Revised Mechanism of Boyland-Sims Oxidation

New computational insights into the mechanism of the Boyland-Sims oxidation of arylamines with peroxydisulfate (S2O82-) in an alkaline aqueous solution are presented. The key role of arylnitrenium cations, in the case of primary and secondary arylamines; and arylamine dications and immonium cations, in the case of tertiary arylamines, in the formation of corresponding o-aminoaryl sulfates, as prevalent soluble products, and oligoarylamines, as prevalent insoluble products, is proposed on the basis of the AM1 and RM1 computational study of the Boyland-Sims oxidation of aniline, ring-substituted (2-methylaniline, 3-methylaniline, 4-methylaniline, 2,6-dimethylaniline, anthranilic acid, 4-aminobenzoic acid, sulfanilic acid, sulfanilamide, 4-phenylaniline, 4-bromoaniline, 3-chloroaniline, and 2-nitroaniline) and N-substituted anilines (N-methylaniline, diphenylamine, and N,N-dimethylaniline). Arylnitrenium cations and sulfate anions (SO42-) are generated by rate-determining two-electron oxidation of primary and secondary arylamines with S2O82-, while arylamine dications/immonium cations and SO42- are initially formed by two-electron oxidation of tertiary arylamines with S2O82-. The Subsequent regioselectivity-determining reaction of arylnitrenium cations/arylamine dications/immonium. cations and SO42-, within the solvent cage, is computationally found to lead to the prevalent formation of o-aminoaryl sulfates. The formation of insoluble precipitates during the Boyland-Sims oxidation of arylamines was also computationally studied.