Solvation of tetrabutylammonium bromide in water + acetonitrile mixtures at 298.15 K from vapour pressure measurements of dilute solutions

Abstract
The standard free energies of transfer ΔG° t of tetrabutylammonium bromide (n-Bu4NBr) from water to water + acetonitrile mixtures have been determined at 298.15 K from precise vapour pressure measurements of dilute solutions. The excess free energies of water + acetonitrile mixtures have also been measured at the same temperature. The results obained are compared with previous determinations of the ΔG° t of n-Bu4NBr from water to water + acetone and to water + tetrahydrofuran mixtures. Using extrathermodynamic assumptions the contribution of the tetrabutylammonium ion to ΔG° t is calculated. It is shown that the cavity effect of this ion, as deduced from the scaled-particle theory, represents the major part of the experimental ΔG° t value. The remaining contribution to ΔG° t is discussed in terms of the influence of solvent-solvent interactions on ΔG° t; a correlation is noted between the standard free energy of transfer of the tetrabutylammonium ion and the excess entropy function of the binary system studied.

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