New insights into the oxidative electrochemistry of vitamin E

A combination of electrochemical and spectroscopic experiments have proven that the α-, β-, γ-, and δ-forms (vitamers) of the tocopherols (vitamin E) undergo a series of chemically reversible proton- and electron-transfer steps in dry organic solvents, such as acetonitrile or dichloromethane, to form cationic compounds: the cation radical, the dication, and the phenoxonium cation. The cationic compounds are extremely unusual in their high persistence compared with what is presently known about the oxidative stability of other phenols, particularly the phenoxonium cation of α-tocopherol, which is stable for at least several hours in non-aqueous solvents and is formed quantitatively by oxidation of the starting material at an applied potential of approximately +0.5 V vs ferrocene^0/+ or with 2 mol equiv of NO⁺.