Quantitative analysis of azo-quinonehydrazone tautomeric equilibrium

Abstract In order to evaluate the influence of various factors affecting the azo-quinonehydrazone tautomeric equilibrium, a quantitative spectrophotometric method for the analytical determination of this tautomerism was developed. The method can be utilised to obtain the values of percentage content for the two tautomeric species, the constant K T of this equilibrium and the individual spectral curves for the pure tautomeric forms. These data were used for analysis of the influence of solvents, substituents and temperature on the position of the tautomeric equilibrium in 1-phenylazo-4-naphthol and its derivatives. The method may also be applied to the analysis of other tautomeric systems, in which the absorption spectra of the individual tautomeric species cannot be experimentally observed.