Collection of Czechoslovak Chemical Communications - digital archive 

Abstract

The mechanism of the electrochemical carboxylation of several benzophenones (X-C₆H₄COC₆H₅; X = 4-OCH₃, 4-CH₃, H, 3-Cl, 3-CF₃, 4-CF₃ and 4-CN) and several ring-substituted acetophenones (Y-C₆H₄COCH₃; Y = 4-OCH₃, H, 3-OCH₃, 3-Cl, 3-CF₃, 4-CF₃, 3-CN and 4-CN) has been investigated by cyclic voltammetry in dimethylformamide. In the presence of CO₂, all compounds exhibit a single irreversible peak representing a 2 e reduction process. The reaction mechanism has been analysed using the dependence of the peak potential E_p on various experimental parameters such as the concentrations of the reactant, the scan rate and the temperature. Also the kinetics of the electrocarboxylation reaction has been examined. The whole set of results has been carefully analysed in the framework of an ECE-DISP mechanism. It has been found that, under the conditions employed, the electrocarboxylation reaction is always under a mixed ECE-DISP1 kinetic control. The first step of the reaction is an attack, via the oxygen atom, of the electrogenerated ketyl radical anion RR'CO^•- at CO₂. Further reduction of the carbonate-like adduct arising by such an attack followed by a second carboxylation reaction gives an arene-2-carboxylic acid.

Keywords: Cyclic voltammetry; Benzophenones; Carbon dioxide; Acetophenones; Ketyl radical anion; Electrocarboxylation; Electrochemistry; Carboxylic acids.

References: 26 live references.