GB331216A - Process for the manufacture of tanning agents - Google Patents

Abstract

331,216. Carpmael, A., (I. G.À Farbenindustrie Akt.-Ges.). March 25, 1929. Phenol - aldehyde condensation products.- Water-soluble, tanning agents are prepared by condensing 3 mols. of resorcinol or pyrogallol with 1-1.5 mols. of benzaldehyde or a substitution product thereof in an aqueous medium in the presence of a small amount of acid, the reaction being interrupted by neutralizing the acid when little or none of the phenol can be detected; the progress of the reaction may be followed by noting the colour given by very dilute test portions with ferric chloride. The tanning properties of the products vary with the stage of condensa. tion. When substituted benzaldehydes are used, the reaction mixture may deposit sparingly soluble triphenylmethane derivatives, which should be removed before further working up. The products can be used to increase the tanning action of other synthetic or vegetable tanning substances. According to the examples (1) a mixture of resorcinol, benzaldehyde, and water acidified with hydrochloric acid is heated to 30‹ C., the temperature then rising to 40‹ C.; after 4 hours, the mixture is neutralized, concentrated in vacuo, and freed from aldehyde by treatment with bisulphite; (2) the reaction mixture of example (1) is left to stand at 20-25‹ C. for 28 hours; it is then neutralized, freed from aldehyde by steam-distillation, and concentrated in vacuo; À (3) a mixture of resorcinol, salicyl aldehyde, and water acidified with sulphuric acid is maintained at 20-24‹ C. for 26 hours, and then worked up as in example (2); (4) a mixture of resorcinol, ochlorobenzaldehyde, and water acidified with hydrochloric acid is stirred for 2 hours at 20-24‹ C. and then neutralized, filtered, and concentrated; (5) a mixture of pyrogallol, benzaldehyde, and water acidified with hydrochloric acid is stirred for 20 hours, neutralized, steam-distilled, and concentrated. Specification 189,190 is referred to.