GB161859A - Improvements in the manufacture of certain naphthylamine sulphonic acids - Google Patents

Abstract

1 :4 :8-Naphthylamine disulphonic acid is separated from the isomeric acids, principally the 1 :3 :8-acid, which accompany its production, by taking advantage of the relative insolubility of the normal barium salt in hot water. The 1 :3 :8-acid is then separated from the remaining acids by taking advantage of the sparing solubility in hot water of its acid barium salt. According to the process, a solution of a barium salt is added to a concentrated solution of the crude disodium salts of the acids resulting from the process of preparation described in Specification 4625/88, or a solution of the acids themselves is boiled with barium carbonate, oxide or hydroxide, whereby the normal barium salt of the 1 :4 :8-acid is precipitated. The filtrate is acidified, when the acid barium salt of the 1 :3 :8-acid is thrown down. The resulting barium salts can be converted into other salts by double decomposition. A preliminary purification of the solution of the crude disodium salts may be effected by adding acid to precipitate the acid sodium salts and then neutralizing these before treatment with the barium salt; or the acid sodium salts may be suspended in water, acid then added, and the solution boiled with barium carbonate for the separation treatment. The process may be applied to the purification of individual salts of the 1 :4 :8- and 1 :3 :8-acids.