Peroxy acids sulfides

Peroxy acids usually in dichloromethane as the solvent are also reliable reagents for converting sulfides to sulfoxides... 

One equivalent of a peroxy acid or of hydrogen peroxide converts sulfides to sulf oxides two equivalents gives the corresponding sulfone... 

Section 16 16 Oxidation of sulfides yields sulfoxides then sulfones Sodium metaper lodate IS specific for the oxidation of sulfides to sulfoxides and no fur ther Hydrogen peroxide or peroxy acids can yield sulfoxides (1 mole of oxidant per mole of sulfide) or sulfone (2 moles of oxidant per mole of sulfide)... 

The overall transformation is the conversion of the carbon-sulfur bonds bond to a carbon-carbon double bond. The original procedure involved halogenation of a sulfide, followed by oxidation to the sulfone. Recently, the preferred method has reversed the order of the steps. After the oxidation, which is normally done with a peroxy acid, halogenation is done under basic conditions by use CBr2F2 or related polyhalomethanes for the halogen transfer step.92 This method was used, for example, to synthesize 1,8-diphenyl-1,3,5,7-octatetraene. 

According to this correlation model, in which the principles of steric control of asymmetric induction at carbon (40) are applied, the stereoselectivity of oxidation should depend on the balance between one transition state [Scheme 1(a)] and a more hindered transition state [Scheme 1(6)] in which the groups and R at sulfur face the moderately and least hindered regions of the peroxy acid, respectively. Based on this model and on the known absolute configuration of (+)-percamphoric acid and (+)-l-phenylperpropionic acid, the correct chirality at sulfur (+)-/ and (-)-5 was predicted for alkyl aryl sulfoxides, provided asymmetric oxidation is performed in chloroform or carbon tetrachloride solution. Although the correlation model for asymmetric oxidation of sulfides to sulfoxides is oversimplified and has been questioned by Mislow (41), it may be used in a tentative way for predicting the chirality at sulfur in simple sulfoxides. 

Figure 3.95 Selective oxidation of sulfoxide over sulfide in the presence of peroxy acid anion.

Sulfides are readily oxidiz by peroxy acids as well as TBHP/Mo. Hence the chemoselective epoxidation of the unsaturated sulfide (183) has been effected by an indirect method the alkene is first trans-... 

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). ... 

Many other peroxy acids, such as trifluoroperacetic acid (equation 26), peroxydodecanoic acid (equation 27) and various perbenzoic acids " are also useful oxidants to give a high yield of sulfones from sulfoxides or directly from sulfides under suitable conditions. 

Organic hydroperoxides are generally used for the preparation of sulfoxides from sulfides, - while sulfones can be obtained in neutral organic solvents in the presence of metal catalysts such as V, Mo and Ti oxides at 50-70 C. Two polymer-supported reagents which involve peroxy acid groups and bound hypervalent vanadium(V) and molybdenum(VI) compounds have been developed for facile oxidation of sulfoxides to sulfones. 

In shaip contrast to peroxy acid oxidation the oxidation of sulfoxides to sulfones with various transi tion metal salts proceeds much faster than that of sulfides to sulfoxides and consequently sulfoxides may be selectively oxidized to sulfones in the presence of sulfides. 

Since the first report in 1960, many procedures have been reported for the synthesis of optically pure sulfoxides by chemical oxidation of suMdes. Typical examples are as follows (i) the oxida-don of achiral sulfides by chiral peroxy acids,(ii) oxidation by TBHP in chiral solvents or in dra presence of chiral catalysts, and (iii) diasteieoselective oxi tion of sulfides containing another chiral center. Similar medradologies have been reported using other oxidants such as organic... 

Another clilTerence between sulfides and ethers is that sulfides are easily oxidized. Treatment of a sulfide with hydrogen peroxide, H2O2, at room temperature yields the corresponding sulfoxide (R2SO), and further oxidation of the sulfoxide with a peroxy acid ydelds a sulfone (R2SO2). 

In addition to the ozonolysis of alkenes and a few aromatic compounds [93, 104], ozone oxidizes other groups. Thus saturated hydrocarbons containing tertiary hydrogen atoms are converted into tertiary alcohols [105, 106], and some alkenes are transformed into epoxides [107] or a,p-unsat-urated ketones [108], Benzene rings are oxidized to carboxylic groups [109, ethers [110] and aldehyde acetals [111] to esters aldehydes to peroxy acids [772] sulfides to sulfoxides and sulfones [775] phosphines and phosphites to phosphine oxides and phosphates, respectively [775] and organomer-cury compounds to ketones or carboxylic acids [114]. 

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). 

The oxidation reagents used most frequently for the conversion of sulfides into sulfoxides and sulfones are hydrogen peroxide, peroxy acids, and periodates. Periodates usually do not oxidize sulfoxides to sulfones [770 771, 772, 776, 775], In addition, many other, even rather exotic, oxidants have been used especially for chemoselective oxidations of sulfides containing functional groups vulnerable to attack by peroxy compounds, such as double bonds and carbonyl groups. 

In most instances, double and triple bonds remain unaffected by the oxidation of sulfides to sulfoxides or sulfones, even when hydrogen peroxide and peroxy acids are used [163, 264, 322, 324, 506, 521], Evidently, the affinity of sulfur to oxygen is higher than that of the carbon-carbon multiple bonds (equations 574 and 575). 

Hydrogen peroxide or peroxy acids can yield sulfoxides (1 mol of oxidant per mole of sulfide) or sulfone (2 mol of oxidant) per mole of sulfide. 

Ozonation of Heteroatoms. Phosphines are converted to phosphine oxides and phosphites to phosphates by ozone. These reactions are quite general and a wide range of sub-stitutents can be tolerated. Phosphine oxides also can be produced by the ozonation of alkylidenetriphenylphosphoranes or of thio- or selenophosphoranes. Organic sulfides are converted to sulfoxides and sulfones by ozonation. Tertiary amines are converted to amine oxides, while nitro compounds can be produced in modest yields by ozonation of primary amines. This preparation of nitroalkanes compares well with alternate approaches using peroxides, peroxy acids, permanganate, or Monoperoxysulfuric Acid, but ozonation on silica gel has proven to be superior (see Ozone-Silica Get). Selenides are converted to selenoxides by ozone and this reaction is often used to achieve overall production of unsaturated carbonyl compounds. An example is shown in eq 25. ... 

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