The reaction products of lead dioxide oxidation of the synthetic biological 4antioxidant dl-α-tocopherol in hexane were investigated at different molar ratios. Products were separated by normal phase high-performance liquid chromatography (HPLC) and isolated using semi-preparative HPLC. Four isomeric trimers and three isomeric spirodimers were obtained as the major reaction products in the presence of 10 and 40 molar excess of the oxidant PbO, respectively, whereas the aldehyde, 5-formyl-γ-tocopherol, was obtained as a minor product at 40 molar excess of PbO. Dihydroxydimers were formed as minor products at the stoichiometric ratio of tocopherol to PbO, and were also obtained as major products from a reaction of the spirodimer with LiAlH4; three isomeric dihydroxydimers were obtained from both reactions. The structures of the different products were characterised by FTIR, UV-vis, 1H-NMR, 13C-NMR, EI-MS and FAB-MS, and based on these results possible structures of the isomeric forms of the products are suggested. Characterisation of products obtained from the oxidation of DL-α-tocopherol in solution reported here has enabled the identification of a large number of oxidation products, including isomeric forms, detected and isolated from high-temperature melt reactions of the antioxidant DL-α-tocopherol in polyethylene and polypropylene.
Bibliographical noteFunding: We are grateful to Hoffmann la-Roche (Switzerland and USA) for financial support of this work.
- vitamin E