Electrochemically controlled chemically reversible transformation of alpha-tocopherol (vitamin E) into its phenoxonium cation |
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Authors: | Williams Leodrina L Webster Richard D |
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Institution: | Research School of Chemistry, Australian National University, Canberra ACT 0200, Australia. |
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Abstract: | Alpha-tocopherol (alpha-TOH) can be electrochemically oxidized in CH(3)CN containing Bu(4)NPF(6) in a chemically reversible two-electron/one-proton (ECE) process to form the phenoxonium cation (alpha-TO(+)) that is stable for at least several hours at 243 K. In the presence of up to approximately 1% CF(3)SO(3)H, alpha-TO(+) exists in equilibrium with the alpha-tocopherol cation radical (alpha-TOH(+)(*)), whereas at concentrations between approximately 1-3% CF(3)SO(3)H the electrochemical oxidation of alpha-TOH occurs by close to one-electron to form alpha-TOH(+)(*).alpha-TOH(+)(*) can be further oxidized in a one-electron process to form the alpha-tocopherol dication (alpha-TOH(2+)). The identity and stability of the phenolic cationic compounds were determined by a combination of electrochemical (cyclic voltammetry and controlled potential electrolysis) and in situ spectroscopic (UV-vis-NIR, FTIR, EPR, and NMR) analysis. |
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