Oxidations of aromatic sulfides promoted by the phthalimide N-oxyl radical (PINO)

Abstract

The oxidation of a series of alkyl aryl sulfides promoted by the phthalimide N-oxyl radical (PINO) has been investigated by kinetic and product analysis. Sulfoxides are formed as major reaction products in the oxidation of thioanisoles and benzyl phenyl sulfides. The observation of fragmentation products in the oxidation of 2-phenyl-2-propyl phenyl sulfide and diphenylmethyl phenyl sulfide indicates that the reaction involves an initial electron transfer reaction from the sulfide to PINO with the formation of aryl sulfide radical cations and the anion PINO^-. Combination of the species then leads to a radical adduct precursor of sulfoxides while the rapid C–S cleavage occurs with aryl sulfide radical cations that can form the stable 2-phenyl-2-propyl or diphenylmethyl carbocation.

GRAPHICAL ABSTRACT

KEYWORDS:

• N-hydroxyphthalimide
• oxidation
• sulfides
• electron transfer
• radical

Disclosure statement

No potential conflict of interest was reported by the author(s).

Supplementary materials

Dependence of k_obs for the decay of PINO on the concentration of aryl methyl sulfides. Hammett plot for the reaction of para-substituted thioanisoles with PINO. NMR and GC analysis of the oxidation of sulfides promoted by PINO.

Additional information

Funding

This work was supported by Sapienza University of Rome [grant number RM120172A308C63D]; Sapienza University of Rome [grant number AR12117A76D23906]; Sapienza University of Rome [grant number RP118164212B42FE].