Effect of H-bond formation on the electronic spectra of some azo compounds derived from 3-amino-1,2,4-triazole

Abstract

The UV-visible spectra of some azo compounds derived from 3-amino-1,2,4-triazole and various active-methylene or active-hydrogen compounds have been investigated in organic solvents of different polarities. The spectral bands obtained are assigned to the possible electronic transitions. It was found that the azo compounds containing the acetylacetone moiety exist mainly in the hydrazone form, while those containing ethylcyanoacetate, α or β-naphthol substituents exist in an azo ⇔ hydrazone tautomeric equilibrium in solution. The extra visible band exhibited in the spectra ofo-hydroxyazo compound is assigned to an intermolecular electronic transition. The spectral shifts observed in the various organic solvents are discussed on the basis of the solute-solvent interaction through the formation of hydrogen bonds with different species. The variation of the absorbance with pH is employed to determine the acid dissociation constants.