The synthetic reactions of triphenyl phosphate from diphenylphosphoryl chloride and sodium phenoxide and of benzyl benzoate from benzyl chloride and sodium benzoate with phase-transfer catalyst were studied in a heterogeneous liquid-liquid reaction system using an agitated vessel with a flat interface. Tetrabutylammonium bromide and 1,2-dichloroethane were used as a catalyst and a solvent, respectively. The behavior of the observed overall reaction rates was explained well by the proposed model. The overall reaction rates were proportional to the organic-phase interfacial concentrations of the actual reactants, tetrabutylammonium phenoxide for the synthesis of triphenyl phosphate and tetrabutylammonium benzoate for that of benzyl benzoate. Their interfacial concentrations were a unique function of the concentrations of tetrabutylammonium bromide and the respective sodium salts. The intrinsic reaction rate constants, for the synthetic reactions of triphenyl phosphate and benzyl benzoate, which were evaluated by fitting the rate data to the model prediction, were 2.33 x 10(6) and 2.56 m3/kmol.s at 303 K, respectively.