Enthalpies and entropies of solution of electrolytes containing 4-hydroxyphenylazobenzoate and chloro-4-hydroxyphenylazobenzoate anions in water and in methanol. Derived single-ion values for the transfer of these anions from water to methanol

Abstract

Heats of solution of electrolytes containing 4-hydroxyphenylazobenzoate and 2-chloro-4-hydroxyphenylazo-benzoate anions in water and in methanol have been measured calorimetrically at 298.15 K. Enthalpies of transfer of these electrolytes from water to methanol are reported. Combination of these data with transfer free energies values yields the entropies of transfer of the dissociated 1:1 electrolytes in the water–methanol solvent system. Single-ion quantities of transfer (ΔH^°_t and ΔS^°_t) from water to methanol for seven anions based on the Ph₄AsPh₄B convention are reported. Two different combinations of ΔH^°_t and ΔS^°_t values lead to the negative ΔG^°_t values observed for the transfer of these anions from water to methanol. The transfer process is entropically controlled for ortho and chloro-substituted o-(4-hydroxyphenylazobenzoate) anions. For meta and para and chloro-substituted m- and p-(4-hydroxyphenylazobenzoate) anions, the transfer process is enthalpically controlled.