Hydrogen atom abstraction from resveratrol and two lipophilic derivatives by tert-butoxyl radicals. A laser flash photolysis study.

Abstract

The reactions of tert-butoxyl radicals with resveratrol (1) and two acetylated derivatives (2 and 3) have been investigated by laser flash photolysis techniques in 1∶2 (v/v) benzene–di-tert-butyl peroxide at room temperature. The transient absorption spectra of the phenoxyl radicals generated upon H atom abstraction by tert-butoxyl radicals from the phenols have been detected and assigned. The absolute rate constants for these reactions have been evaluated to be 45 × 10⁷, 25 × 10⁷ and 4 × 10⁷ M⁻¹ s⁻¹ for 1, 2 and 3, respectively. The order of reactivity 1 ≥ 2 ≫ 3 has been rationalized in terms of the position and effect of the acetyl groups on the aromatic rings. Of the three OH groups present in resveratrol, the one in position 4′ appears to be the most reactive due to the large stability of the corresponding phenoxyl radical by conjugation with the rings. However, in our system, the H-atom-donating ability of resveratrol turns out to be inferior to that of α-tocopherol by ca. one order of magnitude.