Methanethiol, oxidation

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. 

Methanethiol oxidizes easily to dimethyldisul-fide, which can disproportionate to dimethylsul-fide and dimethyltrisulfide (Formula 5.8). 

Mercury(II) oxide Chlorine, hydrazine hydrate, hydrogen peroxide, hypophosphorous acid, magnesium, phosphorus, sulfur, butadiene, hydrocarbons, methanethiol... 

Mesitylene [Benzene, 1,3,5-tnmethyl-], 86 Z Met Gly Gly OEt [Gly cine,V-[Ar-[A-[(phenylmethoxy)carbonyl] -L-methionyl] glycyl] -, ethyl ester], 9 3 Methane, iodo-, hazard note 127 Methyl chlonde polystyrene [Benzene, diethenyl-, polymer with ethenyl-benzene, chloromcthylatcd], 96 Methyl iodide [Methane, iodo-], 79 Methyl mercaptan [Methanethiol], 73 Moffat oxidation, 99... 

Hyphomicrobium sp. strain EG is able to grow at the expense of dimethyl sulfide or dimethyl sulfoxide (DMSO) and prodnces methanethiol initially. This is then further oxidized to formaldehyde, sulfide, and Ft202 by an oxidase that has been purified (Suylen etal. 1987). 

The use of aqueous foams to control fume or vapour release from reactive chemicals is discussed. An acid-resistant foam NF2 controlled fume emission from 35% and 65% oleum, and from titanium tetrachloride, but was not effective for sulfur trioxide and chlorosulfuric acid. An alcohol-resistant foam NF1 suppressed ammonia vapour emission by 80%, and Universal fire foam reduced evaporation of ethylene oxide, vinyl chloride and methanethiol, and reduced vapour emission of 1,3-butadiene by 60%. Safety aspects of foam blanketing are discussed [1]. Equipment and application techniques are covered in some detail [2],... 

In the presence of a catalytic amount of methanethiolate-bridged diruthenium complex (la abbreviated as met-DIRUX), reactions of propargylic alcohols (2) with a variety of heteroatom-centered nucleophiles such as alcohols, thiols, amines, amides, and diphenylphosphine oxide gave the corresponding propargylic substituted... 

Another cycloaddition to an a,(3-unsaturated compound involves the reaction of nitrile oxides with 3-methoxy- or 3-methylthio-1 -phenyl-2-propene-1 -one (Scheme 6.18) (133,134). The isoxazoles that are isolated are considered to arise from the respective intermediate isoxazolines by subsequent elimination of methanol or methanethiol. The regioselectivity observed was attributed to the presence of substituents with strong electron-donating ability, and this was accommodated in terms of the FMO theory (133,134). 

When present in excess methionine is toxic and must be removed. Transamination to the corresponding 2-oxoacid (Fig. 24-16, step c) occurs in both animals and plants. Oxidative decarboxylation of this oxoacid initiates a major catabolic pathway,305 which probably involves (3 oxidation of the resulting acyl-CoA. In bacteria another catabolic reaction of methionine is y-elimination of methanethiol and deamination to 2-oxobutyrate (reaction d, Fig. 24-16 Fig. 14-7).306 Conversion to homocysteine, via the transmethylation pathway, is also a major catabolic route which is especially important because of the toxicity of excess homocysteine. A hereditary deficiency of cystathionine (3-synthase is associated with greatly elevated homocysteine concentrations in blood and urine and often disastrous early cardiovascular disease.299,307 309b About 5-7% of the general population has an increased level of homocysteine and is also at increased risk of artery disease. An adequate intake of vitamin B6 and especially of folic acid, which is needed for recycling of homocysteine to methionine, is helpful. However, if methionine is in excess it must be removed via the previously discussed transsulfuration pathway (Fig. 24-16, steps h and z ).310 The products are cysteine and 2-oxobutyrate. The latter can be oxidatively decarboxylated to propionyl-CoA and further metabolized, or it can be converted into leucine (Fig. 24-17) and cysteine may be converted to glutathione.2993... 

A theoretical analysis of methanethiol + OH reaction at the QCISD(T)/6-311+G (2df,2pd)//UMP2/6.311+G(d,p) level indicated that the oxidation proceeds mainly by a direct hydrogen atom transfer. The cysteine + OH system presented slight variations in major parameters from those of methanethiol. The calculated rate constants, in aqueous solution, are found to be in good agreement with the experimental rate... 

Several of the partially lower-alkylated derivatives of non-metal hydrides are pyrophoric in air. With other gaseous oxidants (halogens, etc.) the reaction may be explosive. The class includes the groups and the individually indexed compounds Diethylarsine, 1714 Dimethylarsine, 0933 Ethylmethylarsine, 1289 Methanetellurol, 0488 f Methanethiol, 0487 ALKYLBORANES... 

Figure 2. Aerobic catabolism of methylated sulfides (adapted from Kelly, 1988). 1) DMSO reductase (Hyphomicrobium sp.) 2) DMDS reductase (Thiobacillus sp. 3) trimethylsulfonium-tetrahydrofolate methyltransferase (Pseudomonas sp.) 4) DMS monooxygenase 5) methanethiol oxidase 6) sulfide oxidizing enzymes 7) catalase 8) formaldehyde dehydrogenase 9) formate dehydrogenase 10) Calvin cycle for CO2 assimilation (Thiobacillus sp.) 11) serine pathway for carbon assimilation (Hyphomicrobium sp.).

Fume, J. et al., Oxidation of hydrogen sulfide and methanethiol to thiosulfate by rat tissues a specialized function of the colonic mucosa, Biochem. Pharmacol., 62, 255-259, 2001. 

The 1-oxide function appears to play a major role in the cleavage of the tetrahydrothiopyran ring in the 2-(3-pyridinyl)tetrahydrothiopyran 1-oxide derivative 397, promoting nucleophilic attack by the methanethiol anion at the tricoordinate S atom (Equation 104) <1996JOC8701>. 

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