不飽和度の異なるトリグリセリド中におけるトコフェロールの熱酸化による二量体の生成 (第1報)

α-トコフェロールからエタン型二量体の生成

抄録

The oxidative decomposition of dl-α-tocopherol (α-Toc) and the formation of its dimer during the course of thermal oxidation of trilaurin and of trilinolein was studied.
Triglycerides, in which α-Toc dissolved in the concentration o 5%, were oxidized with air in an oil bath controlled at 150±1°C or 180±1°C under the condition of specific surface area 0.5 cm²g. Two oxidation products were obtained from the reaction mixture by the chromatography on a silicic acid column eluted with n-hexane -diethyl ether mixtures (Fig.-4). The product [II], which is the main oxidation product, was identified as the dimer of α-Toc, 1, 2-bis- (γ-tocopherol-5'-yl) -ethane, by means of UV absorption, IR absorption, NMR and mass spectroscopy (Table-2). This compound was also confirmed by TLC and high-speed liquid chromatography (HSLC) of the reaction mixture (Figs.-1 and 2). Furthermore, it was assumed that the yellow substance in fraction 7 (product [I]) is 5-formyl-γ-tocopherol-3-ene, from the results of TLC and HSLC of this fraction (Figs.-5 and 6).
The decrease of α-Toc concentration and the formation of its dimer during the course of thermal oxidation was followed by HSLC. The decrease of α-Toc concentration at 180°C was more rapid than that at 150°C, but the difference between the rate of decrease in trilaurin and that in trilinolein was not so remarkable (Fig.-7). On the other hand, a conspicuous formation of the dimer in trilaurin at 150°C was observed, and the amount of the dimer in the reaction mixture reached to maximum by the oxidation for 5 hours. Smaller amount of the dimer formed in the oxidation product in trilinolein than in that in trilaurin (Fig.-8).