Reaction kinetics in films. The hydrolysis of γ-stearolactone

Abstract

In previous communications it was shown that it was possible from observation of the phase boundary potential to study the kinetics of reactions proceeding at air liquid interfaces. A chemical change occurring in a unimolecular film at an air liquid interface my result in ( a ) a change in the magnitude of the vertical component of the apparent electric moment of the film-forming molecule, as observed in the oxidation of unsaturated acids; ( b ) an aggregation due to greatly reduced adhesion as in the spontaneous oxidation of long chain mercaptans to form disulphides; or ( c ) the diffusion of the product away from the surface as is the case in hydrolysis of γ -stearolactone. A consideration of such heterogeneous systems reveals several factors of interest in the sphere of reaction kinetics. In some instances it is evident that the velocity of the process may be governed by the rate of diffusion of products away from the surface rather than by the rate of chemical reaction. If the chemical process is the slower, then it will determine the velocity of the reaction. In a surface reaction, not complicated by diffusion, the velocity would be determined by the collision frequency, the probability of energy transfer involved in activation, and an orientation factor. This latter factor of molecular orientation, doubtless present in many heterogeneous catalyses, is clearly defined in the oxidation of films of unsaturated acids, and as it will be shown an alteration in the inclination of the polar group result in a significant change in the reaction velocity constant, also in the hydrolysis of the lactone.