Dimethyl disulfide oxidation

Scheme 8.13 and Eqs. 8.6-8.10 reveal that lithiated methoxyallene 42 is sufficiently reactive towards a variety of electrophiles such as alkyl halides [44, 45], ethylene oxide [12c], tosylated aziridine 45 [46], dimethyl disulfide [12b], trialkylstannyl and trialkylsilyl chlorides [47, 48] and iodine [49]. These substitution reactions proceed with excellent regioselectivity and the corresponding a-functionalized products are obtained in good to high yields. An exceptional case was found by treatment of 42 with a guanidinium salt, which led to a 60 40 mixture of a- and y-adducts 50 and 51 (Eq. 8.11) [50],... 

Example The oxidative addition of dimethyl disulfide (DMDS) transforms the double bond to its 1,2-bis-thiomethyl derivative (a). Induced by charge localization at either sulfur atom, the molecular ions of DMDS adducts are prone to a-cleavage at the former double bond position (b). This gives rise to sulfonium ions that are readily identified from the mass spectrum (Chap. 6.2.5). The method can be extended to dienes, trienes, and alkynes. [70,71] (For the mass spectral fragmentation of thioethers cf. Chap. 6.12.4). 

They et al. (1993) evaluated the degradation of aldicarb at nine different temperatures. When aldicarb was oxidized at a temperature range of 275-650 °C, the following reaction products were identified by GC/MS acetone, 2-methyl-2-propenenitrile, methylthiopropene, dimethyl disulfide, carbon dioxide, carbon monoxide, nitrous oxide, isocyanatomethane, hydrogen azide, sulfur dioxide, hydrogen cyanide, and 2-propenenitrile. 

Biogenic processes, however, emit reduced forms of sulfur, including dimethyl sulfide and hydrogen sulfide, with lesser amounts of carbon disulfide (CS2), dimethyl disulfide (CH3SSCH3), carbonyl sulfide (COS), and methyl mercaptan (Cl I3SH). These reduced sulfur compounds are then oxidized in the atmosphere as described in detail in Chapter 8.E. 

JOC1500,6lAK(l8)i5l, 72AJC985). Both the thiocyanopyrroles from the first method and the thiouronium salts from the second can be hydrolyzed to pyrrole-2-thiols. These compounds are evidently quite sensitive to oxidation so that in situ alkylation is frequently done, resulting in isolation of 2-alkylthiopyrroles as indicated in reactions (213) and (214). 2-Methylthiopyrrole is also obtained in low yield by reaction of the magnesium iodide salt of pyrrole with dimethyl disulfide (6lAK(l8)i5i). 

Thermal Stability. Dimethyl sulfoxide decomposes slowly at 189°C to a mixture of products that includes methanetliiol. formaldehyde, water, bis(methyhhio)methane, dimethyl disulfide, dimethyl sulfone, and dimethyl sulfide. The decomposition is accelerated by acids, glycols, or amides. Sulfoxides undergo oxidation, reduction, carbonsulfide cleavage, and Pttmmerer reactions. 

The initial pathways of oxidation of dimethyl sulfide, dimethyl disulfide, and meth-anethiol with the nitrate radical have been examined using DFT and ab initio methods. 

Methylbis(methylthio)sulfonium hexachloroantimonate ([CH3S(SCH3)2][SbCl6]) was isolated from the reaction mixture at -40°C by the oxidation of nonpoly -merizable dimethyl disulfide [86], This result suggests that the phenylbis(phenyl-thio)sulfonium cation is produced by the oxidation of diphenyl disulfide in the acidic reaction mixture [87-89], This cation acts as the active species for the polymerization and electrophilically reacts with the / -position of the benzene ring to yield PPS [90],... 

At present the exact details of the mechanisms leading to each of the products are far from well understood (7.81. However, it seems likely that oxidation of the common naturally-occurring organo-sulfur compounds (dimethyl sulfide, methyl mercaptan and dimethyl disulfide) proceeds, at least in part, through formation of the methyl thiyl radical, CHjS (4.9-111. That is the main reason for carrying out direct studies on CH3S radical reactions where the individual reactions are isolated. 

Dimethyl Disulfide. DMDS has a nauseating odor and solubility of 3.4g/l in water at 25 °C (40). It is particularly resistant to uncatalyzed oxidation. Its oxidation product—methyl sulfonic acid (CH3S03H)—is odorless, nontoxic, nonvolatile and water soluble. 

Table II. Examples of the Oxidation of Dimethyl Disulfide by Hydrogen Peroxide...

Oxidation of DMDS by OH Radical Dimethyl disulfide is oxidized by hydroxyl radicals (50-53) according to the reaction ... 

Oxidation of Mercaptans by O Oxidation of methyl mercaptan in aqueous solution by 03 produces methane sulfonic acid as the major product. The reaction mechanisms are complex with the formation of dimethyl disulfide (CH3SSCH3), methyl methane thiolsulfonate (CH3S02SCH3), and methyl methanethiolsulfinate (CH3SOSCH3) as minor products. Continued ozonation could result in slow formation of sulfuric acid ... 

Methoxyl Groups Lignin is partially demethylated by the action of hydrosulfide ions forming methyl mercaptan which is convertible to dimethyl sulfide by reaction with another methoxyl group. In the presence of oxygen, methyl mercaptan can be oxidized further to dimethyl disulfide (Fig. 7-28). Because the hydroxide ions are less strong nucleophiles than hydrosulfide ions, only small amounts of methanol are formed. Methyl mercaptan and... 

Phenyl-5-chlorotriazole 1-oxides 330 are deprotonated with NaH in DMF. The resulting species 331 react with carbon, silicon, and sulfur electrophiles to give substituted products 332 in good yields. Similarly, deprotonation of 1-substituted pyrazole 2-oxides followed by addition of dimethyl disulfide affords 3- and 5-methylthio as well as 3,5-bis (methylthio)pyrazoles. 

Trimethylsilyl)-l,3-oxathianyllithium 332 was obtained by deprotonation of compound 323 with s-BuLi at —78 °C and reacted with different electrophiles such as deuterium oxide, alkyl iodides, dimethyl disulfide and carbonyl compounds, providing the corresponding products 333 in moderate to good yields. However, the reaction with benzonitrile, followed by acid hydrolysis, gave 2-benzoyl-l,3-oxathiane 334 (X = H) (Scheme 87)503,504. When the last reaction was quenched with methyl iodide before... 

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