Methyl mercaptan, decomposition

Thermal decomposition of methyl xanthates is similar to the pyrolysis of acetates for the formation of the double bond. Olefins are obtained from primary, secondary, and tertiary alcohols without extensive isomerization or structural rearrangement. The other products of the pyrolysis of the methyl xanthates are methyl mercaptan and carbon oxy-sulfide. The xanthates prepared from primary alcohols are more difficult to decompose than those prepared from secondary and tertiary alcohols. Over-all yields of 22-51% have been obtained for a number of tertiary alkyl derivatives of ethylene. Originally the xanthates were made by successive treatment of the alcohol with sodium or potassium, carbon disulfide, and methyl iodide. In a modification of this procedure sodium... 

The pyrolysis of methyl mercaptan was investigated by the toluene flow carrier technique in the range 732-829 °C . The reaction is first order and leads to the formation of CH4, HjS, Hj and bibenzyl in contrast to the photochemical case, the thermal decomposition is undoubtedly initiated by... 

Dimethyl sulfoxide is reasonably stable to heat but upon prolonged reflux it decomposes slightly to methyl mercaptan and bismethylthiomethane. This decomposition is aided by acids, and is retarded by many bases. When heated to decomposition, toxic fumes are emitted. 

Mitsuhashi, S., 1949. Decomposition of thioether derivatives by bacteria. I. Methyl-mercaptan formation and the properties of the responsible enzyme. Jpn. J. Exp. Med., 20 211-222. 

Similar reaction paths can be visualized for condensation of methyl mercaptan or methylamines. It is interesting to note that Corey and Chaykovsky s well-known synthetic studies with the use of dimethylsulfonium methylide mentioned the need to generate the ylide at low temperatures, which otherwise led to decomposition giving ethylene. Indeed, this reaction is similar to that involved in the higher-temperature acid-base catalyzed condensation reaction (Scheme 23). 

Dimethyl sulfoxide is a very polar, high dipole moment, strong hydrogen bond accepting solvent It is has a high viscosity nearly equal to that of IPA. Typical impurities from the manufacturing process include dimethyl sulfide (from whidi DMSO is commonly manufactured) and dimethyl sulfone. Decomposition products include dimethyl sulfide, dimethyl sulfone, methyl mercaptan, and bis(methylthio> methane [1552]. 

The highest concentration of hydrogen sulphide in biogas is noted in the early stages of waste decomposition. The decrease in the concentration of H S is most likely caused by the precipitation of the sulphides in the reaction with heavy metals (such as Cu and Fe) or their oxides, which are present in the deposited material. Sulphides as water insoluble compounds remain in the mass of waste (Parker et al. 2002). The organic sulfur compounds in the greatest concentrations in landfill gas are dimethyl sulphide (DMS), carbon disulphide, methyl mercaptan, dimethyl disulphide (DMDS) at the concentrations of 0.007-180 mg m" 0.09-61.6 mg m" 0.084-17.94 mg m 0.0124-0.942 mg m" respectively (Kim et al. 2005, Shin et al. 2002). 

OSHA PEL TWA 0.5 mg(As)/m3 ACGIH TLV BEL 35 n (As)/L inorganic arsenic and methylated metabolites in urine SAFETY PROFILE Poison by intraperitoneal and intravenous routes. Moderately toxic by ingestion. See also ARSENIC COMPOUNDS, MERCAPTANS, and ESTERS. When heated to decomposition it emits very toxic fumes of As and SOx. 

For this reason a regulator is added. Regulators are substances with very high transfer constants, and therefore only need to be added in small concentrations. SH compounds in particular (mercaptans, thio-glycolic ethyl ester) are suitable regulators. At 60°C, for example, n-butyl mercaptan possesses a Q of 22 (styrene) or 0.66 (methyl methacrylate). Thus, the value for the n-butyl mercaptan/styrene system is higher than that for the pentaphenylethane/styrene system (Table 20-7). These high transfer constants do not occur with the latter because mercaptans lead to an induced initiator decomposition. 

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