Stereoselectivity in the oxidation of thioethers to sulphoxides in the presence of Aspergillus niger

Abstract

Optically active sulphoxides are formed when unsymmetrical thioethers are treated, under aerobic conditions, either with growing Aspergillus niger or with the insoluble material obtained by extracting A. niger with acetone. The stereoselectivity of the oxidation ranges from ca. 4 to 100% depending on the thioether used. t-Butyl p-tolyl sulphide is oxidised most selectively, the R(+)-sulphoxide obtained having a rotation higher than that recorded before. In thioethers of structure, p-X·C₆H₄·S·CH₂Ph, the compound where X = Me is oxidised more selectively than related sulphides where X = H or Bu^t.