Oxidation thioether, hydrogen peroxide

In an attempt to protect thiophenols during electrophilic substitution reactions on the aromatic ring, the three substituted thioethers were prepared. After acetylation of the aromatic ring (with moderate yields), the protective group was converted to the disulfide in moderate yields, 50-60%, by oxidation with hydrogen peroxide/boiling mineral acid, nitric acid, or acidic potassium permanganate. ... 

The thioether side chains of methionine units in proteins can be oxidized with hydrogen peroxide to the corresponding sulfones (Eq. 3-48). They can also be alkylated, e.g., by CH3I to form R—S+(CH3)2. 

Starting from 2-mercaptothiazoles 192 and 197, alkylation leads to the respective thioethers 485a-c (Scheme 128) and 489a,b (Scheme 129), whereas oxidation by hydrogen peroxide gives the disulfides and/or the parent compounds (e.g., 479 64BCJ1526 and 62BCJ1998, respectively). 

Mercury chloride thioether complexes have been oxidized to the corresponding sulfoxide complexes by treatment with hydrogen peroxide (76) [Eq. (30)]... 

There is huge potential in the combination of biocatalysis and electrochemistry through reaction engineering as the linker. An example is a continuous electrochemical enzyme membrane reactor that showed a total turnover number of 260 000 for the enantioselective peroxidase catalyzed oxidation of a thioether into its sulfone by in situ cathodic generated hydrogen peroxide - much higher than achieved by conventional methods [52],... 

In natural water, singlet oxygen originating from humic substances has been shown, for example, to oxidize thioether pesticide contaminants such as disulfoton (Zepp et al. 1981). Irradiation of dilute hydrogen peroxide in the presence of various non-sunlight-absorbing herbicides results in enhanced oxidation of these substances (Draper and Crosby 1981). 

The addition of a phenylsulfoxide moiety to the end of the side chain markedly changes the activity of this class of compounds. This product, sulfinpyrazone (97-11), stimulates uric acid excretion, making it a valuable dmg for dealing with the elevated serum uric acid levels associated with gout. The compound is stiU one of the more important uricosuric agents available today. The starting ester (96-9) is available by alkylation of the dianion from ethyl malonate with 2-chloroethylphenyl thioether. Condensation with diphenylhydrazine (97-3) in the presence of a base then affords the pyrrazolodione (97-10). Oxidation of sulfur with a controlled amount of hydrogen peroxide leads to the sulfoxide and thus sulfinpyrazone (97-11) [107]. 

The oxidation of thioethers with hydrogen peroxide to form sulfoxides can be affected by the competition reaction to sulfone. 

Several replacement reactions at C-4 in sydnones may be carried out but aqueous bases must be avoided. Butyllithium can be used to displace bromine from a 3-phenylsydnone the resulting organolithium salt can be carbonylated, will add to ketones, and forms a silyl derivative (80CB1830). A sydnone Grignard derivative can also be made and will add ketones in the normal way (80JCS(Pl)20). Sodium borohydride will reduce a sydnone sulfone, formed by oxidation of a thioether (Table 5) with hydrogen peroxide, back to the unsubstituted sydnone (74T409). 

Table 3.9 Selective oxidation of thioethers to sulfoxides with hydrogen peroxide in the presence of molybdate or tungstatea...

Oxidation of S and As compounds. Thioethers can be oxidized to sulfoxides with hydrogen peroxide in acetone with hydrogen peroxide in 50% acetic acid they yield the corresponding sulfones. Thus 16.1 ml. of 30% hydrogen peroxide is added with... 

The oxidation of various thioethers with hydrogen peroxide has been carried out using TS-1 and Ti-beta as catalysts, in an organic solvent. The concentration of both substrate and H2O2 was 0.19 M. In this section we report the catalytic performances of these catalysts with respect to thioether structure, solvent nature and reaction temperature. 

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