Vegetable tanning agent

Vegetable tanning agent - Names and Identifiers

Name	Vegetable tanning agent

Vegetable tanning agent - Introduction

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Organic compounds that are extracted from the dry, skin, roots, leaves or fruits of plants with water and can be tanned into leather are called vegetable tannins, and their main components are natural tannins. Its nomenclature is generally determined by its natural origin.

There are two classification methods for tannins, namely, practical classification and chemical classification.

1. Practical taxonomy

According to the 180~200 ℃ dry distillation products can be divided into three categories.

① tannins without food: products obtained by dry distillation contain pyrogallic acid.

② catechin tannins: where the products obtained by dry distillation contain pyrocatechol.

③ mixed tannins: where the products obtained by dry distillation contain cartan phenol (gallic acid) and pyrocatechol.

2. Chemical Classification

Classification according to the chemical structure of tannins.

① hydrolyzed tannins: tannins containing ester bonds (-COOR) or glycoside bonds (C-O-C) can be specifically divided into three sub-categories: shrinkage esters, tannic acid and ellagic acid.

② Condensed tannins: All aromatic nuclei in these tannins are covalently bonded by carbon bonds (-Ar-C-).

③ mixed tannins: the structural feature of this kind of tannins is that there are both ester bonds and carbon bonds between aromatic nuclei.

Tannins have the following properties.

① tannin can be dissolved in water, but also dissolved in alcohol, acetone, acetic acid, ethyl acetate, but insoluble in benzene, chloroform, petroleum ether, etc.;

②Tannins can dissociate hydrogen ions in aqueous solution and become negatively charged ions, making the solution weakly acidic;

③ The aqueous solution of tannins has a certain degree of astringency;

④ Tannins are easily oxidized into dark black in alkaline solution;

⑤ tannins interact with calcium, barium, aluminum and other metal ions to produce corresponding metal salts.

Last Update：2023-05-03 15:16:29