Products and Mechanism of the Oxidation of 9-Methylanthracene by Peroxydisulfate. Proton Loss and Nucleophile Addition Reactions of the 9-Methylanthracene Radical Cation

Article abstract of DOI:10.1021/jo00369a023

The Cu(II)-S2O8^2- oxidation of 9-methylanthracene (1) was studied in refluxing CH3CN/acetic acid and aqueous CH3CN.Side-chain and nuclear oxidation products and the dimeric compound lepidopterene (7) were produced.The lepidopterene was determined to be formed by the reaction of intermediate anthracenylmethyl cation with 1.In CH3CN/H2O nuclear oxidation products, 10-hydroxy-10-methyl-9-anthrone (2) and 10-methylene-9-anthrone (3) and dimer 7 were produced, with the nuclear products predominating.In CH3CN/HOAc the dimer and side-chain substitution products, 1-OAc (5a) and 1-NHAc (5c), were predominant over the nuclear products, which consisted mainly of 3 and 10-acetoxy-9-methylanthracene (4a).A mechanism is proposed where the initially formed radical cation undergoes competing proton loss and reversible nucleophile addition reactions to form respectively the anthracenylmethyl radical and nucleophile adduct radicals.Oxidation of the radicals by Cu(II) or S2O8^2- yield the corresponding cations that react to form the products 4,5, and 7.Compounds 2 and 3 form by subsequent oxidation of the nuclear oxidation product, 10-methyl-9-anthrol.The results suggest that nucleophile addition is faster than proton loss and that it is more reversible in CH3CN/HOAc than in CH3CN/H2O