Optimisation of the synthesis of a water-soluble sulfur black dye

A water-soluble sulfur black dye containing carboxylic acid groups was prepared by reducing C.I. Sulfur Black 1 to its leuco form followed by reaction with chloroacetic acid. In conducting this reaction, variables studied included the order of adding reactants, the amount of Na2S and chloroacetic acid employed, and the time and temperature of the reaction. It was found that the carboxylic acid group content and reaction yield were maximized by controlling the amount of Na2S and chloroacetic acid employed, and by conducting the reaction for 2 h at 60 °C.