Kinetic study of the Hofer-Moest reaction

Abstract

The anodic decarboxylation of acetate ions has been studied potentiostatically, using both a conventional steady-state method, and a novel non-steady state square d.c. pulse technique. The products observed were carbon dioxide, oxygen, ethane, and methanol. Most of the steady state and non-steady state data are explained by a rapid discharge of acetate ions to form methyl radicals which replace an adsorbed intermediate in the oxygen evolution reaction. The methyl radicals are common to tlze formation of ethane and methyl alcohol. As it is not possible to simulate all the observations by analogue computation, it is suggested that the progressive formation of oxide films with time have also to be taken into account.

A Novel Electrochemical Cell Employing a Rotating Bipolar Electrode

“…Under particular conditions of voltage and current pulsing the product spectrum of some electrode reactions can be altered, e.g., in the electrolysis of aqueous acetate solutions (21)(22)(23)(24)(25)(26)(27)(28)(29). Normal steady-state electrolysis at potentials greater than 2.1V yields largely ethane via the Kolbe dimerization reaction…”

“…In previous discussions of the unsteady-state nature of the Kolbe reaction [e.g., by Fleischmann etal. (21,25,27), Hickling and Wilkins (23), Vijh and Conway (193), and Nadebaum and Fahidy (28)], the particular importance of the oxide film thickness has not been adequately taken into account, and a new appraisal of the factors involved in the kinetics of the Kolbe dimerization reaction is required.…”

“…Many other electrode reactions can be significantly affected by voltage and current pulsing. It has been reported, for example, that pulsing can be used to control the product spectrum of electrolysis (21)(22)(23)(24)(25)(26)(27)(28)(29), to prevent passivation and improve the quality of deposits in the electrodeposition of metals and alloys (30)(31)(32)(33)(34)(35), to avoid fouling of electrodes by alkaline earth salts during the electrochemical sterilization of sewage (36)(37)(38)(39), and to prevent passivation during the electrochemical production of acrolein (40).…”

Phenomenology related to the kinetics of Kolbe electrosynthesis

“…The most extensively studied reaction is the electroformation of ethane from the acetic acid/potassium acetate buffer at acid pH values on platinum [4-181. This reaction also occurs on iridium [6]. At pH > 7, the electrochemical reaction yields alcohol as the main product (Hofer-Moest reaction) [19,20].…”

Closing the Gap: Towards a Fully Continuous and Self‐Regulated Kolbe Electrosynthesis

“…[8,[12][13][14] Kolbe reactions are generally performed at slightly acidic pH values. [15] This pH range can be understood as a compromise between the necessary acidic reaction conditions to avoid the Hofer-Moest-reaction [16] (see Scheme 1) on the one hand and the required deprotonation of the carboxylic group for a sufficiently high carboxylate concentration. Since pK a values of typical, unsubstituted aliphatic acids are around 4.7-4.9 (e. g., pK a, valeric acid = 4.84), [17] the reaction pH is often set to about 5.5.…”