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

Abstract

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, Δ_tG^⊖, have been determined from solubility product or potentiometric measurements, and the enthalpies of transfer, Δ_tH^⊖, have been determined calorimetrically. The entropies of transfer, Δ_tS^⊖, have been calculated from the experimentally obtained Δ_tG^⊖ and Δ_tH^⊖ 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 Δ_tG^⊖ and Δ_tH^⊖ terms counterbalance each other in such a way that the Δ_tS^⊖ 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 Δ_tS^⊖ values are pronouncedly negative, while the anions with hydrocarbon groups are more strongly solvated in the non-aqueous solvents and with positive Δ_tS^⊖ values.