Process for the preparation of an organic pigment on the basis of 4,4',7,7'-tetrachloro-thio-indigo

摘要

A process for the preparation of 4,4',7,7'-tetrachloro-thioindigo pigment which comprises treating a finely divided crude 4,4',7,7'-tetrachloro-thioindigo pigment in anhydrous form at temperatures of from 50 DEG to 180 DEG C. with a nitroaromatic substance which is volatile in steam and has a melting point of 50 DEG C. or below under normal conditions.