Thermodynamic functions of solvation of benzene in various binary aqueous-organic solvents

Abstract

Composition dependences of the thermodynamic functions of solvation in various aqueous-organic mixtures are studied. Limiting activity coefficients and solvation Gibbs free energies of benzene in the mixtures of water with acetone, 1,4-dioxane, dimethyl sulfoxide, and tert-butanol with different compositions at 298K were determined. The results were combined with literature data for the enthalpies of solution in these mixtures and known values of thermodynamic functions of solvation of benzene in several other aqueous-organic solvents. We observed general tendencies of nonlinear enthalpy-entropy compensation, preferential solvation, and existence of a critical composition of the mixtures when the maximum of ΔsolvH and the bend in ΔsolvG vs ΔsolvH plot are observed. The nature of both organic cosolvent and solute influences the concentration of water corresponding to this critical composition. For benzene, it lies between 0.75 and 0.95 mole percent of water in all considered systems. In the same range of compositions, extrema of many other properties of aqueous-organic mixtures were observed. It is concluded that at these compositions, solvation in the mixture is characterized with the highest enthalpy cost of reorganization of binary solvent upon insertion of solute molecules and diminishment of the hydrophobic effect.