Product distribution in preparative scale electrolysis: Part V. EC reaction schemes followed by competition between dimerization and first-order deactivation or further electron transfer

Abstract

The problem of product distribution is analyzed for two reaction schemes involving the dimerization of the product formed upon electron transfer followed by a first-order chemical reaction. The first of these involves a competition between dimerization and first-order deactivation. The product distribution then depends upon a single competition parameter containing the rates of the three chemical reactions and the operational parameters, substrate concentration and diffusion layer thickness for the potentiostatic electrolysis regimes and current density for galvanostatic electrolysis. In the second reaction scheme dimerization competes with further electron transfer. The latter reaction may occur at the electrode and/ or in the solution leading to a three-cornered Dim-ECE-Disp competition. A detailed analysis of the limiting Dim-ECE and Dim-Disp behavior is carried out as a function of a single competition parameter having a different expression for each case. This allows the product distribution to be predicted as a function of the intrinsic (rates) and operational (concentration, diffusion layer thickness, current density) parameters for the two limiting situations. In the general case a zone diagram is given which represents the effect of the parameters on the outcome of the three-cornered competition. The reductive cleavage of aromatic and aliphatic organic molecules is discussed in this context, illustrating the application of the results to experimental systems.