The oxygenation of sulfides to the corresponding sulfoxides catalyzed by H5PV2Mo10O40 and other acidic vanadomolybdates has been shown to proceed by a low-temperature electron transfer-oxygen transfer (ET-OT) mechanism. First, a sulfide reacts with H 5PV2Mo10O40 to yield a cation radical-reduced polyoxometalate ion pair, R2+·, H5PVIVVVMo10O40, that was identified by UV-vis spectroscopy (absorptions at 650 and 887 nm for PhSMe +· and H5PVIVVVMo 10O40) and EPR spectroscopy (quintet at g = 2.0079, A = 1.34 G for the thianthrene cation radical and the typical eight-line spectrum for VIV). Next, a precipitate is formed that shows by IR the incipient formation of the sulfoxide and by EPR a VO2+ moiety supported on the polyoxometalate. Dissolution of this precipitate releases the sulfoxide product. ET-OT oxidation of diethylsulfide yielded crystals containing [V(O)(OSEt2)x(solv)5-x]2+ cations and polyoxometalate anions. Under aerobic conditions, catalytic cycles can be realized with formation of mostly sulfoxide (90%) but also some disulfide (10%) via carbon-sulfide bond cleavage.
ASJC Scopus subject areas
- Colloid and Surface Chemistry