Variable Scan Rate Cyclic Voltammetry and Theoretical Studies on Tocopherol (Vitamin E) Model Compounds
journal contributionposted on 05.06.2008, 00:00 by Wei Wei Yao, Hong Mei Peng, Richard D. Webster, Peter M. W. Gill
Variable scan rate (0.1−500 V s−1) cyclic voltammetry experiments were performed on a series of model tocopherol (vitamin E) compounds with differing degrees of methyl substitution around the aromatic (phenolic) ring. α-Tocopherol, with a fully methylated aromatic ring, produced stable phenoxonium cations upon oxidation in CH3CN, and was modeled via an ECE mechanism (where “E” represents an electron transfer and “C” a chemical step). Compounds with less methyl substitution around the aromatic ring were more reactive following oxidation, and formed additional oxidation products (hemiketals and p-quinones), and were modeled according to a more complicated ECECC mechanism. The equilibrium and rate constants associated with the chemical steps were estimated by digital simulations of the variable scan rate data over a range of temperatures (T = 253−313 K) in acetonitrile containing 0.5 M Bu4NPF6 as the supporting electrolyte. The relative lifetimes of the phenoxonium cations of tocol and the tocopherols were compared with theoretical results obtained from molecular orbital calculations.