Sulfide to Sulfoxide Oxidation

When the desired product is a sulfoxide sodium metaperiodate (NaI04) is an ideal reagent It oxidizes sulfides to sulfoxides m high yield but shows no tendency to oxidize sulfoxides to sulfones... 

Purified mammalian- and bacterial-derived enzymes were used by Oae, Walsh and their coworkers to oxidize sulfides to sulfoxides. The emphasis in these studies was on the characteristics of the enzymes rather than on the use of the enzymes to prepare homochiral sulfoxides. 

As shown in Table 12,H202 and fBuOOH have been used frequently as oxygen donors in peroxidase-catalyzed sulfoxidations. Other achiral oxidants, e.g. iodo-sobenzene and peracids, are not accepted by enzymes and, therefore, only racemic sulfoxides were found (c.f. entries 34-36). Interestingly, racemic hydroperoxides oxidize sulfides to sulfoxides enantioselectively under CPO catalysis [68]. In this reaction, not only the sulfoxides but also the hydroperoxide and the corresponding alcohol were produced in optically active form by enzyme-catalyzed kinetic resolution (cf. Eq. 3 and Table 3 in Sect. 3.1). 

Oxidation of a snlfide to sulfoxide is known to be an electrophilic reaction, in contrast with nncleophUic oxidation of sulfoxide to sulfone. Since 2-nitrobenzenesulfinyl chloride/KOi oxidizes sulfides to sulfoxides selectively, intermediate 48 must be the actual active intermediate. Moreover, in the presence of l,4-diazabicyclo[2.2.2.]octane (DABCO), which is a radical capturing reagent, the oxidation of methyl phenyl sulfide to the sulfoxide was inhibited. In order to further detect the intermediate 48, pure 5,5-dimethyl-l-pyrroUne-l-oxide (DMPO) was used as a trapping reagent and spin adduct was obtained. The ESR spectrum of the DMPO spin adduct was obtained by the reaction of 02 with 2-nitrobenzenesulfinyl chloride (hyperfine coupling constants, aH = 10.0 G and aN = 12.8 G). 

Oxidations. This reagent oxidizes sulfides to sulfoxides in refluxing chloroform in 70 90% yield. It effects oxidative decarboxylation of a-hydroxy carboxylic acids to the noraldchydc in 85 90% yield (equation I). It also oxidatively cleaves aromatic compounds of the type ArCOCHjBr to ArCOOH in about 75% yield.1... 

Ti(IV) alkylperoxides oxidize sulfides to sulfoxides. Kagan found that, although the standard Sharpless conditions for epoxidation of allylic al-... 

In recent years, hypervalent iodines have been employed to oxidize various organic substrates. H5l06 is also capable of oxidizing sulfides to sulfoxides in pyridine [160], However, it has been established that the oxidation of sulfides in the presence of catalytic amounts of FeCl3 (3 mol%) takes place in shorter reaction times than that without the catalyst, indicating the catalytic effect of this iron salt (Scheme 3.51) [ 161 ]. 

Oxidation of DMS to DMSO and DMSO. DMS is chemically and biochemically oxidized to dimethylsulfoxide (DMSO). Mechanisms for the in situ oxidation of DMS to DMSO in seawater have received little attention, even though this may be an important sink for DMS. Hydrogen peroxide occurs in surface oceanic waters (22) and is produced by marine algae (98). It may participate in a chemical oxidation of DMS, since peroxide oxidizes sulfides to sulfoxides (991. Photochemical oxidation of DMS to DMSO occurs in the atmosphere and DMSO is found in rain from marine regions (681. DMS is also photo-oxygenated in aqueous solution to DMSO if a photosensitizer is present natural compounds in coastal seawater catalyzed photo-oxidation at rates which may be similar to those at which DMS escapes from seawater into the atmosphere (1001. 

Tetracyanoethylene oxide (TCNEO) not only oxidizes sulfides to sulfoxides but also reduces sulfoxides to sulfides with generation of two molecules of carbonyl cyanide (17). The reduction mechanism involves a zwitterion intermediate (15) that produces sulfide and two molecules of (17) by simultaneous cleavage of the C—C and O—S bonds. A mechanism (Scheme 14) that involves a zwitterion (16) as a common intermediate is proposed for the formation of ylide and sulfoxide.311... 

RlSR2 —> R S(0)R2. This sulfinyl chloride is oxidized by potassium superoxide to a sulfinyl peroxy intermediate that oxidizes sulfides to sulfoxides at —25° in >90% yield with only traces of the corresponding sulfones.1... 

Complexes based on titanium excess tartrate combination (the Padova system). In 1984, the same year the Orsay group developed their system, a group in Padova, Italy, headed by Modena,47 developed a different system, able to oxidize sulfides to sulfoxides with high selectivity, also based on a modification of the Sharpless catalyst. The Padova group used TBHP in the presence of 1 mol equiv of Ti(0-/-Pr)4/(/ ,/ )-DET, 1/4 combination. The reactions were performed at -20... 

Bipyridinium chlorochromate (4) is a mild, air stable nonhygroscopic oxidant. It is weaker than PCC, and thus 2-4 equiv. are required to obtain good yields of carbonyl compounds. The bipyridyl system acts as an internal buffer, permitting the ready oxitktion of alcohols in sul trates with acid labile groups. Bipyridinium chlorochromate will also oxidize sulfides to sulfoxides and sulfones." ... 

Dialkyl sulfoxides such as DMSO work as oxidants for the selective preparation of disulfides. The order of thiol reactivity is ArSH > ArCH2SH > RSH. Several amine oxides, such as pyridine N-o -ides and triethylamine oxide, also oxidize sulfides to sulfoxides, but the reaction generally requires higher temperatures. 

Organic peroxides such as cyclohexyl or r-butyl hydroperoxide and benzoyl peroxides can oxidize various sulfides to the corresponding sulfoxides where oxidation with TBHP in alcohols or benzene appears to be synthetically useful. 2-Hydroperoxyhexafluoro-2-propanol [(Cp3)2C(OH)OOH], formed in situ from hexafluoroacetone and H2O2, is also a very effective and convenient reagent for this puipose. 4a-Hydroperoxylumifiavin (14) oxidizes sulfides to sulfoxides in organic solvents such as Bu OH or dioxane at 30 C much more effectively than The reactivi of the flavins was... 

A variety of organic peroxy acids such as perbenzoic acid, MCPBA. monoperoxyphthalic acid, peracetic acid and trifiuoroperacetic acid are much stronger oxidants dian H2O2, and oxidize sulfides to sulfoxides under very mild conditions. Usually 1 equiv. of peroxy acid to sulfide is employed, otherwise overoxidation easily occurs to give sulfones. Among these, MCPBA has die advantage of being convenient to use and Ae oxidation is normally carried out at 0 C or lower temperatures, in di-chloromethane. The preparations of the base-sensitive sulfoxide (15), a new dienophile alkynyl sulfoxide (16), " and thiiraneradialene S-oxide (17) are typical examples. Selective oxidation of the sulfur atom of penicillins by polymer-supported peroxy acids in DMF or acetone is also known (equation 17). ... 

Although many oxidizing reagents remove the chromium tricarbonyl group, benzylic alcohols can be oxidized to benzaldehydes using dimethyl sulfoxide with acetic anhydride, trifluoroacetic anhydride, or sulfurtrioxide with minimal decomplexation. Asymmetric oxidation of aUcylthio-substituted complexes can be achieved using titanium tetraisopropoxide and an optically active tartrate ester (Scheme 108). Dimethyloxirane can also be used to oxidize sulfides to sulfoxides. 

Earlier 3-phenyl-2- /t-butyloxaziridine 129 was reported not to be able to oxidize sulfides to sulfoxides even on heating and to undergo thermal rearrangement to A -/r /z-butyl-a-phenylnitrone. However, Shimizu et al. demonstrated that under 800 MPa at 100 °C, this oxaziridine behaves as an oxidant and was able to oxidize thioanisole to the sulfoxide <1997J(P1)3491>. 

Oxaziridines oxidize sulfides to sulfoxides. Again, the A -sulfonyl derivatives seem to be the best oxidizing agents. They react with sulfides at room temperature to produce sulfoxides uncontaminated with sulfones chiral oxaziridines produce chiral sulfoxides. In addition, chiral thiolsulfinates can be obtained from... 

Organic peroxy acids, especially at low temperatures, oxidize sulfides to sulfoxides 163, S24], whereas tetrabutylammonium persulfate 209] at room temperature and hydrogen peroxide at higher temperatures yield sulfones 163, 324], However, hydrogen peroxide in acetic anhydride at room temperature yields sulfoxides 166], Under these conditions, double bonds resist epoxidation 163, 166, 324] (equation 553). 

Different microorganisms oxidize sulfides to sulfoxides, usually in low yields but with high enantiomeric excesses [1046, 1047, 1068] (equation... 

Oxidation of sulfur compounds. The copper(lI) nitrate complexed with dimerizes thiols to afford disulfides and oxidizes sulfides to sulfoxides. 

Perfluoro-cfv-2,3-dialkyloxaziridines (64a) also selectively oxidizes sulfides to sulfoxides at — 40°C in CFC13 <94JOC2762>, for example, the hydrochloride of promazine (67), a neuroleptic drug, is oxidized to (68) in 90-94% yield (Equation (14)). At higher temperatures and/or with excess oxidant the corresponding sulfones are rapidly formed even at —20 to 0°C. 

The reagent is reported1 to form a very stable complex with bromine. This complex oxidizes sulfides to sulfoxides in high yield ... 

Sulfides - sulfoxides. Like /-butyl hypochlorite, this positive-chlorine compound oxidizes sulfides to sulfoxides without formation of sulfones. The reaction is carried out in methanol at —78°. Yields are usually high.2 Note that oxidation of sulfides of the type RSCH2R with positive-halogen compounds results in part or entirely in substitution at the a-methylene group.3... 

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