Computational Insights into the Mechanism of Boyland-Sims Oxidation Reaction

Abstract

The Boyland-Sims oxidation is the reaction between peroxydisulfate ions and arylamines to form the aryl amine ortho sulfate with minor para isomer. The long-standing mechanism involves a nucleophilic attack by the amine on peroxide oxygen to form arylhydroxylamine-O-sulfonate intermediate, which subsequently rearranges to the arylamine o-sulfate. Marjanović et al. have challenged this long-standing mechanism, proposing a nitrenium ion intermediate as the reactive species instead of the uncharged amine. The nitrenium ion proposal was based on relatively low-level calculations. We previously computed the energetics of reaction intermediates in both mechanisms for aniline, 2,4-dinitroaniline, and N,N-dimethylaniline using high-level of density functional theory (B3LYP/6-311++G**) calculations. We present here new computations using density functional theory (B3LYP/6-311++G**) to model both arylhydroxylamine-O-sulfonate and nitrenium ion pathways in a series of aromatic amines. The transition state calculations revealed two possible energetically feasible pathways for the rearrangement of arylhydroxylamine-O-sulfonate to arylamine o-sulfate. Additionally, we computationally modeled the feasibility of the reaction of aniline and tetrathionate to yield 2-aminothiophenol product via Boyland-Sims Oxidation reaction. The results indicate tetrathionate ion is less reactive with aniline than the peroxydisulfate ion.