sulfoxidation

Sulfoxidation is the chemical process of oxidizing sulfur-containing substrates, most commonly sulfides or thioethers, to sulfoxides. In this transformation, sulfur is oxidized from the sulfide oxidation state to sulfur in the sulfoxide (R-S(=O)-R'), typically representing a two-electron oxidation with the introduction of a single oxygen atom. Sulfoxidation preserves most other functional groups and is widely used in organic synthesis to install or reveal sulfoxide functionality. Sulfoxides are valuable intermediates and motifs in pharmaceuticals, agrochemicals, and natural products, and they also appear as chiral sulfoxide ligands and catalysts as well as in fragrances.

Common oxidants include m-chloroperbenzoic acid (mCPBA), hydrogen peroxide under catalytic activation (for example with chiral or achiral metal complexes or organocatalysts), iodosylbenzene (PhIO), and Oxone. Other methods use catalytic systems that enable enantioselective sulfoxidation, transferring oxygen to a prochiral sulfide with stereochemical control to give enantioenriched sulfoxides. Typical reaction conditions emphasize controlled stoichiometry to avoid overoxidation to the sulfone (R-SO2-R) and to minimize oxidation of other sensitive functionalities. The mechanism generally involves electrophilic oxygen transfer to sulfur, forming the S–O bond prior to potential further oxidation.

Industrially and synthetically, sulfoxidation is a routine step in the preparation of sulfoxide-containing drugs and materials, and many naturally occurring sulfoxides are formed via similar oxidation chemistry. Typical examples include oxidation of simple thioethers such as thioanisole to the corresponding sulfoxide, and selective oxidation in more complex molecules where regio- and chemoselectivity are required.