Tocopherylacetic acid

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... 

FIGURE 6.38 Redox behavior and thermal degradation of 5-tocopherylacetic acid (51), involving an o-QM formed by involvement of C-4 and 0-1. 

Rosenau, T. Habicher, W. D. Chen, C. L. Novel tocopherol compounds IV. 5-Tocopherylacetic acid and its derivatives. Heterocycles 1996, 43, 787-798. 

While tocopherylacetic aicd (51), the lower Crhomologue of 3-(5-tocopheryl)-propionic acid (50) showed a changed redox behavior (see Section 6.5.1), compound 50 displayed the usual redox behavior of tocopherol derivatives, that is, formation of both ortho- and para-quinoid oxidation intermediates and products depending on the respective reaction conditions. Evidently, the electronic substituent effects that... 

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