Evidence for the development of persistent carbon-centered radicals from a benzyl phenolic antioxidant: an electron paramagnetic resonance study

Radicals have been generated from the benzyl phenolic antioxidant 1,3,5-trimethyl-2,4,6-tris(3,5-di-tert-butyl-4-hydroxybenzyl) benzene, carrying out oxidative and hydrogen abstraction reactions. Transient phenoxyl radicals were directly visualized but only persistent carbon-centered radicals were monitored by electron paramagnetic resonance (EPR). The experimental EPR results let us rationalize our analysis as the sum of two different radicals. One, called the methylene radical, developed from the loss of a benzylic hydrogen gave place to a doublet of triplets with a(CH)(H) congruent to 2.7 mT and a(PH)(H) = 0.165 mT. Besides, the methyl radical, developed after an intramolecular hydrogen transfer involving a methyl group on the central aromatic ring of the molecule, formed a triplet of triplets, with a(1)(H) around 0.060 mT and a(2)(H) = 0.169 mT. All the contact interactions were tested by EPR simulation of the experimental data.