Oxidation studies involving copper and silver electrodes

A study of the reactions that occur at copper and silver electrodes in alkaline solutions, at potentials between those corresponding to hydrogen and oxygen evolution reactions, has been effected. The major reactions that have been identified are, at a silver electrode: (i) 2Ag + 2OH¯ → Ag2O + H2O + 2e; (ii) Ag2O + 2OH¯ → 2AgO + H2O + 2e; at a silver electrode: (iii) 2Cu + 2OH¯ → Cu2O + H2O + 2e; (iv) Cu + 2OH¯ → CuO + H2O + 2e; (v) Cu + 2OH¯ → Cu(OH)2 + 2e. Of these reactions (i), (ii), (iii) and (iv) have been shown to be controlled by solid phase processes, whereas reaction (v) is thought to be controlled by a dissolution precipitation mechanism. The oxidation of α-amino acids at copper and silver anodes yielded the nor-nitrile as the major reaction product in every case investigated. The reaction is thought to occur with the α-amino acid in an adsorbed state at the electrode. It is suggested that the oxidation proceeds through an imine intermediate and that the release of this intermediate into the solution produces a trace of the nor-aldehyde as the only other reaction product. These oxidations have been shown to be specific and to occur readily at these electrodes, whereas no such reactions occur if these electrodes are replaced by Pt, Au or PbO2 electrodes.