The oxidation of alpha-tocopherol (vitamin E), alpha-TOH, in 1,2-dichloroethane, DCE, by NO or MnO(4)(-) in water (pH = 1-9), W, at the W/DCE interface was investigated by voltammetry for charge (ion or electron) transfer at the interface of two immiscible electrolyte solutions, VCTIES, and controlled potential difference electrolysis at the interface. A positive current wave due to the interfacial redox reaction producing alpha-tocopherone cation alpha-TO(+) and H(+) in DCE was observed by VCTIES. The H(+) transferred to W, and a part of alpha-TO(+) was converted to alpha-tocopheryl quinone, alpha-TQ, by the hydrolysis with the water dissolved in DCE. Even when the potential difference at the interface, E, was in the range where any faradaic current was not observed by VCTIES, the interfacial reaction proceeded and gave alpha-TQ in DCE. The reduction products of NO or MnO(4)(-) in W at E in both ranges were N(2)O or Mn(2+) and MnO(2), respectively. When the oxidant in W was MnO(4)(-) and E was available for the transfer of MnO(4)(-) to DCE, the redox reaction between MnO(4)(-) and alpha-TOH in DCE proceeded in addition to the interfacial redox reaction. alpha-Tocopherol spiro-dimer, alpha-TD. alpha-TQ and MnO(2) were produced by the reaction in DCE. The oxidation reaction of alpha-TOH at the W/DCE interface was compared with that at a platinum electrode in the bulk of DCE. (C) 2009 Elsevier B.V. All rights reserved.