The antioxidant role of vitamin E in polymers. IV. Reaction products of DL-alpha-tocopherol with lead dioxide and with polyolefins

The reaction products of lead dioxide oxidation of the synthetic biological antioxidant DL-alpha -tocopherol in hexane were investigated at different molar ratios. products were separated by normal phase high-performance liqu id chromatography (HPLC) and isolated using semipreparative HPLC. Four isom eric trimers and three isomeric spirodimers were obtained as the major reac tion products in the presence of 10 and 40 molar excess of the oxidant PbO2 , respectively, whereas the aldehyde, 5-formyl-gamma -tocopherol. was obtai ned as a minor product at 40 molar excess of PbO2. Dihydroxydimers were for med as minor products at the stoichiometric ratio of tocopherol to PbO2, an d were also obtained as major products from a reaction of the spirodimer wi th LiAlH4; three isomeric dihydroxydimers were obtained from both reactions . The structures of the different products were characterised by FTIR, UV-v is, H-1-NMR, C-13-NMR, EI-MS and FAB-MS, and based on these results possibl e structures of the isomeric forms of the products are suggested. Characterisation of products obtained from the oxidation of DL-alpha -tocop herol in solution reported here has enabled the identification of a large n umber of oxidation products, including isomeric forms, detected and isolate d from high-temperature melt reactions of the antioxidant DL-alpha -tocophe rol in polyethylene and polypropylene. (C) 2001 Elsevier Science Ltd. All r ights reserved.