Substituent-stabilized tocopherols

Selected Substituent-Stabilized Tocopherols and Conjugatively Stabilized Ortho-Quinone Methides... 

An interesting feature of 5-tocopherylacetic acid (51) and its derivatives was their appreciable thermal stability up to 200 °C. In contrast to 5a-substituted tocopherols carrying an electronegative substituent at C-5a, the homopolar C—C bond in the C2-unit at the 5-position of the tocopherol skeleton was shown to be very stable. Thermal decomposition of 51 at temperatures above 250 ° C caused a complete breakdown of the chroman structure, the C3-unit consisting of C-2, C-2a, and C-3 being eliminated as propyne, the side chain as 4,8,12-trimethyltridec-l-ene (Fig. 6.38). Fragmentation... 

Products studies provide more direct evidence than the kinetic approach for the stoichiometry of lipid oxidation inhibited by phenolic antioxidants. Thus, n equals 2 with various phenolic compounds, because both the peroxide products (LOOA) of reaction (6) and the dimers (A-A) of reaction (7) were identified from tri-substituted phenols and from less hindered phenols containing more methyl than ferf-butyl substituents and from a-tocopherol (Figure 9.3). Reactions (6) and (7) are supported by product studies with various trialkylphenols varying in stability according to their substituents. 

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