PROCESS FOR MAKING A THERMOSTABLE CRYSTALLINE FORM OF A BIS-TRIAZINYLAMINO STILBENE OPTICAL BRIGHTENER

摘要

1,208,216. Bis - triazinylamino stilbene optical brightener. J. R. GEIGY A.-G. 10 May, 1968 [12 May, 1967], No. 22352/68. Heading C2C. A thermostable α - crystalline form of the compound is obtained by heating at reflux temperature a thermally unstable physical form of the compound wherein X represents 2 monovalent cations or one divalent cation, in a reaction medium comprising an inert water-soluble organic solvent and an aqueous solution of an electrolyte consisting of a water-soluble, sodium salt of an inorganic or organic acid and where X is a divalent cation, a sequestering agent, the concentration of said sodium salt in said electrolyte being sufficient to prevent the compound of Formula I from dissolving in the electrolyte solution. The organic solvent is preferably a C 1-5 alkyl ketone or alkanol, particularly methyl ethyl ketone. The electrolyte preferably has a normality of at least 2À5 and may be a sodium halide e.g. NaCl. The addition of seed crystals of the thermostable disulphonic salt and of alkaline substances such as alkali hydroxides or amines is advantageous. The ratio of organic solvent to water in the reaction medium may be 5-50% by weight solvent to 95-50% water, preferably 15-35% solvent to 85-65% water. Sodium 4,41 - bis - [211,411 - diphenylamino - s - triazinyl - (611) - amino]stilbene - 2,21 - disulphonate is prepared by adding cyanuric chloride to diamino stilbenedisulphonic acid, then adding aniline to the product and finally N - methylethanolamine is added.