NEW APPROACHES TO THE STUDY OF ELECTROCHEMICAL DECARBOXYLATION AND THE KOLBE REACTION: PART II. THE MODEL REACTION WITH TRIFLUOROACETATE AND COMPARISONS WITH AQUEOUS SOLUTION BEHAVIOR

Abstract

Electrochemical kinetic studies on the Kolbe reaction have been carried out in the trifluoroacetate–100% trifluoroacetic acid system, where the reaction can be examined from an electrochemical viewpoint with minimum complication by oxidative side reactions. High yields of the Kolbe products C2F6 and CO2 are obtained and current–potential curves exhibiting transition behavior and linear Tafel regions are found. Tafel slopes are deduced for "Langmuir" and "Temkin" conditions of surface coverage by intermediates and compared with the experimental observations. Plausible reaction mechanisms are proposed, which are supported by galvanostatic discharge transients; the latter indicate that the coverage by adsorbed intermediates in the trifluoroacetate reaction approaches a monolayer. In the aqueous formate systems, multilayer formation is indicated, including deposition of layers of different species corresponding to different arrest regions in the galvanostatic discharge transients. It is suggested that these layers may consist of oxide and the discharged carboxylate and that the transition behavior and critical potentials in the Kolbe reaction correspond to conditions for passivation of the metal by oxide and carboxylate species.