Ionic entropies of transfer from water to nonaqueous solvents

Abstract

Heats of solution of 1:1 electrolytes in acetonitrile have been determined, and enthalpies of transfer of the electrolytes from water to acetonitrile thus calculated. Free energies of transfer of a number of electrolytes from water to nonaqueous solvents have also been determined. Together with previous data, these measurements yield entropies of transfer of electrolytes from water to N-methylformamide (NMF), methanol, ethanol, dimethyl sulphoxide (DMSO), acetonitrile, NN-dimethylformamide (DMF) and acetone; single-ion entropies of transfer from water to these solvents are tabulated for up to 11 cations and 5 anions. It is shown that ΔS^° _t(M⁺+ X^–) is relatively independent of M⁺ and of X^– if M⁺ is Na⁺, K⁺, Rb⁺, and Cs⁺ and if X^– is Cl^–, Br^–, I^–, and ClO^– ₄. For transfers to or from water and methanol, this constancy of ΔS^° _t(M⁺+ X^–) is not maintained if M⁺ is R₄N⁺, Ph₄As⁺, and Ph₄P⁺ and if X^– is Ph₄B^–. “Absolute” single-ion entropies of transfer have been obtained, and a treatment is given that enables these single-ion values to be reproduced accurately, and further single-ion values to be predicted, for transfers from water to NMF, methanol, ethanol, DMSO, acetonitrile, DMF, acetone, formamide and liquid ammonia. For these solvents (other than water and methanol) only one adjustable parameter per solvent is required. It is also shown that the so-called “iceberg effect” for solution of organic ions is very large in water, small in methanol, and non-existent in NMF, ethanol, acetonitrile, DMF, acetone and (possibly) DMSO.

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