Product distribution in preparative scale electrolysis: Part IV. EC reaction schemes followed by competition between first-order chemical reaction and further electron transfer. Electrocatalytic systems

Abstract

The dependence of product distribution on the intrinsic and operational parameters of the system is established for electrochemically catalyzed processes, in which catalysis is in competition with electrode or solution electron transfer leading to an overall two-electron reduction or oxidation of the starting material. The main interest of such relationships is the prediction of the yield and the selection of the best experimental conditions for optimizing the production of the desired product. The extent of the competition between catalysis and electron transfer is also reflected by the apparent number of electrons, which varies between zero and two. Two different potentiostatic electrolysis regimes are considered, in which the substrate is either kept in constant concentration or exhaustively electrolyzed. Two limiting situations are of particular interest, corresponding to an easy characterization of the system. They involve the predominance of one of the modes of electron transfer, either heterogeneous or homogeneous. The operational parameters have no influence on the course of the competition in the first case, while electrocatalysis is favored by low concentrations and large diffusion layer thickness in the second. The electrochemically catalyzed substitution of 2-chloroquinoline by benzenethioalate in liquid ammonia is discussed as an example of the application of the theoretical relationships.