Halomethanes

All 4 chlorocompounds, namely methyl chloride, methylene dichloride, chloroform and carbon tetrachloride, are of commercial importance they are produced by successive chlorination of methane, followed by separation and purification of the halomethanes mixture [40]. 

An alternative feedstock of growing significance is methanol, which may be transported much more easily than methane. In this case, the first stage is hydrochlorination which yields methyl chloride, which is then further chlorinated. 

A traditional process for the production of carbon tetrachloride, which is still in use, consists of the reaction of chlorine with Carbon Disulphide conversion efficiency is high and there are few chlorinated by-products. Sulphur is recovered as such, or reconverted to CS2. 

Carbon tetrachloride may also be co-produced with perchloroethylene, by chlorination of propane, propylene, ethylene, or on its own from a whole series of chlorinated residues. 

Other halomethanes may be synthesised by routes analogous to the chloromethanes, but are not of commercial significance. 

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Sodium bromide is the most rapidly growing antimicrobial ia water treatment appHcations (25). Chlorine dioxide [10049-04-4] has not been historically important, but may have a bright future because of its excellent antimicrobial activity without formation of halomethanes or chloramines (26). 

Halomethanes (other than those listed elsewhere)... 

E. A. Davidson, in Production and Consumption of Greenhouse Gases Methane, Nitrogen Oxides, and Halomethanes, ed. J. E. Rogers and W. B. Whitman, American Society for Microbiology, Washington, 1991, p. 219. 

One of the older preparative free-radical reactions is the addition of polyhalomethanes to alkenes. Examples of addition of carbon tetrabromide, carbon tetrachloride, and bromoform have been recorded. The reactions are chain processes that depend on facile abstraction of halogen or hydrogen from the halomethane ... 

The efficiency of the halomethane addition process depends on the relative rate of halogen-atom abstraction versus that of addition to the alkene ... 

O Paleta, Ionic Addition Reactions of Halomethanes with Fluoroolefins... 

Ionic Addilion Reactions of Halomethanes aiih Ruoroolcfins... 

Halofluoroalkenes may be prepared by using fluorodihalomethanes or fluoro-halomethanes in olefination procedures similar to those descnbed above. Ruoro-trichloromethane treated with tris(dimethylamino)phosphine forms the corresponding phosphomum salt, which can then be used in the Wirtig procedure. The reaction depends on the nature of the solvent in tetrahydrofuran, little olefination if any occurs however, when benzomtrile is added to the mixture, ylide formation is promoted [50] (equation 48) (Table 19). 

The effects of a- vs. P-fluonnation imply that fluoroolefms normally react regioselectively with electrophiles to minimize the number of fluorines p to the electron-deficient carbon in the transition state. Diverse types of electrophilic additions follow this rule (equations 6-8, for example), although there aie exceptions, especially for ionic addiPons of halomethanes to fluoroolefins [124]... 

Dipole moment (n ), 38 halomethanes, 335 polar covalent bonds and, 38-39 table of, 39... 

The breakdown of organic contaminants present in the MU water to produce ammonia (from nitrogenous contaminants), phenols and carboxylic acids (from humic and fulvic acids), and tri-halomethanes (from the by-products of chlorination)... 

Coulter C, JTG Hamilton, WC McRoberts, L Kulakov, MJ Larkin, DB Harper (1999) Halomethane bisulfite/halide ion methyltransferase, an unusual corrinoid enzyme of environmental significance isolated from an aerobic methylotroph using chloromethane as the sole carbon source. Appl Environ Microbiol 65 4301-4312. 

McAnulla C, CA Woodall, IR McDonald, A Studer, S Vuilleumier, T Leisinger, JC Murrell (2001a) Chloro-methane utilization gene cluster from Hyphomicrobium chloromethanicum strain CM2 and development of functional gene prohes to detect halomethane degrading bacteria. Appl Environ Microbiol 67 307-316. 

With methane the reaction produces a mixture of halomethanes and a HX. 

Chlorination reactions. Chlorination of hydrocarbons has been carried out in Japan, chlorination of toluene in the United States, chlorination of tetrachloropentane in the former U.S.S.R. to give octachlorocy-clopentane, and chlorination of propanoic acid in France to give chloro-propanoic acid. Chlorination of methane by irradiation to give lower halomethanes was found to be cost-effective. Chlorination of various amorphous polymers such as polypropylene, polybutadiene, and PVC, has also been carried out. 

For n = 1, this is the standard synthesis of [l.l.l]propellane 40a.20,21 Also for n = 3, this method makes [3.1.1]propellane 40c accessible with reasonable effort.22 Although [2.1.1]propellane 40b was detected by its IR spectrum at liquid nitrogen temperature,23 it could not be obtained as a stable compound via this route.22 The addition of halomethanes across the central bond by a radical chain mechanism is common to 40a and 40c. The addition of carbon tetrabromide to 40c afforded a 45% yield of 41.18 Likewise, a number of bicy-clo[l.l.l]pentane derivatives 42 were obtained by reaction of the corresponding halomethanes with 40a.17,24... 

The addition of halomethanes across the central bond of [l.l.l]propellane 78 leads to l-halo-7-(n-halomethyl)tricyclo[4.2.0.02,7]octanes 79, which are suitable precursors for the generation of type 80 carbenes.26... 

Reynolds ES. 1972. Comparison of early injury to liver endoplasmic reticulum by halomethanes, hexachloroethane, benzene, toluene, bromobenzene, ethionine, thioacetamide and dimethylnitrosamine. 

Cai Z, Mehendale HM. 1991b. Hepatotoxicity and lethality of halomethanes in Mongolian gerbils pretreated with chlordecone, phenobarbital or mirex. Arch Toxicol 65(3) 204-212. 

Klingensmith JS, Mehendale HM. 1981. Potentiation of brominated halomethane hepatotoxicity by chlordecone in the male rat. Toxicol Appl Phannacol 61(3) 378-384. 

Mehendale HM. 1984. Potentiation of halomethane hepatotoxicity Chlordecone and carbon tetrachloride. Fundam Appl Toxicol 4(3) 295-308. 

Mehendale HM. 1990b. Potentiation of halomethane hepatotoxicity by chlordecone A hypothesis for the mechanism. Med Hypotheses 33(4) 289-299. 

Watts and Goldstein 21) provide further support for the primacy of hydrogen bonding effects on /13 by examining thirteen different halomethanes as the... 

Douglas, A. W., Dietz, D. 13C-H Coupling Constants. III. 13C-H Coupling in the Vapor Phase and its Dependence on Medium Effects. J. Chem. Phys. 46, 1214 (1967). 21) Watts, V. S., Goldstein, J. H. Solvent Effects on 13C-H Coupling Parameters and Chemical Shifts of Some Halomethanes. J. Phys. Chem. 70, 3887 (1966). 

Values for incremental lifetime cancer risk of 10" for halomethanes as a class based on carcinogenicity of chloroform. 

EPA. 1980a. Ambient water quality criteria for halomethanes. Washington, DC U.S. Environmental Protection Agency, Office of Water Regulations and Standards Criteria and Standards Division. 

Kudchadker AP, Kudchadker SA, Shukla RP, et al. 1979. Vapor pressures and boiling points of selected halomethanes. J Phys Chem Ref Data 8 499-517. 

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