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

Abstract

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.