An experimental study of an exothermic reaction is carried out in a heterogeneous liquid-liquid reaction mixture, producing simultaneously a surfactant and a cosolvent. The mass transfer kinetic is influenced by the presence of these products, as reaction advances. The global rate of the chemical transformation is thus accelerated. The chosen reaction is the saponification of methyl benzoate with a soda solution at 2 M. The reaction is carried out in a Mettler (TM) RC1 calorimetric reactor. Thermal power profiles released by reaction mixture are used to estimate energetic and chemical kinetic parameters, as well as those linked with mass transfer. Mass balance uses a chemical kinetic law of second order. The quantification of mass transfer between phases is solved using double-film model. (c) 2007 Elsevier B.V. All rights reserved.