Halogenated hydrocarbons methyl bromide

In the late 1980s, however, the discovery of a noble metal catalyst that could tolerate and destroy halogenated hydrocarbons such as methyl bromide in a fixed-bed system was reported (52,53). The products of the reaction were water, carbon dioxide, hydrogen bromide, and bromine. Generally, a scmbber would be needed to prevent downstream equipment corrosion. However, if the focus of the control is the VOCs and the CO rather than the methyl bromide, a modified catalyst formulation can be used that is able to tolerate the methyl bromide, but not destroy it. In this case the methyl bromide passes through the bed unaffected, and designing the system to avoid downstream effects is not necessary. Destmction efficiencies of hydrocarbons and CO of better than 95% have been reported, and methyl bromide destmctions between 0 and 85% (52). 

Evidence that many of these compounds can have adverse effects on the immune, endocrine and nervous systems and that some are carcinogenic has grown during the last decade. The role of chlorofluorocarbons (CFCs) and of methyl bromide in the ozone layer depletion is well established (ref. 3).It is therefore not surprising that many halogenated derivatives are cast as environmental and health villains by various concerned groups who call for total phase out of chlorine and chlorinated hydrocarbons. 

P.M. Jeffers and N.L. Wolfe, Hydrolysis of methyl bromide, ethyl bromide, chloropicrin, 1,4-dichloro-2-butene, and other halogenated hydrocarbons, in Fumigants Environmental Fate, Exposure, and Analysis, ed. J.N. Seiber, J.A. Knuteson, J.E. Woodrow, N.L. Wolfe, M.V. Yates, and S.R. Yates, ACS Symposium Series No. 652, American Chemical Society, Washington, DC, pp. 32-41 (1997). 

MacKenzie Peers A. 1985. The determination of methyl bromide in air-method 8. In Fishbein L, O Neill IK, ed. Environmental carcinogens selected methods of analysis. Vol. 7. Some volatile halogenated hydrocarbons. Lyon France International Agency for Research on Cancer, 227-233. 

Most of the nematocides marketed are halogenated hydrocarbons. They are either saturated organic halides, such as methyl bromide, ethylene dibromide, and dibromochloropropane, or unsaturated organic halides, such as dichloropropene and dibromobutene. Among the nematocides, a few exceptions to this class of compounds are chloropicrin, a thiocarbamate (Vapam), two organophosphates (V-C 13 and Zino-phos), and a thiadiazine (Mylone). 

Diverse chemicals have been reported to affect measured endpoints of fish thyroidal status. These chemicals include aromatic hydrocarbons, planar halogenated aromatic hydrocarbons (dioxans, furans, coplanar PCBs), organochlorine, organophosphorus and carbamate pesticides, chlorinated paraffins, cyanide compounds, methyl bromide, phenol, ammonia, metals (aluminum, arsenic, cadmium, lead and mercury), low pH conditions, environmental steroids and a variety of pharmaceutical agents. For the following reasons their modes of action appear complex and are poorly understood16. 

Although most of the halogenated hydrocarbons that are commonly used are liquids at ambient temperature and pressure, the low-molecular-weight compounds such as 1,2-difluoroethane, methyl bromide, or vinyl chloride are gases, whereas those of higher molecular weight, such as iodoform or hexachloronaphthalene, are solids. Halogenated hydrocarbons are used as solvents. 

Hahns are fire-fighting gases of halogenated hydrocarbons. Formerly, methyl bromide (CHsBr) and carbon tetrachloride (CCI4) were involved but they were withdrawn on account of their toxicity. 

The thienothienoimidazolium salts 29 were prepared by the reaction of thiophanes 362 with HX (X = halogen) and crystallization from solvents selected from ketones, aromatic hydrocarbons, and halohydrocarbons. l-(—)-3,4-(l, 3 -dibenzyl-2 -ketoimidazolido)-2-(u -ethoxypropyl)tetrahydrothiophene 362 was reacted with HBr at 99-103 °G for 2h and crystallized from methyl-Tro-butyl ketone to give l-(—)-3,4-(T,3 -dibenzyl-2 -ketoimidazolido)-l,2-trimethyle-nethiophanium bromide 29 (95%, 98.7% purity) (Scheme 75) <2001JAK100477>. 

The halogen compounds used were methylene dichloride, chloroform, carbon tetrachloride, ethylene dichloride, ethyl bromide, ethylene dibromide, bromoform, methyl iodide, and ethyl iodide. The hydrocarbons selected for their interesting combustion properties were hexane, 2-methylpentane, 2,2-dimethylbutane, hex-l-ene, heptane, methylcyclo-hexane, isooctane, diisobutylene, benzene, toluene, m-xylene, and ethylbenzene. 

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