Process for purifying crude isoindolinone series pigments

摘要

Isoindolinone pigments of an extremely high purity, which are represented by the following general formula: <IMAGE> wherein R represents a carbocyclic bridge member such as: an unsubstituted phenylene or diphenylene group, a phenylene or diphenylene group substituted by chlorine atoms, methyl groups or methoxy groups, or a group expressed by the formula <IMAGE> where X is oxygen or a methylene group; or R represents a heterocyclic bridge member such as: a pyridylene group; or R represents a direct bond, are prepared by a process wherein a crude isoindolinone pigment is dispersed in an aromatic hydrocarbon; (a) an alcoholate or hydroxide of an alkali metal and (b) a lower alcohol and/or water are incorporated in the crude isoindolinone pigment dispersion thereby forming an alkali metal salt of the isoindolinone pigment; and then, the so formed pigment salt is contacted with an acid thereby hydrolyzing the pigment salt into the free acid form.