Process for purification of crude 4,4'-diamino-1,1'-dianthraquinonyl-3,3'-disulfonic acids and salts thereof

摘要

Crude 4,4'-diamino-l,l'-dianthraquinonyl-3,3'-disulfonic acids or salts thereof are purified by subjecting an aqueous solution containing the crude products to salting-out using inorganic salts, the aqueous solution being adjusted within a range of from acid to neutral region, whereby a product usable as such for the production of 4,4'-diamino-1,1'-dianthraquinonyl red pigments having excellent pigmentary properties is obtained in high yields with industrial advantages.