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 NOSbF(6) in a 4:1 ratio (v/v) of dichloromethane:acetonitrile to form the β-carotene dication (β-Car(2+)). Voltammetric monitoring of the chemical oxidation experiments over a range of temperatures indicated that the half-life of β-Car(2+) 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 NOSbF(6) 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-Car(2+) was formed in high yield in a homogeneous two-electron transfer, according to the reaction α-TO(+) + H(+) + β-Car → α-TOH + β-Car(2+).