Synthesis of 4-amino-1H-benzo[4,5]imidazo[1,2-a]pyrimidin-2-one and its disperse azo dyes. Part 2: Hetarylazo derivatives

4-Amino-1H-benzo[4,5]imidazo[1,2-a]pyrimidin-2-one (I) was synthesized by reaction of 2-aminobenzimidazole with ethyl cyanoacetate and coupled with diazotized hetaryl amines to give the corresponding hetarylazo dyes (1–9). The structures of new hetarylazo dyes were confirmed by UV–vis, FT-IR and 1H NMR spectroscopic techniques and elemental analysis. The solvatochromism of dyes was evaluated with respect to absorption maxima in various solvents. The color of the dyes is discussed with respect to the nature of the heterocyclic ring and the substituent therein. The effects of temperature, concentration as well as acid and base on the visible absorption maxima of the dyes are also reported.