Hydroxyl radical reactions with phenols and anilines as studied by electron spin resonance

Abstract

The radicals produced by reaction of OH with a number of carboxy-substituted phenols, aminophenols, and anilines have been studied by the in situ radiolysis esr technique. The radicals produced from the phenols are identified as of the phenoxyl type and are formed by addition of OH to the ring followed by elimination of water. In the case of 5-hydroxyisophthalic acid the intermediate hydroxycyclohexadienyl radical was of long enough lifetime to be observed. Also present in the esr spectra of the phenols were signals from corresponding ortho and para semiquinone radical anions. These latter radicals are believed to be produced in secondary reactions from dihydroxy compounds formed upon bimolecular reaction of the phenoxyl radicals. The aminophenols produced spectra with g factors of ∼2.0037 in contrast to the values of ∼2.0047 found for phenoxyl radicals. These spectra are assigned to aminophenoxyl radicals. A small amount of deamination to form the corresponding semiquinone radical was also found. The three anilines studied all gave spectra which could be ascribed to anilino radicals (RNH). Parameters of the unsubstituted radical C6H5NH are g = 2.00331 and aN = 7.95, aNHH = 12.94, aoH = 6.18, amH = 201, and apH = 8.22 G.