Thermodynamic functions for the transfer of 1-naphthoic acid from water to mixed aqueous solvents at 298 K

Abstract

Values of free energies, ΔG^⊖_t, enthalpies, ΔH^⊖_t, and entropies, ΔS^⊖_t, of transfer of 1-naphthoic acid from water to water + ethanol, water + t-butyl alcohol and water + dimethyl sulphoxide (DMSO) mixtures at various mole fractions have been determined from solubility measurements at different temperatures. Variations of ΔG^⊖_t with x_cosolvent in the water-rich alcoholic mixtures are governed by the sign of the entropy term. For water + DMSO mixtures ΔG^⊖_t is negative, but the variation of ΔH^⊖_t with x_DMSO shows different behaviour from that of water + alcohol mixtures. We have calculated molecular pair-interaction parameters (g_xy, h_xy and TS_xy) in water for the three systems studied; h_xy > 0 for water + alcohol mixtures and h_xy < 0 for water + DMSO mixtures. The results are discussed in terms of solute–cosolvent and solute–water interactions.