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.