Study of tautomerism and solvatochromism of 5-(substituted phenylazo)-3-cyano-6-hydroxy-4-methyl-2-pyridones

Abstract

In this study, ten 5-(substituted phenylazo)-3-cyano-6-hydroxy-4-methyl-2-pyridone dyes were synthesized, differing in both the position and the nature of substituents on the phenyl ring. The structural characterization of the dyes was performed using melting point analysis, FT-IR, NMR, and UV-Vis spectroscopy. The study includes spectral determination of the possible tautomeric forms in both the solid state and various solvents. Solvatochromic properties are investigated in 21 solvents with varying properties to assess the impact of solvent-solute interactions and effects of substituents electronic nature on the absorption maxima. For quantitative evaluation of the non-specific and specific solvent effects on the UV-Vis absorption maxima, the principles of the linear solvation energy relationships are used, i.e. models proposed by Kamlet-Taft and Catalán. Based on electronic distribution and substituent effects, methoxy-substituted dyes in ortho- and para- positions of phenyl ring have emerged as the most promising candidates for corrosion inhibition.