Synthesis and spectroscopic properties of novel phthalimide-derived monoazo disperse dyes containing ester groups

The synthesis and spectroscopic properties of monoazo dye series, whose members consist of N-alkylphthalimide diazo components combined with a coupling component containing two ester groups, are reported. Such colourants are potentially alkali-clearable as a consequence not only of the presence of diester functionality on the coupler, but also through use of the base-sensitive phthalimide system. Shortening the N-alkyl group by removing one or two methylene units from a butyl chain made little difference to absorption properties, as would be expected given the relatively minor differences in inductive character produced. Shifts in the absorption maximum of the dyes associated with dibromination of the phthalimidylazo motif and its subsequent cyanodehalogenation were in agreement with theory and literature data for related series. Diester substitution on the coupling component brought about hypsochromism and hypochromism.