Effect of solvent in azo-hydrazone tautomerism of 1 phenylazo-2-naphthol (Sudan I)

Abstract

The increasing usage of azoic dyes in textile, food, paper printing and cosmetic industries, in electronic industry, such as colorimetric sensors, nonlinear optical (NLO) devices and liquid crystalline displays (LCDs) has attracted much attention in the study of synthesis and properties of different azo dyes. The azodyes with atleast one protic group in conjugation with azo linkage shows azo-hydrazone tautomerism. The importance and various applications of azo dyes promted us to study the solvent effect of 1-phenylazo-2-naphthol (Sudan I) in neat and binary mixture of solvents. Sudan I was synthesized purified and characterized. Absorption spectra of Sudan I in different binary hexane-alcohol mixtures were recorded spectrophotometrically by using a Shimadzu model UV-Visible spectrophotometer. Effect of solvent in azo-hydrazone tautomerism of Sudan-I is studied using UV-Vis spectroscopic method. The percentage of tautomers in neat solvent and binary solvent mixtures of hexane with alcohols were calculated from the absorbance data and correlated with various solvent parameters. In highly nonpolar solvents like hexane, both the forms contribute equally to the equillibrim mixture. With increase in polarity and hydrogen bonding ability, the stability of hydrazone form increases. The contribution of different parameter have been calculated using multiparametric regression equation and explained considering specific solute-solvent interaction and through cooperative hydrogen bonding. In binary mixtures of hexane-alcohol, the change in amount of tautomers with change in volume percent of alcohols is explained through preferential solvation.