Application of benzil for direct electrocatalytic reduction of CO2 as well as indirect reduction of pyridine

The problem of atmosphere contamination by carbon dioxide has become a global problem during these years [1]. Consumption of CO2 in synthesis of useful organic compounds is a good idea for the decrease of this contamination. Due to the high stability of CO2, electrochemical reduction is a method that helps to convert it to an active species. However, a large overpotential is required for the electrochemical reduction of CO2 at ordinary electrode surfaces [2]. Hence, introducing new catalysts that can decrease the reduction overpotential of CO2 is important [3]. In this research, benzil, 1,2-diphenylethane-1,2-dione, was used as an excellent electrocatalyst for reduction of carbon dioxide, CO2. The reduction overpotential of CO2 was reduced about 900 mV in the presence of this mediator. By chronoamperometry, the catalytic rate constant, k, for the electron transfer between benzil and CO2 was obtained as 8.1 ± 0.4 M-1 s-1. Also, the spectral characterizations of FTIR, 1H and 13C NMR of the coulometry product, proved that the electrocatalytically reduced CO2 in the presence of benzil, CO2•−, participates in the electrocarboxylation of pyridine, and the final product is isonicotinic acid. Isonicotinic acid is a useful compound for the synthesis of some pharmaceuticals, such as isoniazid, 6-aminonicotinic acid and terefenadine [4]. Use of this compound as an anticorrosion reagent and a photosensitive resin stabilizer has been reported in the literature.