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

In many organic electrochemical reactions, the initially formed ion radical undergoes a rapid and irreversible reaction leading to an electrochemically and chemically reactive secondary radical. In the cases where this secondary radical is easier to reduce (or to oxidize) than the starting compound and at the same time undergoes a chemical reaction yielding an electroinactive species, a three-cornered ECC-ECE-Disp competition occurs involving the concurrent formation of two final products. The product distribution is determined as a function of the intrinsic-rates, rate ratios, diffusion coefficient- and operational-concentration, diffusion layer thickness and current density-parameters of the system. Two limiting situations are of particular interest, each corresponding to a two-term competition between chemical reaction and electron transfer, the latter process occurring predominantly at the electrode (ECE) or in the solution (Disp) respectively. Zone diagrams are drawn which provide a quick and convenient view of the effect of all the intrinsic and operational parameters on the ECC-ECE-Disp competition in terms of product distribution.