A thermodynamic relationship between the chemical equilibrium constant and the dielectric properties of the reaction medium: Solvent mixtures and universal solvents

Abstract

We introduce a novel thermodynamic model oriented toward accurately predicting the effect of solvent polarity on chemical equilibrium. Our approach is based on the fundamental principles of thermodynamics of continuum medium and can be applied generally to estimate the Gibbs free energy contribution resulting from electrostatic interactions between the solvent and chemical species to the corresponding equilibrium constant in the solution phase. Using a set of assumptions, we have developed a practical calculation methodology that employs multivariate fitting to determine the dependence of 27 different reactions, including tautomerizations, dimerizations, and acid–base dissociations, on solvent polarity. From this approach, we estimated all the contributions to the Gibbs free energy of reaction in the solution phase of some of these processes, including the gas phase Gibbs free energy of reaction, the electrostatic (continuum) contribution to the solvation Gibbs free of the involved solutes and, even, the Gibbs free energy contribution due to specific (intramolecular) solute–solvent interactions, albeit indirectly.