Thermodynamic properties for transfer of cations from propylene carbonate to dimethylsulphoxide and to propylene carbonate + dimethylsulphoxide mixtures

Abstract

The free energies, ΔG_tr, enthalpies, ΔH_tr and entropies, ΔS_tr, of transfer of Li⁺, Na⁺ and Ag⁺ from propylene carbonate to dimethylsulphoxide and to their mixtures, have been estimated from electrochemical and calorimetric measurements. The free energies and enthalpies of transfer decrease monotonically with increasing dimethylsulphoxide concentration, the decrease being most pronounced in the neighbourhood of pure propylene carbonate. The entropies of transfer pass through a sharp minimum upon the addition of the first few per cent of dimethylsulphoxide.

These results are compared with those calculated upon the assumption that the changes in the thermodynamic parameters arise solely from changes in the coordination of the ions by the solvent components.

The agreement for ΔG_tr is practically quantitative in all cases. The values of ΔH_tr and ΔS_tr, including the minima in ΔS, which is identified with the unfavourable entropy effects arising from preferential inclusion of dimethylsulphoxide in the ionic coordination sphere, agree qualitatively with the calculated values but show systematic deviations with increasing dimethylsulphoxide concentration. These, presumably, arise from changes in the bulk solvent properties. The values of ΔG_tr appear to be influenced less by changes in bulk solvent properties than ΔH_tr and ΔS_tr as effects on the last two are largely compensating.