抄録
d-γ-Tocopherol (γ-Toc), which was dissolved in saturated and unsaturated triglycerides, was oxidized in air. Experimental conditions were the same as those described in Part I of this series. After the oxidation of γ-Toc in trilaurin at 180°C for 10h, the reaction mixtures were separated by chromatography on a silicic acid column eluted with n-hexane-diethyl ether mixtures and three main products were isolated (Table-1). Products [I] and [III] were identified as the dimers of γ-Toc, 5-(γ-tocopheroxy)-γ-tocopherol (γ-TED) and 5-(γ-tocopherol-5-yl)-γ-tocopherol (γ-TBD), respectively, by means of UV absorption, IR absorption, NMR and MS spectroscopy (Table-2). These compounds were also confirmed by TLC and HSLC (Figs.-1 and 2). Product [II] was confirmed as the atropisomer of γ-TBD only by TLC and HSLC, for this compound could not be satisfactorily purified by chromatographic techniques.
The oxidative dimerization of γ-Toc during the course of thermal oxidation in trilaurin (Tri-La), in triolein (Tri-Ol) and in trilinolein (Tri-Li) was followed by HSLC. The concentrations of these dimers in reaction mixtures increased with the oxidation time, and reached maximum by the oxidation for 5h. The quantities of formed γ-TED were greatly affected by the species of triglyceride molecules and were in the order of Tri-La>Tri-Ol>Tri-Li (Fig.-5), but the difference between the amount of γ-TBD formed in Tri-La and those in Tri-Li was not so remarkable (Fig.-6). This fact shows that the phenoxy radical of γ-Toc is more stable in saturated triglyceride than in unsaturated one under the condition of thermal oxidation.
