Ionic solvation in water–cosolvent mixtures. Part 15.—Free energies of transfer of single ions from water into water–dimethylformamide mixtures

Abstract

The free energy of transfer of the proton between water and water-rich mixtures of dimethylformamide (DMF) with water, ΔG°_t(H⁺), has been determined using the spectrophotometric examination of competitive equilibria in the mixtures. ΔG°_t(Cl^–) has then been calculated from ΔG°_t(HCl) by difference using these values for ΔG°_t(H⁺) and the values for ΔG°_t(Cl^–) used to derive ΔG°_t(M⁺) for a range of cations. ΔG°_t(K⁺) has then been used to calculate ΔG°_t(X^–) for other anions from ΔG°_t(KX). The free energy of transfer of the charge alone, ΔG°_t(i)_e, has been derived for a range of large organic cations and for two organic anions using the pK_a values for the organic acids. These values for ΔG°_t(i) and for ΔG°_t(i)_e for water–DMF are compared with those for water-rich mixtures of other cosolvents with water and with ΔG°_t(i) obtained using the ‘reference-electrolyte’ method.