Electron-transfer reactions between the diamagnetic cation of α-tocopherol (Vitamin E) and β-carotene

β-Carotene (β-Car) was chemically oxidized in a -2e^- process using 2 mol equiv of NOSbF₆ in a 4:1 ratio (v/v) of dichloromethane:acetonitrile to form the β-carotene dication (β-Car²⁺). Voltammetric monitoring of the chemical oxidation experiments over a range of temperatures indicated that the half-life of β-Car²⁺ was approximately 20 min at -60 °C, and approximately 1 min at -30 °C. α-Tocopherol (α-TOH) was chemically oxidized in a -2e^-/-H⁺ process using 2 mol equiv of NOSbF₆ to form the diamagnetic cation (α-TO ⁺) which survives indefinitely at -60 °C in a 4:1 ratio (v/v) of dichloromethane:acetonitrile. Cyclic voltammetry experiments indicated that the oxidative peak potential for α-TOH was approximately +0.4 V more positive than the oxidative peak potential of β-Car. When solutions of α-TO⁺/H⁺ (prepared by chemical oxidation of α-TOH with 2 NO⁺) were reacted with solutions containing equal molar amounts of β-Car, voltammetric monitoring indicated that α-TOH was quantitatively regenerated and β-Car²⁺ was formed in high yield in a homogeneous two-electron transfer, according to the reaction α-TO⁺ + H⁺ + β-Car → α-TOH + β-Car²⁺.