Reply to “Comment on ‘Revised Mechanism of Boyland–Sims Oxidation’”

Abstract

Recently, we reported the new computational insights into the mechanism of Boyland !Sims oxidation of arylamines with peroxydisulfate (S 2O8 2! ) in an alkaline aqueous solution. 1 The classic Behrman ’s mechanism 2 has been revised; i.e., we proposed 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, based on the AM1 and RM1 semiempirical quantum chemical study of the Boyland !Sims oxidations of aniline, 12 ringsubstituted and 3 N-substituted anilines, which were experimentally studied by Boyland and Sims more than !ve decades ago. 3 Quantum chemical results indicate that arylnitrenium cations and sulfate anions (SO4 2! ) are generated by the rate-determining two-electron oxidation of primary and secondary arylamines with S2O8 2! , while arylamine dications/immonium cations and SO 4 2! are initially formed by two-electron oxidation of tertiary arylamines with S 2O8 2! . For the !rst time the regioselectivity of Boyland !Sims oxidation was explained. It was computationally found that the regioselectivity-determining reaction of arylnitrenium cations/arylamine dications/immonium cations and SO4 2! , within the solvent cage, leads to the prevalent formation of o-aminoaryl sulfates. The formation of insoluble oligomeric/ polymeric precipitates during the Boyland!Sims oxidation of arylamines was also computationally studied. We proposed that the reaction between arylamine and its nitrenium cation, whenever the formation of p-/ o-iminoquinonoid product is not possible, represents dimerization route in the oxidative oligomerization of primary and secondary arylamines with S 2O8 2! which generally leads to the formation of N !C4 coupled arylamine dimers. The oxidative co-oligomerizations of arylamines with more oxidizable aminoaryl sulfates and aminophenols, 4 formed by the reaction of arylnitrenium cations/ arylamine dications/immonium cations with the hydroxide anions in highly alkaline solution and with water molecules in highly diluted aqueous solutions, are proposed to lead to