Electrochemical Oxidation of Aliphatic Carboxylates: Kinetics, Thermodynamics, Mechanism, and the Role of Hydrogen Bonding

Abstract

Abstract The oxidation of tetra‐n‐butylammonium acetate, propionate, and pivalate was studied in rigorously anhydrous acetonitrile by conventional linear sweep and convolution voltammetry (LSV and ConV, respectively). The results suggest oxidation occurs via a concerted dissociative electron transfer pathway (RCO2−→R⋅+CO2+e−). The addition of water lowers the intrinsic barrier, signaling a possible change in mechanism to stepwise dissociative electron transfer. In rigorously dry acetonitrile, the oxidation potentials of CH3CO2− (0.60±0.09), CH3CH2CO2−, (0.47±0.05) and (CH3)3CCO2− (0.40±0.04 V vs. Ag/AgNO3 (CH3CN, 0.1 M)) are reported. These values parallel the stabilities of the resulting free radicals, consistent with a possible concerted pathway, although differential solvation of the carboxylate anions cannot be completely excluded as a contributor to this trend.

Keywords

• Carboxylate anion
• hydrogen bonding
• oxidation potential, decarboxylation
• dissociative electron transfer (DET)