Saponification of ethyl palmitate at the oil—water interface

Abstract

The study of chemical reactions at an interface using a theory of the dynamics of interfaces is of great interest. Here we studied the saponification taking place at a hexane—water interface when ethyl palmitate transfers from hexane to aqueous alkali solution. During saponification at the interface, the interfacial tension decreases as a function of time; after a certain time, the interfacial tension passes through a minimum, then reaches a steady state. The minimum is due to the difference in the adsorptions of reactants, intermediates and products. The steady state values are described by a new surface equation of state which is established by modifying the Langmuir equation for a surfactant system with an adjustable parameter (1 + 2 x S 2/ x S 1 where x S 2 and x S 1 are the mole fractions of surfactants 1 and 2 in the surface). The dynamic and steady state values are treated theoretically and compared with experimental values. Rather good agreement between theory and experiment is achieved.