Free energies and entropies of transfer of ions from water to methanol, ethanol and 1-propanol

Abstract

Solubilities of 30 1:1 electrolytes in 1-propanol have been determined and have been combined with association constants and corrections for activity coefficients to yield standard free energies of solution in 1-propanol of the ionic species (M⁺+ X^–). From like data in water, free energies of transfer from water to 1-propanol have been calculated and split into single-ion values through the assumption that ΔG^°_t(Ph₄As⁺)=ΔG^°_t(Ph₄B^–); values for 12 cations and 6 anions are tabulated. The above assumption yields reasonable single-ion values which show that the free energy of simple cations and anions increases along the series of alcohols MeOH < EtOH < 1-PrOH.

With previous results on enthalpies of transfer, single-ion entropies of transfer from water to 1-propanol have been calculated using both the Ph₄As⁺/Ph₄B^– assumption and the correspondence plot method. Entropies of transfer from water to ethanol have also been calculated, and compared with previous results for transfer from water to methanol. For all three sets of transfers it is shown that the correspondence plot method leads to single-ion ΔS^°_t values of cations that are more positive by about 7 cal K^–1 mol^–1 than values obtained by the Ph₄As⁺/Ph₄B^– assumption. On both methods of assigning single-ion values, entropies of the simple alkali halide ions are more negative in 1-propanol than in ethanol than in methanol. The prediction of ΔS^°_t values by Criss's boiling point method is shown to yield values for transfer to 1-propanol which are more negative than observed by only about 3 cal K^–1 mol^–1. Entropies of transfer of ions from water to all three alcohols are well correlated by the method of Abraham, except for the ion Ph₄B^– which behaves anomalously.