Benzothiophene oxidation sulfoxide

FIGURE 10.51 Transformation of benzothiophene involving microbial oxidation and chemical reaction of the sulfoxide. (From Neilson, A.H. and Allard, A.-S., The Handbook of Environmental Chemistry, Vol. 3J, pp. 1-80, Springer, Heidelberg, 1998. With permission.)... 

Another useful source of the CS fragment in this synthesis scheme is dichlorosulfine. It has been shown to react with diaryldiazomethanes to yield 2-chlorobenzo[h]thiophene 1-oxides in reasonable yields (72RTC1345). The reaction is quite successful when X = H, 4-Me, 4-C1 or 3-OMe (Scheme 20) but failed when X = 4-OMe. The reaction presumably proceeds by a [3 + 2] cyclization to form an intermediate thiadiazole derivative, which loses nitrogen to give an episulfoxide that can rearrange to the final product (Scheme 20). Since benzothiophene sulfoxides are easily reduced, this constitutes a new thiophene synthesis. 

Figure 8. Oxidation products found in aerobic cultures growing on naphthalene and co-metabolizing benzothiophene. (I) benzothiphene-sulfoxide, (II) 2,3-dihydrobenzothiophene-2,3-diol (III) 2,3-dihydrobenzothiophene-2, 3-dione.

The Friedel-Crafts sulfonylation of aromatics with alkane- and arenesulfonyl halides and anhydrides has been studied (Eq. 9) [23]. In the reaction of pentafluorobenzenesul-fonyl fluoride with pentafluorobenzene, decafluorodiphenyl sulfone is formed with deca-fluorodiphenyl [23c]. Certain phenylacetylenes react with SO2 and benzene in the presence of SbFs to form benzothiophene 5-oxide [24]. (Eq. 10). Sulfinyl fluoride reacts similarly with arenes under SbFs catalysis to give sulfoxides (Eq. 11) [25]. 

Various refractory thiophenes that are often not reductively removable by conventional refining processes cab be oxidized undo these conditions. For example, benzothiophenes are oxidized to the corresponding sulfoxides and sulfones using microwave or ultrasonic irradiation, respectively, in the presence of Nal04-silica (38). 

Structure-variation showed that the benzothiophene ring system, which is oxidized to the sulfoxide/sulfone, is absolutely necessary for the activity. Substituents at position 3 (R ) of the benzothiophene diminish the biological activity, whereas aryl amides are very similar in activity compared to alkyl amides but have a slightly yellow colour. Alkyl esters show no enhanced activity compared to amides, but are less stable. 

Oxidative desulfurizabon (ODS) of benzothiophenes and dibenzothiophenes has proved to be a promising alternative to hydrotreatment used to remove sulfur from oil heavy fractions, due to its moderate process conditions and lack of hydrogen consumption. In this process, organosulfur compounds in fuels are oxidised to form sulfoxides and sulfones. Alumina-supported vanadium-oxide catalysts have been... 

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