC V OH + OH OH + +It is obtained by extracting myrabolams for one hour and a half, under +reflux condenser, with pyridine, filtering and adding twice the volume +of water to the filtrate and boiling till complete solution is +obtained. After about thirty hours a reddish powder deposits, from which +ellagic acid may be extracted with pyridine; the mother-liquor on being +concentrated yields luteic acid. It is also obtained by oxidising tannin +with hydrogen peroxide, the other oxidation product being ellagic acid, +and the two may then be separated as indicated above. Luteic acid forms +reddish needles which are decomposed, with evolution of gas, at +338°-341° C. Heated with 10 per cent. caustic soda solution it yields +ellagic acid. In pyridine solution the carboxyl group maybe eliminated +by hydrogen iodide, whereby pentoxybiphenylmethylolide is formed as long +silky needles, which do not melt below 300° C. The same substance may +also be obtained when ellagic acid is boiled with concentrated caustic +potash solution. When luteic acid is treated with diazomethane, it +yields the methyl ester of pentamethoxybiphenylmethylolidcarboxylic +acid. + + +4. DEPSIDES + +The most common decomposition products of the natural tannoids are +hydroxybenzoic acids, notably gallic and proto-catechuic acids; +furthermore, other aromatic and aliphatic hydroxy compounds frequently +occur. So far, however, attempts at explaining the constitution of the +complex decomposition products obtained by hydrolysing high molecular +tannoids have not been successful. On the other hand, the constitution +of the simpler natural tannoids is known to a greater or less extent; of +these, lecanoric acid (Lecanorsäure) is the best known, being an ester +anhydride of orsellic acid (a dihydroxytoluylic acid). It combines with +erythrite, forming another tannoid, erythrine. The fact that +hydroxybenzoic acids are constantly encountered together with the +products obtained on hydrolysis of the tannins, seems to point toward +the conclusion that anhydrides of hydroxybenzoic acids are frequent +constituents of the natural tannoid molecules. + +The assumption that, for instance, in tannin at least part of the gallic +acid radicals are combined with one another is highly probable, and is +supported by the formation of tri- and dimethylgallic acid from +methylotannin, [Footnote: Herzig, _Monatshefte f. Chemie_, 1909, 30, +343.] and by the formation of ellagic acid when tannin is oxidised. +[Footnote: Nierenstein, _Ber_., 1908, 41, 3015.] Further proof is +brought forward by the existence of the pentacetyl-tannin, [Footnote: +Schiff, _Ann. d. Chem_., 1873, 170, 73.] and by the results of +hydrolysis which has yielded up to 104 per cent. anhydrous gallic acid +fiom tannin [Footnote: Sisley, _Bull. Soc. Chim_. 1909, 5, 727.] + +Of the three classes of isomeric anhydrides which can be formed from +hydroxybenzoic acids, the chemistry of the natural tannins is only +concerned with the class comprising the ester anhydrides. If the +carboxyl of the first molecule combines with a hydroxyl of the second +molecule (ester formation), then a substance possessing character +similar to that of a hydroxybenzoic acid is formed, which is capable of +combining up with a further molecule in the same way. It is natural to +assume that this ester form is much more prevalent in Nature than a +combination of two carboxyls by the elimination of water. From the point +of view of the chemistry of the tannins, therefore, the starting-point +would naturally be that of synthesising the ester anhydrides of +hydroxybenzoic acids. Amongst the small number of synthetically prepared +ester anhydrides of hydroxybenzoic acids, a few occur exhibiting the +properties of the natural tannoids. + +In order to simplify the terminology of these substances, Fischer +[Footnote: Liebig's _Ann_., 1910, 372, 35.] proposed the name +"Depsides" from [Greek: depheiv] = to tan. In analogy with peptides +and saccharides, the names di-, tri-, and polydepsides of hydroxybenzoic +acids would be suitable for these substances. + +The principles underlying the synthesis of depsides are the +following:--If the chlorides of carbomethoxy (or carbethoxy) +hydroxybenzoic acids are coupled with the sodium salts of hydroxybenzoic +acids, esters are formed, _e.g._, + + CH_3CO O.O.C_6H_4.CO.Cl + NaO.C_6H_4.COO.Na = NaCl + + CH_3.COO.O.C_6H_4.CO.O.C_6H_4.COO.Na + +On gently saponifying the esters, these are converted into the +corresponding hydroxy derivatives-- + +OH.C_6H_4.CO.O.C_6H_4.COOH + +According to Fischer and Freudenberg, [Footnote: Liebig's _Ann._, 1909, +372, 32.] this method possesses the following advantages:-- + +1. The synthesis takes place at low temperatures, so that any +intramolecular rearrangements are improbable. + +2. The composition of the substances is controlled by the intermediary +compounds, the carboalkyloxy derivatives. + +3. The synthesis permits of more definite evidence as regards the +structure of the resulting compounds. + +4. The substances obtained are easily purified. + +Depsides produced in this manner are by no means new, and were obtained +by Klepl by simply heating _p_-hydroxy-benzoic acid (_cf._ Introduction, +p. 4). This simple procedure, however, is not applicable to most other +hydroxybenzoic acids which are decomposed at the high temperature +necessary to induce reaction. Lowe and Schiff (_loc. cit._) have +obtained products similar to tannins, the latter investigator by +removing the elements of water from gallic acid, protocatechuic acid, +salicylic acid, _m_-hydroxybenzoic acid, cresotinic acid, phloretinic +acid, and pyrogallolcarboxylic acid. These depsides, however, are +amorphous substances, and it is hence difficult to substantiate their +homogeneity. + + +Carbomethoxylation of Hydroxybenzoic Acids + +Amongst other compounds chlorphydroxybenzoic acid is used in the +preparation of the materials employed in the synthesis of depsides; the +free phenolic group, however, exerts a disturbing influence when +aromatic acids are acted upon by phosphorus chloride, and another group, +which can subsequently be easily removed, must therefore be introduced +to cover the disturbing influence referred to. For this purpose, Fischer +[Footnote: _Ber_., 1908, 41, 2860.] chose the carbomethoxy group, and +this investigator succeeded, by the action of chlorocarbonic alkyl +ester and alkali upon hydroxybenzoic acid in cold aqueous solution, in +obtaining substances with the properties required. [Footnote: _Ber._, +1908, 41, 2875.] In such substances (_e.g._, salicylic acid) where the +hydroxyl occupies the ortho-position to the carboxyl, complete +carbomethoxylation does not take place, whereas the _m_- or _p_- +positions offer no hindrance. In the case of the _o_-position, however, +the action of chlorocarbonic alkyl ester is successfully assisted by the +presence of dimethylaniline in an inert solvent, _e.g._, +benzene.[Footnote: U.S. Pat, 1,639,174, 12, xii., 1899.] The difficulty +encountered by the _o_-position is eliminated when the carboxyl is not +directly linked to the benzene nucleus, _e.g._, _o_-cumaric acid. Many +hydroxybenzoic acids require an excess of chlorocarbonic methyl ester, +which then also, to some extent, attacks the carboxyl group; but on +dissolving the product in acetone and treating it with bicarbonate the +carboxyl group as such is again restored without splitting off the +carbomethoxy group.[Footnote: _Ber._, 1913, 46, 2400.] In this way all +hydroxybenzoic acids may be carbomethoxylated. [Footnote: _Ibid._, +1908, 41, 2877, 2881, 2882; 1909, 42, 226, 218, 223, 225; Liebig's +_Ann._, 1912, 391, 357, 366; _Ber._, 1913, 46, 1145, 2390, 2400.] The +carbomethoxy group is easily removed by excess of aqueous alkali in the +cold, and is also partially removed when insufficient alkali is present; +the latter fact is of importance in the synthesis of didepsides. + + +Chlorides of Carbomethoxyhydroxybenzoic Acids + +The chlorides of these compounds are obtained when phosphorus +pentachloride is allowed to act upon the acids, and are as a rule +crystalline. For the purpose of synthesis they may be employed as +follows: + +1. They readily form esters with alcohols, which on subsequent +saponification with alkali are converted into the esters of the free +hydroxybenzoic acids. + +2. The chlorides interact energetically with esters of amino-acids, and +may be coupled with amino-acids in aqueous alkaline solution. On +subsequently removing the carbo-methoxy group derivatives of +hydroxybenzoic acids are obtained, _e.g._, + + CH_3.CO_2.O.C_6H_4.CO.Cl + 2NH_2CH_2.CO.C_2H_5 + = NH_2.CH_2.CO_2.C_2H_5 + HCl + CH_3.CO_2.O.C_6H_4 CO.NH.CH_2CO_2C_2H_5. + CH_3.CO_2.O.C_6H_4.CO.NH.CH_2.CO_2.C_2H_5 + 3NaOH + = Na_2CO_3 + C_2H_5OH + CH_3OH + HO.C_6H_4.CO.NH.CH_2.COONa. + +3. In the presence of AlCl_3 the chlorides easily combine with benzene, +and on removing the carbomethoxy group unsymmetrical hydroxy derivatives +of benzophenone are formed:-- + + CH_3.CO_2.O.C_6H_4.CO.Cl + C_6H_6 = CH_3.CO_2.O.C_6H_4.CO.C_6H_5 + HCl + CH_3.CO_2.O.C_6H_4.CO.C_6H_5 + 3NaOH + = NaO.C_6H_4.CO.C_6H_5 + Na_3CO_3 + CH_3OH + H_2O + +4. The chlorides may be coupled with free hydroxybenzoic acids, and on +removing the carbomethoxy group didepsides are obtained. Repetition of +these operations yields tri- and tetradepsides. + + +Preparation of Didepsides + +A simple application of these syntheses is offered by _p_-hydroxybenzoic +acid. When the chloride of its carbomethoxy derivative is allowed to +interact with _p_-hydroxybenzoic acid in aqueous alkaline solution, in +the cold, the alkali salt of carbomethoxy-_p_-hydroxybenzoic acid is +formed:--[Footnote 1: _Ber._, 1909, 42, 216.] + + CH_3.CO_2.O.C_6H_4.CO.Cl + NaO.C_6H_4.COONa + = CH_3.CO_2.O.C_6H_4.CO_2.C_6H_4.CO_2.Na + NaCl. + +Being sparingly soluble, the salt in this case is readily deposited as +crystals, but is readily converted into the free acid by hydrochloric +acid. In most other cases, however, the alkali salts are easily soluble +and the aqueous solution is then directly acidified with a mineral +acid. The chlorides, being for the most part solids, the mode of +procedure is as follows:--the hydroxybenzoic acid required for coupling +is dissolved in normal or double-normal alkali (the volume calculated +per molecule acid), a little acetone added, and the mixture well cooled; +a further molecule of 2N caustic soda and the chloride (I molecule) +dissolved in dry acetone are added in small portions, whilst stirring, +to the mixture. In spite of the low temperature the coupling proceeds +quickly and the sparingly soluble product can in most cases be +precipitated from the solution by acidifying and diluting with water. In +case of more easily soluble coupling products the acetone is driven off +under reduced pressure or the liquid acidified and diluted, and the +substance extracted with ether. Instead of alkali, dimethylaniline may +be employed, with the exclusion of water as a solvent for the purpose of +coupling. + +Another suitable method of obtaining _o_-didepsides is that of treating +_o_-hydroxybenzoic acids with phosphorus trichloride and dimethylaniline +(_e.g_., synthesis of disalicylic acid, Boehringer & Sons).[Footnote: +Ger. Pat., 211,403.] + +The carbomethoxy derivatives of the depsides are as a rule crystalline +substances of distinct acidic character, and decompose alkaline +carbonates. + +The elimination of the carbomethoxy group may be brought about by dilute +alkaline solutions in the cold, or by aqueous ammonia. If the depside +formed is so stable as to resist the action of alkali for several hours, +the use of the latter is very convenient for the purpose required. The +substance is dissolved directly in sufficient normal alkali to +neutralise the carboxyl group and a further 2 molecules of caustic soda +for each carbomethoxy group to be eliminated are added. The temperature +should be about 20° C., when the reaction as a rule is completed after +one-half to three-quarters of an hour. It is usual, however, to use an +aqueous ammonia solution in considerable excess, whereby the temperature +should again be about 20° C., and the solution of ammonia normal or half +normal. + +The didepsides so far investigated are crystalline bodies, sparingly +soluble in cold water; they--as a rule--decompose when fused, possess +acid reaction, and are dissolved by bicarbonates. On account of the +presence of a free phenolic group they give a coloration with ferric +chloride; if the phenolic group occupies the _o_-position to carboxyl, +the coloration with ferric chloride is red or bluish-violet Excess of +dilute alkali resolved all didepsides into their components at ordinary +temperatures. The didepsides of gallic, proto-catechuic, gentisinic, and +[Greek: b]-resorcylic acids precipitate gelatine and quinine acetate, +and in this respect approach the natural tannins. + +The following summary gives an account of depsides which have been +prepared synthetically or which occur naturally:--[Footnote 1: _Ber._, +1908, 41, 2888; 1909, 42, 217; 1913, 45, 2718; 1913, 46, 1130, 2396, +1141, 1143; Liebig's _Ann._, 384, 230, 233, 238; 391, 356, 362.] + + Di-_p_-hydroxybenzoic acid. + Di-_m_-hydroxybenzoic acid. + Disalicylic acid. + Diprotocatechuic acid. + Digentisinic acid. + Di-[Greek: b]-resorcylic acid. + _p_-Diorsellic acid. + _o_-Diorsellic acid. + _m_-Digallic acid. + Disyringic acid. + Di-_o_-cumaric acid. + Diferulic acid. + Di-[Greek: b]-hydroxynaphthoic acid. + _p_-Hydroxybenzoyl-_m_-hydroxybenzoic acid. + _m_-Hydroxybenzoyl-_p_-hydroxybenzoic acid. + Salicyl-_p_-hydroxybenzoic acid, + Vanilloyl-_p_-hydroxybenzoic acid. + Feruloyl-_p_-hydroxybenzoic acid. + [Greek: a]-Hydroxynaphthoyl-_p_-hydroxybenzoic acid. + Orsellinoyl-_p_-hydroxybenzoic acid. + Protocatechuyl-_p_-hydroxybenzoic acid. + Galloyl-_p_-hydroxybenzoic acid. + Pyrogallolcarboy _p_-hydroxybenzoic acid. + Syringoyl-_p_-hydroxybenzoic acid. + _p_-Hydroxybenzoyl-syringic acid. + Pentamethyl-_m_-digallic acid. + Pentamethyl-_p_-digallic acid. + Vanilloyl vanillin. + + +Preparation of Tridepsides + +Monohydroxybenzoic acids allow theoretically of tri-depsides of the type +HO.C_6H_4COO.C_6H_4.COO.C_6H_4.COOH only; if, on the other hand, di- or +trihydroxybenzoic acids are dealt with, two formulae are possible, +viz.:-- + + HO.C_6H_4.COO + } C_6H_3.COOH + HO.C_6H_4.COO + +Of the former type, two compounds are known, _i.e._, +di-_p_-hydroxybenzoyl-_p_-hydroxybenzoic +acid and vanilloyl-_p_-hydroxybenzoyl-_p_-hydroxybenzoic acid-- + + HO + } C_6H_3.COO.C_6H_4.COO.C_6H_4.COOH + CH_3O + +The first named of these two compounds was obtained by Klepl, in +addition to the didepside, by heating _p_-hydroxybenzoic acid. Fischer +and Freudenberg obtained a beautifully crystalline form in the following +way: carbethoxyhydroxy-benzoyl chloride was coupled with +_p_-hydroxybenzoyl-_p_-hydroxybenzoic acid in alkaline solution, the +compound dissolved in a mixture of pyridine and acetone, and ammonia +added for the purpose of removing the carbethoxy group. The tridepside +was then obtained as long needles by re-dissolving in acetone. + +Both tridepsides melt well above 200° C., are practically insoluble in +water, and are but sparingly soluble in practically all organic +solvents. In alcoholic solution they give colour reaction with ferric +chloride similar to those given by _p_-hydroxybenzoic acids. + + +Preparation of Tetradepsides +[Footnote: Fischer and Freudenberg, Liebig's _Ann._, 1910, 372, 32.] + +Here, again, two forms are known, _e.g._, +tri-_p_-hydroxybenzoyl-_p_-hydroxybenzoic acid-- + + HO.C_5H_4.COO.C_6H_4.COO.C_6H_4COO.C_6H_4 COOH + +and vanilloyl-di-_p_-hydroxybenzoyl-_p_-hydroxybenzoic acid-- + + HO + } C_6H_3.COO.C_6H_4.COO.C_6H_4.COO.C_6H_4.COOH + CH_3O + +The former has been prepared from +carbethoxyhydroxy-benzoyl-_p_-hydroxybenzoyl chloride and +_p_-hydroxybenzoyl-_p_-hydroxybenzoic acid in alkaline solution; the +second tetradepside was prepared from +carbomethoxyvanilloyl-_p_-hydroxybenzoyl chloride and +_p_-hydroxybenzoyl-_p_-hydroxy-benzoic acid. + +The preparation of these compounds is rendered difficult by the slight +solubility of the substances and their slight affinities for entering +into reaction. Both tetradepsides were obtained in crystalline form, and +are but very little soluble in most organic solvents. They decompose on +being fused. + + +Tannoid Substances of the Tannin Type + +The preparation of pentagalloyl glucose has proved this compound to be +nearly identical with tannin obtained from galls (_tannin_); a few other +natural tannins belong to this type which Fischer terms acyl compounds +of sugar with hydroxybenzoic acids. The method of preparation employed +in the synthesis of pentagalloyl glucose may be easily applied to other +hydroxybenzoic acids, _e.g._ penta[_p_-hydroxybenzoyl] glucose +[Footnote: Fischer and Freudenberg, _Ber._, 1912, 45, 933.] was +prepared in this way. Similar characteristics are exhibited by +pentasalicylo glucose. Mention must also be made of the corresponding +derivative of pyruvic acid and the compound with pyrogallolcarboxylic +acid, penta-[pyrogallolcarboyl]glucose. [Footnote: Fischer and +Rapoport, _Ber._, 1913, 46, 2397.] The latter is isomeric with +pentagalloyl glucose and possesses similar properties; there is, +however, a vast difference in the solubility of the two. Whereas the +galloyl compound is easily soluble in cold water, its isomer is hardly +soluble in hot, and completely insoluble in cold water. Considering the +very similar structure of these two tannins, such differences appear +surprising, but an analogy may be readily found in the existence of +colloidal solutions of tannin and the (nearly) identical pentagalloyl +glucose. These properties clearly show how dependent is the colloidal +state on small differences in the structure of two substances. On the +other hand, the formation of hydrosols is of the greatest importance +relatively to the part played by these substances in Nature as well as +relating to their chemical characteristics; thus it is extremely +difficult to make a solution of penta-[pyrogallolcarboyl]-glucose, at +the same time ascertaining its astringent taste and its property of +precipitating gelatine. + +The experience gained by the methyl glucosides makes it exceedingly +probable that the simpler polyhydric alcohols also are suitable +substances to employ in these syntheses; as a matter of fact, glycerol +has been condensed with gallic acid. [Footnote: Fischer and Freudenberg, +_Ber., 1912, 45, 935.] + +One of the chief characteristics of synthetic tannins is their high +molecular weight; for instance, the molecular weight of +penta-[tricarbomethoxygalloyl]-glucose is 1,810, that of +penta-[pentamethyl-_m_-digalloyl]-glucose 2,051. Employing gallic acid +derivatives, especially the tribenzoyl compounds, coupled with glucose, +_e.g._, mannite, yielded a neutral ester of molecular weight 2,967. + +The determination of the elementary composition of compounds of high +molecular weight is greatly facilitated by employing their halogen +derivatives; so, for instance, is _p_ iodophenyl maltosazone very +suitable. Coupling the latter with tribenzoylgalloyl chloride yielded +hepta-[tribenzoyl-galloyl]-_p_-iodophenyl maltosazone, the structure of +which is represented by-- + + CH:N_2H.C_6H_4I + | + C:N_2H.C_6H_4I + | + CH.O.R R = CO.C_6H_2(O.CO.C_6H_6)_2 + | + CH.O.R + | + CH.O.R R R R R + | O O O O + | | | | | + CH_2.O.CH.CH.CH.CH.CH.CH_2 + | | + ---O--- + +The molecular weight of this substance is 4,021, and probably represents +the highest molecular organic body obtained in any chemical synthesis. + +From a physiological standpoint the recognition of tannins as esters of +glucose and hydroxybenzoic acids, possessing characteristics similar to +those of tannin, is of great importance. Especially interesting appears +the fact of plants utilising sugars for the esterification of acids, +just as glycerol or monohydric alcohols may be employed for the same +purpose. Free acids, as a rule, are only tolerated in certain parts of +the organism, the latter usually striving to neutralise acidic groups +which may be brought about by salt formation; formation of amino +compounds (proteins) or esterification (fats); and, lastly, +esterformation by means of sugars. + +Why Nature should always build up substances of very complex +constitution can only be explained by biochemical investigations, but it +may, at any rate, be assumed that by this means any substance poisonous +to the living organism is rendered inactive. The function of the tannins +present in plants may thus be explained; if, for instance, phenols are +formed by the oxidation of corresponding sugars, [Footnote: Mielke, +"Ueber die Stellung der Gerbstoffe im Stoffwechsel der Pflanzen" +(Hamburg, 1893).] the poisonous character of the former would be +lessened by the introduction of the carbonic acid esters and subsequent +coupling of the substances (depside formation). The depsides thus formed +would serve as vehicle of the sugars and transport the migrating +tannins, [Footnote: Kraus, "Grundlinien zu einer Physiologie der +Gerbstoffe" (1889).] and, after subsequent deposition of the sugars, +would then be eliminated from the plant organism, either by oxidation +into ellagic acid and phlobaphenes or by condensation with the formation +of cork. + +Diagrammatically, the following would represent the physiology of the +tannins:--[Footnote: Nierenstein, "Chemie der Gerbstoffe" (Stuttgart, +1910).] + + Sugar-->Phenol-->Hydroxybenzoic Acid-->Depside--> + + |Phlobaphene + -->Migrating Depside-->Glucoside-->Free Depside-->-{Ellagic Acid + |Cork. + +[Illustration: Chart Showing the Decomposition of Products of Tannin.] + + + + +SECTION II + +SYNTHESIS OF TANNING MATTERS + + +1. AROMATIC SULPHONIC ACIDS + +In organic chemistry distinction is made between sulphonic acids of the +aliphatic and the aromatic series, the characteristic group of these +acids being the so-called _sulphonic acid group_, HSO_3. + +When sulphides or mercaptans in glacial acetic acid solution are heated +with permanganate, the resulting sulphonic acid compounds exhibit great +similarity to compounds containing free carboxyl groups. The sulphonic +acid group may also be directly introduced either by concentrated, or by +fuming sulphuric acid, or by elimination of halogen by the action of +sodium or silver sulphite on the halogen derivatives of the aliphatic +compounds. Saturated hydrocarbons do not react with sulphur trioxide, +but unsaturated hydrocarbons are readily attacked by SO_3. Similarly, +halogenated compounds and alcohols react with concentrated or fuming +sulphuric acid forming sulphonic and hydrosulphonic acids respectively. +The aromatic compounds form, as a rule, sulphonic acids with much +greater facility. Benzene, for instance, is easily converted into the +_m_-disulphonic acid by gently heating with fuming sulphuric acid; +stronger heating converts the _m_- into the _p_-disulphonic acid, and at +190° C. the trisulphonic acid is formed. Toluene treated with fuming +sulphuric acid first yields _o_- and _p_-sulphonic acids, finally _o_- +and _p_-disulphonic acids, ethylbenzene at the boiling point +_p_-ethylbenzene-sulphonic acid. Of the three isomeric xylenes _o_- and +_m_-xylene dissolve in concentrated, _p_-xylene in fuming sulphuric acid +only. + +The action of sulphuric acid on naphthalene is stronger even than on +benzene. Equal parts of naphthalene and sulphuric acid heated to 100° +C. yield 80 per cent. [Greek: a] and +20 per cent. [Greek: b]-monosulphonic acid. At 160°-170°C. 25 per cent +[Greek: a]- and 75 per cent. [Greek: b]-sulphonic acid is formed, and at +higher temperatures [Greek: b]-monosulphonic acid only. If, on the other +hand, 8 parts of naphthalene are heated with 3 parts of concentrated +sulphuric acid to 180° C., two different naphthyldisulphonic acids are +obtained. + +Complete solution of the substance in sulphuric acid is, generally +speaking, a criterion of complete sulphonation. A completely sulphonated +compound should remain clear on dilution with water, or, in case +precipitation occurs, the precipitate should be completely soluble in +alkali or ammonia. It is necessary to submit the product to this test, +since many organic substances are soluble in concentrated sulphuric acid +without undergoing any alteration in composition. + +Phosphoruspentoxide or potassium sulphate considerably increase the +sulphonating property exhibited by fuming sulphuric acid. + +The separation of the sulphonic acids from sulphuric acid is effected by +salting out the former with common salt, or by removing the sulphuric +acid with calcium, barium, or lead salts, provided that the sulphonic +acid salts of these metals are soluble in water. + +The sulphonic acid, in its chemically pure state, is best obtained from +its crystalline barium salts, which are decomposed with the equivalent +of sulphuric acid; another way is to decompose the calcium salts of the +sulphonic acids with oxalic acid. The sulphonic acids are frequently +hygroscopic and are easily soluble in water; the majority of their +barium and lead salts are also soluble in water. The sulphonic acids are +insoluble in ether. The halogens do not easily react with sulphonic +acids, but when they do they usually replace the sulphonic acid +group. In order to prepare the halogen substitution products, therefore, +use is made of sulphonic chlorides. The latter are obtained by the +action of chlorosulphonic acid on aromatic hydrocarbons; a simpler +method, however, is to treat the dry alkali sulphonates with phosphorus +pentachloride-- + + C_6H_5SO_3Na + PCl_5 = C_6H_5SO_2.Cl + NaCl + POCl_3 + +Derivatives of sulphonic chlorides are sulphonamides, which are easily +prepared from the former by grinding with ammonium carbonate-- + + C_6H_5SO_2.Cl + (NH_4)_2CO_3 = C_6H_5.SO_2.NH_2 + NH_4Cl + CO_2 + H_2O + +Sulphonic chlorides react with alkaline sulphides to form +thiosulphonic acids-- + + C_6H_5SO_2.Cl + K_2S = C_6H_5SO_2.SK + KCl + +Sulphonic chlorides, dissolved in ether, yield sulphinic acids on +reduction with zinc dust or metallic sodium-- + + C_6H_5SO_2.Cl + H_2 = C_6H_5SO_2.H + HCl + +In the sulphonic acid compounds it is assumed that the sulphur is +hexavalent, and it is hence possible to consider the sulphones to be +esters of sulphinic acid. + + ==O +R--S==O + --H + +The sulphones are mostly solid bodies, which soften prior to melting +when heated. They are very stable towards chemical reagents; for +instance, saponification of a mono-sulphone very rarely yields sulphinic +acid. + +If a hydroxyl is substituted for a hydrogen atom in the aromatic +hydrocarbons, the action of sulphuric acid is greatly facilitated; thus, +by merely mixing phenol with sulphuric acid, the sulphonic acid is at +once formed, whereby, in the cold, _o_-phenolsulphonic acid prevails +which on heating for some time to 100°-110° C. is completely converted +into _p_-phenolsulphonic acid. In the absence of free sulphuric acid the +conversion of _o_- into _p_-phenolsulphonic acid is brought about by +heating the aqueous solution. Phenol-2,4-disulphonic acid is prepared +from _o_- or _p_-phenolsulphonic acid, whereas phenol-2,4,6-trisulphonic +acid is prepared directly from phenol by heating with concentrated +sulphuric acid in presence of phosphorus pentoxide. Phenolsulphonic +acids are also obtained by fusing benzenedisulphonic acid with alkali. + +Cresol is not so easily sulphonated as is phenol; _o_-cresol when heated +eight to ten hours at 90° C. with one and one-half times its weight +of concentrated sulphuric acid, yields _o_-cresol-_p_-sulphonic acid. + +The phenolsulphonic acids are strong, rather stable acids; their +alcoholic hydroxyl-hydrogen atom may, similarly to that of the phenols, +be substituted by a metal or an alkyl radical. + +From [Greek: a]- and [Greek: b]-naphthol a number of sulphonic acids may +easily be prepared; viz., mono-, di-, and trisulphonic acids. Nearly +all these acids are important as basic materials in the dyestuff +industry, especially 2,6-[Greek: b]-naphtholmonosulphonic acid (S-acid), +2,3,6-[Greek: b]-naphtholdisulphonic acid (R-acid) and 2,6,8-[Greek: +b]-naphtholdisulphonic acid (G-acid). + + +2. Condensation of Phenols + +Phenolsulphonic acids exhibit pronounced tendencies to condensation, for +which purpose A. v. Baeyer (1872) employed aldehydes. The reaction is +rather violent, and yields, in addition to well-defined crystalline +substances, amorphous bodies resembling rosins. In addition to +formaldehyde, paraformaldehyde, trioxymethylene, methylal, +hexamethylene-tetramine, and other substances containing a reactive +methylene group, as well as acetaldehyde, benzaldehyde and other +aldehydes may be employed to induce reaction. + +A number of these condensation products are derivatives of diphenylamine +or hydroxybenzyl alcohols. When the latter are heated, either by +themselves or in presence of acids, anhydrides and polymerisation +products are formed producing hard, brittle, fusible substances, +insoluble in water but fairly soluble in organic solvents. The same +substances are formed when phenols are condensed with formaldehyde, +especially in the presence of acid contact substances and excess of +phenol by sufficiently long heating at certain temperatures. The +substances referred to are termed "Novolak": similar to these are the +so-called "Resols," insoluble and non-fusible substances, very resistant +to chemical and physical action. Another member of the series is the +so-called "Bakelite" or "Resitol," which does not fuse but softens when +heated and swells in organic solvents. The ultimate product of this +class of substances is "Resit" which is obtained when concentrated +hydrochloric acid is allowed to act upon a mixture of phenol and +formaldehyde; the temperature rises spontaneously, and a hard, porous, +insoluble mass of great resistance is obtained. By heating resols, +resitols are formed which, on further heating, are finally converted +into resits. [Footnote: _Ber.,_ 1892, 25, 3213.] + +Of all these products, bakelite (resitol) has found the greatest +industrial application; in its purest form, this substance is a nearly +colourless or light yellow body of sp. gr. 1.25 and, being a poor +conductor of heat and electricity, constitutes an excellent insulating +material; it is exceedingly resistant towards most chemical reagents +even in concentrated forms of the latter. Its pronounced refractivity, +and the ease with which it may be worked, makes bakelite a favourite +substitute for amber (Ger. Pat, 286, 568). Similarly, the resols which +can be easily moulded are used either as such or mixed with sand, +pulverised cork, asbestos or wood, and the moulded substances then +converted into the more highly resistant bakelite by heating. + +The constitution of these bodies no doubt depends largely on their +method of preparation; Baekeland [Footnote: _Chem. Ztg.,_ 1913, 73, +733.] considers resit a polymerised hydroxybenzylmethylene glycol +anhydride; Raschig, a diphenylmethane derivative (e.g., +dihydroxydiphenylmethane alcohol); Wohl [Footnote: _Ber.,_ 1912, 45, +2046.] considers them polymerisation products of methylene derivatives +of tautomeric phenol. + + CH===CH + H_2C:C{ }CO + CH===CH + [Note: Lower Right CH has double bond to CO] + +This group possesses the characteristic property of being capable of +converting animal hide into leather when suitably dissolved. The author +has dissolved a number of these water-insoluble condensation products in +alkali and alcohol and was able to demonstrate their tanning effects on +pelt; bakelite is easily soluble in alkali; a faintly alkaline solution +partially precipitates gelatine, and completely so when the alkali is +neutralised. This latter solution gives a dirty brown precipitate with +iron salts. + +These condensation products gained extraordinary importance for the +tanning trade when Stiasny [Footnote: Ger. Pat, 262,558; Austr. Pat, +58,405.] succeeded in preparing them in water-soluble form when they are +enabled to directly exert their tannoid properties. This may be done by +acting upon two molecules of concentrated phenolsulphonic acid with one +molecule of formaldehyde, the temperature thereby not exceeding 35°C. By +condensation, however, considerable heat is liberated, and hence the +rise in temperature can only be limited by adding the diluted +formaldehyde drop by drop, whilst stirring and cooling, to the +phenolsulphonic acid. The original letters patent is worded as follows: +10 kilos each of crude phenol and sulphuric acid (66° Bé.) are heated +with stirring for two hours at 105°-106°C., cooled to about 35°C., and +463 kilos 30 per cent. formaldehyde added during three hours, the +temperature thereby not exceeding 35°C.; the stirring is continued for a +couple of hours after the final addition of formaldehyde. This yields +about 24 kilos of the crude condensation product. On a commercial scale, +however, cresol (cresylic acid) is substituted for phenol. There are +three isomers of cresol, viz., _o_-, _m_-, and _p_-cresol, and it was +naturally of interest to investigate whether one or the other of the +isomers exerted any particular influence on the properties of the final +product. It was found, however, that condensation products from the +three isomers were distinguishable from one another neither in physical +nor in tannoid properties. It is hence possible to employ crude cresol, +which contains varying quantities of the _o_-, _m_-, and _p_-compounds, +in the manufacture of these tanning matters. [Footnote: Gen Pat, +291,457.] + +The tar obtained from the Rochling coal-gas generator contains +considerable quantities of phenols (B.P.=200°-250°C.), and the author +has protected the use of these for the production of synthetic tannins +by Ger. Pat, 262,558. A deep brown viscous mass is obtained which, when +partly neutralised, yields similar results to those given by the product +above referred to. + +It may be anticipated that by analogy from the chemical reactions taking +place in the condensation of phenols on the one hand and cresolsulphonic +acid on the other, that all other homologues of phenol, its polyvalent +derivatives, substitution products and acids, would yield similar +condensation products. + +The particular position occupied by the aromatic hydroxy compounds in +the chemistry of substance possessing tannoid character is not only +evidenced by the natural classification of the tannins, tannin +derivatives, and decomposition products so far isolated and +investigated, but also by other chemical behaviour shown by these +substances. Meunier and Seyewetz [Footnote:_Collegium_, 1908, 315, +195.], for example, were able to show that phenol, _p_-aminophenol, +chlorophenol, trinitrophenol, catechol, resorcinol, hydroquinone, +monochlorohydroquinone, orcinol, pyrogallol, and gallotannic acid +precipitate gelatine from its aqueous solution, that is, to a certain +extent possess tanning properties. + +The author has extended this series somewhat and obtained the following +results:-- + + Relative Behaviour Towards + Substances Gelatine. Hide Powder. Pelt. + Tribromophenol Slight ppte. Tans Surface tannage + [Footnote: In alcoholic solution] + _o_-Nitrophenol No ppte. " " + Br-_o_-Nitrophenol Slight ppte. " " + Tribromopyrogallic Ppte. " " + acid + Bromophloroglucinol " " No tannage + Galloflavine Slight ppte. " " + Bromosalicylic acid " " " + Bromo-[Greek: b] " " Tans + -naphthol + [Footnote: In alcoholic solution] + Rosolic acid " " " + [Footnote: In alcoholic solution] + Gallic acid No ppte. No tannage No tannage + + +By the condensation of their sulphonic acids, it may be demonstrated +experimentally how the tannoid properties of nearly every member of the +series are intensified. Investigattion in this direction, however, has +not been systematically undertaken, for which reason the author +determined to examine this subject; but the enormous number of samples +required, obtainable only with great difficulty during the war, made it +impossible to conclude completely the researches in this field. What +little has so far been done relatively to this subject should, when +collected, indicate the way to be pursued in this wide field of +investigation. What follows will hence comprise the conversion of a few +of the most important members of this series of substances into their +methylene-condensation products with a brief discussion of the +qualitative and tannoid reactions of the latter. + +The didepside of phenolsulphonic acid is obtained by condensing +carbomethoxyphenolsulphonic chloride with sodium phenolsulphonate in the +presence of the calculated amount of caustic soda. A product of the +composition + + CH_3.0.COO.C_6H_4SO_2.0.C_6H_4.SO_3Na + +is first obtained, which on saponification with soda yields the +pure didepside-- + + HO.C_6H_4.SO_2.C_6H_4.SO_3.Na + +By acidifying the concentrated solution the didepside is obtained as a +white crystalline substance; a solution of which precipitates gelatine +without, however, exhibiting any tanning effect upon animal hide. If, on +the other hand, the above ester is converted into the chloride + + CH_3O.COO.C_4H_4SO_2.O.C_6H_4.SO_2Cl + +by treatment with PCl_5, and the chloride thus obtained further +condensed with sodium phenolsulphonate, saponified, and the solution +acidified, the pure tridepside + + HO.C_6H_4.SO_2.O.C_6H_4.SO_2.O.C_6H_4.SO_3Na + +is precipitated as white crystalline needles which not only precipitate +gelatine, but are capable of converting animal hide into +leather.[Footnote: _Chem. Ztg._, 1919, 43, 318.] + +Of the class of hydroxy-cymenes _thymol_, + + C_6H_3.CH_3.C_3H_7OH, + +was converted into the water-soluble sulphonic acid by warming with +concentrated sulphuric acid at 50° C., the sulphonic acid being +subsequently easily condensed with formaldehyde by slightly heating the +mixture. The condensation product thus obtained is a viscous brown mass +which is easily soluble in water, precipitates gelatine completely, +gives a bluish-black coloration with iron salts, and gives a precipitate +with aniline hydrochloride. To investigate its tannoid properties, the +mixture was brought to the acidity 1 gm = 10 c.c. N/10 NaOH and a piece +of bated calf skin was then introduced into a solution measuring about +2° Bé. After eighteen hours the pelt was nearly tanned through, and a +further twenty-four hours completed the tanning process, after which a +light fat-liquor was given. The dried leather was brownish-grey in +colour, possessed soft and full feel and good tensile strength. + +On account of their importance, the three dihydroxybenzenes were +examined with a view to test their suitability for conversion into +tannoid substances. + +_o_-Dihydroxybenzene, catechol, yields a sulphonic acid easily soluble +in water, which on the careful addition of formaldehyde assumes a blue +colour. The compound thus obtained may be heated to 100° C., without +depositing insolubles. A further addition of formaldehyde, however, +results in the formation of a considerable quantity of insolubles whilst +the liquid assumes a brown coloration. If, on the other hand, the +sulphonic acid is diluted with twice its volume of water, formaldehyde +added and the mixture heated on the water bath, the liquid immediately +turns brown, the formaldehyde is completely fixed, and a condensation +product soluble in water results. The latter gives a brownish-black +coloration with ferric chloride, completely precipitates gelatine, but +gives no opalescence with aniline hydrochloride. Tanning experiments +with the partly neutralised (1 gm.= 10 c.c. N/10 NaOH) substance +resulted in both grain and flesh being tanned with a black colour, +whereas the interior of the pelt was pickled (white colour). After a +further forty-eight hours, however, the black colour penetrated the +pelt, and tannage was complete. The washed and lightly fat-liquored +leather was soft, of full feel and good tensile strength, and was +greyish coloured throughout. + +With regard to the black colour possessed by leathers tanned with +synthetic tannins the following should be noted. When sulphonating and +especially when condensing substances, black dyestuffs or very finely +divided carbon in the colloidal state are often formed. Such a substance +does not deposit the black particles, even when filtered through kaolin, +and hence convert pelt into leather possessing black colour on the +surface. The hide in this case acts as a perfect filtration medium, +whereby the surface layers retaining the coloured particles assume their +colour; thus only the pure tanning matter enters into the interior, +which then, according to the composition of the former, imparts a colour +varying from white to light brown to the inner layers. + +_m_-Dihydroxybenzene, resorcinol, is also easily sulphonated by +concentrated sulphuric acid, the brownish-coloured sulphonic acid being +easily soluble in water. If the sulphonic acid is diluted with three +times its volume of water, cooled down, a few drops of formaldehyde +added and the mixture heated on the water bath to completely fix the +formaldehyde, and this process repeated till no more formaldehyde is +taken up, a brown water-soluble condensation product results, the +aqueous solution of which precipitates gelatine completely, aniline +hydrochloride only partly and which gives a deep blue colour with ferric +chloride. + +A piece of calf skin immersed in a solution of the partly neutralised +(as above) product was tanned through in twenty-four hours; when lightly +fat-liquored, the resulting leather possessed a yellowish-green colour +and good tensile strength, and was soft and full. + +_p_-Dihydroxybenzene, hydroquinone, was converted into the water-soluble +sulphonic acid by heating it with concentrated sulphuric acid at 100° +C.; the sulphonic acid, mixed with formaldehyde at ordinary temperature, +immediately solidifies to a white mass, which is soluble in water and +which had completely fixed the formaldehyde. If, however, this mass is +heated for some time to 100°C, it assumes a light brown coloration and +its solubility in water is diminished. A slight excess of formaldehyde +and the application of heat result in dark violet insoluble condensation +products. The aqueous solution precipitates gelatine, gives a deep blue +colour with ferric chloride, but gives no precipitate with aniline +hydrochloride; on the other hand, addition of potassium nitrite produces +the yellow colour characteristic of hydroquinone. + +The product effects a slower tannage (seven days) than the former +product, when a brown, soft, but rather empty leather of good tensile +strength is obtained. + +Of the _trihydroxybenzenes_ pyrogallol and phloroglucinol only were +included in these investigations. + +When pyrogallol is sulphonated with concentrated sulphuric acid a +violet-coloured sulphonic acid, soluble in water, is obtained, which, +when treated with formaldehyde first in the cold and then when heated, +yields a solid deep red-coloured mass, which precipitates gelatine but +not aniline hydrochloride, and gives a blackish-brown colour with ferric +chloride. The partly neutralised substance in aqueous solution tans pelt +in twenty-four hours with black colour on the surface only, the +intermediary layer being pickled (white colour) only, but the +black-coloured tanning matter ultimately penetrates the pelt, which +tanned through in seven days. The resultant leather is coloured black +throughout, is full, soft, and possesses good tensile strength. + +Sulphonation of phloroglucinol succeeds at higher temperatures only, the +sulphonic acid being a solid which is scarcely soluble in water, the +latter then assuming a wine-red colour. The condensation +product--prepared as described for resorcinol, but requiring higher +temperature--is a brick-red powder, insoluble in water. + +The same end-product also seems to be obtained by simply heating the +sulphonic acid at a higher temperature; this also induces condensation +with the formation of a reddish-brown mass insoluble in water. It is, of +course, impossible to attempt any tanning experiments with this product +in aqueous solution; attempts at dissolving the condensation product in +alcohol proved barren of result, since only traces of impurities +accompanying the substance dissolved, imparting a light reddish-brown +colour to the solution. In highly concentrated alcohol, however, the +condensation product is somewhat soluble, yielding a reddish-brown +solution. A piece of pelt introduced into the alcoholic solution was +surface tanned only after forty-eight hours, leaving the remainder of +the pelt pickled; extending the experiment over a further four days +produced no change in the pelt. The latter was therefore rinsed with +water, lightly fat-liquored and dried, when a soft but empty leather of +grey colour and good tensile strength was obtained. It appears, +therefore, to be a case of pseudo-tannage, where an infinitesimal amount +of synthetic tannin produces a tanning effect without, however, a true +tannage being effected. + +The Elberfelder Farbenfabriken have protected the use of the +condensation products of di- and polyhydroxybenzenes by Ger. Pat., +282,313; owing to the high cost of the latter substances, however, it is +doubtful whether synthetic tannins prepared from these materials would +not be too expensive for any other than pharmaceutical purposes. + +Before leaving the phenols, mention must be made of the quinones, the +use of which for tanning purposes was first protected by Ger. Pat., +206,957 (30th April 1907). According to this patent, only 400 gm. of +quinone are required for the conversion into leather of 400 kilos pelt, +drum tannage being preferable. During the process the leather first +assumes a reddish colour, changing through violet to brown; its +resistance to water, acids, and alkalies is said to be considerably +greater than that exhibited by all other kinds of leather. + +The chemistry of the quinone tannage has been investigated, and an +explanation given by Thuau [Footnote: _Collegium_, 1909, 363, 211.] +assumes a reaction between the quinone and the amino groups of the hide +protein with the formation of hydroquinone-- + + +-O OH + | | | + 2R.NH_2 + 2C_8H_4 | = C_6H_4 + C_6H_4(O.NH.R)_2 + | | | + +-O OH + (Pelt.) (Leather.) + +Fahrion has shown that, during the tanning process, the quinone loses +its active oxygen, and this can only be brought about by the amino group +of the hide protein, the amino group only being capable of effecting +reduction of the quinone. An analogy is here offered by +dianilinoquinone. A spent quinone liquor contains considerable amounts +of hydroquinone. The tannage may also be effected by exposing pelt +saturated with hydroquinone to oxidation by the air. The pelt, which is +unaltered by the hydroquinone bath, on being removed from the latter, +and in the presence of alkali, assumes a red colour at first, which +changes into violet, blue, and finally brown, the pelt being thereby +converted into a quinone-tanned leather. + +It may be noted that quinone only effects pseudo-tannage; quinone mixed +with water deposits, in time, a black amorphous substance practically +insoluble in water. This substance is easily adsorbed by hide powder, +but is not capable of converting the latter into that insoluble form +into which it is converted by the natural tannins. + +Amongst polyhydric alcohols, the behaviour of the methyl ester of +catechol, _guaiacol_ was investigated. The sulphonic acid was prepared +by heating guaiacol with concentrated sulphuric acid, the resulting +water-soluble product possessing a light, brownish-green colour. On +condensing the sulphonic acid with formaldehyde, the same precautions +were observed as in the case of resorcinol, but complete fixation of the +formaldehyde could only be obtained by finally heating the product for a +short time over a free flame, at about 105° C. Condensation was +indicated by the brownish appearance of the liquid. No insoluble +products were formed. The condensation product easily dissolves in +water, the solution assuming a rich brown colour and exhibiting the +following reactions: gelatine is completely precipitated, aniline +hydrochloride produces opalescence, and ferric chloride a deep brown +coloration. + +Tannage, with the partly neutralised product, was rapid, the pelt being +nearly tanned through in twenty-four hours, excepting a small white +streak in the middle; after a further twenty-four hours this streak had +vanished, and the completely tanned, dark grey-coloured leather, after +washing, fat-liquoring, and drying, was soft, full, and of good tensile +strength, very similar to the leather yielded by the +catechol-condensation product. + +Of the nitro-compounds, trinitrophenol, C_6H_2(NO_2)_3OH (picric acid), +was investigated. If a concentrated solution of picric acid is brought +into contact with pelt it will penetrate the latter completely in a few +days; it is, however, difficult to fat-liquor the resultant leather, +since the fat is absorbed only with difficulty. If a pelt treated in +this way be dried, a soft but rather flat leather results, the colour of +which easily rubs off, the leather also tasting intensely bitter. These +disagreeable qualities prevent a general use of this material for +tanning purposes; in spite of them, however, picric acid, in admixture +with boracic acid, salicylic acid, and glycerol, is used in the +production of the so-called transparent leather. The latter is very +flexible and possesses great tensile strength, but loses the latter +quality when exposed to heat, and, when stored, also loses its +flexibility. By simply washing with water, the leather is reconverted +into pelt. + +When picric acid is treated with hot sulphuric acid and formaldehyde +gradually added, a dark coloured water-soluble condensation product is +formed which strongly precipitates gelatine. Exposed to the action of +bromine, the condensation product yields a mass which is insoluble in +water. + +Experience has taught that the amino bodies--the basic N-derivatives of +the phenols--do not yield substances possessing tannoid properties on +condensation. On account of their importance, however, a few have been +included in this series of investigations. + +Aminobenzene, C_6H_5NH_2, aniline, treated with sulphuric acid, yields +the water-soluble aniline sulphate, which, on cautious addition of +formaldehyde, yields a reddish-coloured gel, insoluble in water, in +addition to a small volume of a reddish-yellow liquid. The latter +precipitates gelatine, but is not capable of converting pelt into +leather. The insoluble gel is likewise insoluble in alcohol, so that +tanning experiments with this substance are excluded. + +Dimethylaniline, C_6H_5N(CH_3)_2, when treated with sulphuric acid, yields a +product soluble in water which neither reacts with nor fixes +formaldehyde. Hence the substance does not precipitate gelatine. + +If, on the other hand, nitrosodimethylaniline, + + NO + | + C_6H_4 + | + (CH_3)_2 + +is sulphonated, and the water-soluble sulphonation product heated with +formaldehyde for some time, the product remains soluble in water and +precipitates gelatine. No tanning effect could, however, be detected. + +Arylsulphaminoarylsulphonic acids and arylsulphoxyarylsulphonic acids +precipitate gelatine but are devoid of tannoid character. The latter is +acquired by compounds belonging to this class containing two or more +sulphamino groups, or when they, in addition to one sulphamino group, +contain a sulphoxy group and another sulphonic group. According to +Ger. Pat., 297,187 (Society oc Chemical Industry, Basle), such compounds +are obtained when, for instance, sodium sulphanilide in alkaline +solution acts upon nitrotoluenesulphochloride, and the resulting +nitrotoluenesulphamino compound is subsequently reduced with acetic acid +and iron. The resulting aminotoluenesulphaminobenzenesulphonic acid is +finally treated with p-toluenesulphonic chloride till the latter +disappears. A compound of the composition + + -----NH-----SO_2----- + ^ ^ ^ + | | | | | | + | | | |---NH---| | + V V V + SO_2Na CH_2 + +is thereby obtained, which, when acidified, is readily capable +of being used for tanning purposes. + +The intermediary product of the aminotoluenesulphaminobenzenesulphonic +acid obtained by this process may again be employed for the purpose of +reacting with one-half molecule soda and 1 molecule +nitrotoluenesulphonic chloride. The following compound is obtained-- + + ---NH---SO_2--- ---NH---SO_2--- + ^ ^ ^ CH_3 ^ + | | | | | | | | + | | | | | | | | + v v ---NH---SO_2--- v v + SO_3Na CH_3 CH_3 + +If _p_-toluenesulphaminobenzenesulphonic chloride is condensed +with sodium sulphanilide, a compound, + + ---SO_2---NH--- NaSO_3 + ^ ^ ^ + | | | | | | + | | | | | | + v v ---SO_2---NH--- v + SO_3Na + +is obtained which, when acidified, exhibits tannoid properties. + +On condensing sodium phenolsulphonate with nitrotoluenesulphonic +chloride, reducing the condensation product and condensing the latter +with _p_-toluenesulphonic chloride, a compound similar to the above is +obtained-- + + ---O---SO_2--- + ^ ^ ^ CH_3 + | | | | | | + | | | | | | + v v ---NH---SO_2--- v + NaSO_3 CH_3 + +Again, a similar product is obtained when +_p_-toluenesulphaminobenzenesulphonic chloride or its homologues or +isomers are condensed with sodium-_o_-cresylsulphonate-- + + ---SO_2---NH--- SO_3Na + ^ ^ ^ + | | | | | | + | | | | CH_3| | + v v ---SO_2---O--- v + CH_3 + +The chloride of this compound may again be condensed, for instance, with +sodium aminotoluenesulphaminobenzene-sulphonate, and yields the +compound-- + + ---NH---SO_2--- + ^ ^ ^ ---NH---SO_2--- ^ + | | | | | | | | + | | | | | | | | + v v ---NH---SO_2--- v v CH + NaSO_3 CH_3 + +The three latter compounds, when dissolved in water and the solution +acidified, exert tanning action. + +It is also possible to employ mixtures of arylsulphaminobenzylsulphonic +acids in acidified aqueous solution for tanning purposes. According to +Ger. Pat., 297,188, such mixtures are obtained by nitrating +benzylchloride and heating with an equimolecular amount of sodium +sulphite; the sodium nitrobenzylsulphonate thus obtained is reduced to +aminobenzylsulphonic acid with iron and acetic acid, and finally +condensed with the calculated amount of _p_-toluenesulphonic chloride. A +mixture _o_- and _p_-toluenesulphaminobenzylsulphonic acid [Footnote 1: +Cf. also Ger. Pat, 319,713 and 320,613.] thus results. + +Amongst _aromatic alcohols_ the dihydric alcohols show characteristic +behaviour; the latter combine with sulphonic acids with the elimination +of water, condensation taking place without formaldehyde, and the +resulting products being soluble in water and possessing tannoid +properties. [Footnote 2: Ger. Pat., 300,567, of 20th September 1917.] +In addition to phenolic mono- and disulphonic acids (and higher +sulphonation compounds), the homologues, cresols, xylenols, and +naphthols enter into reaction. The two components condense with great +ease, liberating heat; dilute solutions (of the components) are heated +to about 100° C., the process being complete in a few minutes. The +products obtained are exceedingly pure and are easily +crystallisable. Employing 1, respectively 2, molecules of sulphonic +acid, the reactions take place according to:-- + + OH CH_2.OH OH OH + }C_6H_4 + HO.C_6H_3{ = H_2O + }C_6H_3-CH_2-C_6H_3{ +HSO_3 CH_2.OH HSO_3 CH_2.OH + + OH + OH CH_2.OH CH_2.C_6H_3{ + }C_6H_4 + HO.C_6H_3{ = 2(H_2O) + HO.C_6H_3{ HSO_3 +HSO_3 CH_2.OH | OH + CH_2.C_6H_3{ + HSO_3 + + OH CH_2.OH OH OH + }C_6H_3.CH_3 + HO.C_6H_3{ = H_2O + }C_6H_2.CH_3.CH_2.C_6H_3{ +HSO_3 CH_2.OH HSO_3 CH_2.OH + + OH + OH CH_2.OH CH_2.C_6H_2.CH_3{ + }C_6H_3.CH_3 + HO.C_6H_3{ =2(H_2O) + HO.C_6H_3{ HSO_3 +HSO_3 CH_2.OH | OH + CH_2.C_6H_2.CH_3{ + HSO_3 + + OH CH_2.OH OH OH + }(C_10)H_6 + HO.C_6H_3{ = H_2O + }(C_10)H_5.CH_2.C_6H_3{ +HSO_3 CH_2.OH HSO_3 CH_2.OH + + OH + OH CH_2.OH CH_2.(C_10)H_5{ + }(C_10)H_6 + HO.C_6H_3{ =2(H_2O) + HO.C_6H_3{ HSO_3 +HSO_3 CH_2.OH | OH + CH_2.(C_10)H_5{ + HSO_3 + +The condensation products above enumerated were tested with regard to +their tanning power, both non-neutralised and partly neutralised (1:10, +1:20, and 1:30 c.c. N/10 NaOH) samples being examined. In all cases +rapid tannage was observed yielding firm and soft leathers of light +brown colour and varying degrees of swollenness. + +Relatively to their reactions, all the products strongly precipitate +gelatine, whereas only the condensation products of phenol, cresol, and +xylenol derivatives give a characteristic coloration with iron salts. + +The tannin contents of the non-neutralised condensation products lie +between 72-80 per cent.--figures which clearly indicate the purity and +efficiency of these substances. + +Notable amongst _aromatic acids_ is salicylic acid, C_6H_4.OH.COOH, +which at higher temperatures is easily sulphonated with concentrated +sulphuric acid; the sulphonation product represents a white solid, which +easily dissolves in water forming a clear liquid. The sulphonic acid, +when mixed with about one-third of its weight of water and heated to +about 120° C., is easily condensed with formaldehyde. Towards the end +of the reaction, considerable frothing sets in, but in spite of the high +temperature required by this reaction no insoluble bakelites are +formed. A reddish-brown fluid is obtained easily soluble in water, to +which it imparts a brown colour. An aqueous solution of the product +completely precipitates gelatine, gives a strong opalescence with +aniline hydrochloride and a deep violet coloration with ferric chloride. +Neutralised as usual, the product, in a 3° Bé solution, converts pelt +within three days into a white, full leather of good tensile strength. + +This process has been patented by the Deutsch-Koloniale Gerb und +Farbstoff Gesellschaft (German-Colonial Tanning and Colour Extracts +Ltd.) in Karlsruhe, the letters patent also including the ring +homologues of salicylic acid. Similar results are obtained when +cresotinic acid (hydroxy-toluic acid), OH.C_6H_3.CH_3.COOH, is employed +as base. + +If the phenyl ester of salicylic acid, _Salol_, + +HO.C_6H_4.CO.O.C_6H_5 + +is sulphonated, a product is obtained which is easily soluble in water, +but which is identified as a mixture of the sulphonation products of +salicylic acid and phenol, the salol being dissociated on +sulphonation. The temperature must not exceed 80° C. by condensation +with formaldehyde, or insoluble bakelite will be formed from the phenol; +the aldehyde must also be added gradually. An aqueous solution of the +partly neutralised condensation product has a pronounced tanning effect +on pelt, and converts the latter into leather in one to two days; the +leather being very similar to that produced by the salicylic acid +condensation product. The qualitative reactions of the product in +aqueous solution are the same as those given by the salicylic acid +condensation product. + +Salicylic acid may, however, also be condensed with formaldehyde without +first being sulphonated; in this case, a little hydrochloric acid should +be present. A product slightly soluble in water is obtained, which may +be looked upon as being methylenedisalicylic acid. In alkaline solution +it is easily soluble, + +[Footnote 1: Its solubility in alcohol and alkalies renders this product +an effective and cheap substitute for shellac.--_Transl._] + +the liquid possessing an intensely bitter taste. The sodium salt gives a +deep violet coloration with ferric chloride, a slight precipitate with +gelatine, and slight opalescence with aniline hydrochloride. In contact +with pelt, however, it exhibits no tanning effect, but when dissolved in +alcohol, a pickling effect may be observed. + +[Footnote 2: A similar reaction is observable in the case of the sodium +salts of METHYLENEDISALICYLIC acid brommated or iodised, which form a +clear solution varying from red to reddish-brown.] + +The attempt at preparing a condensation product from +sodium-_m_-hydroxybenzoate by means of formaldehyde and bisulphite is +worthy of attention. A dark brown, viscous liquid is obtained which is +perfectly soluble in water, and the aqueous solution of which gives +opalescence with gelatine, a precipitate with aniline hydrochloride, and +a bluish-black coloration with ferric chloride. Its behaviour towards +pelt is very similar to that of phenolsulphonic acid, and it yields a +similar leather. + +A very similar condensation product was obtained by condensing +sodium-_p_-hydroxybenzoate with formaldehyde and subsequent sulphonation +with sulphuric acid. From a practical standpoint, however, these +substances cannot be employed, since their tanning action is only +effective in acid solutions of such concentration of acid as would +gelatinise the pelt.3 + +If, on the other hand, non-condensed methane derivatives of phenol, +_e.g._, hydroxyphenylmethanesulphonic acid, are partly neutralised and a +solution of the product thus obtained used for tanning experiments, no +tanning action is observable. The acidified solution does not +precipitate gelatine, and gives a dark brown coloration only with ferric +chloride. + +GALLIC ACID, C_6H_2(OH)_3COOH, when heated with sulphuric acid, is +easily converted into the insoluble rufigallic acid, which is also +insoluble in alcohol. If, however, gallic acid is heated with an excess +of sulphuric acid, the product cooled and treated with formaldehyde, a +deep brown condensation product is obtained which is soluble in alcohol, +and in this state is capable of converting pelt into a substance similar +to leather which, though rather hard, possesses good tensile +strength. This water-insoluble condensation product is also soluble in +alkalies, the solution exhibiting properties similar to that described +above. Gallic acid, therefore, is not a suitable base for the production +of synthetic tannins soluble in water. + +Phthalic acid also is difficult to sulphonate: the sulphonated compound +treated with formaldehyde gives only water-insoluble condensation +products. + + +3. Condensation Of Naphthalene Derivatives + +The simplest method of condensing [Greek: b]-naphthalene-sulphonic acid +is to heat it at 135° C. at a pressure of 20 mm. for several +hours.[Footnote: Austr. Pat., 61,061, of 10th September 1913.] The +resulting product is a cheesy mass which reacts strongly acid. By +reducing the acidity of the substance to 1 gm. = 10 c.c. N/1O NaOH, a +grey, cheesy mass results, which easily dissolves in water, the solution +being coloured a light yellow-brown and precipitating gelatine aniline +hydrochloride; no coloration, however, appears on adding ferric +chloride. + +The condensation of [Greek: b]-naphthalenesulphonic acid, however, +proceeds with much greater energy in the presence of formaldehyde. In +practice, for instance, 10 kilos of naphthalene is heated with the same +weight of concentrated sulphuric acid (66° Bé), when the mixture is +converted into [Greek: b]-naphthalenesulphonic acid by heating for +several hours at 150°-160° C; the sulphonation completed, the sulphonic +acid is cooled to about 85° C., and 4 kilos of formaldehyde (30 per +cent, by weight) slowly added; finally, the product is stirred at the +temperature mentioned till all formaldehyde has combined.[Footnote: +Austr. Pat., 69,194, of 25th June 1915; Ger. Pat, 290,965.] + +Tanning experiments with this product yielded, in a short time, a nearly +white coloured leather (see later). + +In addition to formaldehyde, there are other substances which induce +condensation of naphthalenesulphonic acid; if, for instance, sulphur +chloride is allowed to act upon [Greek: b]-naphthalenesulphonic acid, a +light brown solid of pronounced acidic character is obtained; if the +latter is partly neutralised with caustic soda, a greyish-brown solid +results, which dissolves in water with a light brown colour, the +solution precipitating gelatine and aniline hydrochloride, but giving no +coloration with ferric chloride.[Footnote: Austr. Pat., 96,194.] + +Tanning experiments with this product in aqueous solution gave a light +brown, rather soft leather, and this, in addition to the qualitative +reactions of the substance, prove that this method of condensation +hardly alters the character of the product from a tanning point of +view. The brown coloration imparted to the leather tanned with this +condensation product owes its existence to coloured intermediary +products. + +Attempts at condensing chloronaphthalenesulphonic acid and +nitronaphthalenesulphonic acid resulted in soluble condensation products +which gave some of the reactions given by the tannins (precipitation of +gelatine and aniline hydrochloride), but which were incapable of tanning +pelt, a light tannage being effected on the surface only. + +[Greek: a]-Naphthol dissolved in hot concentrated sulphuric acid and +heated for some time on the water bath, yields the light brown, +water-soluble [Greek: a]-naphtholsulphonic acid. A dilute solution of +the latter, when treated with formaldehyde in the cold, undergoes no +change; on heating the mixture on the water bath a brown precipitate is +thrown down. If gelatine solution is added to the opaque liquid, a +yellow flocculent precipitate separates. If caustic soda is added to the +opaque liquid containing the condensation product described above, a +clear solution results from which no deposit separates on the addition +of acetic acid. Gelatine is precipitated by this solution. + +The concentrated hot a-naphtholsulphonic acid, upon addition of +sufficient formaldehyde, effervesces strongly and yields a dark brown +condensation product insoluble in water, but soluble in caustic soda. If +acetic acid is added in excess to the alkaline solution, the resultant +solution strongly precipitates gelatine. + +A suspension in water of the insoluble condensation product does not +precipitate gelatine. + +b-Naphthol, dissolved in hot concentrated sulphuric acid and heated for +some time, yields the light brown, viscous b-naphtholsulphonic acid. A +dilute solution of the latter, mixed with formaldehyde, remains clear; +when heated on the water bath, however, it assumes a dark, +reddish-yellow colour, and remains soluble in water and precipitates +gelatine strongly. This condensation product, on adding excess of +caustic soda, assumes a deep blue coloration, the alkaline solution +giving no precipitate with gelatine; on adding acetic acid the solution +turns brown, remains clear, and now precipitates gelatine. + +The concentrated b-naphtholsulphonic acid heated with formaldehyde on +the water bath yields as condensation product a dark, reddish-yellow +mass, soluble in water, which precipitates gelatine. A dilute solution, +when allowed to act upon pelt, gave in a few days a light brown leather, +the properties of which are very similar to those possessed by vegetable +tanned leathers. + +The use of naphtholsulphonic and aminonaphtholsulphonic acids for the +manufacture of synthetic tannins is protected by Ger. Pats., 293,640, +293,693, 293,042, and 303,640. [Footnote: _Cf._ Austr. Pat., 70,162.] + +It is a remarkable fact that non-condensed methane derivatives of +naphthol, _e.g._, b-naphthol-a-methanesulphonic acid, dissolved in water +and partly neutralised, are devoid of tanning character when allowed to +act upon pelt. Neither does this substance precipitate gelatine, but it +does give a deep blue coloration with ferric chloride. + +The condensation product of b-naphthol above referred to precipitates +gelatine and aniline hydrochloride and gives a brown coloration with +ferric chloride. + +Thionaphtholsulphonic acid, when acted upon by formaldehyde, yields a +condensation product of the following constitution:-- + + HSO_4 ^ ^ SH SH ^ ^ HSO_4 + | | | | | | + | | |_____CH_2_____| | | + v v v v + +This is a light yellow powder which, dissolved in water, yields an +opaque solution; the latter only exhibits any tanning properties when it +is not neutralised and even slightly acidified and then precipitates +gelatine, aniline hydrochloride and barium chloride; dissolved in +alkali, it forms a clear, yellow solution devoid of tannoid +properties. Leather tanned with the acidified solution is very similar +to those tanned with the phenolsulphonic acid condensation products; its +colour, however, is more pronouncedly yellow. + +b-Naphthol condensed with hydrochloric acid and formaldehyde yields a +methylenedinaphthol, which is insoluble in water; the sodium salt, +however, easily dissolves. The same condensation, however, takes place +in alkaline solution with direct formation of the sodium salt. The +condensation product gives a slight precipitate with gelatine, and a +bluish-grey precipitate with ferric chloride; acids re-precipitate the +insoluble methylene compound. Towards pelt it exhibits tanning +properties, whereby the insoluble product referred to above is +deposited, and soft, full, and white leather is obtained, possessing, +however, but little tensile strength. + + +4. Condensation of the Anthracene Group + +Anthracene heated with excess sulphuric acid yields the water-soluble +anthracenesulphonic acid; the latter, when heated with formaldehyde, +yields water-soluble, reddish-brown condensation products, which remain +soluble on prolonged heating with formaldehyde. The aqueous solution of +the condensation product shows no particular reactions; it gives a +flocculent precipitate with gelatine and a green precipitate with copper +sulphate, soluble with blue colour in excess of the reagent. + +The partly neutralised solution tans pelt--to which it imparts a brown +colour--in eight days, but on the surface only; the inner layers are +merely pseudo-tanned (white colour). When dried, pelt thus treated +yields a full and soft leather with brown grain and flesh possessing but +little tensile strength. Hence, this condensation product exerts a +pickling rather than a tanning effect. + +Anthraquinone heated with sulphuric acid and treated with formaldehyde +in the usual manner, yields a substance which, when mixed with water, +forms an opaque, milky solution. This is not altered by excess of +caustic soda. The aqueous solution precipitates gelatine and aniline +hydrochloride; all other tannin reagents give no reaction. + +The partly neutralised solution of the condensation product exerts, in +the main, a pickling action on pelt; only the surface of which is +tanned, with brown colour, the remainder being merely pickled (white +colour). During "tannage," bakelite is formed in the liquid, and +practically all solubles originally present are deposited. The tannage +completed, a light brown, fairly soft and full leather, possessing +little tensile strength, results; this leather can be washed only with +great difficulty and approaches more the character of a pickled pelt. + +1-Hydroxyanthraquinone, 1,5-dichloroanthraquinone, +l,5-diaminoanthraquinone, 1-methylaminoanthraquinone, +1-benzoylamino, 6-chloranthraquinone, 1-_m_-toluidoanthraquinone, when +treated with sulphuric acid and formaldehyde, all yield condensation +products which are but little soluble in water, and which do not at all +precipitate gelatine. Tanning experiments with these condensation +products in alcoholic solution yielded empty leathers of pronounced +pickle character. + +If, however, 1-methylamino-4-bromanthraquinone is condensed with +sulphuric acid and formaldehyde, a condensation product is obtained +which is but slightly soluble in water, but which precipitates gelatine. + +When phenanthrequinone is heated with excess of sulphuric acid for some +time, a water-soluble, reddish-yellow coloured condensation product +results. The latter, when treated with formaldehyde in the cold and then +finally heated, gradually fixes the formaldehyde and forms a substance +soluble in water. If the heating, however, is prolonged, insoluble +bakelites are formed, which are neither soluble in alkali nor in +alcohol. + +An aqueous solution of these condensation products gives no reactions +with the usual tannin reagents, though it completely precipitates +gelatine. When acting upon pelt, the partly neutralised dilute solution +of the condensation product pickles the former, and after a few days the +pelt is converted into a light brown, full, and rather soft leather +possessing good tensile strength. + +When the condensation product is acted upon by bromine in hot aqueous +solution, an additive compound is formed and the resulting product is +soluble in water. The aqueous solution of the brominated product gives +no special reactions with the usual tannin reagents, but precipitates +gelatine completely. Its tanning action upon pelt is much slower than +that of the original condensation product; the surface of the pelt only +is tanned with brown colour, the inner pelt being only pickled (light +brown colour). When dried, a hard and empty leather of good tensile +strength is obtained, possessing mainly the properties of a pickled +pelt. + + CO OH + ^ ^ ^ +QUINIZARENE, | | | | , treated with sulphuric acid + | | | | + v v v + CO OH + +and formaldehyde, yields a condensation product which is but little +soluble in water and which does not precipitate gelatine. + +QUINOLINE, when sulphonated and condensed with formaldehyde, yields a +dark coloured condensation product, completely soluble in water; the +solution does not precipitate gelatine. + +OXYQUINOLINE exhibits similar behaviour. + +On the other hand, the use of _retene_ (methylisopropylphenanthrene), + + CH_3 ^ ___________ ^ + | | | | + | |___CH:CH___| | +C_3H_7 v v + +for the production of synthetic tannins, is protected by +Ger. Pat., 290,965 [Footnote 1: _Cf_ Austr. Pat., 69,194] + + +5. Di- and Triphenylmethane Groups + +If DIPHENYLMETHANE, (C_6H_5)_2CH_2, is heated with excess sulphuric +acid, a dark blue mass, easily soluble in water, is obtained. The +product gently heated with formaldehyde yields a brown, water-soluble +condensation product; once condensation is complete, the product will +stand stronger heat. If, on the other hand, more formaldehyde is added, +brown, water-insoluble bakelites are formed. The water-soluble +condensation product precipitates gelatine, but not aniline +hydrochloride. Dissolved in water, it possesses tannoid properties: the +pelt is, however, tanned on the surface only, the intermediary layers +being merely pickled; after four days in the solution, the pelt after +drying was found to be converted into a greyish-brown, badly coloured +leather, which was empty, hard, and possessed but little tensile +strength. + +CARBAZOLE (dibenzopyrrole), + + ^ _____ ^ + | | | | + | |__ __| | + v v v + N_3 + +on the other hand, was found a suitable base for the commercial +production of synthetic tannins; its use is protected by Ger. Pat, +290,965. + +TRIPHENYLMETHANE, (C_6H_5)_3CH, heated with excess sulphuric acid, +yields a nearly black mass which, when condensed with formaldehyde in +the cold, and subsequently heated, yields a mass which is soluble in +water. With gelatine and aniline hydrochloride it exhibits reactions +similar to those given by the diphenylmethane condensation products; its +tanning properties also are similar to those of the latter. The +resultant leather is black, but is soft and full and possesses good +tensile strength. + +Baeyer's observation, [Footnote: _Ber_., 1872, 5, 280, 1096.] that +pyrogallol on condensation with formaldehyde yields an amorphous body +soluble in water, which precipitates gelatine and is very similar to +tannin, was confirmed by Caro [Footnote: _Ibid_., 1892, 25, 947.] and +Kahl. [Footnote: _Ibid_., 1898, 31, 114.] These investigators found +that by the condensation of phenols and hydroxybenzoic acids with +formaldehyde, diphenylmethane derivatives were formed; pyrogallol yields +hexahydroxydiphenylmethane-- + + C_6H_2(OH)_3 + CH_2{ + C_6H_2(OH)_3 + +Nierenstein [Footnote: _Collegium_, 1905, 221.] repeated these +experiments, and found that in addition to the insoluble +diphenylmethanes, water-soluble bodies were formed, which latter +precipitate gelatine. The condensation product yielded by gallic acid +was identified as hexahydroxyaurinecarboxylic acid-- + + _C_6H(OH)_3COOH + C{-C_6H(OH)_3COOH + | }C_6H(OH)_2COOH + O + +which is formed in addition to hexahydroxydiphenylmethane-dicarboxylic +acid-- + + C_6H(OH)_3COOH + CH_2{ + C_6H(OH)_3COOH + +Baeyer's experiment with pyrogallol probaly also yields, according to +Nierenstein, another compound of the following constitution-- + + C_6H_2(OH)_3 + C{-C_6H_2(OH)_3 + |_}C_6H_2(OH)_2 + O + +Nierenstein considers these bodies confirmation of his hypothesis of the +existence of a "tannophor,"--CO--, in the tannins. + +This supposition was adopted by Stiasny [Footnote: _Gerber_, 1905, 233.] +and Kauschke [Footnote: _Collegium_, 1906, 362.] and the latter points +out that these easily soluable substances exhibit tanning +properties. Nierenstein [Footnote: _Ibid_., 1906 424.] was further able +to show that by all processes of condensation between phenols (or +hydroxybenzoic acids) and formaldehyde, compounds of the character of +hydroxyaurine (or hydroxyaurinecarboxylic acid) were formed in addition +to the insoluble hydroxydiphenylmethanes (or +hydroxydiphenylmethanecarboxylic acids), the former possessing the +characteristic tannophor group and hence precipitating gelatine, _i.e._, +exerting tanning action. If the formation of leather is viewed in the +light of Schiff's base, [Footnote: _Ibid_., 1905, 159.] one may +consider the constitution of a hexahydroxyaurinecarboxylic acid leather +as follows:-- + + _C_6H_2(OH)_3.COOH + C{-C_6H_2(OH)_3.COOH + |_}C_6H_2(OH)_2.COOH + R-N + +In the preparation of these and similar condensation products, +Nierenstein and Webster [Footnote: _Ber_., 1908, 41, 80.] observed a +peculiar steric effect of the carboxyl group. Each 2.5 gm. of the phenol +or the acid in question were dissolved in 30 c.c. of water, the solution +brought to boil and 5 c.c. formaldehyde (20 per cent.) and 2.5 +c.c. hydrochloric acid added drop by drop; the precipitate formed was +filtered off after twenty-four hours, dried at 110° C. to constant +weight, extracted (in a Gooch crucible) freely with water, and the +residue again dried at 110° C. till constant. The following values were +obtained:-- + + Total Insol. Aq. Sol. Aq. Oxy- + Precipitate Diphenylmethane aurinecarboxylic + in Grammes. Derivatives Acid. + + Per Cent. Per Cent. +Phloroglucinol 2.4002 100 ... +Hydroquinone 2.3716 100 ... + " 2.0542 100 ... +Pyrogallol 2.5150 100 ... + " 2.7940 100 ... +Pyrocatechol 2.9805 100 ... + " 2.9574 100 ... +Resorcinol 2.9954 100 ... + " 2.9725 100 ... +Gallic acid 2.0706 78.84 21.16 + " 1.2240 83.18 16.82 + " 1.1405 59.94 41.06 +[Greek: b]-Resorcylic acid 2.1040 51.08 48.92 + " " 2.2008 47.12 52.88 +Protocatechuic acid ... ... ... + " " ... ... ... +Vanillic acid ... ... ... +Tannin 2.0599 ... Nearly all sol. +Digallic acid 2.1042 80.16 19.84 +Leucodigallic acid 2.0041 1.94 98.06 + + +With the introduction of the carboxylic group the tendency of +condensation to diphenylmethane derivatives is lessened; by +protocatechuic acid the tendency is nil. Nierenstein considers this +reaction analogous to the formation of cork, to the genetic relation of +which with the diphenylmethane formation Drabble and Nierenstein have +referred in an earlier publication. [Footnote: _Biochemical Jour._., +1907, 2, 96.] It is hence possible that the plants may employ +formaldehyde as a methylation medium, and produce these insoluble +condensation products for the purpose of ridding themselves of the +poisonous phenols and aromatic hydroxy acids (and tannins), in addition +to oxidising processes whereby +phlobaphenes, ellagic acid, etc., are formed. + +The reaction between phenols and aldehydes has been further studied by +Michael, [Footnote: _Amer.Jour_., 5, 338; 9, 130.] who prepared a +condensation product from phenol and resorcinol with benzaldehyde, and +Russanow, [Footnote: _Ber_.9 1889, 22, 1944.] who also employed +benzaldehyde and phenol. Lipp [Footnote: Diss., Bern., 1905.] +investigated the action of benzaldehyde and piperonal on phenols, +anisoles, cresols, cresylic ether, resorcinol, and the ether of the +latter and phenol, and showed that when free phenols are condensed with +benzaldehyde the hydroxyls occupy the same position as by the +interaction between benzaldehyde and the corresponding phenolic +ethers. The resulting dihydroxytriphenylmethane derivatives form +beautiful crystals, which on oxidation are converted into benzaurines, +the constitution of the latter probably being-- + + O= ^=_____ ^ OH + | | | | + | |== __| | + =v v v + C + | + C_6H_5 + +In alkalies, the hydroxylated triphenylmethanes dissolve without +imparting any colour to the solution; by concentrated sulphuric acid +they are taken up with intense coloration. + +If the hydroxyls occupy the ortho-position to methyl, they may form +xanthenes by splitting off water-- + + O + ^ ^ ^ + | | | | + | | | | + CH_3 v v v CH_3 + CH + | + C_6H_5 + +In the benzene series this reaction is difficult to establish, and has +to be induced by distilling the particular dihydroxy-diphenylmethane at +ordinary pressure. In the naphthalene series, on the other hand, the +ring closes up by, for instance, the condensation of [Greek: b]-naphthol +with benzaldehyde or paraldehyde, and yields the following compounds:-- + + C_10H_6 C_10H_6 + C_6H_5-CH{ }O CH_3-CH{ }O + C_10H_6 C_10H_6 + +These xanthenes are white, silk-glossy needles, which are soluble in +water and in alkalies. In concentrated sulphuric acid, they are taken up +with beautiful fluorescence. + + +6. Summary + +From the qualitative reactions of the different condensation products +described it may be seen that their tannoid properties are not dependent +on whether they precipitate gelatine or are adsorbed by hide powder or +not. Hydroxynaphthylmethanesulphonic acid, for instance, precipitates +gelatine but does convert pelt into leather; on the other hand, sodium +dicresylmethanesulphonate does not precipitate gelatine, and neither +does it tan pelt; nevertheless it is adsorbed by hide powder as "tanning +matter". The author discovered that _o_-nitrophenol does not precipitate +gelatine, but has some tanning action on both hide powder and pelt. + +Relatively to the possibilities of forming condensation products +possessing tannoid properties, the following may be stated:-- + +All mono- and polyhydric phenols may be converted into true tanning +matters by either condensing them as such, or after their conversion +into the corresponding sulphonic acids, by substances capable of +eliminating the elements of water. It makes no difference to the final +product whether the condensation is the first step followed by +sulphonation and consequent solubilisation of the intermediary insoluble +product, or whether, vice versa, the sulphonic acid is subjected to +condensation. Alkaline solution of phenols may also be condensed, the +reaction products, when condensed, constituting tanning matters soluble +in water. + +Among the substitution products of the phenols, the thio-, chloro-, +bromo-, nitro-, and aminophenols as a rule yield tanning matters similar +in character. + +The quinones are as such--_i.e._, without being condensed--substances +possessing tannoid properties. + +The aromatic dihydric alcohols are easily condensed with the different +sulphonic acids and yield valuable tanning matters. + +Of aromatic acids all those which yield water-soluble sulphonation +products seem suitable for the industrial production of tanning +matters. If the acids themselves do not yield water-soluble sulphonation +products, the alkali salts of the latter may be condensed with +formaldehyde, and the resulting products then constitute tanning matters +provided their solutions can be neutralised or faintly acidified without +the solute being thrown out of solution in insoluble form. + +The diphenyl derivatives of the above groups often possess tannoid +properties. + +The same holds good of those compounds with condensed nuclei +(naphthalene, anthracene, etc.), and all their derivatives which satisfy +the above conditions. + +The choice of condensing agent is, as a rule, of little +significance. Elimination of the elements of water by the mere +application of heat succeeds in few cases only, since the high +temperature required to induce reaction in many cases causes +decomposition of the substances. This difficulty is overcome by heating +_in vacuo_. Condensation with formaldehyde always succeeds, with +acetaldehyde and benzaldehyde only partly. + +The action on hide powder, pelt, and gelatine by these characteristic +substances is tabulated below:-- + Relative Behaviour towards +Substance. Gelatine. Hide Powder Pelt +Formaldehyde ... ... Tanning +Phenol Ppte. ... ... +Chlorophenol " ... ... + Surface +Tribromophenol Slight ppte Tanning tanning +_o_ Nitrophenol No ppte " " +Bromonitrophenol Slight ppte " " +Trinitrophenol Ppte " Tanning +Bromotrinitrophenol Slight ppte " " +_p_ Aminophenol Ppte ... ... +_m_ Dihydroxybenzene " ... ... +Orcinol " ... ... +_p_ Dihydroxybenzene " Tanning Tanning +Monochloro _p_ +dihydroxybenzene " ... ... +_o_ Dihydroxybenzene " ... ... +Pyrogallic acid " ... ... + Surface +Tribromopyrogallic acid " Tanning Tanning +Gallic acid No ppte Not tanning Not tanning +Bromophloroglucinol Ppte Tanning " +Gallotannic acid " " Tanning +Galloflavine Slight ppte " Not tanning +Quinone " " Tanning +Bromosalicylic acid " " Not tanning +Dinaphthylmethanedisulphonic acid Ppte " Tanning +Diphenylmethanedisulphonic acid " " " +Dicresylmethanedisulphonic acid " " " +Sodium +dicresylmethanedisulphonate acid No ppte " Not tanning +Dixylylmethanedisulphonic acid Ppte " Tanning +Naphtholdisulphonic acid " Not tanning Not tanning +Methylenedinaphthol " Tanning Tanning +Hydroxyphenylmethanesulphonic " " " +acid Not tanning +Hydroxynaphthylmethanesulphonic Slight ppte " " +acid +Diaminonaphthylmethanedisulphonic Ppte Tanning Not tanning +acid +Dihydroxynaphthylmethanedisulphonic +acid " " " +Dichloronaphthylmethanedisulphonic +acid " " Surface tanning +Dinitronaphthylmethanedisulphonic +acid " " " +Dithionaphthylmethanedisulphonic +acid " " Tanning +Bromo _[Greek: b]_ naphthol [1] Slight ppte " " +Rosolic acid_ [1] Ppte " " + +[Footnote 1: In alcoholic solution.] + + + + +SECTION III + +TANNING EFFECTS OF MIXTURES AND NATURAL PRODUCTS + + +1. Mixture of Phenolsulphonic Acid and Formaldehyde + +The most important invention relatively to the search for new tanning +materials was that of Weinschenk,[Footnote: Ger. Pat., 184,449.] who +first showed that pelt may be converted into leather by the action upon +it of mixtures of naphthols and formaldehyde. This process consists of +two steps: the pelt is first immersed in a 0.25-0.50 per cent, +formaldehyde solution, and secondly in an aqueous solution of -[Greek: +a] or -[Greek: b] naphthol; this order may be reversed. If, on the other +hand, a pasty mixture is made of formaldehyde and naphthol, and this is +allowed to act upon the pelt, the latter is rapidly converted into +leather, but the mixture must be administered very gradually or +otherwise the insoluble methylenedinaphthol is formed outside the pelt +and hinders any tanning effect. + +Leather obtained through the action of [Greek: a]-naphthol is, when +freshly tanned, pure white and sufficiently soft and firm, but quickly +assumes a brown colour on storing; if, however, [Greek: b]-naphthol is +employed, a cream-coloured leather results, the colour of which turns +only slightly more yellowish even when exposed to the direct rays of the +sun. + +A similar process has recently (25, xii., 1915) been protected by +Ger. Pat, 305,516, granted to the Deutsch-Koloniale Gerb--und Farbstofif +Gesellschaft, in Karlsruhe. According to this patent, pelt is treated +in separate solutions, one of which is formaldehyde, the other being +that of such aromatic compounds or their salts which yield water-soluble +condensation products with formaldehyde; for example, pelt is immersed +in 2-5 per cent, solution of formaldehyde for a few days, and is +subsequently treated with 1-2 per cent neutral or faintly acidified +solutions of [Greek: a]-naphthylamine hydrochloride, resorcinol or +sodium phenate or cresylate, for several days. The resultant leather is +claimed to be soft and full and to possess good tensile strength. + +The tanning properties of mixtures of phenolsulphonic acid and +formaldehyde have been examined by the author with the following +results:-- + + I. II. III. + +Grammes formaldehyde 10 20 40 + " phenolsulphonic acid 20 50 100 + " caustic soda (sol, 40 per cent.) 10 20 40 + " water 500 500 500 + +The above solutions were made up and allowed to act upon pelt pieces +weighing 15 gm.; whereas Solution I. remained clear throughout the +experiment, Solution II. became somewhat clouded, and Solution +III. assumed a milky appearance. The pelts were tanned through in seven +days and yielded leathers which, after drying and finishing, possessed +yellow colour, long fibre, and good tensile strength, but a rather empty +feel. + +To prevent separation of insoluble matter during tannage, another +experiment was carried out, in which the pelts were first submitted to +the action of formaldehyde (10, 20, and 40 gm. in 500 c.c. water) for +three days, being subsequently removed to fresh solutions of partly +neutralised phenolsulphonic acid (_cf_. above). Similar results were +obtained, but the leather felt even more empty than those obtained by +the former experiment. + +Attempts at converting pelt into leather by first immersing the pelt in +a partly neutralised solution of phenolsulphonic acid, and subsequently +transferring it to fresh solutions of formaldehyde, gave merely negative +results; the phenolsulphonic acid effected pickling action upon the +pelt, but was subsequently quickly replaced by the formaldehyde, before +the latter had penetrated the pelt in sufficient quantity to induce +condensation, thereby exerting tanning action. + +To explain the tanning effects of these mixtures, the author analysed +the leathers resulting from the effects of the latter, and was able to +show, that in these cases also, condensation of phenolsulphonic acid and +formaldehyde takes place _inside_ the pelt, since on the one hand the +analyses left no doubt but that true tannage had been effected, and on +the other hand an ammoniacal extract of the leathers gave the typical +reaction for condensation products of phenolsulphonic acid, with aniline +hydrochloride. [Footnote: _Collegium_ 1913, 516, 142.] + +The leather analyses gave the following figures:-- + + Moisture - - - 18.30 per cent. + Fats - - - - 0.47 " + _ Ash - - - - 0.98 " +Leather { Tannin - - - 26.37 " +substance { Hide substance - - 53.88 " + +A characteristic feature is the low value of tannin, which is +considerably higher [Footnote: _Ibid_., 1913, 521, 478.] where +condensation products of phenolsulphonic acids are used as tanning +agents; the action effected by the separate constituents, therefore, is +more that of pickling. + + +2. Mixture of Phenolsulphonic Acid and Natural Tannins + +A piece of pelt was immersed in a half-neutralised solution, measuring +6° Bé., of phenolsulphonic acid, and left sixteen hours in the solution, +which completely penetrated the pelt during this time; it was then +transferred to a 12° Bé. solution of a mixture of quebracho and +chestnut, which in two days converted the pelt into a light coloured +leather possessing good tensile strength. + +By using a bath composed of half-neutralised phenolsulphonic acid and +quebracho extract in 7° Bé. solution, another piece of pelt was +completely tanned in two days. The same result was obtained by first +half neutralising the phenolsulphonic acid and then adding sulphited +quebracho extract till a 5° Bé. solution was obtained. + +A piece of pelt received a 2ş Bé. liquor composed of 3 parts of +phenolsulphonic acid and 1 part of formaldehyde for sixteen hours, and +was then completely penetrated; it was subsequently transferred to a 10ş +Bé. liquor composed of chestnut and quebracho, being completely tanned +in two days. The same result was obtained on adding sufficient sodium +sulphate to the above mixture of phenolsulphonic acid and formaldehyde +to raise the density from 2ş-3ş Bé. + +Sixty grammes of phenolsulphonic acid were partly neutralised with 100 +c.c. of a 10 per cent solution of caustic soda, and 10 c.c. formaldehyde +added to 400 c.c. of the mixture (2ş Bé.): a piece of pelt was +completely penetrated by the solution in sixteen hours, and was +subsequently tanned in two days, using an extract of 10ş Bé. Similarly, +by treating a pelt with 400 c.c. of a half-neutralised solution of +phenolsulphonic acid (3ş Bé.) plus 8 c.c. formaldehyde, and adding after +eighteen hours sulphited quebracho extract to the same bath, +strengthening the latter to 6ş Bé., the pelt was converted into leather +in two days; in this case, however, much of the tannin was precipitated +by the formaldehyde present in the solution. If, on the other hand, a +mixture of 80 gm. dilute phenolsulphonic acid (1:1 aq) and 14 gm. of +formaldehyde were cooled for several hours and subsequently strengthened +with sulphited quebracho extract to 7ş Bé., no tannin was precipitated +in the liquor, and a piece of pelt immersed in the latter was completely +tanned in sixteen hours. + +To prevent the precipitation of tannin caused by the formaldehyde, +sulphite cellulose extract (wood pulp) was substituted for sulphited +quebracho extract, and the following experiments carried out:-- + +To 200 c.c. of a 6ş Bé. sulphite cellulose extract plus 200 c.c. of +half-neutralised phenolsulphonic acid solution was added 15 +c.c. formaldehyde, and this solution tanned pelt in four days; the +resultant leather was light brown, firm, and possessed good tensile +strength and long fibre. + +Another piece of pelt was immersed in a solution of 400 +c.c. phenolsulphonic acid of 3şBé. plus 15 c.c. formaldehyde for +eighteen hours, and was then tanned in a 6ş Bé. solution of sulphite +cellulose extract. The resultant leather was extremely light coloured, +and possessed qualities similar to those described in the former +experiment. Finally, pelt was immersed in a 6° Bé. solution composed of +140 gm. of a 15° Bé. sulphite cellulose extract, 10 gm. of formaldehyde, +400 gm. water, 15 gm. phenolsulphonic acid, and 30 gm. of a 10 per cent +caustic soda solution, and was tanned in four days. This leather also +was coloured light brown, of good tensile strength, and rather firm. + +These experiments prove that when pelt is treated with formaldehyde, +phenolsulphonic acid, and vegetable tannins, the two former components +effect, more or less, actual tannage; it is admittedly a matter of some +difficulty to establish whether the effect is one of pickling or +pseudo-tannage, or whether the tannage may be considered a true one. The +final effect, however, is nearly always that of a true tannage, _i.e_., +by varying the composition of the tanning solutions leather is obtained +with properties identical with those tanned with true tannins of +vegetable origin. The only difficulty encountered in these combinations +is the property of formaldehyde, of precipitating the natural tannins, +and it is hence essential, for practical purposes, to so arrange the +combination that their value is not reduced by the property referred to. +The fact that not only compounds already existing may convert pelt into +leather, but that a similar effect is obtained _inside the pelt_, by +their components, is indeed of theoretical interest. + + +3. Tanning Effects of Different Natural Substances + +In addition to the vegetable tannins, Nature has also provided other +substances of vegetable origin, which, admittedly, do not effect tannage +in their original state, but which may, by suitable treatment, acquire +this property. The oldest information on this point is supplied by +Resch, [Footnote: _Scherer's Jour_., 1801, 6, 495.] who carried out +tanning experiments, using three parts of peat and one part of oak bark. + +By the action of nitric acid on substances of vegetable and animal +origin, Hatchett, [Footnote: _Gehlen's Jour_., 1805, 1, 545.] Chevreul, +[Footnote: _Ann. Chim_., 1810, 73, 36.] and Vogel [Footnote: +_Jour. Chem. Phys_., 1812, 6, 101.] claim to have obtained tanning +materials, whilst later, Buff [Footnote: _Ibid_., 1827, 51, 38.] +obtained a material suitable for tanning purposes from indigo. + +By subsequent treatment with lime and soot, or tar, Ashmore [Footnote: +_Dingier's Jour_., 1833, 48, 67.] claims to have converted pelt into +leather. + +By treating peat with nitric acid, Jennings [Footnote: +_Jahresber. d. Chem_., 1858, 666.] and Payne [Footnote: _ +Chem. Centralbl_., 1908, ii. 554; Ger. Pat., 200, 539.] have produced +artificial tanning materials. + +Skey [Footnote: _Chem. News_, 1866, 206; _Zeits. f. Chem_., 1866, 753.] +obtained a dark brown extract, soluble in water and precipitating +gelatine, by treating bituminous coal or lignite with nitric acid; by +extracting coal with alkalies, Reinsch [Footnote: _Pharm. Centralh_., +1887, 141.] isolated a substance (pyrofuscine) which, when partly +neutralised with carbon dioxide, was capable of converting pelt into +leather. + +In addition to these tanning materials the recovery of a substance +possessing tanning properties from the so-called acid rosins has been +made the subject of a patent; [Footnote: _Ger. Pat_., 36,019.] this +rosin is formed when crude oil is treated with concentrated sulphuric +acid in the oil refineries. The greasy substance is partly neutralised +with alkali and is claimed to produce a very springy leather. + +The waste liquors obtained in the manufacture of cellulose, the +so-called sulphite and sodium cellulose waste, have, however, been the +subject of numerous investigations, and several hundred publications +have appeared and a great number of patents [Footnote: "Literatur +überiSulfitablauge" 1910-13. (Reprint from +_WocheWochenblPapiePapierfabrikation_)] taken out, the first one being +that of Mitscherlich [Footnote: _Jahresber. d. Chem_., 1893, 890; +Ger. Pat., 72,161.] and Hönig [Footnote: _Chem. Centralbl_., 1902, +ii. 174; Ger. Pat., 132,224.] + +The waste liquors contain large quantities of acids and lime, and in +order to utilise the liquors for tanning purposes, the excessive +sulphuric and sulphurous acids as well as the lime must be removed. The +active tannin is no doubt the ligninsulphonic acid, and those cellulose +extracts containing the largest amounts of free ligninsulphonic acid may +also be considered the most efficient. + +According to the author,[Footnote: _Technikum_, 1912, 20, 156.] such +sulphitecellulose extracts precipitate gelatine, aniline hydrochloride, +ammoniacal zinc acetate, and basic coal-tar dyes, and give a +greenish-black coloration with ferric chloride. These reactions indicate +the presence of tanning matters in cellulose extracts. + +The official shake method of analysis gives the following +results:--[Footnote: _Ibid_.] + +Tanning matters 23.0 per cent. +Non-tannins 30.3 " +Insoluble matters 0.7 " +Water 46.0 " + --------------- + 100.0 per cent. + +Ash 4.3 " +Sulphurous acid 0.6 " + +Many other substances have been used for tanning experiments, a number +of them precipitating gelatine. Zacharias [Footnote: +_Zeits. f. Ang. Chem_., 1907, 1645.] obtained leather by the action of +many coal-tar dyes on pelt, similarly Herzog and Adler, by using +Prussian blue, Neufuchsin, patent blue V, crystal violet, and colloidal +gold. + +Most inorganic substances possess tanning properties when in the +colloidal state, _e.g_., sulphur, halogens, chromium salts, iron salts, +silver oxide, and the salts of mercury, copper, bismuth, zinc, lead, +platinum, cesium, vanadium, and the rare earths (salts of cerium, +lanthanum, didymium, neodymium, thorium, and zerconium). + +For practical purposes, however, only sulphur, chrome, and alum salts +are used, the latter two being of the greatest importance. + + + + +SECTION IV + +METHODS OF EXAMINING TANNING MATTERS + +Whereas the evaluation of vegetable tanning matters necessitates +determinations of their practical applicability in addition to +qualitative and quantitative analyses, the latter two determinations are +of practically no value when dealing with synthetic tannins. The way in +which tanning matters obtained by chemical means exert their action, in +addition to the intensity with which they convert pelt into leather, is +the only criterion of their quality for practical (tanning) purposes; +both may be demonstrated by experimental tests. + +When dealing with the natural tanning materials it is desirable to know +their contents of actual tanning matter, from which their special +qualities as tanning agents may be deduced. Where the vegetable tanning +materials have already been converted into extracts, it is essential to +establish the identity of the original material used by the qualitative +reactions of the extract in addition to the quantitative estimation of +actual tannin contents. It is frequently necessary to examine whether +the extract in question has been actually prepared from the material +giving the extract its name, or whether the extract has suffered the +addition of other extracts of tanning materials of but low quality. Such +determinations may be undertaken by microscopical observations and by +means of qualitative and quantitative reactions; for this purpose many +colour reactions and precipitation methods are available in addition to +the determination of the molybdenum figure (Lauffmann),[Footnote: +Collegium, 1913, 10.] the alcohol and ethyl acetate figures and +microscopical examination (Grasser).[Footnote: Ibid., 1911, 349.] Of +other adulterants tending to reduce the quality of extracts may be +mentioned sugars, mineral salts, and coal-tar dyes; [Footnote: Grasser, +_Collegium_, 1910, 379.] for the determination of these, the special +literature should be consulted. [Footnote: Grasser, "Handbuch +f. gerbereichem. Laboratorien" (Leipzig, 1914); +Procter-Paessler, "Gerbereichem. Untersuchungen" (Berlin, 1901).] + +Two methods are devised for the purpose of quantitatively determining +the tannin contents, both of which employ hide powder, and which are +known as the "shake method" and the "filter bell method" respectively: +the former is adopted as the official method of the "International +Association of Leather Trades' Chemists" (I.A.L.T.C.). [Footnote: And +also by the Society of Leather Trades' Chemists.-_Transl._] + +The original method, [Footnote: _Leather Manufacturer_, 1894, No. 9 +J.S.C.I.,1894, 494.] worked out in the laboratory of the Yorkshire +College (now the University of Leeds), essentially consists in +introducing 6-9 gm. of hide powder in a shaker, washing it at least +twice with distilled water and carefully squeezing out the powder in a +linen cloth between each washing. 100 c.c. of the solution to be +examined, which may not contain more than 1 per cent, total solids, are +introduced into the shaking bottle which is then weighed. About +one-third of the washed hide powder is then added, and the bottle shaken +ten to fifteen minutes; another third is then added and, after shaking, +the third portion. The bottle plus contents is now weighed, and the +amount of hide powder introduced ascertained by difference of the two +weighings. The liquid is then filtered through filter paper, 50 c.c. of +the clear filtrate evaporated in a basin, dried and weighed. The residue +in the original solution is then obtained by multiplying the former by +100 (plus weight of water added with hide powder), and dividing by 100. + +This method was closely investigated by a large number of leather +trades' chemists, was considerably improved, and in its final form +presented a method of the highest degree of accuracy; the method was +therefore adopted as _The Official Method of Tanning Analysis_ by the +I.A.L.T.C., which body, at the same time, gave precise instructions as +to the details of the method. The latest instructions, which are +reprinted below, permit of any method of analysis which observes the +following conditions:-- + +1. The solution for analysis must contain between 3.5 and 4.5 gm. of +tanning matter per litre, and solid materials must be extracted so that +the greater part of the tannin is removed at a temperature not exceeding +50° C. + +2. The total solubles must be determined by the evaporation of a +measured quantity of the solution previously filtered till optically +clear, both by reflected and transmitted light. This is obtained when a +bright object such as an electric light filament is distinctly visible +through at least 5 cm thickness, and a layer of 1 cm. deep in a beaker +placed on a black glass or black glazed paper appears dark and free from +opalescence when viewed from above. Any necessary mode of filtration may +be employed, but if such filtration causes appreciable loss when applied +to a clear solution, a correction must be determined and applied as +described in paragraph 6. + +Filtration shall take place between the temperatures of 15° C. and 20° +C. Evaporation to dryness shall take place between 98.5° C. and 100° +C. in shallow, flat-bottomed basins, which shall afterwards be dried +until constant at the same temperature, and cooled before weighing for +not less than twenty minutes in air-tight desiccators over dry calcium +chloride. + +3. The total solids must be determined by drying a weighed portion of +the material, or a measured portion of its uniform turbid solution, at a +temperature between 98.5° C. and 100° C. in shallow, flat-bottomed +basins, which shall afterwards be dried until constant weight at the +same temperature, and cooled before weighing for not less than twenty +minutes in air-tight desiccators over dry calcium chloride. + +"Moisture" is the difference between 100 and the percentage of total +solids, and "insoluble" the difference between "total solids" and "total +solubles." + +4. _Non-Tannins._--The solution must be detannised by shaking with +chromed hide powder till no turbidity or opalescence can be produced in +the clear solution by salt-gelatine solution. The chromed powder must be +added in one quantity equal to 6.0-6.5 gm. of dry hide powder per 100 +c.c. of the tanning solution, and must contain not less than 0.2 per +cent. and not more than 1 per cent. of chromium calculated on the dry +weight, and must be so washed that in a blank experiment with distilled +water, not more than 5 mg. of solid residue shall be left on evaporation +of 100 c.c. All water contained in the powder should be determined and +allowed for as water of dilution. + +5. _Preparation of Infusion_.--Such a quantity of material shall be +employed as to give a solution containing as nearly as possible 4 gm. of +tanning matter per litre, and not less than 3.5 or more than 4.5 +gm. Liquid extracts shall be weighed in a basin or beaker and washed +with boiling water into a litre flask, filled up to the mark with +boiling water, and well mixed and rapidly cooled to a temperature of +17.5° C., after which it shall be accurately made up to the mark, again +well mixed, and filtration at once proceeded with. Sumac and myrabolam +extracts should be dissolved at a lower temperature. + +Solid extracts shall be dissolved by stirring in a beaker with +successive quantities of boiling water, the dissolved portions being +poured into a litre flask, and the undissolved being allowed to settle +and treated with further portions of boiling water. After the whole of +the soluble matter is dissolved, the solution is treated similarly to +that of a liquid extract. + +Solid tanning materials, previously ground till they will pass through a +sieve of sixteen meshes per square centimetre, are extracted in Koch's +or Procter's extractor with 500 c.c. of water at a temperature not +exceeding 50° C.; the extraction is then continued with boiling water +till the filtrate amounts to 1 litre. It is desirable to allow the +material to soak for some hours before commencing the percolation, which +should occupy not less than three hours, so as to extract the maximum of +tannin. Any remaining solubles in the material must be neglected or +reported separately as "difficultly soluble" substances. + +The volume of liquid in the flask must, after cooling, be accurately +made up to 1 litre. + +6. _Filtration_.--The infusion shall be filtered till optically clear +(_vide_ 2). No correction for absorption is needed for the Berkefeld +candle, or for S. and S. 590 paper [Footnote: Schleicher and Schüll, +Düren (Rheinland), Germany.] if a sufficient quantity (250-300 c.c.) is +rejected before measuring the quantity for evaporation, and the solution +may be passed through repeatedly to obtain a clear filtrate. + +If other methods of filtration are employed, the average correction +necessary must be determined in the following manner:--About 500 c.c. of +the same or a similar tanning solution is filtered perfectly clear, and +after thorough mixing 50 c.c. is evaporated to determine "Total Soluble +A." A further portion is now filtered in the exact method for which the +correction is required (time of contact and volume rejected being kept +as constant as possible), and 50 c.c. is evaporated to determine "Total +Soluble B." The difference between "A" and "B" is the correction sought, +which must be added to the weight of the total solubles found in +analysis. An alternative method of determining correction, which is +equally accurate and often more convenient, is to filter a portion of +the tanning solution through the Berkefeld candle till optically clear, +which can be generally accomplished by rejecting 300 or 400 c.c., and +returning the remaining filtrate repeatedly; and at the same time to +evaporate 50 c.c. of the clear filtrate obtained by the method for which +correction is required, when the difference between the residues will be +the correction sought. An average correction must be obtained from at +least five determinations. It will be found that this is approximately +constant for all materials, and amounts in the case of S. and S. 605, +150 c.c. being rejected, to about 0.005 gm., and where 2 gm. of kaolin +are employed in addition to 0.0075 gm. The kaolin must be previously +washed with 75 c.c. of the same liquor, which is allowed to stand +fifteen minutes and then poured off. Paper 605 has a special absorption +for a yellow colouring matter often contained in sulphited extracts. + +7. Hide powder shall be of a woolly texture, thoroughly delimed, +preferably with hydrochloric acid. It shall not require more than 5 +c.c. or less than 2.5 c.c. of decinormal NaOH or KOH to produce a +permanent pink colour with phenolphthalein on 6.5 gm. of the dry powder +suspended in water. If the acidity does not fall within these limits it +must be corrected by soaking the powder before chroming for twenty +minutes in ten to twelve times its weight of water, to which the +requisite calculated quantity of standard alkali or acid has been +added. The hide powder must not swell in chroming to such an extent as +to render difficult the necessary squeezing to 70-75 per cent. of water, +and must be sufficiently free from soluble organic matter to render it +possible in the ordinary washing to reduce the total solubles in a blank +experiment with distilled water below 0.005 gm per 100 c.c. The powder, +when sent out from the maker, shall not contain more than 12 per +cent. of moisture, and shall be sent out in air-tight tins. + +The detannisation shall be carried out in the following manner:-- + +The moisture in the air-dried powder is determined, and the quantity +equal to 6.5 gm. actual dry powder is calculated, which will be +practically constant if the powder be kept in an air-tight vessel. Any +multiple of this quantity is taken according to the number of analyses +to be made, and wet back with approximately ten times its weight of +distilled water. Two grammes per 100 of dry powder of crystallised +chromic chloride, CrCl_3.6aq., is now dissolved in water and made basic +with 0.6 gm. of Na_2CO_3 by the gradual addition of 11.25 c.c. of normal +Na_2CO_3, thus making the salt correspond to the formula +Cr_2Cl_3(OH)_3. In laboratories where analyses are continually being +made, it is more convenient to employ a 10 per cent stock solution, made +by dissolving 100 gm. of Cr_2Cl_6.6aq. in a little distilled water in a +litre flask and very slowly adding a solution containing 30 gm. of +anhydrous sodium carbonate, with constant stirring, finally making up to +the mark with distilled water and well mixing. Of this solution 20 +c.c. per 100 gm., or 1.3 c.c. per 6.5 gm. of dry powder, should be +used. This solution is added to the powder, and the whole churned for +one hour. At the end of the one hour the powder is squeezed in linen to +free it as far as possible from the residual liquor, and washed and +squeezed repeatedly with distilled water, until, on adding to 50 c.c. of +the filtrate one drop of 10 per cent. K_2CrO_4 and four drops of +decinormal silver nitrate, a brick-red colour appears. Four or five +squeezings are usually sufficient. Such a filtrate cannot contain more +than 0.001 gm. of NaCl in 50 c.c. + +The powder is then squeezed to contain 70-75 per cent, of water, and the +whole weighed. The quantity Q containing 6.5 gm. dry hide is thus found, +weighed out, and added immediately to 100 c.c. of the unfiltered tannin +infusion along with (26.5-Q) of distilled water. The whole is corked up +and agitated for fifteen minutes in a rotating bottle at not less than +60 revs. per minute. It is then squeezed through linen, the fitrate +stirred and filtered through a folded filter of sufficient size to hold +the entire filtrate, returning till clear. Sixty c.c. of the filtrate +is then evaporated and calculated as 50 c.c., or the residue of 50 +c.c. multiplied by 6/5. The non-tannin filtrate must give no turbidity +with a drop of a solution of 1 per cent, gelatine and 10 per cent, +common salt. [Footnote: It is convenient for technical purposes to +employ the commercially obtainable chromed hide powder as prepared, for +instance, by the German Experimental Station at Freiberg, Saxony.] + +One gramme of kaolin, freed from all soluble matter, may be added to the +filtrate, or it may be used by mixing it with the hide powder in the +shaking bottle. + +The analysis of used liquors and spent tans shall be made by the same +methods as are employed for fresh tanning materials; the liquors being +diluted, are concentrated by boiling _in vacuo_, or in a vessel so +closed as to restrict access of air, until the tanning matter is if +possible between 3.5 and 4.5 gm. per litre, but in no case beyond a +concentration of 10 gm. per litre of total solids, and the weight of +hide powder used shall not be varied from 6.5 gm. + +The results shall be reported as shown by the direct estimation, but it +is desirable that in addition efforts shall be made, by determination of +acids in the original solution and in the non-tannin residue, to +ascertain the amount of lactic and other non-volatile acids absorbed by +the hide powder, and hence returned as "tanning matters." + +In the case of tanning materials it must be clearly stated in the report +whether the calculation is on the sample with moisture as received, or +upon some arbitrarily assumed percentage of water; and in that of +liquors whether the percentage given refers to weight or to grammes per +100 c.c., and in both cases the specific gravity shall be reported. + +All analyses reported must be the average result of duplicate +determinations, which must agree in the case of liquid extracts within +0.6 per cent, and of solid extracts within 1.5 per cent, or the analysis +shall be repeated until such agreement is obtained. + +All reports shall be marked: Analysed in accordance with the rules of +the S.L.T.C. (I.A.L.T.C.)--when the analyses have been carried out +according to the method described above. + +As has been repeatedly emphasised in this treatise, the synthetic +tannins form a special class of substances, and the results obtained by +either of the two hide-powder methods do not give figures which are +always comparable to those of the natural tannins. An example of the +inapplicability of the methods where synthetic tannins are concerned is +illustrated by the behaviour towards hide powder of them when partly +neutralised to varying degrees: commercial Neradol D of acidity 1 gm.= +10 c.c. N/10 NaOH contains 33 per cent. tanning matters, completely +neutralised Neradol D, which exerts no true tanning action on pelt, +still contains 20 per cent tanning matter when analysed according to the +Official Method; a difference hence exists regarding the adsorption by +hide powder of a tannin and the adsorption of the latter by hide. As, +however, we are unable to make a distinction between these two different +properties by using hide powder only, we are also unable to draw the +factor into account. + +Another source of error is the swelling influence on hide powder by +acids; for instance, an acid extract of vegetable tannins would show +higher tannin contents in the analysis than would the same extract when +less acid. The free sulphonic acid, however, is the active principle in +synthetic tannins, and since the latter always contain other acids (of +organic and inorganic origin) devoid of tannoid character, a source of +error is thus introduced, which we cannot eliminate by the present +method of analysis. + +Of other methods of estimating the quality of a tanning material or +tanning extract the _determination of solubility_, _ash_, _colour_, and +_weight-giving properties_ in addition to the _firmness imparted to the +leather_ by the particular material are of importance. As regards the +synthetic tannins they are as a rule very soluble and it will generally +be found sufficient to subject them to the ordinary qualitative +examination. The ash determination in synthetic tannins, on the other +hand, is not of such value as in the case of natural tanning +extracts. From their composition we know that synthetic tannins contain +considerable quantities of mineral salts, the presence of some of which +on the one hand emphasises their pickling effect, and that on the other +hand the property of dissolving phlobaphenes exhibited by the synthetic +tannins is closely connected with their salt contents. + +A colour determination of synthetic tannins is not of much importance, +since synthetic tannins nearly always impart a white or light brown +colour to the hide. In those cases only where coloured decomposition +products appear as a result of intermediary reactions, may the former +impart greyish or dirty colorations of little beauty to the hide. This +is easily ascertained by lightly tanning a pelt. + +The determination of the weight and solidity-giving properties is +important both for leathers tanned with vegetable tanning extracts and +for those treated with synthetic tannins, but the results obtained when +using animalised cotton are not directly convertible into figures +required for practical purposes. Comparative figures are better +obtained by actually tanning pieces of pelt on as practical a scale as +is possible, and testing the weights and tensile strengths of the pieces +as against those of the original pelts, whereby in the former case the +yield (pelt --> leather) is obtained. + +Its capability as a tanning agent may be ascertained by submitting the +synthetic tannin to an actual test tannage. The latter is carried out +by introducing the dilute extract into open glass jars, holding about +400 c.c. at a width of about 8 cm. [Footnote: Accumulator jars are +excellent for the purpose.--_Transl_.] The concentration of the +solution is chosen according to acidity and salt contents of the +synthetic tannin, the most suitable being 1.5°-2.5° Bé. A piece of bated +pelt is suspended in the liquor in such a way that the pelt is +completely surrounded by liquor, without, however, being creased or +touching the bottom. If the pelt were creased during tannage, the +wrinkles would become fixed and would show in the finished leather. Thus +an unfair judgment of the extract would be delivered, since similar +results are produced by liquors which are either too concentrated or are +not properly composed, and naturally this property of an extract would +be greatly to its disadvantage. + +The various stages of tannage may be judged from various standpoints +when examining the pelt as tannage proceeds. On the one hand, the +surface of the but slightly porous pelt is altered so as to present a +more porous appearance, which is now rendered more capable of absorbing +liquids. On the other hand, a similar alteration takes place _within_ +the pelt, to the extent to which the tanning matter has penetrated it. +How far the penetration has proceeded is easily determined by utilising +the different adsorption of coal-tar dyes by untanned and tanned pelt +(see p. 121). An indicator for those synthetic tannins, which are +derived from the phenols, is ferric chloride, which only colours those +parts of the pelt which have been penetrated by the synthetic tannins; +clearer and better results are, however, obtained when the dyestuffs +referred to above are employed. + +As soon as the tanning matter has completely penetrated the pelt, the +total time of tannage is noted, and the velocity with which the tanning +matter converts the pelt into leather at that particular concentration +is thus obtained. The tannage completed, the leather must be well washed +in running water to remove excess of synthetic tannin and then dried. On +examining the dry leathers, the colour may then be observed, and a cut +will give an idea of the tensile strength and the length of fibre of the +leather. The tensile strength is, however, not of much value in such a +barely tanned leather and cannot be compared with that obtained in +leathers tanned on a practical scale. The length of fibre is, however, +of some importance, since a special feature of finished leathers tanned +with synthetic tannins is the beautifully long fibre--a property which +manifests itself when the leather is torn and in which an expression of +the quality of the synthetic tannin may be found. + +Similarly, tanning experiments combining synthetic and natural tannins +may be carried out, the most interesting features of these being the +different proportions in which the two products are mixed. Such +experiments may be done, for instance, by preparing 2° Bé. solutions of +each extract and then mixing them in proportions of, say, 10:90, 20:80, +30:70, etc. Here it is again possible to infer the _tanning intensity_ +of the synthetic tannin from the concentration and the time used for +tannage. + +A further determination of the quality of a synthetic tannin is the +capability of the latter of dissolving or precipitating the natural +tannins. As is well known, synthetic tannins frequently possess the +practically important property of rendering natural tannins easily +soluble in water. In some cases, however, synthetic tannins appear to +solubilise natural tannins in concentrated solutions; when, however, the +latter are diluted, the natural tannin is precipitated with varying +completeness, the reason of which is often the presence of excessive +acid or the presence of such salts as have no phlobaphene-solubilising +properties. + +For practical purposes this determination may be carried out by mixing, +in different proportions, concentrated tannin solutions and the +synthetic tannin; heating the mixture on the water bath for a short +time, cooling and finally diluting 10, 20, and 30 gm. of the mixture to +100 c.c., which are then left in measuring cylinders for twelve to +twenty-four hours; the amount deposited will then be an indication of +the solubilising or precipitating effect exhibited by the synthetic +tannin. + +Other properties of the synthetic tannins connected with their practical +application will be discussed in Part II. of this treatise. + + + + +PART II + +SYNTHETIC TANNINS: THEIR INDUSTRIAL PRODUCTION AND APPLICATION + +With regard to their _industrial production_, but few synthetic tannins +are, to-day, of practical and commercial interest. In addition to +simplicity in the method of manufacture a certain degree of purity of +the raw materials constitutes the criterion of their suitability. The +methods of manufacture, of which nearly all are the property of the +B.A.S.F., have been so worked out that the production of synthetic +tannins presents no difficulties on a practical scale. Cresols, +naphthalenes, and higher hydrocarbons are used as starting materials in +the production of synthetic tannins; the former substances or their +oxidation products are sulphonated by means of concentrated sulphuric +acid, and the tanning matter produced by condensing the sulphonic acids +with formaldehyde. The crude synthetic tannin thus obtained has yet to +be diluted and partly neutralised before it can be applied in practice, +and this is carried out by mixing the crude product with strong caustic +lye. By these means the high acidity is reduced to a suitable degree +learned from experience on the one hand; on the other hand, the salts of +the sulphonic acids form valuable components of the commercial synthetic +tannins. + +The first product placed on the market was named _Neradol D_; this +represents the condensation product of cresolsulphonic acid. The second +synthetic tannin was _Neradol N_, which represents the condensation +product of naphthalenesulphonic acid; when diluted and neutralised to +the same extent as is done in the case of Neradol D, the product is +named _Neradol N D_. The latest synthetic tannin has been called +_Ordoval G_, the starting material of which is a still higher +hydrocarbon. + +The tannoid-chemical properties of these synthetic tannins have been +exhaustively determined by the author, who employed Neradol D, which is +most suitable for such a purpose, and the investigations relating to it +will now be treated fully in the following chapters. The two other +synthetic tannins exhibit very similar properties, but their few +characteristics shall be shortly dealt with. + +The condensation product obtained by the method described on p. 55 forms +a viscous, dark coloured mass, the analysis of which by the shake method +gives the following figures:- + +Tanning matters 62.6 per cent. +Non tannins 6.4 " +Insolubles 0.0 " +Water 31.0 " + --------------- + 100.0 per cent. + +Acidity: 1 gm. = 40 c.c. N/10 NaOH. + +According to its chemical constitution, this product may +be considered to be dinaphthylmethanedisulphonic acid. + +Samples of this crude, strongly acid material were partly +neutralised, and the following figures obtained on analysis:-- + +Acidity. Tanning Soluble Water. + Matters. Non-tans. + + Per Cent. Per Cent. Per Cent. +1 gm. = 35 c.c. N/10 NaOH 61.8 7.0 31.2 +1 " = 30 " " 58.9 7.1 34.0 +1 " = 25 " " 50.1 7.9 42.0 +1 " = 20 " " 42.2 8.9 48.9 +1 " = 15 " " 37.4 10.4 52.2 +1 " = 10 " " 31.6 13.6 54.8 +1 " = 5 " " 26.3 16.6 57.1 + +Experimental tanning tests which were carried out with the various +partly neutralised samples yielded leathers which, on an average, were +nearly white, but which in comparison with a leather tanned with Neradol +D appeared rather more greyish and were much harder. + +A solution of the half-neutralised substance (1gm. = 20 c.c. +N/10 NaOH) gives the following reactions:--- + +Gelatine--Precipitate, partly soluble in excess tannin solution. +Ferric chloride-----No coloration. +Barium chloride-----Precipitate, insoluble HNO_3. +Bromine water-----No reaction. +Silver nitrate-----No reaction. +Aniline hydrochloride----Precipitate, dissolves when solution +is heated. + +This condensation product is very soluble in water, but insoluble in +most solvents, excepting methyl and ethyl alcohols. The above reactions +show the similarity of this dinaphthyl derivative to the dicresyl +derivative, and the absence in the former of characteristic reactions +with iron salts is mainly accounted for by its lack of phenolic groups. +The absence of this reaction does not, of course, influence the tannoid +character of dinaphthylmethanedisulphonic acid in the least, and is of +no importance in practice, since the various stages of tannage may be +demonstrated by means of a solution of indigotine. + +From a technical point of view the absence of this reaction is +advantageous to this extent, that it eliminates the exceedingly great +care to avoid the contact of tan liquors and tanned pelt with iron +particles which has to be observed when tannins of phenolic character +are employed. + +In a chemical and technological evaluation of this tanning matter, all +those details apply which will be described when discussing Neradol +D. The most important advantage possessed by this tanning matter, from a +commercial point of + +view, is the lower price which it owes to the greater ease with which +naphthalene may be obtained. + +By treating the non-condensed crude product with barium chloride, a +product completely devoid of sulphuric acid is easily obtained; the +contents of sulphuric acid calculated as BaSO_4 is about 9.5 per +cent. This value is higher than that found by Neradol D, and may be +explained by the fact that a slight excess of sulphuric acid is +necessary for the preparation of [Greek: b]-naphthalenesulphonic acid. + +Comparative tanning tests using products containing sulphuric acid and +products free from sulphuric acid (neutralised to the same degree of +acidity) yielded leathers which were very similar; the liquor containing +no sulphates yielded slightly softer leather than that obtained from a +liquor containing sulphates. + +An experiment was also carried out, using a liquor containing the tannin +completely neutralised with caustic soda and subsequently acidified with +acetic acid till the acidity of 1 gm. = 10 c.c N/10 NaOH; here, again, +no essential difference could be detected in the leather as compared +with that from a liquor containing sulphates. + +One of the most striking properties of this tanning matter is its +solubilising effect on natural tannins and the phlobaphenes; this +property may mainly be compared to the similar one of other condensed +sulphonic acids in their behaviour towards natural tannins. + +If, therefore, natural tannins are mixed with this product and the +solution used for tanning purposes, the resultant leather will possess a +dark colour owing to the presence of solubilised phlobaphenes; if, on +the other hand, a dark coloured leather, which has been tanned with +natural tannins, is washed over with a 5° Bé solution of this synthetic +tannin, or immersed for some time in the solution, the leather assumes a +lighter colour owing to the phlobaphenes being dissolved and removed +from the leather by the synthetic tannin. + +The presence of Neradol ND in leathers is detected by methods to be +described under Neradol D (_cf_. p. 108). The oxyazo reaction only +succeeds when the solution has been boiled with a few drops of +hypochlorite solution, quickly cooled and excess of ammonia added. When +applying the indophenol reaction, the solution must be treated as +follows: 3-4 drops of hypochlorite solution is added, and the solution +heated for a short time; or 5-6 drops hypochlorite solution may be +added, and the solution left for some time, in which case the heating +may be omitted. The solution is then made distinctly ammoniacal, 1-2 +drops of dimethyl-_p_-phenylenediamine solution and a layer of alcohol +poured on the top. In most cases a blue coloration will appear; the +addition of 1-2 drops of potassium ferricyanide solution with formation +of a blue coloration indicates the presence of Neradol ND without fail. + +The fact that a product possessing tanning properties may be obtained by +condensing [Greek: b]-naphthalenesulphonic acid makes it interesting to +investigate the behaviour of a non-condensed [Greek: +b]-naphthalenesulphonic acid towards pelt. The following solutions were +allowed to act upon pelt for twelve days:-- + +(1) Concentrated solution of [Greek: a]-naphthalenesulphonic acid (10° Bé). +(2) " " [Greek: b]- " " (6° Be.) +(3) " " 2,7- " " (18° Bé.). + +Solution 1 swells the pelt to a considerable extent without, however, +solubilising it. Solution 2 produces a similar effect. Solution 3 +dissolves the pelt appreciably on the first day; after six days, +solubilisation is complete. The reason of this different behaviour of +the mono- and disulphonic acids is mainly to be sought in their +difference of solubility; the monosulphonic acids are not very soluble, +and are only capable of giving solutions measuring 10° and 6° Bé, +respectively, whereas the disulphonic acid yields an 18° Bé solution, in +addition to which the much higher acidity of the latter quickly +gelatinises the pelt. + +As regards the capability of the naphthalenesulphonic acids of +dissolving phlobaphenes, the following results were obtained:--solid +Argentine quebracho extract was mixed with-- + + +5 percent, [Greek: a]-naphthalenesulphonic acid: opaque sol., + large quantity of insolubles. +10 " " " lesser " " +20 " " " no insolubles. +30 " " " " +5 " [Greek: b]-naphthalenesulphonic acid: opaque sol., + lesser quantity of insolubles. +10 " " " " +20 " " " clear solution, no insolubles +30 " " " " +5 " 2,7-naphthalenedisulphonic acid: opaque sol., + large quantity of insolubles. +10 " 2,7 " " as above. +20 " 2,7 " " slightly opaque, some insolubles. +30 " 2,7 " " nearly clear solution, no insolubles. + + +It is hence clear that the [Greek: b]-sulphonic acid possesses +phlobaphene-solubilising qualities greater than those of the [Greek: +a]-sulphonic acid or the disulphonic acid; the Greek: b]-sulphonic acid +was therefore made the subject of Ger. Pat., 181,288 (8th February +1917). + +The synthetic tannin, _Ordoval G_, is the formaldehyde condensation +product of higher hydrocarbons (mainly _retenes_), and is a partly +neutralised product containing no sulphuric acid. The author's analysis +gave the following figures:-- + + Tanning matters 10.7 per cent. + Soluble non-tannins 16.4 " + Insolubles 0.0 " + Water 73.0 " + + Acidity: 1 gm. = 4 c.c. N/10 NaOH. + Density: 23° Be. + +Ordoval G is completely soluble in water and glacial acetic acid. Only +its organic constituents are soluble in alcohol, ethyl acetate, and +acetone, whereby a dark coloured crystalline mass separates. Ordoval G +is insoluble in benzene. + +The aqueous solution of Ordoval G gives the following reactions:-- + +Gelatine Moderate flocculent precipitate. +Ferric chloride Darkish coloration. +Potassium dichromate No reaction. +Aniline hydrochloride Dark brown precipitate. +Formaldehyde hydrochloric acid No precipitate. +Bromine water No reaction. +Zinc acetate Very slight opalescence. +Barium chloride Slight opalescence. + +Its capability of solubilising and consequent saving of natural tannins +is shown by the fact that 100 kilos of vegetable tanning material may be +substituted by 40 kilos of Ordoval G and the material in question in +order to obtain the entire tanning intensity of the latter. + +In one respect--that of its salts--Ordoval G differs from the Neradols; +whereas the chromium and aluminium salts of the latter possess no such +tannoid properties as will make the resultant leather exhibit any of the +characteristics of either tannage, it is possible to carry out combined +tannage with a mixture of Ordoval G and metallic salts. Tanning +experiments carried out with the chromium, iron, aluminium, and calcium +salts of Ordoval G yielded leathers which possessed proportionate +characteristics of either kind of tannage to the extent to which either +material was present. This combination tannage seems to be assured of a +great future; especially may a combination tannage of iron salts and +Ordoval G eventually entirely replace chrome tannage. + +The detection of Ordoval G in leather is carried out as follows: 10 +gm. of leather are boiled with 150 c.c. of acetic acid, a solution of 25 +gm. of CrO_8 in 25 c.c. of a 50 per cent, solution of acetic acid +gradually added, and the mixture boiled for three hours, till the +leather is decomposed and the solution has assumed a brown instead of +the original light yellow colour. The solution is then evaporated, the +residue dissolved in 600 c.c. hot water, and the chromium precipitated +with a 40° Bé. solution of caustic soda. The solution is filtered and +cooled, and a little hydrosulphite is added to 20 c.c. of the cold +alkaline filtrate; in the presence of Ordoval G, a red colour will +appear (oxanthranolsulphonic acid). + +Brief mention must be made of the so-called _Corinal_ [Footnote: Swiss +Pat, 78,282, 78,797, 79,39.] a synthetic tannin placed upon the market +by Chem. Fabrik Worms A.-G., in Worms-on-the-Rhine. It is a viscous, +brown fluid, containing the aluminium salts of the tannoid acids. The +latter are formaldehyde-condensation products of sulphonated tar oils, +or the hydroxylated derivatives of the latter. The density being 33° Bé, +it contains 28.1 per cent. tanning matters, 13 per cent. soluble +non-tannins, and 10.8 per cent. inorganic matter (3.2 per cent. Al_2O_3 +and 7.6 per cent. Na_2SO_4. + +A similar product, containing chrome salts as base, is the so-called +ESCO-EXTRACT, [Footnote: Schorlemmer, _Collegium_, 1917, 124] +manufactured by the Chem. Fabrik Jucker & Co. in Haltingen +(Baden). This product is a dark, reddish-brown fluid, possessing acid +reaction, which strongly precipitates gelatine. Analysed by the filter +method it contains 12-15 per cent. tanning matters, 17-20 per cent. +soluble non-tannins, and 18 per cent. ash, of which 3 per cent. is +Cr2O_3. This synthetic tannin may be employed alone or in conjunction +with other tannins, and yields a leather similar to that obtained by +chrome tannage. + + +A. Condensation of Free Phenolsulphonic Acid + +In practice, the results of condensing phenolsulphonic acid with +formaldehyde are manifold, according to whether these materials are used +in their concentrated or dilute state; whether they interact in the cold +or when heated; or whether their interaction is gradual or rapid. + +1. If a moderately dilute solution of phenolsulphonic acid (1:1) is +mixed with one-sixth of its volume of a dilute formaldehyde solution (1 +part 30 per cent. HCHO solution plus 3 parts of water) in the cold, with +continuous stirring, the solution remains clear and assumes a brown +colour. When left several hours, a light, white flocculent precipitate +deposits, which increases in quantity on diluting with water. The +solution precipitates gelatine; the flocculent precipitate is easily +soluble in hot caustic soda solution, and, when subsequently neutralised +with acetic acid, precipitates gelatine. + +If equal parts of dilute phenolsulphonic acid and dilute formaldehyde +(concentrations as above) are gradually mixed in the cold, whilst +stirring, the mixture soon becomes opalescent, and a flocculent deposit +separates after eighteen to twenty-four hours. + +These experiments carried out on the water bath immediately yield +opalescent liquids, from which an insoluble, brown, gluey, and very +sticky mass separates after twenty-four hours; the latter is sparingly +soluble in alkalies, partly so in organic solvents. + +2. If a moderately dilute solution of phenolsulphonic acid (1:1) is +gradually mixed with one-sixth of its volume of a concentrated (30 per +cent.) formaldehyde solution in the cold, whilst stirring, slight +opalescence immediately results, and a flocculent deposit separates +after about twenty minutes, which gradually increases in quantity during +the next few hours. If the volume of formaldehyde is increased to the +same as that of phenolsulphonic acid solution, the flocculent deposit +immediately separates, and after twenty-four hours a brown, gluey, and +very sticky mass--of the same solubility as that described in the +previous experiment--is to be found at the bottom of the vessel used. + +It should be noted that in both these experiments with concentrated +formaldehyde solution a slight increase in temperature occurs +concurrently with the process of condensation. If the experiments are +carried out on the water bath, a gelatinous mass is instantly formed, +which assumes the colours of grey, dirty light violet and dark violet, +in the order named, and which, whilst left several hours--or when heated +on the water bath--is suddenly converted into the insoluble, brown, +gluey mass above referred to. + +3. If, for the purpose of condensation, phenolsulphonic acid to which 10 +per cent, of water has been added, is employed, the reaction proceeds +very quickly and energetically. If one-sixth of its volume of +formaldehyde (1:3 of the 30 per cent. solution) is added drop by drop to +a cold solution of phenolsulphonic acid, a reddish, milky solution +results, which assumes a slightly lighter colour on addition of more +formaldehyde and deposits an insoluble flocculent precipitate. If the +solution is kept below 45° C., by artificial cooling, the light colour +is maintained, but a gelatinous precipitate is soon formed, the +viscosity of which increases on stirring, and finally is converted into +an insoluble, tough, gummy mass. If, on the other hand, the mass is +heated at the beginning of the reaction, or if the amount of +formaldehyde is increased and the mass cooled during reaction, +effervescence occurs, and a cheesy, dirty-coloured mass results, which, +on cooling, rapidly becomes solid and yields a very firm, elastic, +rubbery mass, which is absolutely insoluble in water. + +4. The condensation proceeds exceedingly violently when concentrated +phenolsulphonic acid is acted upon by one-sixth of its volume of +formaldehyde. If the latter is firstly added drop by drop to the +phenolsulphonic acid, a gel immediately results, the temperature of +which quickly increases on further addition of formaldehyde and suddenly +boils over, yielding a reaction product which, when cooled, forms a +dirty violet, firm, elastic, and rubbery mass, insoluble in alkalies and +hardly affected by organic solvents. + +Finally, if the amounts of concentrated phenolsulphonic acid and +formaldehyde stated above are mixed, strong effervescence occurs and +heat is evolved, and a dirty blackish-violet mass is instantly formed +which, on cooling, yields a rather brittle, hard product insoluble in +water. + +5. Totally different end-products are, however, obtained when the +addition of formaldehyde (30 per cent.) in the proportion of one-sixth +of the volume of dilute phenolsulphonic acid (1 plus 9 aq.) to the +latter is extended over several hours. In this case a slightly +opalescent liquid is obtained which, when left twelve hours, is +transformed into a brown mass soluble in water, which strongly +precipitates gelatine and possesses tanning properties. Hence direct +tannoid substances are obtained by this method of condensation. + +Whereas no direct tanning experiment can be carried out with the +insoluble compact mass obtained in the preparations described above on +account of their absolute insolubility, it is still possible to carry +out tanning experiments with opalescent colloidal solutions in the +following ways:-- + +(a) If a bated pelt is immersed in a liquid containing a condensation +product obtained by gradually mixing a moderately dilute solution of +phenolsulphonic acid and a dilute solution of formaldehyde, the pelt is +rapidly tanned on the surface. Complete penetration of the substance +does not occur even after several days, since the strong acidity of the +solution causes a strong swelling of the pelt. + +(b) If a pelt is shaken for six hours in a shaking apparatus containing +the liquid mentioned under (a), tannage again only takes place on the +surface, penetration being impeded by the strong swelling effect of the +liquid. Repetition of the latter two experiments, with the addition of +15 per cent, common salt, increases the tanning effect to some extent; +the pelt, however, is not tanned through, but the non-tanned layers may +be clearly seen to be pickled. + +The tanning effects described above are only exhibited when the +colloidal tan-liquor is present in great excess over the pelt, since the +former obviously only contains small amounts of tanning matter, and even +the presence of common salt does not bring about complete tannage of the +pelt. + +In order to prove the presence of "tanning matters" in the liquid +described above, several freshly prepared samples of the latter were +analysed by the shake method of analysis without being first filtered +and the following figures obtained:-- + + 1. 2. 3. 4. + Per Cent. Per Cent. Per Cent. Per Cent. +Tanning matters 6.4 7.7 8.2 9.1 + +Soluble non-tannins 15.2 17.4 14.5 11.8 + +These condensation products suspended in water all precipitate gelatine +strongly and leave behind a perfectly clear liquid. In all cases, an +intense blue colour was obtained on adding ferric chloride, a slight +precipitate only was obtained with aniline hydrochloride, and bromine +was rapidly absorbed with the separation of an insoluble white deposit. + +The condensation products obtained by the interaction of dilute +solutions of phenolsulphonic acid and formaldehyde at moderately high +temperature, which form slimy masses and are insoluble in water, are +soluble in alcohol. An alcoholic solution of such a product was used in +a tanning experiment, and a piece of pelt immersed in the solution was +tanned through in a few days; the resultant leather being rather firm, +springy, and slightly hard, and the colour was a light brownish-grey. + +All those condensation products which are easily or partly soluble in +alcohol dissolve in caustic soda, sodium carbonate, in some cases also +in borax and sodium sulphite. They are rendered soluble with greater +ease when the _freshly prepared_ solution is heated on the water bath +with the alkali; the alkaline solution, neutralised as far as is +possible with acetic acid, yields light brown coloured solutions, the +tanning effects of which have proved very satisfactory. Leathers tanned +in such solutions, however, are rather empty and hard, possess but +little resilience and an uneven, dirty greyish-brown colour. + +A sample of such a product, as nearly as possible neutralised with +acetic acid, contained 14.8 per cent. tanning matters, by the shake +method of analysis. + + +B. Condensation of Partly Neutralised Phenolsulphonic Acid + +Attempts were made at condensing partly neutralised phenolsulphonic +acid; the latter was obtained by mixing equal quantities of +phenolsulphonic acid and sodium phenolsulphonate (prepared by exactly +neutralising phenolsulphonic acid with a concentrated solution of +caustic soda). + +The consequent dilution and decrease in acidity, however, considerably +diminished the velocity of the reaction. Hence, if the half-neutralised +Solution A1 (_cf_. p. 98) is diluted with water, taking equal volumes, +and one-sixth of the volume of dilute formaldehyde (1:3) gradually added +in the cold, condensation is not induced. When heated several hours an +opalescent liquid results from which, however, no flocculent deposits +separate when left for some time. Using a concentrated solution of +formaldehyde (Experiment A2, p. 98) in the cold produces no reaction, +but after heating for a time an opalescent liquid is obtained. Both +liquids give only slight precipitates with gelatine. Excess formaldehyde +does not influence the reaction. + +A repetition of Experiment A3 (_cf_. p. 99), using the above +half-neutralised phenolsulphonic acid, similarly required heat to induce +condensation, when a milky liquid of light reddish colour resulted. + +Whereas the addition of formaldehyde to non-neutralised concentrated +phenolsulphonic acid caused violent reaction, this proceeded very slowly +in the case of half-neutralised phenolsulphonic acid, resulting in the +formation of a semi-solid mass, which on heating became more viscous, +and finally, when left twenty-four hours, became a solid, compact, +insoluble mass possessing a dirty light violet colour. + +Tanning experiments with these opalescent solutions proved them to exert +a rapid penetration on the surface, complete tannage, however, taking +place after eight days only, when a flat, greyish-coloured and rather +hard leather resulted. + + +C. Condensation of Completely Neutralised Phenolsulphonic Acid + +If concentrated phenolsulphonic acid is gradually neutralised with +concentrated caustic soda solution till the former is faintly alkaline, +the sodium salt thus obtained is not so easily condensed with +formaldehyde as is the case with the free acid. + +1. If formaldehyde is gradually added to the neutralised phenolsulphonic +acid in the cold, opalescence immediately results; on addition of water, +the liquid assumes a milky appearance. On adding gelatine to this +liquid, a slimy precipitate is thrown down, leaving a slightly +opalescent liquid. + +2. If formaldehyde is added to neutralised phenolsulphonic acid whilst +it is heated on the water bath, a slimy mass instantly separates, which +on cooling solidifies and forms a greyish-blue brittle mass, insoluble +in water and but sparingly soluble in alcohol; the alcoholic solution is +capable of converting pelt into leather. + +The filtrate from the solidified mass strongly precipitates gelatine, +whereas the insoluble condensation product is soluble in caustic soda; +this alkaline solution also precipitates gelatine and the addition of +acetic acid transforms the mixture into the gel state. + +If the insoluble condensation product is dissolved in warm concentrated +sulphuric acid, the solution remains clear upon the addition of water, +but does not precipitate gelatine. If, finally, this solution is +neutralised with caustic soda, the solution remains clear and +precipitates gelatine strongly. + + +D. Condensation of Cresolsulphonic Acid + +Experiments were carried out with the object of condensing _o_-, _m_-, +and _p_-cresolsulphonic acids with formaldehyde in various ways; no +essential differences could be detected as regards the mode of reaction +or the properties of the intermediary and end-products as compared to +those of phenolsulphonic acid. Similarly, condensation of different +samples of crude cresol containing varying quantities of _o_-, _m_-, and +_p_-cresol did not yield end-products sufficiently different to justify +describing them in detail. + + +E. Relative Behaviour of an Alkaline Solution of Bakelite and Natural +Tannins + +Phenolsulphonic acid was condensed with a little formaldehyde, and the +reddish pasty condensation product dissolved in caustic soda. This +alkaline solution of bakelite was exactly neutralised with acetic acid +and mixed with strong solutions of an untreated quebracho extract. It +was observed that the solubility of the quebracho extract was not +increased by this treatment, but the faintly acidic character of the +natural tannin caused the bakelite to be thrown down as an insoluble +precipitate. + +Crude phenolsulphonic acid, when added to a solution of the quebracho +extract referred to, does not increase the solubility of the latter, +which even deposits considerable amounts of insoluble tannin particles. + +Quite different properties are exhibited by sodium phenolsulphonate, +which completely converts quebracho tannin into a water-soluble +substance, the aqueous solution of which deposits no insolubles. The +partly neutralised condensation product of phenolsulphonic acid and +formaldehyde exhibits similar properties [Footnote: Grasser, _Collegium_, +1913, 521, 478.] (see later). + +F. Dicresylmethanedisulphonic Acid (Neradol D) [Footnote: Ger, Pat., +291, 457; Austr. Pat., 61, 057.] + +Neradol D is a viscous liquid, measuring about 33° Bé., which is similar +to extracts of natural tannins. One of its characteristics is its +phenolic odour; it is completely soluble in water, forming a clear, +semi-colloidal solution, but is insoluble in all organic solvents with +the exception of alcohol, glacial acetic acid and ethyl acetate, which +dissolve all but its inorganic constituents. The latter owe their +presence to the neutralisation of the crude Neradol with caustic soda, +and are composed of sodium salts of the sulphonic acid in addition to +Glauber salts. + +The aqueous solution of Neradol D shows properties similar to those +exhibited by solutions of natural tannins and reacts as +follows:--[Footnote: Grasser, _Collegium_, 1913, 520, 413.] + +Methyl orange Acid reaction. +Barium chloride White precipitate, insoluble in HNO_3. +Ferric chloride Deep blue coloration. +Silver nitrate Slight opalescence. +Bromine water No precipitate. +Formaldehyde hydrochloric acid No precipitate. +Gelatine Complete precipitation. +Aniline hydrochloride Strong precipitate. + +The reactions with ferric chloride and gelatine should be especially +noted, since they are analogous to those given by natural tannins. On +the other hand, the reactions with BaCl_2, bromine water and formaldehyde +hydrochloric [Footnote: Stiasny carries out the reaction with +formaldehyde-hydrochloric acid as follows:--50 c.c. of the tannin +solution, plus 5 c.c. concentrated hydrochloric acid and 10 +c.c. formaldehyde (40 per cent.) are heated under reflux condenser for +ten minutes; most natural tannins are completely precipitated +(_Collegium_, 1906, 435; 1907, 52 _et_ 188).] acid prove the different +chemical composition of Neradol D as compared to that of the natural +tannins. + +The fact that a positive reaction is given with aniline +hydrochloride [Footnote: This reaction is carried out as follows:--5 +c.c. of the tannin solution to be examined (about 4 gm. tanning matter +per litre) are shaken violently in a test tube with 0.5 c.c. aniline and +2 c.c. concentrated HCl added. All natural tannins are unaffected by +this treatment, ligninsulphonic and other sulphonic acids cause +opalescence. _Note_.--Employing formic acid in lieu of hydrochloric +acid (Knowles) renders the reaction no more reliable.--_Transl_.] is +very puzzling; none of the natural tannins are precipitated by this +reagent, but only sulphite cellulose on account of its content of +ligninsulphonic acid. One is justified in assuming that there is at +least some connection between the constitution of ligninsulphonic acid +and that of dicresylmethanedisulphonic acid. + +Stiasny [Footnote: _Collegium_, 1913, 516, 142.] recommends the +following reaction for the detection of and differentiation between +Neradol D and wood pulp extract:--10 c.c. of a 5 per cent. solution of +the extract to be analysed are violently shaken with 1-2 drops of a 1 +per cent. alum solution and about 5 gm. of ammonium acetate. If only +Neradol D is present no precipitate separates even after twenty-four +hours, but if wood pulp be present, a precipitate is thrown down in a +quantity corresponding to the amount of wood pulp present. + +The official analysis gives the following figures: +[Footnote: Grasser, _loc. cit._] + + Tanning matters 32.5 per cent. + Soluble non-tannins 33.0 " + Insolubles 0.0 " + Water 34.5 " + ------------- + 100.0 per cent. + + Ash 17.0 " + + Acidity: 1 gm. = 10 c.c. N/10 NaOH. + Density: 33ş Bé. + +A comparison of its quantitative analysis to that of a natural tanning +extract is illustrated by the following figures of a chestnut and a +quebracho extract of same density (26ş Bé):-- + + Chestnut Quebracho + Per Cent. Per Cent. + Tanning matters 32.0 34.0 + Soluble non-tannins 12.0 8.0 + Insolubles 1.5 2.0 + Water 54.5 56.0 + ----- ----- + 100.0 100.0 + + Ash 0.4 2.0 + +This comparison shows that extracts of natural tannins firstly contain +certain amounts of "insolubles," whereas Neradol is completely soluble +in water, forming a clear solution; secondly, natural tanning extracts +contain smaller quantities of soluble non-tannins, consisting of +colouring matter and sugars, in addition to small quantities of mineral +matters (ash). Neradol D contains considerable amounts of soluble +non-tannins, derived from salts of sulphonic and sulphuric acids, again +offering a satisfactory explanation of the high ash. If, therefore, a +mixture of Neradol D and a natural tanning extract was submitted to a +quantitative analysis, the higher non-tannins and the high ash would +indicate the presence of Neradol D, provided that wood pulp or a highly +sulphited extract were not components of the mixture. + +The chemical reactions taking place in the preparation of +Neradol D may be expressed thus:- + + OH OH OH OH + H ^ H___O_____H ^ H H ^ H__CH_2__H ^ H + | | || | | = | | | | + H_2O + | | CH_2 | | | | | | + H v CH_3 CH_3 v H v CH_3 CH_3 v H + HSO_3 HSO_3 HSO_3 HSO_3 + + + +1. Neradol D Reactions + +1. The quantitative determination of phenols introduced by Bader, +[Footnote: _Bull. soc. scient., Bucarexi_, 1899, 8, 51.] which consists +in precipitating them as oxyazo compounds, has been modified by Appelius +and Schmidt [FootNote: _Collegium_, 1914, 597.] for the purpose of +detecting Neradol D:--To 50 c.c. of the tannin solution (analytical +strength) 15 c.c. of diazo solution are added, the mixture filtered, if +necessary, and the filtrate made alkaline with caustic soda; in the +presence of Neradol D in sufficient quantity, a blood-red coloration +results. If but little Neradol D be present, the procedure is altered as +follows:--The tannin solution, to which the diazo solution has been +added, is filtered, and the filtrate poured on a piece of filter paper +which is then dried; a solution of caustic soda is spotted on the paper, +when, if Neradol D be present, a red-edged spot will appear. + +According to Tschirch and Edner, [Footnote: _Archiv. d. Pharm_., 1907, +150.] the diazo solution is prepared as follows:--5 gm._p_-nitraniline +are introduced into a 500 c.c. measuring flask, 25 c.c. of water and 6 +c.c. concentrated sulphuric acid added, the mixture shaken and a +solution of 3 gm. of sodium nitrite in 25 c.c. of water plus 100 c.c. of +water added, and the whole then filled up to 500 c.c. The solution +should be stocked in the dark. + +2. A less sensitive reaction for Neradol and wood pulp extract +constitutes that of Appelius and Schmidt employing cinchonine, +[Footnote: _Collegium_ 1914, 597.] while the presence of the substances +in question yields characteristic precipitates. + +3. Seel and Sander [Footnote: _Zeits. f. ang. Chem._, 1916, 333.] +recommend the following method of detecting Neradol D:-- + +_(a) Oxyazo Reaction_.--About 5 c.c. of the tannin solution are rendered +alkaline with caustic soda; after cooling with ice, about half the +volume of alcohol is added. 3-4 drops of diazo solution are then +added. Frequently, this results in the solution assuming a blue +coloration. If not, the solution is acidified with hydrochloric acid, +ether added, and the mixture well shaken. The water is now separated +from the mixture, fresh water added, together with some caustic soda +solution, when, if Neradol D be present, the salt of the colour acid +formed dissolves in the water with a beautiful green or bluish-green +colour. At the place of contact of the water and the ether a +bluish-green ring appears. + +The diazo solution is prepared by dissolving _p_-aminophenol or its +hydrochloric in a little dilute hydrochloric acid, cooling in ice and +carefully diazotising in the cold till a slight excess of nitrous acid +is present. It is essential that this solution should be tested before +use, and this is carried out by coupling it with an alkaline phenol +solution; if a dark blue oxyazo colour is formed, the solution may be +used. It must be kept cool by surrounding it with ice. + +_(b) Indophenol Reaction_.--To 5 c.c. of the solution to be tested, a +drop of a solution of dimethyl-_p_-phenylenediamine is added, the +solution rendered alkaline with caustic soda and 1-2 drops of a 5 per +cent. solution of potassium ferricyanide added. If Neradol D be present, +a blue colour appears, either immediately or after some time. The +reaction is rendered more sensitive if alcohol is carefully poured on +the solution after it has been rendered alkaline, and potassium +ferricyanide is then added. At the place of contact a blue layer is +formed, which ultimately diffuses into the alcohol. + +According to Lauffmann [Footnote: _Collegium_, 1917, 233.] the presence +of natural tannins as well as that of wood pulp diminishes the +sensitiveness of the reactions described above; [Footnote: +_Zeits. f. ang. Chem._, 1916, 333.] this investigator recommends a +modification of these reactions. + + +2. Electro-Chemical Behaviour of Neradol D + +The author's investigations of the electro-osmosis of an aqueous +solution of Neradol D [Footnote: _Collegium_, 1920, 597, 24.] proved +that dicresylmethanedisulphonic acid exhibits anodic migration; hence +this product possesses negative charge and acidic character. The +impurities accompanying the synthetic tannin, _i.e._, salts, free +sulphuric acid, and some phenols, migrated anodic and cathodic +respectively, according to their charges. A Neradol D purified by +electro-osmosis finally yielded a pure solution of +dicresylmethanedisulphonic acid, which precipitated gelatine and +exhibited pronounced tanning effects, but gave a greenish-black +coloration with iron salts. This conclusively proves that the blue +coloration given by Neradol D with iron salts is no characteristic +feature of the _pure_ synthetic tannin, but is caused by the phenolic +impurities accompanying the latter. Especially the first stage of the +electro-osmosis produces a cathodic migration of the phenols, which may +then be detected at a cathode by means of the iron and bromine +reactions. + +It is characteristic of a dicresylmethanedisulphonic acid purified by +electro-osmosis that it does not precipitate aniline hydrochloride. It +appears, therefore, that this reaction--which is characteristic of most +synthetic tannins--is again caused by the presence of impurities. + + +3. The Influence of Salts and Acid Contents on the Tanning Effect of +Neradol D + +Chemical analysis of crude Neradol revealed a natural +dicresylmethanedisulphonic acid (the tanning agent) contents of about 68 +per cent, which agrees fairly well with the calculated amount. Like +other "strong" and "weak" acids this sulphonic acid exercises a strongly +swelling influence on pelt. Whereas the effect of acid present in +solutions of Neradol D of medium concentration and its tanning effect +both influence the pelt and are fairly well balanced, this is not the +case as regards highly concentrated and very dilute solutions. If, for +instance, a very dilute solution of crude Neradol (about 0.25° Bé.) is +used, the tanning effect of this solution is exceedingly small and does +not show itself till after several hours. The relatively high +dissociation of the acids at this high degree of dilution causes an +extremely rapid and strong swelling of the pelt, which has therefore +absorbed its maximum amount of water (maximum swelling) before the +tanning effect of the sulphonic acid comes into play and by fixing the +surface of the pelt is enabled to prevent the excessive swelling effect +of the acids. + +The addition of neutral salts to the tan liquor diminishes the effect of +the acids on pelt (dehydrates the pelt) and prevents "drawing" of the +grain. If, for instance, common salt be added to a solution of crude +Neradol, the original quantity of sulphonic acid present would remain +constant, but the presence of salt would diminish the degree of +dissociation and consequently the swelling. This effect is still more +pronounced when the absolute amount of free sulphonic acid is +diminished. Hence, if crude Neradol is treated with increasing amounts +of caustic soda, a series of products containing increasing quantities +of salt and decreasing concentrations of sulphonic acid is obtained. + +The acidity of the Neradols may be determined by titration with N/10 +caustic soda; this procedure hence establishes a means of determining +the (unknown) acidities which may be expressed in terms of c.c. N/10 +NaOH. The acidity of crude Neradol was found to be-- + +1 gm. = 50 c.c. N/10 NaOH + +_i.e._, 1 gm. of crude Neradol requires 50 c.c. N/10 NaOH for complete +neutralisation; the decrease in acidity causes a decrease in contents of +tanning matters and the quantities of salts increase. The following +table gives the figures obtained by differently neutralised neradols:-- + + Acidity. Tanning Matters. Na_2SO_4. + + Per Cent. Per Cent. + 1 gm. = 50 c.c. 68 ... + 1 gm. = 40 c.c. 59 4 + 1 gm. = 30 c.c. 50 8 + 1 gm. = 20 c.c. 41 12 + 1 gm. = 10 c.c. 33 17 + 1 gm. = 5 c.c. 28 20 + 1 gm. = 0 c.c. 20 ... + +Tanning experiments with these different neradols (employing solutions +of 1° Bé. strength) demonstrated that neradols of acidity 50°, 40°, and +30° exerted strong swelling and gave comparatively hard leathers; +neradols of acidity 20°, 10°, and 5° exert no swelling, yield quick +tannage and soft leather. The swelling (hardening) effect of the acid +and the dehydrating (softening) effect of the salts in this case, +therefore, are well balanced, and this fact affords an explanation of +the rapid change from hardening to softening effects exhibited by partly +neutralised Neradol where less acid and a greater quantity of salts +respectively are present. + +It may finally be noted that the acidity of Neradol D, 1 gm. = 10 +c.c. N/10 NaOH, has been found to be the most suitable one for practical +purposes. The author has, however, successfully employed some neradols +of considerably higher acidities. The acidity above mentioned is +possessed by a Neradol D containing 17 per cent. ash and 30 per cent. +sodium sulphonates and Glauber's salts crystals respectively. This +large quantity of salts present on the one hand effects the rapid pickle +and tanning effect exhibited by Neradol D, on the other hand it also +effects the softness in the leather resulting from its use either alone +or in admixture with natural tannins. + + +4. Phlobaphene Solubilising Action of Neradols + +A special feature of Neradol D is its property of solubilising +phlobaphenes, which may be ascribed to its contents of sulphonic acids +or their salts. In order to demonstrate whether the sulphonic acids and +their salts are capable of solubilising the insoluble or sparingly +soluble anhydrides of the tannins (the phlobaphenes) before and after +condensation, the following experiments were carried out:-- + +Crude Argentine solid quebracho extract was converted into a highly +viscous liquid by treating it for several hours with water at 100° C., +and the anhydrides rendered insoluble by diluting the liquid with a +large volume of cold water. The precipitate formed, consisting of +quebracho phlobaphenes, was separated from the liquid by decantation, +and purified by washing it several times with water. Each 10 gm. of this +moist paste were treated in the cold with (_a_) free phenolsulphonic +acid; (_b_) sodium phenolsulphonate; (_c_) crude Neradol and (_d_) +Neradol D, 20 c.c. of water at 45° C. added, and the mixture allowed to +cool slowly; the following solutions resulted:-- + + (_a_) Opalescent solution, much deposit, + (_b_) Clear solution, no deposit. + (_c_) Nearly clear solution, very little deposit. + (_d_) Clear solution, no deposit. + +This clearly proves that free and condensed phenolsulphonic acids as +such are not capable of completely solubilising phlobaphenes, whereas +the sodium salts of free and condensed phenolsulphonic acids possess +this property. The salt contents of Neradol D, therefore, constitute an +advantage in this respect, that not only may Neradol D be mixed with +solutions of any natural tannin without insolubles being thereby +deposited, but it may also be added in large quantities to a tannin +solution with the result that the sparingly soluble and wholly insoluble +constituents (phlobaphenes) are completely brought into solution. + +The practical importance of the solubilising effect of Neradol D +relating to solid Argentine quebracho extract is demonstrated in the +following series of investigations carried out by the author:-- +[Footnote: _Collegium_, 1913, 478; Austr. Pat., 68, 796.] + +Solid Neradol Matters Tanning Abs. Increase +Argentine D. Calc. of Mixture Increase per +Quebracho Found. in Tanning 100 gms. +Extract. Matters. Extract. + +Gm. Gm. Per Cent. Per Cent. +100 0 66.0 66.0 ... ... + 0 100 32.5 32.5 ... ... + 90 10 62.7 64.7 2.0 2.2 + 80 20 56.1 58.7 2.6 3.3 + 60 40 52.6 56.9 4.3 7.1 + 50 50 49.3 55.2 5.9 11.8 + 30 70 42.6 47.3 4.7 15.6 + 20 80 39.2 42.3 3.1 15.5 + +The maximum solubilising effect is exhibited in the mixture of 70 parts +of Neradol and 30 parts of quebracho, with an additional percentage of +tanning matters in the mixture of 15.6 per cent.--a figure which is very +nearly identical with that of the insolubles present in the original +Argentine quebracho extract. + +The phlobaphene-solubilising property of Neradol D is closely connected +with the influence of the latter on the colour of leathers tanned with +natural tannins. If, on the one hand, a pelt is tanned with natural +(_i.e._, non-treated) quebracho extract, a rather light coloured leather +results, the fleshy colour of which is characteristic of quebracho. The +dark coloured phlobaphenes present, on account of their insolubility, +will have no influence on the colour of the leather. If, now, the +quebracho extract be treated with sulphite and bisulphite in the usual +way, the phlobaphenes are solubilised, but the reducing effect of the +bisulphite tends to brighten the colour of the otherwise dark coloured +phlobaphenes as well as that of the soluble tannins, and a +reddish-yellow coloured extract results, imparting its own colour to the +pelt. When, on the other hand, the quebracho extract is solubilised by +means of Neradol D, the phlobaphenes are brought into solution without +reduction taking place, and a dark brownish-red extract results, which +imparts a similar colour to the finished leather. This darkening effect +of Neradol D is most conspicuous in the case of mangrove, maletto, and +chestnut, but is absent in the case of algarobilla, dividivi, gambir, +sumac, and valonea. The varying phlobaphene contents of the tannins +easily afford an explanation of the different properties above alluded +to: the mangrove phlobaphenes are dark coloured bodies, those of mimosa, +maletto, and chestnut are of lighter colour, and the last-named tanning +materials enumerated above are either devoid of phlobaphenes or possess +them only as very light coloured bodies. Algarobilla, sumac, gambir, +dividivi, and valonea, on the other hand, are associated with large +amounts of sparingly soluble ellagic acid, known as "bloom" or "mud" +which imparts a light colour to the finished leather, and conveniently +covers the dark colour imparted to the leather by other tanning +materials; for this reason the former are often used in the lay-aways or +in the finishing processes. + +Similar effects to those of Neradol D are exhibited by other salts of +sulphonic acids, _e.g._, sodium benzylsulphanilate (Solvenol B.A.S.F., or +solution salt ("Solutionsalz") Hoechst); the author prepared mixtures of +such salts and untreated quebracho extract in order to determine their +solubilising effects, and arrived at the following results:-- + +30 parts Solvenol plus 70 parts quebracho extract: clear solution, + no deposit. + +25 parts Solvenol plus 25 parts quebracho extract: clear solution, + very little deposit + +20 parts Solvenol plus 80 parts quebracho extract: nearly clear solution, + very little deposit. + +15 parts Solvenol plus 85 parts quebracho extract: slightly opaque solution + some deposit. + +Leathers tanned with these mixtures were more or less dark coloured +according to the amounts used of solvenol and the consequent +solubilisation of the phlobaphenes. + +A similar effect, though of opposite nature from a tanning standpoint, +is exhibited by sulphonates on certain colloidal dark coloured +substances. A phenolsulphonic acid, which had been overheated during +sulphonation and subsequently condensed (crude Neradol), imparted a +conspicuous greyish-brown colour to the leather; samples of this crude +product were then partly neutralised with varying amounts of alkali, and +these samples (containing increasing quantities of salts) tested for +tannin and colour effects. It was found that the more highly neutralised +samples imparted a darker colour to the solutions, but these dark +products did not deposit the dark impurities on the pelt. One may +therefore assume that tannoid substances are colloidally suspended, and +when converted into true solutions are incapable of being fixed in +insoluble form by the pelt. + +Just as, by adding Neradol D to a tanning extract, the phlobaphenes are +solubilised and a dark coloured extract results, it is also possible to +remove the mechanically deposited phlobaphenes and oxidised tannins from +the finished leather, and, as a consequence, lighten the colour of the +leather. For practical purposes, bleaching with Neradol D is carried out +by brushing over the darkly coloured leather with a 2°-3° Bé. solution +of Neradol D, and then rinsing well with water, in order to remove the +solubilised tannin. A lighter colour may also be obtained by immersing +the leather in a liquor of the strength mentioned above for several +hours, and then rinsing with water, but by this procedure not only the +surface tannin is removed, but also tannin from the leather substance +itself; this method is therefore not suitable for heavy leathers which +are sold by weight. + +The advantage of employing Neradol D as a bleach in this way is to be +found in the fact that, on the one hand, the bleaching sulphonic acid +attacks the leather to a much slighter extent than is the case with +inorganic acids usually employed for this purpose; on the other hand, +the method of brushing the sulphonic acid on the leather only introduces +small amounts of sulphonic acid in the leather, thus lessening the +harmful effects of acids upon leather. Furthermore, the common methods +of using alkalies as tannin-solubilising agents with the consequent +running off and waste of alkaline tan liquors are here substituted by a +method leaving liquors rich in tannin and Neradol, and which may be used +in the ordinary procedure of tannage. + +Since Neradol D contains neutral sodium sulphate (about 3 per cent.), +and the latter, by precipitating colouring matters present in tan +liquors, may slightly bleach these, it was of interest to determine +whether the sodium sulphate plays any part in the bleaching effected by +Neradol. Mixtures of chestnut and quebracho extracts were prepared, to +which were added:-- + +(1) 5 per cent. Neradol D. +(2) 5 per cent. Neradol D. free from Na_2SO_4. +(3) ° 15 Per cent. sodium sulphate (corresponding to above +Neradol D). + +These mixtures were allowed to act upon pelt alongside of comparison +tests using quebracho and chestnut extracts only, the strength of the +liquors in all cases being 1.5° Bé; the pelt was left in the solution +till tanned through. The following results were obtained:-- + +(1) Quebracho tanned leather was darker; no difference in +colour by chestnut extract. +(2) Similar to (I). +(3) Same colour as given by the original extracts. + +This experiment demonstrates that absence of sodium sulphate in the +mixture is without influence on the colour of the resulting leather, and +that an addition of sodium sulphate to natural extracts does not affect +the colour imparted by them to pelt + + +5. Effect of Neradol D on Pelt + +Being a sulphonic acid derivative, the chemical constitution of Neradol +is obviously considerably different from that of the natural tannins, +and the question has been asked: Will Neradol D, in its concentrated +form, attack the hide substance?[Footnote 1: _Collegium_, 1913, 521, +487.] Bearing in mind that concentrated extracts of vegetable tannins +in some circumstances effect a "dead" tannage (_cf_. case-hardening) and +hence reduce their practical value, and that for this reason it is +impossible to allow either concentrated extracts or concentrated Neradol +D to act upon pelt, the author still decided to carry out some +experiments in this direction. Concentrated Neradol D (33° Bé.) and +strong aqueous solutions of this material in strengths of-- + + 30° 25° 20° 15° 10° 5° 3° 1° Bé. + +were therefore allowed to remain in contact with pelt for a period of +ten days, when the pelts were taken out and washed in running water for +twenty-four hours, and then dried. The resultant leathers possessed the +following properties:-- + +33° Bé. solution: completely gelatinised.[Footnote 2] +30° " " " [Footnote 2] +25° " two-thirds gelatinised; surface tanned. +20° " one third gelatinised; surface "dead" tanned. +15° " pelt was glassy throughout. +10° " rather cracky leather, but well tanned. +5° " normal tannage. +3° " " " +1° " " " +[Footnote 2: Impossible to subject the pieces to a proper washing out.] + +The interiors of the leathers obtained from the 25° and 20° +Bé. solutions were completely gelatinised; this may be accounted for by +assuming that the surface was "dead" tanned, and that hence the free +dissociated sulphonic acid diffused into the leather, towards which it +exhibited hydrolysing rather than a tannoid effect with the consequent +result described above. Above 10° Bé. the effect is more that of an acid +with concentrations below 10° Bé.--the only ones of technical +importance--however, no ill-effects may be observed. + +For tanning purposes, Neradol D solutions of 2° Bé. are quite +satisfactory, and it has been found [Footnote 1: _Technikum_, 1913, 80, +324.] that solutions of this strength do not dissolve out any protein of +the hide. [Footnote 2: The translator cannot agree with the author on +this point. He has, for instance, found that solutions of analytical +strength dissolve considerable amounts of hide substance, and his +practical experience confirms results arrived at in the laboratory.] + +A purely Neradol D tanned leather may be produced by immersing a bated +pelt, free from lime, in a 2° Bé. Neradol D liquor for about four days; +the resultant leather being nearly white and otherwise very similar to a +leather tanned with vegetable tanning materials. + +The main application of Neradol D is in admixture with vegetable tanning +materials; especially in the early stages of tannage is this substance +of value, since by its use not only a light coloured leather surface is +obtained, but its presence prevents a subsequent dead tannage when +strong vegetable tan liquors are applied, and it also imparts strength +to the grain layer. It is thus possible to shorten the time consumed by +the tanning process by employing Neradol D in the manner described. + +A further explanation as to why the tanning process is considerably +hastened by using Neradol D, either alone or in conjunction with natural +tannins, is afforded by the fact that though Neradol D quickly +penetrates the grain, it is but "loosely" fixed by the latter, _i.e._, +it is not deposited to such an extent that it would prevent penetration +of the vegetable tannins. In the case of a mixture of Neradol D and +vegetable tannins, the former quickly diffuses into the pelt and fixes +the fibres, thus facilitating penetration of the vegetable tannins. +This assumption is justified in view of the speed with which Neradol D +completely penetrates and tans the pelt, since Neradol D containing +acids and salts exhibits effects similar to those of a pickle. + + +6. Reactions of Neradol D with Iron and Alkalies + +A special characteristic of Neradol D tannage is the sensitiveness of +the latter to the action of iron and alkalies. The active principle of +Neradol D being free dicresylmethanedisul-phonic acid, which is easily +neutralised by lime, ammonia, and amino-acids and hence rendered +inactive for tanning purposes, it is essential that the pelt prior to +tannage with Neradol D should be completely delimed, bated, and freed +from all constituents possessing alkaline reaction. It is, however, +possible to regenerate Neradol D liquors contaminated with alkali or +partly neutralised by the addition of small quantities of organic +(formic, acetic, lactic, and butyric) or inorganic (hydrochloric or +sulphuric) acids,_i.e._, the dicresyl-methanedisulphonic acid is again +partly liberated, and this procedure is always preferred where the +tanning process does not allow of a complete deliming of the pelt prior +to introducing the latter into a Neradol D liquor. If, on the other +hand, such liquors are kept properly, and the addition of acid referred +to kept up, they will remain active for weeks and need only +strengthening up with the requisite quantity of Neradol prior to +introducing fresh pack. + +The sensitiveness to alkalies of Neradol D is considerably greater than +in the case of natural tannins, and it appears that a vegetable tan +liquor neutralised with lime will not even surface-tan when acting upon +pelt and will neither impart a dark colour to the leather nor remove +from it any appreciable amount of protein. Similarly, a Neradol D liquor +neutralised with lime exerts no tanning action, but in contradistinction +to the vegetable tan liquor similarly treated, will impart a blue or +blackish-blue colour to the pelt, from which it removes larger +quantities of protein. The author examined two such liquors relating to +their contents of tanning matters and protein and obtained the following +results:-- + + Reaction. Bark. Tans. Non-Tans Insol. Proteins + + Per Per Per Per + Cent. Cent. Cent. Cent. + +Vegetable Slightly 12° 0 2.93 0.35 0.01 +tan alkaline +liquor + +Neradol " " 10° 0 4.43 0.17 0.17 + + +These figures do not only show the higher protein contents of the +Neradol D liquor, but do also show higher contents in soluble +non-tannins, which consist mainly of lime (2.12 per cent.) and sodium +salts (1.8 per cent.), thus establishing the fact of the sensitiveness +of Neradol D to alkalies in addition to its lime-solubilising effects. + +The sensitiveness towards alkalies is also noticeable on a large scale +where the tanpits have been built of cement; though the pelt may be +quite free from lime, the Neradol D is quickly neutralised by the +cement, with results similar to those enumerated above. + +The blue coloured soluble compound of Neradol D and iron salts, to which +frequent reference has been made, is very important from a practical +standpoint. Whereas the catechol tannins (_i.e._, fir, gambir, hemlock, +cutch, mangrove, and quebracho) are coloured black, those of the +pyrogallol class (_i.e._, algarobilla, dividivi, valonea, gallotannic +acid, myrabolams, and sumac) bluish-black, and the "mixed" tannins +(_i.e._, canaigre, oak, and mimosa bark) bluish-purple by iron alum, +Neradol D is coloured a pure blue. How sensitive this reaction is, the +following comparative analyses illustrate: to each litre of tan liquor +containing 4 gm. tanning matter prepared from (_a_) quebracho extract +and (_b_) Neradol D, 10 c.c. of a 10 per cent. iron alum solution were +added, the solutions heated to 100° C., cooled and filtered, and the +colour of the filtrates and the weight of the precipitates determined:-- + +(_a_) Quebracho solution: light reddish-brown filtrate, 3.22 gm. +precipitate. + +(_b_) Neradol solution: deep blue filtrate, 0.02 gm. precipitate. + +Hence, on adding a soluble iron salt to a solution of a natural tannin, +most of the tanning matter is precipitated; the colour of the filtrate, +however, is much the same as that of the original solution. A Neradol D +liquor similarly treated gives no precipitate, but is coloured blue +throughout. The filtrates from the above solutions were allowed to act +upon pelt, and the following observations were made:-- + +(_a_) The light reddish-brown filtrate from the quebracho liquor +exhibited no well-defined tanning effect on pelt, to which it imparted a +light brown colour. + +(_b_) On the other hand, the deep blue filtrate from the Neradol D +liquor exhibited well-defined tanning effects, and imparted a deep blue +colour to the pelt. + +For practical purposes, the sensitiveness of Neradol D to iron is not +only remarkable because any contact with iron particles will colour the +liquor (and hence the pelt) blue, but also because the slight amount of +iron always present in cement renders the use of cement pits prohibitive +where Neradol D liquors are used. + +This intense blue coloration might have made possible a colorimetric +estimation of Neradol D. The author has investigated this possibility, +using different concentrations of Neradol D liquors to which a solution +of iron ammonium alum was added, and found that when, at certain +concentrations, the maximum blue colour had been obtained, it was still +possible to increase the quantity of Neradol without the intensity of +the colour being affected. Addition of a little alkali tends at first to +darken the blue colour, more alkali changes the blue colour to brown and +yellow, successive additions of a weak organic acid (_e.g._, acetic +acid) rapidly lighten the blue colour. Since industrially used Neradol +D liquors always contain varying quantities of acid and may be neutral +or even slightly alkaline, it must be considered impossible to make any +use of such a colorimetric estimation for practical purposes. + +7. Reagents Suitable for Demonstrating the Various Stages of Neradol D +Tannage + +The extent to which tannage with Neradol D proceeds on the surface and +within the pelt may be judged from the feel of the skin, but such a +method is totally unsuited to any but a practical tanner. A suitable and +reliable reagent is indigotine (B.A.S.F.), which clearly distinguishes +tanned and untanned layers of the pelt. If, for instance, a 1-2 per +cent, solution of indigotine is brought into contact with a fresh cut on +a pelt, and the latter subsequently washed with warm water, the +indigotine is only retained by the untanned parts; a leather tanned with +Neradol D is therefore only coloured by indigotine to the extent to +which it has combined with the Neradol. [Footnote: According to Seel +and Sander (_Zeits. f. ang. Chem._, 1916, 333), basic dyestuffs are also +very suitable for demonstrating tanned parts of the pelt.] + +Another reagent is constituted by iron ammonium sulphate; the extent of +the penetration of Neradol D, which gives an intense blue coloration +with iron salts, into the leather may be determined by washing the pelt +treated with Neradol D, making a cut, again washing and treating the cut +with a few drops of a weak solution of iron ammonium sulphate. Those +parts of the pelt which have been converted into leather then appear +deep blue; on the other hand, those which have been in contact with +Neradol D, but have not yet been converted into leather, are light +blue. Those parts which have not yet been in contact with Neradol D +appear pure white; the results of this reaction are therefore opposite +to those obtained by the use of indigotine. + + +8. Combination Tannages with Neradol D + +Whereas mixtures of Neradol D and vegetable tannins impart properties to +the leather consistent with the proportions in which these materials are +present, it is not possible to combine Neradol D with mineral tanning +agents or fats (_e.g._, fish oils, etc.) in such a way that a leather +characterised by the properties of either material is +obtained. Experiments were carried out using (1) chrome salts plus +Neradol D; (2) aluminium salts plus Neradol D; and (3) oils plus Neradol +D, and the following conclusions were arrived at:-- + +1. CHROME-NERADOL D liquors, containing comparatively larger amounts of +Neradol D, act too rapidly on the pelt and draw the grain; smaller +amounts of Neradol D seem without influence on the finished leather, +which possesses pronounced characteristics of chrome leather. Another +disagreeable factor is the following: the chrome salts must possess a +certain degree of basicity in order to produce good leather; the Neradol +D must, on the other hand, possess a certain acidity to produce the +optimum results, and it is hence impossible to balance practically the +basicity of the chrome salts and the acidity of the Neradol in order to +justify the presence of both. If one of the two is used separately +before the other, a leather always results possessing the +characteristics of the material first employed, provided the time of +action has been sufficiently extended. If insufficient time has been +allowed, the characteristics imparted by the main tanning agent are not +altered. + +2. ALUMINIUM SALTS AND NERADOL require practically the same basicity and +acidity respectively, and when combined always yield a leather +possessing mainly the properties of one of the components. In addition +to this fact, leathers tanned with aluminium salts possess great +softness and stretch, those tanned with Neradol D greater firmness and +less stretch, and these opposing qualities completely compensate one +another and render _nil_ the value of such mixtures. + +In addition to this, the presence of aluminium salts produces no better +fixation on the leather fibre of basic coal-tar dyes, so that in this +respect also a combination of aluminium salts and Neradol D is of no +value. + +3. FAT NERADOL D TANNAGE: Just as aluminium salts impart special +characteristics to leather, this property is exhibited by fatty matters, +especially so as regards stretchiness and softness. Both of the latter +are not apparent to the same extent in an oil tannage into which Neradol +D and oil enter as constituents. It is, however, not excluded that, in +view of the fact that the combination of oils and Neradol D appear to +produce the most promising results of the three from a technical point +of view, such combination would yield products possessing less stretch +and greater softness which, by occupying an intermediary position, might +possess certain advantages and be useful for certain technical purposes. + + +9. Analysis of Leather Containing Neradol D + +Chemical examination of leathers tanned with Neradol D or with mixtures +of natural tannins and Neradol D often involve a determination of the +materials employed in tannage. In most leathers exclusively tanned with +vegetable tanning materials, it is usually possible to determine at +least the nature of the main tanning agent, whereas the attempts at +determining those tannins which are only present in minor quantities +rarely succeed. Since Neradol D usually is employed in comparatively +small quantities, it has been imperative to find a method which also +permits of the detection of smaller quantities of Neradol D. Provided +the presence of not less than 5 per cent. (on the weight of the leather) +of Neradol D, the following method yields reliable results:--20-30 +gm. of the leather are ground or sliced as finely as possible and the +powder (or the slices) treated in the cold with a sufficient volume of +dilute ammonia solution (5 c.c. ammonia plus 95 c.c. of water) for +eight to twelve hours. The object of this is to dissolve the tannins, +but no protein should go into solution. The solution is filtered and +the filtrate evaporated on the water bath till it occupies a volume of +about 30 c.c. A few c.c. of aniline hydrochloride are now cautiously +added, when it should be carefully noted if a precipitate is thrown down +which might be either completely or only partly soluble in excess of +aniline hydrochloride. A precipitate is always thrown down when Neradol +D or wood pulp is present; only the Neradol D precipitate is soluble in +excess of aniline hydrochloride. Partial solubility of the precipitate +therefore indicates the presence of both wood pulp and Neradol D. + +The quantitative determination of sulphuric acid--the detection and +estimation of which in leather is important--is considerably influenced +by the presence of Neradol D. Practically all methods in vogue dealing +with its determination were based on the estimation of the sulphur +introduced into leather by sulphuric acid. The presence of Neradol D, +the main constituent of which is dicresylmethanedisulphonic acid, +renders it impossible by such methods to determine whether the combined +sulphur owes its origin to sulphuric or sulphonic acid. It remains yet +to be determined whether the sulphonic acid influences the leather +substance to the extent that sulphuric acid does; it must, however, be +borne in mind that Neradol D in addition to free sulphonic acid also +contains sulphonates and sulphates, which may enter into the leather and +thus increase the sulphur contents of the latter. A method must hence be +devised which estimates the free acid only and provides the means of +distinguishing this from all other acids of organic and inorganic +acids. Paessler, [Footnote: _Collegium_, 1914, 527, 126; 531, 509; 532, +567.] by extracting the leather and dialysing the filtrate, has +effected a separation of the acids and the tanning and colouring matters +and quantitatively estimated the sulphuric acid in the dialysate. + +Immerheiser [Footnote 1:_Collegium_, 1918, 582, 293.] devised a method, +based upon the property of sulphuric acid of combining with ether, for +the purpose of determining free sulphuric acid in leathers:--10 gm. of +the leather, cut into small pieces, are extracted three times with 200 +c.c. distilled water at room temperature, the time of each extraction +being ten to twelve hours, and the combined extracts evaporated to +dryness on the water bath, 5 gm. of quart sand being added. The dry +residue is now powdered, introduced into an Erlenmeyer flask provided +with a glass stopper, and 200 c.c. of anhydrous ether [Footnote 2: To be +tested for water by shaking with anhydrous copper sulphate.] added. +After about two hours, during which the flask is occasionally shaken, +the ether is poured through a filter, the residue washed with a little +ether, and the operation repeated twice with each 40 c.c. anhydrous +ether, using the same filter. To the combined ether extracts (about 200 +c.c.) HCl and [Greek: b]aCl_2 are added, the ether distilled off and the +residue evaporated on the water bath, in order to decompose the +ether-sulphuric acid compound. 50 c.c, of hot water acidified with HCl +are now added, the precipitate allowed to settle, filtered, washed, +dried, and weighed. The sulphuric acid thus estimated was present in the +leather as _free sulphuric acid_. That present as sulphates soluble in +water is estimated in the residue on the filter: the residue is +extracted with hot water, the sand filtered off, the filtrate acidified +with HCl, boiled for one quarter hour and filtered if necessary. The +clear filtrate, which may be coloured, is brought to boil and +[Greek: b]aCl_2 is added. The barium sulphate indicates the sulphuric +acid present in the leather as water-soluble sulphates. + +Whether the latter be sulphates or bisulphates may be indicated by the +aqueous extract of the above residue, since neutral reaction would +indicate the absence of bisulphates, acid reaction their presence in +addition to possible normal sulphates; the quantitative estimation of +the metals would decide this point definitely. + + +10. Properties of Leathers Tanned with Neradol D + +Whereas the colour of leathers tanned with Neradol D only is nearly a +pure white, those tanned with mixtures of Neradol D and vegetable +tanning materials are more or less light coloured according to the +quantity of Neradol D present, as has been explained when discussing the +phlobaphene-solubilising action of Neradol D. In any case, all leathers +tanned with Neradol D possess fibre of remarkable length, which explains +their increased tensile strength and elasticity. The tensile strength +of a leather tanned with a mixture of Neradol D and vegetable tannins +was 3.7 per cent, as compared to 3 per cent when no Neradol was used; +the extension was 56 per cent, when tanning with Neradol D as against 36 +per cent, without the latter. + +The sensitiveness to light of leathers tanned with Neradol D may be +mentioned. Exposed to direct sunlight, the surface of the leather +assumes a yellowish colour after two days' exposure, and assumes a pure +yellow colour after a further three days. A further fifteen days' +exposure only darkens the leather slightly, the final colour being very +little different from the one obtaining after five days' exposure. + +In passing, it may be remarked that this yellow colour is observed on +the surface only, the grain otherwise possessing that pure white colour +characteristic of Neradol D tanned leather. Further, it may be noted +that leathers tanned--with Neradol D fix basic coal-tar dyes +excellently, whereas acid and substantive dyestuffs are fixed with other +than their natural shades. + +The author has analysed a leather exclusively tanned with Neradol D, and +has obtained the following results:--[Footnote: _Collegium_, 1913, 521, +478.] + +Moisture - - - - - 15.53 per cent. +Ash - - - - - - 0.93 per cent. +Fats- - - - - - 1.26 per cent. +Extraneous matters - - - 0.00 per cent. +Leather Substance |Tanning matters- 36.92 per cent. +Leather Substance |Hide substance - 45.36 per cent. + --------------- + 100.00 per cent. + [Footnote: Sp. gr., 0.642.] + +From these figures, those of "degree of tannage" and "yield" +(pelt-->leather) are calculated as 81.4 and 220 respectively. + +These figures correspond closely to those obtained by the analysis of +leathers tanned with vegetable tanning materials, and this proves the +similarity between the Neradol D tannage and a vegetable tannage in +their chemical aspects. + + +11. Neradol D Free From Sulphuric Acid + +In order to prepare phenol and cresulphonic acids, such quantities of +technical sulphuric acid are used as do not allow of the assumption of +complete utilisation of the sulphuric acid; hence it was of theoretical +interest to remove eventual traces of free sulphuric acid from the +product. For this purpose, the author diluted crude Neradol to 20° +Bé. and gradually added small quantities of milk of lime; the +precipitates were freed from the liquid by suction and washing, and a +Neradol free from sulphuric acid resulted, which was then brought to the +acidity of Neradol D with the calculated amount of alkali. From the +calcium sulphate precipitate, the amount of sulphuric acid originally +present was calculated, and was found to be only 4 per cent. + +The acid-free sample of Neradol was tested with regard to its +suitability as a tanning agent; leather tanned with this sample differed +from one tanned with an untreated sample (Neradol D) by being harder and +possessing a pronouncedly greyish colour. This difference, however, may +not be due to the absence of sulphuric acid but to the presence of the +slightly soluble calcium sulphate in the sample treated with milk of +lime. To prove this point, another way of preparing Neradol D free from +sulphuric acid was looked out for. Sodium acetate was added to a +solution of crude Neradol until the latter was no longer acid to +congo-red; at this point no free sulphuric acid can be present in the +solution. The product, partly neutralised till the acidity of Neradol D +was reached (part of the acidity then being due to liberated acetic +acid), yielded a leather which neither in colour nor in feel differed +from the usual Neradol D tanned leather. This proves that the grey +colour and the hardness of the leather described in the former +experiment is due to the presence of calcium sulphate. + +If the crude Neradol treated with sodium acetate is not partly +neutralised, the analysis gives the following figures:-- + +Tanning matters 67.3 per cent. +Soluble non-tannins 8.6 " +Insolubles 0.0 " +Water 24.1 " + --------- + 100.0 per cent. + Acidity: 1 gm. = 46 c.c. N/10 NaOH. + +Compared to the analysis of crude Neradol containing sulphuric acid, the +figures show that, on the one hand, the presence of the comparatively +small quantity of sodium acetate but slightly influences the contents of +non-tannins and water, but, on the other hand, reduces the contents of +tannins and also the acidity. The tanning intensity of this product, +however, is considerably increased, and using a 1° Bé. solution a +leather is obtained in a very short time very similar to that yielded by +ordinary Neradol D, but considerably harder; the latter property is due +to higher acidity and almost complete absence of salts in the product +treated with sodium acetate. + +The author finally attempted to partly neutralise crude Neradol with +various hydroxides and carried out tanning tests with samples containing +the different metals. Hardly any difference in the finished leathers +could be observed as regards colour or quality; the tannage could by no +means be described as that of a combination of Neradol D and the +respective metals. + + +12. Neutral Neradol + +Crude Neradol, completely neutralised with caustic soda, yields a +product of the following composition:-- + +Tanning matters 19.8 per cent. +Soluble non-tannins 37.9 " +Insolubles 0.0 " +Water 42.3 " + ------------ + 100.0 per cent. + +The qualitative reactions of this product differ from those of +non-neutralised Neradol to the extent that gelatine is not precipitated +and iron salts are not coloured blue, but dirty brown, by the aqueous +solution of this product. + +The completely neutralised product, diluted to various concentrations +(of 1°, 2°, 3°, and 5° Bé.) and tested as to tanning properties, +revealed the surprising fact that the pelts were not even surface +tanned, and were coloured evenly blue throughout by indigotine. + +It might have been anticipated that sodium dicresylmethanedisulphonate +would be as devoid of tanning powers as is a neutralised vegetable +tannin, but it is difficult to explain the fact of the sodium salt being +adsorbed by hide powder as "tanning matters" in the Official Method of +Analysis. Brought to a logical conclusion, the figure 19.8 per cent, +should be deducted from 32.5 per cent, obtained in the analysis of a +_partly_ neutralised Neradol D, which comparatively large quantities of +the sodium sulphonate also adsorbed by hide powder, leaving the "tanning +matters" of Neradol D at 13.5 per cent. + +This diminished figure, however, does in no way reduce the value as a +tanning agent of Neradol D; it merely shows how inadequate is the hide +powder method of analysis when applied to substances of the composition +of Neradol D. This is further confirmed by the Loewenthal permanganate +method, which yields the following figures:-- + +Tanning matters 7.2 per cent. +Soluble non-tannins 59.1 [Footnote: Collegium, 1913, 521,487.] + +If, on the other hand, completely neutralised Neradol is acidified with +an organic acid, such as acetic acid, till the acidity, (1 gm.= 10 +c.c. N/10 NaOH) is reached, the resulting product is in all respects +similar to Neradol D and yields a corresponding leather. + +It is permissible to assume that the irregularity exhibited by Neradol D +as regards the analytical estimation of its tannin contents is connected +with the low molecular weight of the tanning principle. Whereas all +tannins so far isolated from the natural tanning materials possess +rather high molecular weights, that of Neradol D deviates considerably +from this rule, as is shown by the following table:-- + +Neradol D tannin Cl_5H_16S_2O_8 358 +Mangrove " C_24H_40O_2l 670 +Oak bark " C_28H_28O_23 840 +Myrabolam " C_54H_48O_35 1256 +Dividivi " C_54H_46O_35 1270 +Malletto " (C_4lH_50O_20)_2 1724 + +This low molecular weight may mainly account for the figures obtained by +the incorrect oxymetric estimation with permanganate; the apparent +tannoid property of the tannoid-inactive neutral salt of +dicresylmethanedisulphonic acid may be explained by assuming that though +it is, probably, in the colloidal state, and as such adsorbed by hide +powder, it is still devoid of astringent properties. + + +G. Different Methods of Condensation as Applied to Phenolsulphonic Acid + +In addition to formaldehyde, many other substances may, theoretically, +induce condensation of phenolsulphonic acid; condensation takes place +either with the elimination of water or, in addition to this, with the +introduction of methane group. + +So far, the following condensing agents have been investigated:-- + + (1) Heating _in vacuo_. + (2) Sulphur chloride. + (3) Phosphorus compounds. + (4) Aldehydes. + (5) Glycerol. + + +1. Condensation Induced by Heat + +If phenolsulphonic acid is heated _in vacuo_ at 130° C. for twenty +hours, condensation takes place [Footnote: Austr. Pat., 64,479.] +without the addition of any condensing agent, and an anhydride of the + + ^ __O__ ^ + | | | | + | | | | + v v + HSO_3 HSO_3 + +composition is formed. This product is a viscous liquid, possessing a +very corrosive action. Added to a solution of gelatine, a light, fine +flocculent precipitate is thrown down. Analysed by the shake method of +analysis, the tannin content of the product equals about 46 per +cent. Its strongly acidic and hence swelling character does not express +qualities consistent with the conception of suitability for tanning +purposes: a sample of the product was therefore partly neutralised to +the acidity of Neradol D, when the shake method of analysis yielded the +following figures:-- + +Tanning matters 21.5 per cent. +Soluble non-tannins 48.3 " +Water 30.2 " + -------------- + 100.0 per cent. + +This partly neutralised sulphonic acid represents a white, pasty mass, +which is not particularly easily soluble in water, yielding a solution +of milky appearance. Treated with the usual tannin reagents, it exhibits +the following characteristics:-- + +Gelatine Light Flocculent precipitate. +Bromine water Compete fixation. +Ferric chloride Cherry-red coloration. +Lead acetate Very slight Percipitate, insoluble HNO_3. +Aniline hydrochlonde Slight percipitate. + +Solutions of this product in concentrations from 1°-8° Bé. exerted no +tanning action whatever, whereas more concentrated solutions (15° Bé.) +converted pelt in eight days into a leather very similar to a Neradol D +leather in colour and feel, but considerably harder. + +In order to determine its phlobaphene-solubilising effects, samplesof +the product were mixed with concentrated quebracho extract in the +proportions 5,10, 20, and 30 per cent. on the weight of extract, and the +following observations made:--5 and 10 per cent. were without effect, +20 and 30 per cent. showed some solubilising tendency, but on diluting +the mixture with water the quebracho was completely thrown out of +solution. Apparently this anhydride is, in this respect also, quite +different from the partly neutralised diphenylmethanedisulphonic acid. + + +2. Condensation with Sulphur Chloride + +When sulphur chloride is allowed to act upon phenolsulphonic acid whilst +heat is applied, a yellowish-grey mass results, which dissolves in +water, forming a reddish-yellow solution. Neutralised to acidity 10, it +exhibits the following reactions:-- + + Gelatine----------------Precipitate. + Ferric chloride---------Deep blue coloration. + Lead acetate------------White precipitate, insoluble HNO_3. + Aniline hydrochloride---Precipitate. + Bromine water-----------No reaction. + +The partly neutralised 2° Bé. solution of this product yielded a +reddish-grey coloured leather, the qualities of which were very similar +to that yielded by Neradol D. + + +3. Condensation with Phosphorus Compounds + +Schiff's well-known synthesis, [Footnote: Liebig's _Ann_., 178, 173.] +in which phosphorus oxychloride interacts with phenolsulphonic acid, +yields a product which exhibits some tannin reactions, but which, when +acting on pelt, converts the latter into a leather which, when dried, is +very cracky. If, on the other hand, cresolsulphonic acid is condensed +with phosphorus oxychloride by heating the two together, products +eminently suitable for tanning purposes result. These products are +non-crystalline bodies easily soluble in water, and are coloured +bluish-violet by ferric chloride and precipitate gelatine. Solutions of +the free acids and acidified solutions of the salts convert pelt into +firm and white leathers possessing great softness and +pliability.[Footnote: Austr. Pat, 66,895.] + + +4. Condensation with Aldehydes + +By treating phenolsulphonic acid with acetaldehyde in the usual way, a +viscous brown mass is obtained, which is very soluble in water, the +solution being of a brown colour. When brought to acidity 10, the +following reactions are exhibited by the product:-- + +Gelatine - - - Precipitate. +Ferric chloride - - Deep blue coloration. +Aqueous ammonia - - Cherry-red coloration. +Lead acetate - - - Yellowish precipitate, insoluble + HNO_3. +Aniline hydrochloride - - Yellow precipitate, soluble excess + aniline. +Bromine water- - - No reaction. + +Tanning experiments with this substance yielded, even after extended +tannage, an undertanned leather, the surfaces being coloured brown, the +inner layers, however, white. Further neutralisation reduces the +tanning intensity of the product; the addition of sodium sulphate to the +original partly neutralised product hastened tannage, the leather, +however, possessing dark colour and being undertanned. The following +constitution may be ascribed to this product:-- + + OH OH + ^ ---CH_2---CH_2--- ^ + | | | | + | | | | + v v + HSO_3 HSO_3 + +If benzaldehyde is used in lieu of acetaldehyde for condensing +phenolsulphonic acid, a water-soluble product results, exhibiting +reactions similar to those of the acetaldehyde-condensation product. The +former product is more suitable as a tanning agent and yields a +reddish-brown rather firm and hard leather; it possesses the +constitution-- + + H + OH || OH + ^ ____C____ ^ + | | ^ | | + | | | | | | + v | | v + HSO_3 v HSO_3 + +For the purpose of condensing phenol with formaldehyde, it is not +essential to first convert the phenol into the water-soluble +phenolsulphonic acid, since it is possible to convert the condensation +products of phenol and its derivatives, which are soluble in alkali, +into water-soluble form by either heating the condensation products with +concentrated solutions of formaldehyde and neutral sulphites, or by +dissolving the condensation products in alkali and inducing reaction by +means of formaldehyde bisulphite. [Footnote: _Collegium_, 1913, 518, +324.] Highly concentrated solutions result, which may be concentrated +either as such or after the alkali present has been neutralised. The +sulphurous acid formed prevents oxidation of the product on +evaporation. A special advantage of this method of preparation is the +fact that sulphuric acid, which is but difficultly removed from the +end-product, is not employed at all. + +The product thus obtained is a yellowish-white crumbly mass, which is +very soluble in water, forming a clear solution. The latter exhibits +the following reactions:-- + + Gelatine---------------Precipitate. + Ferric chloride--------Deep blue coloration. + Aqueous ammonia--------Cherry-red coloration. + Lead acetate-----------White precipitate, insoluble in + HNO_3. + Aniline hydrochloride--Precipitate. + Bromine water----------No reaction. + +The product brought to acidity 10, yielded on analysis the +following figures:-- + + Tanning matters------------------ 25.2 per cent. + Soluble non-tannins-------------- 56.3 " + Insolubles----------------------- 0.0 " + Water---------------------------- 18.3 " + ------------- + 100.0 per cent. + +Tanning experiments with this substance yielded white and soft leathers, +which were indistinguishable from those tanned with Neradol D. + +A characteristic feature of this synthetic tannin is its behaviour in +concentrated form towards pelt, which is not attacked by it, but is +readily tanned even at such high concentrations. An explanation of this +is to be found in the large quantity of salts present in the product. A +disadvantage of this synthetic tannin is its complete incapability of +dissolving phlobaphenes, which is even so far extended as to precipitate +otherwise easily soluble tannins when adding it to solutions of the +latter in comparatively large proportions; here, again, the salts are +responsible for this behaviour, their large quantities effecting a +salting out of the natural tannins. + +The class of aldehyde condensations also comprises that of inducing +condensation by means of sugars; if phenolsulphonic acid is heated with +glucose, a reddish-brown liquid results, which is soluble in water. The +solution exhibits reactions similar to those of Neradol D. It is, +however, not possible, by this method of condensation, to prepare as +highly concentrated products as is possible in the case of Neradol D, +since employing sugars as condensation agents means liberation of a +large volume of water. Analysis of this product, using the shake method, +gives a tannin content of 16.2 per cent; tanning experiments +demonstrated that the time of tannage, using a 2° Bé. solution, was the +same as that required by Neradol D, and yielded a leather, the surface +of which was reddish-grey, the inner layers being white, but which is +otherwise very similar to Neradol D tanned leather. [Footnote: +Austr. Pat, 69,375, 69,376, 69,377.] + +Relatively to its capability of solubilising phlobaphenes, this product +exhibits similar properties to that obtained by merely heating +phenolsulphonic acid, to a slight extent only solubilising quebracho +extract, which, on diluting the mixture, is completely thrown out of +solution. + + +5. Condensation with Glycerol + +Phenolsulphonic acid, when heated with glycerol, undergoes the process +of condensation, and forms a brown fluid, which, when brought to acidity +10, exhibits the following reactions:-- + + Gelatine-----------------Precipitate. + Ferric chloride----------Brown-black coloration. + Lead acetate-------------White precipitate, insoluble in + HNO_3. + Aniline hydrochloride----Slight precipitate. + +Tanning experiments with this partly neutralised product resulted in a +very gradual conversion of the pelt into a greenish-grey coloured +leather; the colour, however, does not penetrate the pelt and is hence +caused by colloidally suspended impurities. If the solution is filtered +through a filter candle, a somewhat clearer solution results, but the +latter also tans very slowly and yields a brown coloured leather. + +Analysis of the partly neutralised product reveals a tannin content of +17.6 per cent. A 2° Bé. solution of the non-neutralised product showed a +rapid tanning effect at first, when brought into contact with pelt, on +which it had a strong swelling effect, and to which it imparted a +greenish colour; the tanning effect, however, slowed down considerably, +after a few days, and the solution penetrated the pelt only very +gradually; this is probably due to the presence of large quantities of +colloidally suspended impurities, which, when the substance is partly +neutralised with the formation of salts of the sulphonic acids, are +brought into true solution and hence penetrate the pelt with greater +rapidity. + + + + + +INDEX OF AUTHORS + +Adler +Appelius +Ashmore + +Bader +Badische Anilin u.(German abbreviation for "und") Soda-Fabrik +Baekeland +Baeyer +Berzelius +Biginelli +Boehringer & Sons +Bottinger +Braconnot +Buff + +Caro +Chem. Fabrik Jucker & Co. +Chevreul + +Dekker +Deutsch-Koloniale Gerb u. Farbstoff Gesellschaft +Deyeux +Dizé +Drabble + +Edner +Elberfelder Farbenfabriken + +Fahrion +Feist +Fischer, E. +Freudenberg +Froda + +Gerhardt +Gesellschaft f.(German abbreviation for "für") Chem. Industrie, Basle +Graebe +Graham +Grasser + +Hatchett +Heinemann +Herzig +Herzog +Hönig + +Iljin +Immerheiser + +Jennings + +Kahl +Kauschke +Klepl +König +Kostanecki +Krafft +Krauss +Kunzemüller + +Lauffmann +Liebig +Lipp +Lloyd +Löwe + +Manning +Mauthner +Meunier +Michael +Mielke +Mitscherlich + +Nierenstein + +Paessler +Paternň +Payne +Pelouze +Perkin +Proust + +Rapoport +Raschig +Reinsch +Resch +Russanow + +Sabanajew +Sander +Scheele +Schiff +Schmidt +Schorlemmer +Seel +Seyewetz +Sisley +Skey +Stiasny +Strauss + +Thuau +Tschirch + +Vogel + +Walden +Webster +Weinschenk +Wohl + +Zacharias + + + + +A + +Alcohol figure +Algarobilla +Alizarin +Alizarin yellow, in paste +Alkalies, reaction of, to Neradol D +Alum-neradol tannage +Alum tannage +Aminobenzene +Aminophenol, _p_- +Aniline dyes +Anthracene +Anthraquinone +Arylsulphaminoarylsulphonic acids +Arylsulphoxyarylsulpho acids + +B + +Bakelite +Bakelite solution +Benzoylamino 6-chloranthraquinone +Benzylsulphanilate sodium +Bismuth salts +Bleaching method for leather with Neradol D +Bloom +Bromo-[Greek: b]-naphthol +Bromonitrophenol +Bromophloroglucinol +Bromosalicylic acid +Bromotrinitrophenol + +C + +Carbazole +Carbomethoxyhydroxybenzoic acid, +Carbomethoxyhydroxybenzoic acid chloride, +Catechine +Catechol +Cerium salts +Ceruleoellagic acid +Cesium salts +Chestnut wood extract +Chloronaphthalenesulphonic acid +Chlorophenol +Chrome-Neradol D tannage +Chrome salts +Chrome tannage +Coal, bituminous +Coffee tannin +Combination tannage with Ordoval +Combination tannage with Neradol D +Condensation by heat +Condensation methods +Condensation with aldehydes +Condensation with glycerol +Condensation with phosphorus compounds +Condensation with sulphur chloride +Copper salts +Corinal +Cresol +Cresol-_p_-sulphonic acid, _o_- +Cresolsulphonic acid +Cresotinic acid + +D + +Depsides +Detannisation with hide powder +Diaminoanthraquinone +Diaminonaphthylmethanedisulphonic acid +Dianilinoquinone +Dibenzopyrrol +Di-[Greek: b]-oxynaphthoic +Di-[Greek: b]-resorcylic acid +Dichloranthraquinone +Dichloronaphthylmethanedisulphonic acid +Dicresylmethanedisulphonic acid +Dicresylmethanedisulphonic acid purified electro-osmotically +Dicresylmethane sulphonate sodium +Didepsides +Didymium salts +Diferulic acid +Digallic acid +Digallic acid, [Greek: b]- +Digallic acid, inactive +Digallic acid, _m_- +Digalloylleucodigallic acid anhydride +Digentisinic acid +Dihydric alcohols, aromatic +Dihydroxybenzene, _m_- +Dihydroxybenzene, _o_- +Dihydroxybenzene, _p_- +Dihydroxybenzenes +Dimethylaniline +Dimethylellagic acid +Di-_m_-oxybenzoic acid +Dinaphthylmethanedisulphonic acid +Dinitronaphthylmethanedisulphonic acid +Di-_o_-cumaric acid +Diorsellic acid, _o_- +Diorsellic acid, _p_- +Dioxyellagic acid +Dioxynaphthylmethanedisulphonic acid +Dioxytoluic acid +Diphenylmethane +Diphenylmethanedisulphonic acid +Di-_p_-hydroxybenzoic acid +Diprotocatechuic acid +Disalicylic acid +Disyringic acid +Dithionaphthylmethanedisulphonic acid +Dividivi +Dividivi tannin +Dixylylmethanedisulphonic acid + +E + +Electro-chemical behaviour of Neradol D +Electro-osmosis of Neradol D +Ellagic acid +Ellagitannic acid +Empirical formula of tannin +Erythrine +Esco-extract +Ester formula of tannin +Ethyl acetate figure + +F + +Fat-Neradol D tannage +Feruloyl-_p_-oxybenzoic acid +Flavellagic acid +Fluorene +Formaldehyde +Formaldehyde tannage + +G + +G-acid +Gallate ethyl +Gallic acid +Galloflavine +Galloyl-_p_-hydroxybenzoic acid +Galls, oak +Gall tannin +Generator tar +Guaiacol + +H + +Halogens +Hepta-[tribenzoyl-galloyl]-_p_-iodophenylmaltosazone +Hexahydroxyaurinecarboxylic acid +Hexoxyanthraquinone +Hexoxydiphenyl +Hexoxydiphenyldicarboxylic acid +Hexoxydiphenylmethanedicarboxylic acid +Humic acid +Hydrolysis of tannins +Hydroquinone +Hydroxybenzoate sodium, _m_- +Hydroxybenzoate sodium, _p_- +Hydroxybenzoic acid, _p_- +Hydroxybenzoic acid +Hydroxy-cymenes + +I + +Indophenol reaction +Iron, reaction of, to Neradol D +Iron salts + +K + +Ketone formula of tannin + +L + +Lanthanum salts +Lead salts +Leather analysis in presence of Neradol D +Lecanoric acid +Leucodigallic acid +Leucoellagic acid +Leucotannin +Lignite +Luteic acid + +M + +Malletto tannin +Mangrove tannin +Melangallic acid +Mercury salts +Metellagic acid +Methylamino-4-bromanthraquinone +Methylenedinaphthol +Methylenedisalicylic acid +Methylenedisalicylic acid, brominated +Methylenedisalicylic acid, iodised +Methylisopropylphenanthrene +Methylotannin +Molybdenum figure +Monochloro-_p_-dihydroxybenzene +Mud +Myrabolams +Myrabolams, tannin + +N + +Naphthalenesulphonic acid, [Greek: b]- +Naphthol, [Greek: a]- +Naphthol, [Greek: b]- +Naphthol-[Greek: a]-methanesulphonic acid +Naphtholdisulphonic acid +Naphtholmonosulphonic acid +Naphtholsulphonic acid, [Greek: a]- +Naphtholsulphonic acid, [Greek: b]- +Neodymium salts +Neradol D +Neradol D tannin +Neradol N +Neradol ND +Neradol ND, neutral +Nitronaphthalenesulphonic acid +Nitrophenol, _o_- +Nitrosodimethylaniline +Non-tannins +Novolak + +O + +Oak bark +Oak bark tannin +Official method of tannin analysis +Orcinol +Ordoval G +Orsellic acid +Orsellinoyl-_p_-oxybenzoic acid +Oxyanthraquinone +Oxyazo reaction +Oxybenzoyl-_m_-hydroxybenzoic acid +Oxybenzoyl-_p_-hydroxybenzoic acid, _m_- +Oxybenzoylsyringic acid +Oxynaphthoyl-_p_-hydroxybenzoic acid, _a_- +Oxynaphthylmethanesulphonic acid +Oxyphenylmethanesulphonic acid +Oxyquinoline + +P + +PATENTS-- + _Austrian_ + 58,405; 61,057; 61,061; + 64,479; 66,895; + 68,796; 69,194; + 69,375; 69,376; + 69,377; 70,162 + _German_ + 72,161; 111,408; 112,183; + 132,224; 181,288; + 184,449; 200,539; + 206,957; 211,403; + 262,558; 282,313; + 286,568; 290,965; + 291,457; 293,042; + 293,640; 293,693; + 297,187; 297,188; + 300,567; 303,640; + 305,516; 319,713; + 320,613 + _Swiss_ + 78,282; 78,797; 79,139 + _U.S.A._ + 1,639,174 +Peat +Pelts +Pelts, action on, of Neradol D +Penta-[_p_-hydroxybenzoyl] glucose, +Penta-[_p_-methyl-_m_-digalloyl]-glucose +Penta-[pyrogalloylcarboyl]-glucose +Pentacetylleucotannin +Pentacetyl-_m_-digallic acid +Pentacetyl tannin +Pentadigalloylglucose +Pentagalloylglucose +Pentagalloylglucoside +Pentamethyldigallic acid, methyl ester +Pentamethyl-_m_-digalloyl chloride, +Pentamethyl-_m_-digallic acid +Pentamethyl-_m_-digallic acid methyl ester +Pentamethyl-_p_-digallic acid +Pentamethyl-_p_-digallic acid methyl ester +Pentamethoxybiphenylmethylolide carboxylic acid methyl ester +Pentoxybiphenylmethylolide +Pentoxybiphenylmethylolide carboxylic acid +Phenanthraquinone +Phenolsulphonate sodium +Phenolsulphonic acid +Phenolsulphonic acid anhydride +Phenol, tautomeric +Phenylcarboxylic acid +Phenylhydrazine derivatives of tannin +Phenylhydrazine ellagic acid +Phlobaphene +Phlobaphene-solubilising action of neradols +Phloroglucinol +Phthalic acid +Pickling +Picric acid +Platinum salts +Polydepsides +Polydigalloylleucodigallic acid anhydride +Polyhydroxybenzenes +Pomegranate +Preparation of tannin infusion +Properties of leather tanned with Neradol +Protocatechuic acid +Protocatechuyl-_p_-hydroxybemoic acid +Pseudo-tannage +Purpuro tannin +Pyrogallol +Pyrogallic acid +Pyrogalloylcarboyl-_p_-oxybenzoic acid +Pyruvic acid + +Q + +Quinazarene +Quinoline +Quinone + +R + +R-acid +Reaction, Procter-Hirst +Reagents for Neradol D tannage +Resites +Resitol +Resols +Resorcinol +Resorcylic acid, [Greek: b]- +Retene + +Rosins, acid +Rosolic acid +Rufigallic acid + +S + +S-acid +Salicylic acid +Salicylic acid phenyl ester +Salicyl-_p_-hydroxybenzoic acid +Salol +Silver oxide +Solution salt +Solvenol +Structure of tannin +Sulphinic acid +Sulphite cellulose extract +Sulphite lye +Sulphonamide +Sulphonic acids, aromatic +Sulphonic chloride +Sulphur +Sulphur tannage +Sulphuric acid-free Neradol D +Sulphuric acid in leather +Syringoyl-_p_-hydroxybenzoic acid + +T + +Tannin +Tannin action, real +Tannin analysis +Tanning matters +Tannin molecule +Tannin, pure +Tannophor +Test tannage +Tetradepsides +Tetragalloyl-[Greek: a]-methylglucoside +Tetramethylellagic acid +Tetroxydiphenyldimethylolide +Thionaphtholsulphonic acid +Thiosulphonic acid +Thorium salts +Thymol +Toluidoanthraquinone, l-_m_- +Total solids +Total solubles +Tribromophenol +Tribromopyrogallic acid +Tricarbomethoxygalloyl chloride +Tridepside +Trihydroxybenzenes +Trinitrophenol +Triphenylmethane + +V + +Valonea +Vanadium salts +Vanillic acid +Vanilloyl-di-_p_-oxybenzoyl-_p_-hydroxybenzoic acid +Vanilloyl-_p_-hydroxybenzoic acid +Vanilloyl vanillin + +X + +Xanthenes + +Z + +Zinc salts +Zirconium salts + + + + + +End of the Project Gutenberg EBook of Synthetic Tannins, by Georg Grasser + +*** END OF THE PROJECT GUTENBERG EBOOK SYNTHETIC TANNINS *** + +This file should be named 7981-8.txt or 7981-8.zip + +Produced by Juliet Sutherland, Thomas Hutchinson, Charles Franks +and the Online Distributed Proofreading Team. + +Project Gutenberg eBooks are often created from several printed 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