SU48328A1 - The method of obtaining artificial tanning - Google Patents

Description

The overwhelming majority of artificial tanning agents used by the tanning industry for the purpose of tanning are of the type of aromatic sulfonic acids treated with various condensing substances (aldehydes, ketones, carbohydrates, etc.). These condensation products are mainly used in a mixture with natural tanning agents in various percentages. The presence of active acidity, due to the presence of sulfo groups, is a specific feature of this type of tanning agent. Tanning with such products is carried out at low pH values (pH 2.0-2.5), and skins obtained with their help always contain sulfosilicates. The presence of sulfo compounds in the skin can in some cases adversely affect its quality. In this case, under the action of heat and moisture, hydrolysis of sulfo groups occurs and the process of skin destruction occurs much faster than pure vegetable tanned leather.

The use in the tanning of condensation products of aromatic sulfonic acids in its pure form is not made, since with their help it is impossible to obtain a sufficiently good quality of the skin. They are used in combination and therefore are only partial substitutes for natural tannins. Attempts to create a different type of artificial tanning agents have long been interested in researchers. There are a number of patents for obtaining this type of tannins. For example, German patent No. 282313 recommends obtaining such tanning agents by condensing polyoxide compounds (pyrogallol, pyrocatechin, resorcinol) with aldehydes. Under special condensation conditions, soluble products are obtained which have extremely valuable tanning properties.

The authors of the present invention propose to obtain an oak substance by treating with aldehydes a solution of the molten salt of sulfoaromatic acids, i.e., an intermediate product for the preparation of phenols or polyphenols. This eliminates the operation of separating pure mono- or polyphenols from the melt for their subsequent condensation with aldehydes. As a result, the product of this condensation, obtained directly from the solution of the melt, can be so cheap that synthetic tanning agents of a new type, spread

which was delayed solely by their high price, immediately become important practical value.

According to the proposed method, sodium hydroxide salt of aromatic sulfonic acids is dissolved in water, neutralized with hydrochloric or sulfuric acid until acidic, and condensed with aldehydes (formaldehyde, acetaldehyde, benzaldehyde, furfurol, etc.) so that an insoluble compound is obtained. Salts present in large quantities salt out the condensation product from the solution as a dry substance, which is a concentrated artificial tanning agent that does not contain sulfo groups. This product is dried and consumed for tanning purposes, like all plant extracts.

Example 1. 10 liters of a solution of melt containing 320-350 g of resorcinol (pyrocatechin, pyrogallol, etc.) condense from 300-350 cm of 40% formaldehyde when heated in an acidic or alkaline medium. The precipitation of the condensation product (in the case of acidic condensation) is filtered off.

and dissolves in the presence of sulfite or a mixture of sulfite with bis. In the case of an alkaline medium, the condensation product is released by acidification to a weakly acidic reaction.

Example 2. 10 liters of a solution of melt containing 320-350 g of resorcinol (or pyrocatechin, pyrogallol, etc.) are condensed from 120-140 sdg acetaldehyde in an acidic or alkaline medium at room temperature. The precipitated condensation product is dried and dissolved in water upon heating.

The subject matter of the invention.

The method of obtaining artificial tanning agents by sulphonating benzene followed by alkaline smelting, in order to obtain mono- or polyoxybenzenes and, finally, by condensation of the latter with aldehydes or ketones, characterized in that the mono- or polyoxyhydroxy compounds condense with aldehydes or ketones immediately after alkaline smelting, without prior release of the hydroxy products in the free state.