Solution thermodynamics of haptens containing 4-hydroxyphenylazobenzoate and substituted 4-hydroxyphenylazobenzoate anions in N,N-dimethylformamide

Abstract

Conductances, ion-association constants and solubility data of haptens (o-, m- and p-4-hydroxy-phenylazobenzoate and their chlorosubstituted salts) in N,N-dimethylformamide (DMF) at 298.15 K are reported. The solution free energies, ΔG^°_s, of the dissociated 1 : 1 electrolytes are calculated. These data are combined with corresponding data in water in order to derive their transfer free energies from water to DMF.

Standard enthalpies of solution in DMF determined calorimetrically with free-energy data yield standard entropies of solution of these haptens in this solvent. Transfer enthalpies and entropies from water to DMF are calculated.

Single-ion quantities (ΔG^°_t, ΔH^°_t and ΔS^°_t) for the transfer of seven anions in the water–DMF solvent system based on the Ph₄AsPh₄B convention are reported for the first time. Changes in the ΔH^°_t values are largely compensated for by changes in the ΔS^°_t values. The same compensation effect is observed for the transfer of these anions from water to methanol.