The dissociation enthalpies of 0 - , m -, p - amino benzoic acid in water-ethanol mixtures ranging from pure water up to 0.477 molar fraction of ethano have been determined at 298.15K by the method of mixing-flow microcalorimetry. Combined with the available values of Gibbs free energy reported in the literature, the corresponding values of dissociation entropy were calculated. The enthalpic and entropic effects arising form solvent and substituent are discussed in terms of solute-solvent interaction and tautomeric equilibrium.

Key words: AMINOBENOIC ACID, BENZENECARBOXYLIC ACID P, ISOMER, MICROCALORIMETRIC METHOD, THERMODYNAMICS, HEAT OF DISSOCIATION