Redox reactions of vitamin E in 1,2-dichloroethane with oxidants in water at the water/1,2-dichloroethane interface

The oxidation of α-tocopherol (vitamin E), α-TOH, in 1,2-dichloroethane, DCE, by NO or MnO4- 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 α-tocopherone cation α-TO+ and H+ in DCE was observed by VCTIES. The H+ transferred to W, and a part of α-TO+ was converted to α-tocopheryl quinone, α-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 α-TQ in DCE. The reduction products of NO or MnO4- in W at E in both ranges were N2O or Mn2+ and MnO2, respectively. When the oxidant in W was MnO4- and E   was available for the transfer of MnO4- to DCE, the redox reaction between MnO4- and α-TOH in DCE proceeded in addition to the interfacial redox reaction. α-Tocopherol spiro-dimer, α-TD, α-TQ and MnO2 were produced by the reaction in DCE. The oxidation reaction of α-TOH at the W/DCE interface was compared with that at a platinum electrode in the bulk of DCE.