Homogeneous Electron-Transfer Reaction between Electrochemically Generated Ferrocenium Ions and Amine-Containing Compounds

The homogeneous catalytic oxidation of propylamine (PrA), diethylamine (DEA), pyrrolidine (Pyr), and triethylamine (TEA) has been investigated for the first time in the presence of electrochemically generated ferrocenium ions as the catalyst. Mechanistic details for this electrocatalytic process have been investigated by cyclic voltammetry and other electrochemical techniques. A one-electron oxidative process was observed for all amines. Deviation from this mechanism was only observed during controlled-potential bulk electrolysis of ferrocene in the presence of high concentrations of propylamine, where problems with electrode fouling and catalyst deactivation processes were encountered. The catalytic efficiency and the catalytic oxidation rate constants were estimated and found to follow the order TEA > Pyr > DEA > PrA. Interestingly, the catalytic reaction was not observed when ferrocene was replaced by decamethylferrocene. This observation was analyzed in terms of thermodynamic and structural effects, and a hypothesis is presented. The homogeneous catalytic oxidation reported opens a new avenue to achieve simple, low-cost, and efficient amine oxidation, which is potentially useful in several areas of chemistry