Method of preparing disazo pigments

摘要

An ecologically and economically advantageous process for preparing a disazo pigment of the formula (I) or a mixture of said disazo pigments (I) where D1 and D2 are identical or different and each is unsubstituted phenyl, phenyl with from 1 to 5 substituents, unsubstituted naphthyl, naphthyl with from 1 to 3 substituents, unsubstituted anthraquinonyl, anthraquinonyl with from 1 to 3 substituents, or a radical of a fused aromatic heterocycle which contains from 1 to 3 identical or different heteroatoms from nitrogen or oxygen and sulfur and is unsubstituted or has from 1 to 3 substituents, R1 and R2 are identical or different and each is hydrogen, halogen, C1-C4-alkyl, C1-C4-alkoxy, C1-C5-alkoxycarbonyl, nitro, cyano, phenoxy or trifluoromethyl, by azo coupling, comprises a) azo coupling in an aqueous medium and in the absence of an organic solvent in a single step and b) adding at the latest immediately prior to the isolation of the disazo pigment at least one nonionic surfactant which has a cloud point in aqueous solution.