Electrochemical oxidation of trolox and α-tocopherol in acetic acid:: A comparative study

A comparative study on the anodic oxidation of trolox and their parent compound, alpha-tocopherol, was carried out on GC and Pt electrodes in glacial acetic acid containing sodium perchlorate as the supporting electrolyte. The effect of nucleophilic base, acetate ions, was also investigated. Different electrochemical techniques were used to characterize the electrode mechanism. RDE experiments and chronoamperometry at microelectrodes revealed that the processes investigated occur with loss of two electrons. The overall reaction path involves the loss of one electron and proton (1e(-), 1H(+)) to form a phenoxyl radical. This is further oxidized at the electrode surface by the loss of the second one to generate a carbocation (phenoxonium ion) which is susceptible to nucleophilic attack and undergoes chemical conversion into chromanone. The electrochemical behaviour is strongly influenced by the presence of acetate in the background electrolyte. Quantitative fitting of cyclic voltammograms via comparison with theory, based on digital simulation, was used for the determination of the thermodynamic and kinetic parameters of respective steps of the electrode processes. (c) 2006 Elsevier B.V. All rights reserved.