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Thies Thiemann Discusses Photooxygenation

Posted on 15. December, 2010.

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The photooxygenation of thiophenes, benzo)b)thiophenes and dibenzothiophenes are discussed in the December issue of Journal of Chemical Research, especially in view of the oxidative removal from fuels.



Photooxygenation of thiophenes, benzo[b]thiophenes and dibenzothiophenes presents an interesting platform for the desulfurization of sulfur-contaminated matrices.

While the S-oxides and S,S-dioxides of these contaminants can be removed by extraction, they themselves exhibit interesting photobehaviour, often leading to extrusion of the sulfur moiety from the heterocycle. These reactions are complicated by the fact that thiophene S-oxides and analogs can also undergo photoreduction leading to the starting thiophenes. The deoxygenation can be accompanied by oxidation of a small part of the matrix. Though dibenzothiophene-S-oxides are generally inert towards photodeoxygenation at wavelengths above  > 230 nm in the absence of a photosensitiser, it might be noted that oligomers and polymers with thiophene S-oxide or dibenzothiophene S-oxide units, can serve as building blocks for materials with interesting electronic characteristics, but may exhibit potentially low photochemical stability and should be examined carefully in that regard.

While the thiophene unit can only be oxygenated electrochemically under certain condi¬tions, further electrooxidation of the oxygenated species such as thiophene S-oxides can lead to sulfur extrusion. Within the context of a complementary removal method of dibenzothiophenes and analogs from fossil fuels, a further investigation into the oxidation of thiophenes by photochemical and electrochemical methods is warranted. In particular, a combined photoelectrochemical approach would lend itself to an interesting continuation of studies in this field.

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