Precursor of dimethyl sulfide

ChallengCT R, Simpson MI (1948) Studies mi biological methylation. Part XIL A precursor of dimethyl sulfide evolved by Polysiphoniafastigata. Dimethyl-2-carboxyethylsulphonium hydroxide and its salt J Chem Soc 2 1591—1597... 

Dimethylsulfonium methylide. The reagent can be generated conveniently by reaction of NaOH with trimethylsulfonium chloride rather than NaH, required for generation from trimethylsulfonium iodide, the usual precursor.1 An added advantage is that the chloride can be prepared readily by reaction of dimethyl sulfide with methyl chloroformate in 73% yield.2... 

A novel synthesis of epoxides from aldehydes and sulfur ylides has been reported this past year [94JA5973]. This reaction, which gives predominantly trans epoxides, proceeds through an interesting catalytic cycle in which the sulfur ylide is generated in situ from a diazo precursor, which is slowly added into a reaction medium containing catalytic rhodium(II) acetate and substoichiometric amounts of dimethyl sulfide. The use of a chiral sulfide produced observable (11%) enantioselectivity. 

IR bands of (70) at 935 cm" indicated at the vinyl group substantially took on the trans conformation. The (70) was prepared by the sulfonium salt process using tetrahydrothiophene in place of dimethyl sulfide [131]. In this process, the precursor polymer was soluble in water and a film was formed by casting an aqueous solution. 

The latter is polymerized to yield a water soluble sulfonium salt polyelectrolyte (28d) which is then purified by dialysis [135]. The precursor polymer is converted to PPV (28e) by the thermal elimination of dimethyl sulfide and HCl. The method has been later developed by Horhold et al. [136], Lenz et al. [137,138], Murase et al. [139] and Bradley [140]. One of the major improvements was the use of tetrahydrothiophene instead of dimethyl sulphide in the synthesis of the precursor polymer [141]. The use of the cyclic leaving group facilitates the elimination when the precursor polymer is heated at 230-300 °C and leads to PPV with reduced amounts of defect structures in the polymer chain. 

Particle precursor gases are emitted into the atmosphere either directly by natural and anthropogenic sources or by oxidation processes in the atmosphere. The most prominent precursor gas is probably sulfur dioxide (SO2). It is the precursor for particulate sulfates, such as sulfuric acid (H2SO4) or ammonium sulfate [(NH4)2S04]. Sulfur dioxide is directly emitted by natural sources (e.g., volcano emptions). Anthropogenic sources in industrial regions are mostly associated with combustion processes (e.g., coal combustion). Additional SO2 is derived from oxidation processes of dimethyl sulfide (DMS) over the oceans. Estimations of the global sulfur emissions from these sources are listed in Table 3. 

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... 

Similar data for sulfate have been reported in many studies. Figure 9.36, for example, shows overall average sulfate distributions measured in marine areas as well as at continental sites (Milford and Davidson, 1987). The marine data show two modes, a coarse mode associated with sea salt and a fine mode associated with gas-to-particle conversion. Sulfate in seawater, formed, for example, by the oxidation of sulfur-containing organics such as dimethyl sulfide, can be carried into the atmosphere during the formation of sea salt particles by processes described earlier and hence are found in larger particles. The continental data show only the fine particle mode, as expected for formation from the atmospheric oxidation of the S02 precursors. 

The edible portion of broccoli Brassica oleracea var. italica) is the inflorescence, and it is normally eaten cooked, with the main meal. Over 40 volatile compounds have been identified from raw or cooked broccoli. The most influential aroma compounds found in broccoli are sulfides, isothiocyanates, aliphatic aldehydes, alcohols and aromatic compounds [35, 166-169]. Broccoli is mainly characterised by sulfurous aroma compounds, which are formed from gluco-sinolates and amino acid precursors (Sects. 7.2.2, 7.2.3) [170-173]. The strong off-odours produced by broccoli have mainly been associated with volatile sulfur compounds, such as methanethiol, hydrogen sulfide, dimethyl disulfide and trimethyl disulfide [169,171, 174, 175]. Other volatile compounds that also have been reported as important to broccoli aroma and odour are dimethyl sulfide, hexanal, (Z)-3-hexen-l-ol, nonanal, ethanol, methyl thiocyanate, butyl isothiocyanate, 2-methylbutyl isothiocyanate and 3-isopropyl-2-methoxypyrazine... 

This route was described more or less simultaneously by Karasz et al. 235) and by Murase et al.236). The precursor polymer is typically prepared by reaction of the appropriate bis(chloromethyl)arylene compound with dimethylsulfide in a polar solvent237,238). The product is a water-soluble polymer which can be cast to give thin films. Elimination of hydrochloric acid and dimethyl sulfide takes place on heating the film in the range 200 to 300 °C and can be monitored by thermogravimetry and by the development of colour and conductivity 239. Poly(p-phenylene vinylene), prepared by the precursor route, can be doped to much higher conductivities than the conventionally synthesised polymer. 

The Wessling and Zimmerman aqueous precursor route is illustrated in Scheme 38 [156]. Here, a bis(halomethyl)monomer is reacted with dimethyl-sulfide and subsequent treatment with base affords the high molecular weight precursor polyelectrolyte 31. Due to the instability of 31, polymerization must be carried out at low temperatures (<4 °C) to avoid thermal elimination of the polyelectrolyte. Precursor polymer 31 can be stored in solution with refrigeration, and its shelf life can be increased by the addition of a small amount of pyridine. Precursor polymer 31 can be processed into highly oriented, free-standing films or fibers that can subsequently be converted to PPV with the elimination of gaseous dimethylsulfide and HCl at 200 °C. 

Another interesting application of MDGC is in the rapid determination of isoprene (the most reactive hydrocarbon species) and dimethyl sulfide (DMS) (the major source of sulfur in the marine troposphere and a precursor to cloud formation) in the atmosphere (16). The detection limits were 5 and 25 ng F1, respectively. 

DMS is formed during the biodegradation of organic sulfur compounds and by the biological methylation of sulfide and methanethiol. Precursors of DMS are methionine, S-methylmethionine, dimethylsulfoniopropionate (DMSP), dimethylsulfonioacetate (DMSA), dimethyl sulfoxide (DMSO), methionine sulfoxide and sulfone, trimethylsulfonium salts, S-methylcysteine, homocysteine, dimethyl disulfide (DMDS), 2-keto-4-methiolbutyrate, and 2-mercaptoacetate (thioglycollate). 

One method for the synthesis of hydroxyalkyl-substituted P-lactams is by the Staudinger reaction, the most frequently used method for the synthesis of P-lactams.86 This method for the preparation of 4-acetoxy- and 4-formyl-substituted P-lactams involves the use of diazoketones prepared from amino acids. These diazoketones are precursors for ketenes, in a diastereoselective, photochemically induced reaction to produce exclusively tram-substituted P-lactams. The use of cinnamaldimines 96, considered as vinylogous benzaldimines, resulted in the formation of styryl-substituted P-lactams. Ozonolysis, followed by reductive workup with dimethyl sulfide, led to the formation of the aldehyde 97, whereas addition of trimethyl orthoformate permitted the production of the dimethyl acetal 98 (Scheme 11.26). 

Dimethyl sulfoxide reductases (DMSOR) of bacteria and fungi that catalyze the reduction of DMSO to dimethyl sulfide (DMS). These enzymes play a significant role in the global sulfur cycle, not least because DMS is volatile and is the precursor of the methylsulfonate aerosols that nucleate cloud formation (29). Furthermore, the distinctive smell of DMS acts as a guide to certain seabirds who use it to locate productive regions of the ocean (30). 

Variants of the method are the use of tributylstannyl [59] or trimethylsilyl [60] derivatives of the thiol, which give less odor and sometimes higher yields, due to less formation of 1,2-cA-products and dithioacetals, but these are also more expensive reagents. With the latter type of reagents a-acetates have also successfully been used as precursors using either zinc iodide [61] or iodine [62] as promoter. In the latter publication the authors could not detect any difference in reactivity between the a- and the /3-acetate precursor under these reaction conditions. Furthermore, a cheaper version utilizing dimethyl sulfide/hexamethyldisilane as reagent was found to be equally efficient (O Scheme 5). 

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