Sulfones desulfurization

Diphenylphosphinic chloride reacts with the superoxide anion radical (Oi ) in CH3CN under mild conditions to form the diphenylphosphinic peroxy radical intermediate 77, which shows strong oxidizing abilities in the epoxidation of alkenes, oxidation of sulfoxides to sulfones, desulfurization of thioamides to amides and oxidation of triphenylphos-phines to triphenylphosphine oxide in good to excellent yields (equation 105). ... 

Desulfurization of fl, a-epoxy sulfones 239 prepared from allylic sulfones 238 and m-chloroperbenzoic acid with sodium amalgam leads to the formation of allyl alcohols (240) in good yields (equation 144)138. Allyl alcohols prepared by this method are listed in Table 16. 

Data presentations should include the parent compound and all toxic transformation products. This is particularly important for oxidation of sulfide linkages to sulfoxides or sulfones. These products are often equally toxic to the parent with increased availability. Attention should also be given to oxidative desulfuration of phosphorothionate esters. 

These reactions accomplish the same overall synthetic transformation as the acylation of ester enolates, but use desulfurization rather than decarboxylation to remove the anion-stabilizing group. Dimethyl sulfone can be subjected to similar reaction sequences.232... 

A variation of the pathway in which 2 -hydroxybiphenyl-2-sulfinate is converted to 2 -hydroxybiphenyl-2-sulfonate (HBPSo) has been reported [26,62], In this alternate desulfurization pathway, the HBPSo further spontaneously cyclizes to sultone , BPSo. The latter is a substrate for DszA (Fig. 2), and is desulfurized to 2, 2 -dihydroxybiphenyl (DHBP) and sulfite. 

Rhodococcus strain SY1 was reported to desulfurize dimethyl sulfide, dimethyl sulfoxide, and several alkyl sulfonates [41] in addition to DBT [78], Barium chloride has been used to precipitate sulfate and shown to alleviate sulfate repression partially. The authors proposed a tentative pathway for oxidative removal of sulfur from DBT and other organosulfur compounds. It should be noted that phenyl disulfide and thianaph-thene were not desulfurized by any of the Rhodococcus strains, but have been reported to be substrates of Gordonia CYKS2. 

A strain Arthrobacter DBTS2 was reported to desulfurize DBT sulfone [100], It could also desulfurize DBT sulfoxide, but not DBT itself. The product of desulfurization was sulfite. The oxidation of the substrates was catabolically repressed by succinate or acetate. 

A second strain of Gordonia, G. rubropertinctus T08, capable of BT desulfurization was identified by Matsui et al. [121], This strain was capable of sulfur-specific desulfurization (Fig. 5) however, the end product was 2-coumaranone, instead of HPEal. The strain also desulfurized 2- and 5-methyl BT, but did not desulfurize 7-methyl BT. In addition, the strain could use various non-condensed sulfonates as sulfur sources for growth. 

Rhodococcus sp. Strain WU-K2R A Rhodococcus strain capable of sulfur-specific desulfurization of benzothiophene, naphthothiophene (NT), and some of their alkyl derivatives was reported [35]. The metabolites of BT desulfurization were BT sulfone, benzo[c][l,2]oxanthiin S-oxide, benzo[c][l,2]oxanthiin S,S-dioxide, o-hydroxystyrene, 2,(2 -hydroxyphenyl)ethan-l-al, and benzofuran. The NT metabolites were NT sulfone, 2 -hydroxynaphthyl ethene, and naphtho[2,l-b]furan [35], The exact biochemical pathway was not determined, however, part of the pathway for BT desulfurization was speculated to be similar to Paenibacillus All-2. 

Rhodococcus sp. Strain T09 A Rhodococcus strain T09 was isolated by enrichment on media-containing BT. The desulfurization mechanism of this organism was reported to be similar to Gordonia sp. 213E due to the observation of similar intermediates however, the substrate specificity was different. The strain T09 could use 2-methyl, 3-methyl and 5-methyl BT apart from BT as sole source of sulfur for growth, but not 7-methyl or ethyl derivatives. Additionally, it could also use methyl thiobenzothiazole, marcaptobenzothiazole, as well as benzene sulfide, benzene sulfonate, biphenyl sulfinate, dimethyl sulfate, dimethyl sulfone, dimethyl sulfide, methane sulfonic acid, thiophene, and taurine as sole sulfur sources. However, it could not grow on DBT or DBT sulfone. 

The desulfurization pathway was proposed to be BT -> BT sulfone -> benzo[e][l,2]oxanthiin S-oxide -> o-hydroxystyrene. Additionally, formation of the intermediate benzo(e)(l,2)oxathiin S,S dioxide was inferred to a side pathway resulting in formation of benzofuran as shown in Fig. 7. This pathway is similar to that reported for Sinorhizobium KT55, Paenibacillus sp. strain All-2 and R. erythropolis KT462. 

Desulfurization using purified enzymes Investigations into enzymatic desulfurization as an alternative to microbial desulfurization has revealed several enzymes capable of the initial oxidation of sulfur. A study reported use of laccase with azino-bis-(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) as a mediator for oxidation of DBT [181]. The rate of this reaction was compared to hydrogen peroxide-based phosphotungstic acid-catalyzed oxidation and the latter was found to be about two orders of magnitude higher. The authors also oxidized diesel oil sulfur to no detectable levels via extraction of the oxidized sulfur compounds from diesel. In Table 9, the enzymes used in oxidation of DBT to DBTO are reported. 

A class of enzymes capable of removing sulfur from alkane sulfonates exists, which may have relevance in microbial desulfurization of alkyl sulfides. A gene cluster ssuEADCB was identified in E. coli. The enzyme SsuD was capable of conversion of pentane sulfonic acid to pentaldehyde and sulfite. It was reported to be capable of conversion of alkyl sulfonates from C2 to CIO, as well as substituted ethanesulfonates and sulfonated buffers. The SsuE was a flavin-reducing enzyme that provided FMNH2 to the SsuD. 

Omori, T. Saiki, Y. Kasuga, K., and Kodama, T., Desulfurization of Alkyl and Aromatic Sulfides and Sulfonates by Dibenzothiophene-Desulfurizing Rhodococcus Sp Strain Syl. Bioscience Biotechnology and Biochemistry, 1995. 59(7) pp. 1195-1198. 

Constanti, M. Giralt, J., and Bordens, A., Degradation and Desulfurization of Dibenzothiophene Sulfone and Other Sulfur Compounds by Agrobacterium MC501 and a Mixed Culture. Enzyme and Microbial Technology, 1996. 19 pp. 214-219. 

Ohshiro, T. Kojima, T. Torii, K., et al., Purification and Characterization of Dibenzothiophene (DBT) Sulfone Monooxygenase, an Enzyme Involved in DBT Desulfurization, From Rhodococcus Erythropolis D-l. Journal of Bioscience and Bioengineering, 1999. 88(6) ... 

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