Investigations of benzazoles and naphthazoles

Abstract

1-(5-Benzimidazolyl)-5-phenylformazans, which are isomers of the previously obtained 1-(2-benzimidazolyl)-5-phenylformazans, and 1-(5-benzimidazolyl)-5-(2-benzimidazolyl)formazans, which are isomers of 1,5-bis(2-benzimidazolyl)formazans, were synthesized. In contrast to their isomers, the benzimidazole ring in the formazans obtained is connected to the formazan chain at the 5 position rather than at the 2 position, and this leads to substantial differences in the properties, structures, and chromaticities of the isomeric formazans. The imidazole ring in 1-(5-benzimidazolyl)-5-phenylformazans is far removed from the chain and cannot participate in amino-imino tautomerism, in connection with which, the indicated formazans behave like 1,5-diphenylformazans and do not form complexes with metal ions in the cold. For the same reasons, 1-(5-benzimidazolyl)-5-(2-benzimidazolyl)formazans differ from the isomeric symmetrical 1,5-bis(2-benzimidazolyl)formazans by a hipsochromic shift of the long-wave maximum of the spectrum and are similar (with respect to their spectrophotometric characteristics and complexing properties) to the unsymmetrical 1-(2-benzimidazolyl)-5-phenylformazans. Conclusions regarding the state of the hydrogen bond of the formazan chain were drawn on the basis of the IR spectral data.