Single-ion gibbs energies, enthalpies and entropies of transfer from water to aqueous methanol based on the (Ph4P+, Ph4As+)= Ph4B– assumption

Abstract

Enthalpies of solution of 298 K of the electrolytes NaCl, Ph₄PCl and NaBPh₄ in water and aqueous methanol mixtures are reported. These measurements lead to single-ion enthalpies of transfer based on the assumption that ΔH^⊖_t(Ph₄P⁺)=ΔH^⊖_t(Ph₄B^–). Together with literature values for enthalpies of transfer of electrolytes and additional measurements made in the present work, a set of single-ion ΔH^⊖_t values for 14 ions is constructed. Literature values for Gibbs energies are used to construct a similar set of ΔG^⊖_t values based on ΔG^⊖_t(Ph₄P⁺)=ΔG^⊖_t(Ph₄B^–); the corresponding entropies of transfer are also reported. It is shown that for transfer from water to pure methanol transfer values for Ph₄P⁺ are, within experimental error, the same as those for Ph₄As⁺.

On the (Ph₄P⁺, Ph₄As⁺)= Ph₄B^– assumption it is found that ΔG^⊖_t(H⁺) is slightly negative for transfer to most aqueous methanol mixtures but is very positive (2.49 kcal mol^–1) for transfer to pure methanol. Enthalpies and entropies of transfer of ions do not vary monotonically with solvent composition but reflect changes in solvent structure. There is quite good agreement between the single-ion entropies of transfer and those obtained by the correspondence-plot method for transfer from water to up to 80 wt% methanol mixtures, but not for transfers to 90 wt% methanol mixtures and to pure methanol.