Product distribution in preparative scale electrolysis Part I. Introduction

Abstract

The purpose of the present series is to establish and discuss the relationships between the distribution of products in preparative scale electrolysis and characteristic rates or ratios and magnitude of the operational parameters for a set of reaction schemes that can be encountered in a large variety of electrochemical processes. This can help in optimizing the yield of the target product for a given electrosynthetic reaction by a proper choice of the reaction conditions. Furthermore, systematic analysis of the product distribution as a function of the various parameters may in many cases be the only route to the reaction mechanism due to the time-scale limitations of the standard electrochemical kinetic techniques. The reaction sequences thus considered involve, besids electron transfer at the electrode, fast accompanying chemical reactions and competing chemical or electrochemical follow-up reactions. Reaction intermediates are thus confined within a reaction layer the thickness of which is small as compared to that of the diffusion layer in the context of the Nernst approximation. The other basic assumptions and procedures of resolution of the mathematical models are defined and discussed. Three different electrolysis regimes are considered involving potentiostatic or galvanostatic control and continuous or discontinuous electrolysis operations. A first reaction scheme is analyzed within this context involving the competition between homogeneous and heterogeneous electron transfer after a first electron transfer followed by an irreversible chemical step. The preliminary resolution of this ECE-Disp problem is indeed required for a number of reaction mechanisms of more definite chemical interest.