Oxidation of dimethyl disulfide

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

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). 

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],... 

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 ... 

Oxidation of dialkenyl disulfides gave the stereoisomeric 2,3-dimethyl-5,6-dithiabicyclo[2.1.1]hexane 5-oxides 36 and 37, which are found in extracts of onion. Further conversion and oxidations afforded a series of various 2,3-dimethyl-5,6-dithiabicyclo[2.1.1]hexane derivatives, which were characterized on the basis of the comparative X-ray structural and NMR and IR spectroscopic data. The 111 NMR peak assignments for 36 and 37 were facilitated by LAOCOON III analyses of these 10 spin systems and by examination of the shifts induced by Eu(fod)3 and d6-benzene (fod = 6,6,7,7,8,8,8-heptafluoro-2,2-dimethyl-3,5-octadione) <1996JA2790>. 

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. 

As mentioned elsewhere a typical DTG plot for exhausted carbon after MM adsorption consists of two peaks [1, 2, 9]. One, low temperature, at about 80 °C, represents desorption of water, and second, with maximum at about 200 °C, represents desorption of dimethyl disulfide. Following the assumption that either H2O or DMDS are adsorbed only in pores smaller than SO A, the data was normalized based on that volume. Figure 2 shows the relationship between the normalized amount of DMDS and water. The correlation coefficient and slope are equal to 0.89 and - 0.99, respectively. The slope represents the density of DMDS (1.06 g/cm ). The small discrepancy is likely related to the hict that not all pores are filled by oxidation products owing to the existence of some physical hindrances (blocked pore entrances). The thin line represents theoretical limit of adsorption assuming real density of DMDS and H2O. The fact that almost all points are located below this line validates our hypothesis about the active" pore volume. It is important to mention here that all points represent equilibrium data, if equilibrium... 

Oxidations by chlorine are limited to only few types of compounds. In organic solvents and pyridine [681] or hexamethylphosphoramide (HMPA) [682] as cosolvents, primary alcohols are oxidized to aldehydes and secondary alcohols to ketones [681, 682]. Secondary alcohols are oxidized in preference to primary alcohols [681]. Many oxidations with chlorine are carried out in aqueous media and involve sulfur-containing compounds. Mercaptans [683], alkyl thiolcarboxylates [683], thiocyanates [684], isothioureas [684], disulfides [655], and sulfinic acids [656] are transformed into sulfonyl chlorides. The chlorination of dimethyl disulfide in acetic anhydride yields methanesulfinyl chloride [657]. 

The methanethiol amounts shown in graphs refer to the mass of methanethiol that was present in a 10 ul injection, and not the total mass present in a given headspace bottle. To obtain the amount of methanethiol present in a bottle headspace, the mass obtained from plots must be multiplied by 9500 (i.e., 99 ml headspace/10 ul injection). Further discussions about employing this technique for measuring thiols can be found in reports by Rippe (64), Jansen et al. (66), and Banwart and Bremner (67). It was assumed that the differences in partial pressures of methanethiol and dimethyl disulfide were insignificant between calibration and model systems. However, over time methanethiol oxidizes to dimethyl disulfide in the aerobic environment of sample bottles. 

Another interesting example of the biological influence on atmospheric chemistry is provided by sulfur. Under natural conditions, sulfur compounds in the atmosphere are provided by the oceanic emission of dimethyl disulfide (DMS). This biogenic emission results from the breakdown of sulfoniopropionate (DMSP), which is thought to be used by marine phytoplankton to control their osmotic pre.ssure. The oxidation of DMS leads to the formation of sulfur dioxide, which is further converted to sulfate particles. As indicated above, these particles, by scattering back to space some of the incoming solar radiation, tend to cool the earth s surface. Their presence also affects the optical properties of the clouds, which introduces an indirect climatic effect. 

Disulfides are good soft acceptors. They are reduced to thiols by hydro-selenide ion (90). The utilization of dimethyl disulfide as an indirect oxidant during conversion of aldehyde to acid derivatives via the dithiane synthesis has been reported (91). The alkylation of the lithiodithiane derived from cinnam-aldehyde occurs exclusively at the heterocyclic carbon. This may be indicative of symbiotic stabilization of the transition state and the product. 

However, unheated and heat-treated crude caraway seed extracts did not affect the concentrations of dimethyl disulfide and dimethyl trisulfide in model systems over an extended period (5 hr). Thus, it appeared that the overall suppression of methanethiol-related compounds in sauerkraut by caraway seed (Table I) was dependent on methanethiol which has been shown to be a precursor for both dimethyl disulfide and dimethyl trisulfide under oxidative conditions (18,25). Recently, Chin and Lindsay (25) have shown that methanethiol was readily converted to dimethyl disulfide and dimethyl trisulfide in an aerobic cabbage model system (pH 6.3) consisting of 1 ppm hydrogen sulfide, 450 ppm ascorbic acid and 4 ppm Fe(m). 

The influence of dimethyl disulfide on flavor quality of modified atmosphere stored broccoli florets was further demonstrated by data shown in Table VI which revealed that aroma assessments of undesirable sulfurous aromas in broccoli florets more closely corresponded with concentrations of dimethyl disulfide than with methanethiol. In this experiment broccoli florets were treated by dipping in various solutions containing either ascorbic acid (500 ppm), sodium hy oxide (0.01 M), or phosphoric acid (0.1 M). Broccoli florets dipp in distilled water were used as the control samples. Samples held in sealed Curlon 850 pouches were analyzed after storage for 4 days at 10°C. Ascorbic acid was included in this study because it acts as a reducing agent for methanethiol under anaerobic conditions in model systems (25). 

Alkaline and acidic solutions were employed in the experiment because Marks et al. (20) reported that the formation of -methyl-L-cysteine sulfoxide breakdown products was dependent on pH of the vegetable tissues. Table YU shows that the alkaline treatment had the most pronounced effect among the treatments on suppressing the formation of dimethyl disulfide which appears to contribute strongly to the unpleasant volatile sulfur compound aroma in stored broccoli. This effect probably results from the destruction of methyl methanethiosulfinate by the hydroxide ion (33). Thus, strategies for suppressing undesirable volatile sulfur compounds in cruciferous vegetables and other foods need to incorporate means to minimize contributions by oxidized forms of methanethiol as well as methanethiol itself. 

Mercaptide Elimination. Kallio and Larson have described an oxidative degradation of methionine by a Pseudomonas. A pyridoxal phosphate enzyme eliminates methyl mercaptan and ammonia, leaving a-ketobutyrate. The methyl mercaptide is oxidized to dimethyl disulfide. 

Sulfur compounds comprise only a small fraction of earth s atmospheric composition however, these minor constituents have a significant impact on the atmosphere, hydrosphere, and biosphere. Since the late 1970s, tremendous effort has been expended to illuminate the atmospheric oxidation mechanisms of a variety of sulfur compounds. Section 2 focuses on the atmospheric oxidation mechanisms of two important organic sulfur compounds carbon disulfide and dimethyl sulfide. Because sulfur-centered radicals are key intermediates in the atmospheric oxidation of carbon disulfide and dimethyl sulfide, the oxidation mechanisms of these compounds provide valuable insight into the chemistry of organic sulfur-centered radicals in the gas phase. 

GC-MS. For example, branched-chain primary alcohols have been oxidised to the corresponding acids and methylated for analysis, since the mass spectra of methyl esters are well documented [424,426], Others prepared pyrrolidides, after oxidation to the acids, as these give spectra which are more readily interpreted [46], Similarly, secondary alcohols have been oxidised to ketones as an aid to identification [113], Double bonds in alkyl chains of alcohols have been located by MS after the preparation of suitable chemical adducts, similar to those described for fatty acids in Chapter 7. Oxidation to diols and conversion to the TMS ethers is one method [638], but synthesis of dimethyl disulfide adducts from alcohol acetates is a one-step reaction (see Chapter 4) and is now preferred [143,540], On the other hand, it may be too much to expect that a single method will provide all the information desired on a given sample it required partial hydrogenation, coupled with GC-MS and GC/Fourier-transform IR (to identify frans-double bonds), to determine the structure of a trienoic insect trail pheromone [1006],... 

Carbonyl sulfide and carbon disulfide pass more or less intact through the Stretford absorber, while about half of the thiophene is typically removed. Methylmercaptan is largely oxidized to dimethyl disulfide, DMDS, which is largely incorporated into the sulfur cake. Higher mercaptans are partially oxidized to disulfide, but most are released to the atmosphere in the oxidizer, in some cases causing severe odor problems, which may require incineration of the oxidizer vent stream. 

Oxidation. Disulfides are prepared commercially by two types of reactions. The first is an oxidation reaction uti1i2ing the thiol and a suitable oxidant as in equation 18 for 2,2,5,5-tetramethyl-3,4-dithiahexane. The most common oxidants are chlorine, oxygen (29), elemental sulfur, or hydrogen peroxide. Carbon tetrachloride (30) has also been used. This type of reaction is extremely exothermic. Some thiols, notably tertiary thiols and long-chain thiols, are resistant to oxidation, primarily because of steric hindrance or poor solubiUty of the oxidant in the thiol. This type of process is used in the preparation of symmetric disulfides, RSSR. The second type of reaction is the reaction of a sulfenyl haUde with a thiol (eq. 19). This process is used to prepare unsymmetric disulfides, RSSR such as 4,4-dimethyl-2,3-dithiahexane. Other methods may be found in the Hterature (28). 

Gentle oxidation of thiols leads generally to disulfides When tetrafluoro-1,4-benzeneditliiol is added to dimethyl sulfoxide, a macrocyclic tetradisulfide is formed [102] (equation 94)... 

Sulfur-containing amino acids, such as methionine and cystine, are probably the precursors of the mercaptans, sulfides, and disulfides.3 Dimethyl sulfide yields dimethyl sulfoxide and its oxidized product dimethyl... 

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