PROCESS FOR THE PREPARATION OF 4,4',7,7'-TETRACHLOROTHIOINDIGO PIGMENTS

摘要

1. Process for preparing 4,4',7,7'-tetrachlorothioindigo pigments by oxidising 3-hydroxy-4,7-dichloro-1-thionaphthene in an aqueous alkaline medium in the presence of oxygen or oxygen-containing gases, characterised in that after the oxidation the reaction product is treated at temperatures of 60 degrees C to 200 degrees C for 2 hours or longer with an organic liquid which is added before, during or after the oxidation.