Spin Trapping of Radical Intermediates Generated by the Oxidation of Substituted 4-Methylphenols

A series of substituted 4-methylphenols 1 and 2 was oxidized with PbO(2) in the presence of nitroso compounds 3-10. The formation of adducts of benzyl radicals with the nitroso spin traps in the reaction mixture was established, suggesting the abstraction of an H-atom from the methyl substituent of 1 or 2. In the consecutive steps, the adducts underwent a further rearrangement to the corresponding nitrones. When the starting phenol contained bulky (t)Bu groups in ortho-position (see 2,6-di(tert-butyl)-4-methylphenol (1a)), the stable 2,6-di(tert-butyl)-4R-phenoxy radicals (R=-CH=N(+)(O(-))-X) were detected as the final radical products. The indirect evidence of nitrones in the reaction mixture was performed in one case by the reaction with a RO(2)(center dot) radicals.