Novel azo dyes derived from phthalimide. Part 1: Synthesis and spectroscopic properties

A series of azo dyes has been synthesised based on N-alkylphthalimide diazo components featuring one of three different alkyl groups. An analogous set of dyes was prepared in which the N-alkylphthalimidylazo systems bore an o,o-dibromo-substitution pattern. In these cases, cyanodebromination was performed to give the corresponding dicyano analogues. All the synthesised intermediates and dyes were characterised by mass spectrometry, proton nuclear magnetic resonance spectroscopy and elemental analysis. The absorption maxima of the dyes in dimethylformamide (N,N-dimethyl similar to) were observed to be in the range 435-608 nm and found to be consistent with results seen in previous studies of conventional monoazo disperse dyes. Replacement of both halogens in the dibromo-substituted dyes with cyano groups led to large bathochromic shifts (128-141 nm) in absorption maxima. Bathochromism was also observed when acetylamino groups were present on the coupler ring ortho to the azo link. However, variation of the N-alkyl function on the imido ring from n-butyl to sec-butyl and iso-propyl had little effect on absorption maxima, values being similar to that reported for the parent N-unsubstituted analogue.