Patent ID: 7262284

Claim:
A process for preparing a disazo pigment or a mixture of disazo pigments of the formula (I) by azo coupling wherein, R 1 and R 2 are identical or different and are hydrogen, C 1 -C 4 alkyl, C 1 -C 4 alkoxy, C 1 -C 5 alkoxycarbonyl, nitro, cyano, halogen, phenoxy or trifluoromethyl; D 1 and D 2 are identical or different and are an aromatic heterocycle selected from the group consisting of benzimidazole, benzimidazolone, benzimidazolethione, benzoxazole, benzoxazolone, benzothiazolone, indazole, phthalimide, naphthalimide, benzotriazole, quinoline, benzodiazines, phenmorpholine, phenmorpholinone, benzo[c,d]indolone, benzimidazo[1,2-a]pyrimidone, carbazole and indole, said heterocycles being unsubstituted or substituted by 1, 2, 3 or 4 identical or different radicals selected from the group consisting of halogen, C 1 -C 4 alkyl, acetamido, carbomethoxyamino, C 1 -C 4 alkoxy, nitro, phenyl, phenoxy and trifluoromethyl, wherein the phenyl radical is optionally substituted by chioro, methyl or methoxy, and wherein the heterocycle is attached directly or via a phenylene group to the azo group in formula (I), comprising the step of subjecting the azo coupling product to a finish in at least one organic solvent in the presence of a base selected from the group consisting of alkali metal hydroxides and alkali metal alkoxides, or in an aqueous solution containing the at least one organic solvent, at alkali pH≧9.