1984 年 33 巻 6 号 p. 356-360
The oxidative dimerization and decomposition of dl-α-tocopherol (α-Toc) and d-δ-tocopherol (δ-Toc) during autoxidation of methyl laurate (Me-La) and methyl linoleate (Me-Li) were investi-gated.
Twenty milliliters of fatty acid methyl esters, in which tocopherol had been dissolved at a concen-tration of 0.5%, were autoxidized under A.O.M. conditions. From the unsaponifiable matter obtained from the reaction mixture, the dimers of each tocopherol were confirmed by the same chromatographic techniques described in previous papers. The change in residual tocopherol and dimer content formed in oxidized Me-La and Me-Li, was followed by HPLC.
Both α-Toc and δ-Toc showed good stability in Me-La, but α-Toc was rapidly and δ-Toc gradually oxidized in Me-Li (Figs.-3 and 5).
1, 2-Bis- (γ-tocopherol-5-yl) -ethane [α-TED] was obtained as an oxidation product of α-Toc, and two types of dimers were obtained from the reaction mixture of δ-Toc : 5- (δ-tocopheroxy) -δ-tocopherol [δ-TED], and 5- (δ-tocopherol-5-yl) -δ-tocopherol [δ-TBD (H) and (L)] as the atropisomers of each other. The dimers from α-Toc and δ-Toc were derived in small quantities and seemed stable in Me-La (Figs.-4, 6 and 7). The concentration of α-TED increased early during oxidation and then decreased after a reaction time of 2h in Me-Li (Figs.-3 and 4). Similarly, δ-Toc decom-posed gradually, and a small amount of δ-TBD and a large amount of δ-TED formed rapidly in Me-Li. The total content of δ-Toc and that of the dimers were generally constant during a reaction period of 10h, but decreased following this (Figs.-5, 6 and 7). These results suggest that the phe-noxy type radical from δ-Toc is more stalbe than the phenyl type radical in autoxidized Me-Li.