PREPARATION OF VAT DYES AND PIGMENTS OF THE PERINONE SERIES

摘要

The conventional condensation of naphthalene-1,4,5,8-tetracarboxylic acid with 1,2-diaminobenzene gives the resulting naphthoylenebisbenzimidazole isomers together in the cis and trans form. It is desirable to shift the isomer ratio of the mixture obtained toward the desirable trans product and to reduce the amount of cis product obtained. It is also desirable to develop a process of preparation which optimizes the yield and improves the waste water situation. This object is achieved according to the invention by subjecting virtually stoichiometric amounts of the starting compounds to a precondensation at 60 DEG to 110 DEG C. in an aqueous medium and then completing the condensation in the aqueous medium in a second stage at 130 DEG to 180 DEG C.