Investigation of alkaline hydrolysis of phthalimide‐based azo dye and its application to after‐treatment optimisation for high‐fastness dyeing of polyesters

4‐Amino‐N‐methylphthalimide was prepared from phthalimide for use as a diazo component and was coupled with N,N‐Diethylaniline to produce a phthalimide‐derived monoazo disperse dye. The pseudo first‐order kinetics were confirmed by analyzing the dye hydrolysis under alkaline conditions using high performance liquid chromatography, and the optimal dyeing pH and alkali‐clearing conditions were proposed. The synthesised phthalimidyl disperse dyes exhibited excellent colour fastness with a mild alkaline after‐treatment instead of reduction clearing which results in a high biological oxygen demand and pH in conventional disperse dyeing wastewater.