Chapter I: Front Matter

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