Ionic Solvation in Methanol+Water Mixtures: Free Energies of Transfer from Water

Abstract

The free energy of transfer ΔG°t(H+) of the solvated proton from water to methanol + water mixtures up to 50 % w/w methanol is considered as the sum of two processes, the transfer of a tetrahedral aqua-proton from water into the mixture using the Born expression and the subsequent replacement of an H2O molecule in the tetrahedron by a methanol molecule according to the equilibrium, H+(H2O)4solv+ CH3OHsolv⇌ H+(CH3OH)(H2O)3solv+ water. These values for ΔG°t(H+) are subsequently used to derive values for ΔG°t(halide ion) from the ΔG°t for the appropriate hydrogen halides, and ΔG°t(Cl–) then used to produce values of ΔG°t for other cations from ΔG°t for simple salts. These values for ΔG°t for the single ions are discussed with respect to solvation of ions by H2O and CH3OH molecules and structural effects in the bulk solvent.