A large number of quantitative studies have been made of the Gibbs energy of transfer (the solvent medium effect) for cations transferring from water into mixed aqueous−organic solvent systems, mainly at 25 °C. Nevertheless, no systematic effort appears to have been made to compile and analyze these data, particularly for multivalent cations. A critical review of this information and its presentation in a manner that permits comparison of different cations in a given solvent mixture and of a given cation transferring into different mixtures is therefore of value.

Gibbs energies of transfer of anions from water to mixed aqueous organic solvents.

Property data for tetraalkylammonium cations, [H(CH2)n]4N+, are reviewed. They pertain to the isolated cations and their transfer from the gas phase into aqueous solutions. Various properties of these cations in aqueous and non-aqueous solutions and data for their transfer between these are also reviewed. Emphasis is placed on the dependence of data on the length n of the alkyl chains rather than on the absolute values. Most of the data are available only for the first four members of the series.

Tetraalkylammonium Ions in Aqueous and Non-aqueous Solutions

The transfer thermodynamic functions for 22 monovalent and two divalent ions from water to N,N-dimethylthioformamide, and for the nitrate, hydrogen sulfate, sulfate, permanganate and dichromate anions from water to methanol, acetonitrile, dimethyl sulfoxide and pyridine, have been reported The Gibbs energies of transfer, ΔtG⊖, have been determined from solubility product or potentiometric measurements, and the enthalpies of transfer, ΔtH⊖, have been determined calorimetrically The entropies of transfer, ΔtS⊖, have been calculated from the experimentally obtained ΔtG⊖ and ΔtH⊖ values The extrathermodynamic tetraphenylarsonium tetraphenylborate (TATB) assumption has been applied in order to calculate the contribution from the individual ions Previously determined transfer thermodynamic functions for monovalent ions from water to methanol, acetonitrile, dimethyl sulfoxide, pyridine, tetrahydrothiophene and liquid ammonia are summarized and discussed in this paper The transfer thermodynamic behaviour of the monovalent ions shows that the cations studied can be divided into two groups, metal ions and cations with hydrocarbon groups facing the solvent, and the anions can accordingly be divided into the subgroups inorganic anions and anions with hydrocarbon group(s) facing the solvent The ΔtG⊖ and ΔtH⊖ terms counterbalance each other in such a way that the ΔtS⊖ terms become almost constant for each of these subgroups of ions in a certain solvent The hard alkali-metal ions are as strongly solvated by dimethyl sulfoxide as by any other solvent, while the weakest solvation is found in N,N-dimethylthioformamide among the solvents in this study The soft silver ion is, on the other hand, most strongly solvated in N,N-dimethylthioformamide The strongest solvation of the thallium(I) ion, which is a borderline acceptor, is found in dimethyl sulfoxide and N,N-dimethylthioformamide The transfer thermodynamics of the ammonium and tetraalkylammonium ions display an irregular pattern with the NH4+ ion behaving as the hard monovalent metal ions and the (C4H9)4N+ ion behaves as the tetraphenylarsonium ion The inorganic anions are all more strongly solvated in water than in any other solvent, and the ΔtS⊖ values are pronouncedly negative, while the anions with hydrocarbon groups are more strongly solvated in the non-aqueous solvents and with positive ΔtS⊖ values

Determination of the transfer thermodynamic functions for some monovalent ions from water to N,N-dimethylthioformamide, and for some anions from water to methanol, dimethyl sulfoxide, acetonitrile and pyridine, and standard electrode potentials of some M+/M(s) couples in N,N-dimethylthioformamide

Determination of Gibbs free energy of transfer for some univalent ions from water to methanol, acetonitrile, dimethylsulfoxide, pyridine, tetrahydrothiophene and liquid ammonia; standard electrode potentials of some couples in these solvents

Determination of heats and entropies of transfer for some univalent ions from water to methanol, acetonitrile, dimethylsulfoxide, pyridine and tetrahydrothiophene

The enthalpies of transfer ΔHtro, between water and the aprotic solvents pyridine and acetonitrile have been determined for a number of 1-1 electrolytes. To calculate ΔHtro for the single ions, the tatb assumption that ΔHtro,(Ph4As+) = ΔHtroBPh4-) for all solvents has been applied. The results are compared with those found earlier for the transfer between water and dimethyl sulfoxide. The values of ΔHtro, differ widely between different ions, from exothermic by c. 30 kJ/mol to endothermic by about the same amount. Endothermic values are found for Cl- and, though much smaller, for Br-, and also for the large tetraalkylammonium ion Bu4N+. Compared to the differences in ΔHtro, found between the various ions, the differences found for a certain ion between different solvents are small. The decrease of AH,", in the sequence Cl- > Br- > I- runs almost parallel in the three aprotic solvents, and is much less steep than in water. This reflects the influence of ligand hydrogen bonding in the protic solvent.

Thermodynamics and structures in solvents coordinating through nitrogen. I. Enthalpies of transfer from water to pyridine and acetonitrile for some monovalent cations and anions

S.-I. Ishiguro

Papers

Thermodynamics and structures in solvents coordinating through nitrogen. I. Enthalpies of transfer from water to pyridine and acetonitrile for some monovalent cations and anions