The Electrochemical Oxidation of Organic Selenides and Selenoxides

Abstract

The electrochemical oxidation of alkyl and aryl selenides was investigated in acetonitrile. The oxidation of diphenyl selenide and di(4-methylphenyl) selenide led primarily to the formation of their respective selenoxides, which were identified by exhaustive coulometric oxidation and 1 H and 13 C analysis of the products. The selenoxide itself was not observed in the cyclic voltammetry of the selenide for two reasons: first, the protonation of the selenoxide by the acid formed from the reaction of water with the cation radical and second, the formation of a selenoxide hydrate. The formation of the hydrate with diphenyl selenoxide was verified by isolation of the dimethoxy derivative. In addition to the selenoxide, selenonium compounds, formed by the coupling of the oxidized material, were also observed. The alkyl selenides were generally oxidized at a lower potential than the aryl selenides. This trend is different from the sulfur analogues, where the aryl sulfides are easier to oxidize than their alkyl counterparts. As a result, the difference in their redox potentials is relatively small. These differences may occur because the oxidation of aryl sulfides is more likely to take place on the aromatic ring, which leads to a greater yield of the coupled products (about 100%) when compared to the selenide analogue.

Electrochemistry of Organic Selenium and Tellurium Compounds

“…The formation of radical cations 132a +• in the reversible first step and the following, potential-determining, second-order reaction were proved by the characteristic dependence of E 1/2 on the angular velocity of the rotating electrode, ω, with the slope equal to E 1/2 / log ω = 23 ± 3 mV. Moreover, this following reaction was not identified as dimerization, which was suggested earlier 58,59 , but as the orbital-controlled disproportionation, giving the dication 132 2+ with a positive charge localized on the selenium atom. Dications 132 2+ are more reactive than radical cations 132a +• .…”

“…This article was published in PATAI's Chemistry of Functional Groups in 2011 by John Wiley & Sons, Ltd. DOI: 10.1002/9780470682531.pat0571observed in CV experiments because of its protonation (cf. the product of reaction 30) and the formation of selenoxide hydrate, as verified by isolation of the dimethoxy derivative59 .…”

“…It was produced in a coupling between a radical cation and a parent molecule with the formation of a new C−Se bond. On the other hand, diphenyl selenoxide (135a) was the main product of the oxidation in the presence of water 58,59 . In particular, 135a and 135b were identified 59 by 1 H and 13 C NMR spectra after an exhaustive coulometry of 132a and 132g.…”

Biomimetic electro-oxidation of alkyl sulfides from exfoliated molybdenum disulfide nanosheets

“…Previous reports on the oxidation of DMS have suggested that the reaction proceeds through a one (DMSO) or two electrons (DMSO2) processes. 38,46,47 Instead, our results demonstrate that the DMS is selectively electrochemically oxidized into DMSO via a one-electron reaction on both Pt and MoS2. We anticipate that the oxidation of DMS involves the formation of a radical cation after the electron withdrawal from DMS: ( 3 ) 2 → ( 3 ) 2 •+ + − as proposed by Elinson and Simonet.…”

7.28 Oxidation of Sulfur, Selenium, and Tellurium

“…Confirmation of the process was achieved through the isolation of the hydrate form of diaryl selenoxides. 350 The oxidation of organoselenium acetophenones to selenoxides has recently been accomplished by phenylacetone monooxygenase (PAMO) in high yield. 334c Interestingly, the process is highly chemoselective and the ester formation, derived from Baeyer-Villiger oxidation, is not observed.…”