Isomer Distribution Ratios of Phenols in Aromatic Hydroxylation with the Hydroxy Radical Generated from α-Azohydroperoxide in Anhydrous Organic Media. Comparison with Fenton's Reagent

Article abstract of DOI:10.1021/ja00401a023

New isomer distribution ratios of phenols in aromatic hydroxylation with the hydroxyl radical generated from α-azohydroperoxide (1) in anhydrous organic media are reported.Photodecomposition of 1 (10^-2 M) in anisole, toluene, chlorobenzene, and nitrobenzene under argon or oxygen gas gave methoxyphenol, cresol, chlorophenol, and nitrophenol, respectively, in yield and isomer ratios listed in Table I.Photodecomposition of 1 (10^-2 M) in acetonitrile containing toluene or nitrobenzene with various molar ratios under argon gas or under degassed conditions revealed that the isomer ratios under argon gas presented in Table I were reproducible as long as the reactions were conducted in an excess of the substrate.On the other hand, isomer ratios were varied when the reactions were carried out in an excess of 1 compared with the amount of substrate.The isomer ratios were also varied when oxygen was present in the reactants.On the basis of the isomer ratios found by this study, the degree of electrophilicity of the hydroxyl radical generated from 1 under anhydrous conditions and the mechanism of the aromatic hydroxylation are discussed in comparison with the aromatic hydroxylation with Fenton's reagent and others and with the aromatic phenylation, methylation, and trimethylsilylation reported in the literature.