A facile synthesis of some new pyrazolo[1,5-a]pyrimidine heterocyclic disazo dyes and an evaluation of their solvatochromic behaviour

Hetarylmalononitriles (thiazolylmalononitrile and benzothiazolylmalononitrile) were prepared by the coupling reaction of malononitrile with heterocyclic amines in nitrosyl sulfuric acid. 4-Hetarylazo-3,5-diaminopyrazole compounds were obtained by the reaction of hetarylmalononitriles with hydrazine hydrate (64%). Both compounds can react with arylazo- and hetarylazomalononitriles to give 3,6-di-(aryl or hetaryl)-azo-2,5,7-triaminopyrazolo[1,5-a]pyrimidine heterocyclic disazo dyes. These dyes were characterized by elemental and spectral analyses (IR, 1H NMR and mass). The solvatochromic behaviour in various solvents was evaluated.