Enthalpies and entropies of ionization of 2- and 3-substituted phenols in methanol + water mixtures

Abstract

Enthalpies of solution and enthalpies and entropies of ionization of three (Me, Cl and NO₂) 2-substituted phenols, three (Me, Cl, NO₂) 3-substituted phenols, and 3,5-dinitrophenol in methanol + water mixtures have been determined for the entire range of solvent composition. Comparison of the medium effects on the thermodynamics of ionization of different phenols is made by analyses of the contributions which arise from the separate effects of solvent on the solvation of neutral phenols and phenoxide anions. The results confirm the inadequacy of theories which predict the relative effects of solvent on the thermodynamics of ionization of neutral acids solely by consideration of solvation effects involving the charged acid anions. Compensation between the influence of solvent on enthalpies and entropies of ionization is characterized.