Thermodynamic properties for transfer of electrolytes from water to dimethylsulphoxide and to dimethylsulphoxide + water mixtures

The free energies, enthalpies and entropies of transfer of a variety of electrolytes, including alkali metal halides, silver halides, tetraphenylarsonium and tetraphenylboride salts, from water to dimethylsulphoxide and dimethylsulphoxide + water mixtures have been measured. The values show a simple monotonic variation with solvent composition, in marked contrast to those in the acetonitrile + water and dimethylsulphoxide + propylene carbonate systems. The results suggest that strong preferential solvation of the ions does not take place in the mixtures, in agreement with earlier n.m.r. studies, despite significant differences in the interactions of pure dimethylsulphoxide and pure water with the electrolytes. The lack of preferential solvation in the mixtures is discussed in terms of the effect of the strong interactions between water and dimethylsulphoxide on the ion–solvent interactions.