Electrochemical reduction of butyraldehyde in the presence of CO2

The reduction of butyraldehyde in nominally dry acetonitrile has been investigated using cyclic voltammetry and in situ FTIR spectroelectrochemistry. The major products (butanol, enolate anion equilibrium species and the aldol) have been identified, the formation of which may be attributed to the electrochemical formation of the highly basic radical anion that abstracts protons form free butyraldehyde ultimately resulting in the well-known aldol condensation reaction. However, in the presence of electrophilic CO2, the aldol and enolate formations are suppressed, and to account for this observation a reaction scheme is proposed involving the nucleophilic coupling of the enolate carbanion with CO2 to form the carboxylate. (C) 2002 Elsevier Science Ltd. All rights reserved.