Mechanistic Insight on the Oxidation of Organic Phenylselenides by H₂O₂

The oxidation of organic phenylselenides by H₂O₂ is investigated in model compounds, i.e. n-butyl phenyl selenide (PhSe(n-Bu)), bis(phenylselanyl)methane (PhSeMeSePh), diphenyl diselenide (PhSeSePh) and 1,2-bis(phenylselanyl)ethane (PhSeEtSePh). Through a combined experimental (¹H and ⁷⁷Se NMR) and computational approach, we characterize the direct oxidation of monoselenide to selenoxide, the stepwise double oxidation of PhSeMeSePh leading to different diastereomeric diselenoxides, the complete oxidation of the diphenyldiselenide leading to selenium-selenium bond cleavage and subsequent formation of the phenylseleninic product. Oxidation of PhSeEtSePh also results in the formation of phenylseleninic acid along with 1-(vinylseleninyl)benzene which is derived from a side elimination reaction. The evidence of a direct mechanism, in addition to an autocatalytic mechanism, which emerges from kinetic curves, is discussed. By deliberation of observations of diselenides whose chalcogens are separated by alkyl spacers of different length, a rationale for the advantage of diselenide versus monoselenide catalysts is presented.