Thermodynamic properties for transfer of electrolytes from water to acetonitrile and to acetonitrile + 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 acetonitrile and water + acetonitrile mixtures have been measured. The enthalpies and entropies of transfer show a complex dependence upon solvent composition, which is discussed in terms of the effects of solvent sorting in the immediate neighbourhood of the ions, and of the effect of the solvated ions on the bulk solvent properties. The large structural effects occurring when ions are dissolved in water do not, however, appear to make a net significant contribution to the free energies of solution (and transfer) of electrolytes. Thus the overall free energies of transfer and their dependence upon solvent composition may be very simply interpreted in terms of the assumption that alkali metal and halide ions interact more strongly with water, and silver ions with acetonitrile, without reference to any special structural properties of water.