Methane halogenated

All four chlorinated methanes are produced using methane chlorination or catalytic oxychlorination of methane. The methane chlorination is initiated thermally or photochemical ly. The strongly exothermic free-radical reaction is conducted without external heat at 400-450°C at slightly raised pressure [158], 

Different ratios of C12/CH4 lead to different products. If methyl chloride is preferred a low ratio (1/10) is used otherwise, a higher ratio is used. Higher 

The chlorinated methanes are purified by first scrubbing the HC1 produced in the reaction with water second, condensing them to separate them from methane and finally isolating them into pure form using pressurized distillation [158,159], 

The second route to chlorinated methanes involving methane is oxychlor-ination. Direct oxychlorination has not been used yet commercially however, an indirect chlorination method is used. 

The process operates with a melt consisting of CuCl2 and KC1, which act simultaneously as a chlorine source and catalyst. The melt first produces the chlorinated methanes and is fed into an oxidation reactor, where it is rechlorinated in an oxychlorination reaction with hydrogen chloride or hydrochloric acid and air. The chlorinated methanes then are recovered in a similar manner to the methane chlorination method [158,159], 

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In the known absence of bromoform, iodoform, chloral, and other halogenated methanes, the formation of phenyhsonitrile with aniline provides a simple and faidy sensitive but nonspecific test for the presence of chloroform, the carbylamine test. Phenyhsonitrile formation is the identification test given in the British Pharmacopoeia. A small quantity of resorcinol and caustic soda solution (10% concentration) added to chloroform results in the appearance of a yellowish red color, fluorescing yeUow-green. When 0.5 mL of a 5% thymol solution is boiled with a drop of chloroform and a small quantity of potassium hydroxide solution, a yellow color with a reddish sheen develops the addition of sulfuric acid causes a change to brilliant violet, which, diluted with water, finally changes to blue (33). 

Henson JM, Yates MV, Cochran JW, et al. 1988. Microbial removal of halogenated methanes, ethanes, and ethylenes in an aerobic soil exposed to methane. Published in FEMS Microbiology Ecology. Prepared in cooperation with Northrop Services, Inc. Ada, OK and Oklahoma Univ., Norman Dept, of Botany and Microbiology. EPA/600/J-88/066. 

The cometabolism of halogenated methanes has been examined in Nitrosomonas europaea and may putatively be mediated by ammonia monooxygenase. 

Brinck, T., J. S. Murray, and P. Politzer. 1992b. Surface Electrostatic Potentials of Halogenated Methanes as Indicators of Directional Intermolecular Interactions. Int. J. Quant. Chem., Quant. Biol. Symp. 19, 57. 

The sum of the number of moles of each halogenated methane produced equals the number of moles of methane that reacted.)... 

Benigni, R., Andreoli, C., Conti, L., Tafani, P., Cotta-Ramusino, M., Carere, A., Crebelli, R. Quantitative structure-activity relationship models correctly predict the toxic and aneuploidizing properties of halogenated methanes in Aspergillus nidulans. Mutagenesis 1993, 8, 301-305. 

Mittler R (2002) Oxidative stress, antioxidants and stress tolerance. Trends Plant Sci 7 405 410 Moore RM, Webb M, Tokarczyk R, Wever R (1996) Bromoperoxidase and iodoperoxidase enzymes and production of halogenated methanes in marine diatom cultures. J Geophys Res 101 20899-20908... 

Table 3. Solvent effects on theJ13 of some halogenated methanes C H...

APHA. 1985a. Halogenated methanes and ethanes by purge and trap-method 514. In Standard methods for the examination of water and wastewater. 16th ed. American Public Health Association, Washington, DC, 591-602. 

Hubrich C, Stuhl F. 1980. The ultraviolet absorption of some halogenated methanes and ethanes of atmospheric interest. J Photochem 12 93-107. 

CHCI3 CHBrCl2 CHBr2CI CHBr3 Halogenated methanes... 

Dittman EC, Etschenberg E. 1973. Endoanesthetic and narcotic activity of halogenated methane derivatives. Eur J Pharmacol 24 389-398. 

Hubrich, C., and F. Stuhl, The Ultraviolet Absorption of Some Halogenated Methanes and Ethanes of Atmospheric Interest, J. Photochem., 12, 93-107 (1980). 

Hsu, K. J., and W. B. DeMore, Rate Constants and Temperature Dependences for the Reactions of Hydroxyl Radical with Several Halogenated Methanes, Ethanes, and Propanes by Relative Rate Measurements, J. Phys. Chem., 99, 1235-1244 (1995). 

Roldan-Arjona. T. Pueyo, C. (1993) Mutagenic and lethal effects of halogenated methanes in the Ara test of Salmonella typhimurium. quantitative relationship with chemical reactivity. Mutagenesis. 8. 127-131... 

Strobel, K. Grummt, T. (1987) Aliphatic and aromatic halocarbons as potential mutagens in drinking water. Part I. Halogenated methanes. Toxicol, environ. Chem., 13, 205-221... 

Once again the absorption spectrum of CF2 appears when the ketone is flash photolyzed in the gas phase but the intensity of the lines is much weaker than in the case of 1,3-dichlorotetrafluoroacetone. The yields of the two halogenated methanes rise with increase in temperature showing that they may also arise by an abstraction process which becomes more important at elevated temperatures. When the rate function... 

The effect of wavelength upon the relative proportion of the products is very marked. When the 2537 A. line from a low-pressure mercury arc is used, the yield of all three ethanes is drastically reduced, while the yield of both halogenated methanes is enhanced. The 1,3-dichlorohexafluoropropane can no longer be detected. This effect is unlikely to be due to alternative primary processes, such as mercury photosensitization, since it is also observed under flash photolysis conditions. As before, it is considered that the additional energy given to the radicals at shorter wavelengths, increases the rate of abstraction and decreases the rate of combination because of the third-body restriction. Some evidence for this... 

We conclude this section with some brief comments on the cosolvent effects of partially miscible organic solvents (PMOSs). These solvents include very polar liquids such as w-butanol, w-butanone, w-pentanol, or o-cresol, but also nonpolar organic compounds such as benzene, toluene, or halogenated methanes, ethanes, and ethenes. For the polar PMOS, a similar effect as for the CMOS can be observed that is, these solvents decrease the activity coefficient of an organic solute when added to pure water or to a CMOS/water mixture (Pinal et al., 1990 Pinal et al., 1991 Li and Andren, 1994). For the less polar PMOS there is not enough data available to draw any general conclusions. 

Despite the scatter in the data, we can see that the relative rates for the series of halogenated methanes considered are quite similar in the Fe(II)/goethite and the mercaptojuglone system. Both span a range of about four orders of magnitude. In... 

Hanzlik, R. P., Reactivity and toxicity among halogenated methanes and related compounds. A physicochemical correlate with predictive value , Biochem. Pharmacol., 30, 3027-3030 (1981). 

The photochemistry of halogenated methanes has been of great interest recently ever since it was recognized that chloromethancs in the stratosphere may release Cl atoms upon absorption of solar radiation and that Cl atoms so produced may catalytically decompose 03. 

Primary processes of halogenated methanes may be summarized as follows ... 

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