Synthetic Tannins | Page 2

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