Chloromethane, also called methyl chloride, Refrigerant-40, R-40 or HCC 40, is an organic compound with the chemical formula CH3Cl. One of the haloalkanes, it is a colorless, sweet-smelling, flammable gas. Methyl chloride is a crucial reagent in industrial chemistry, although it is rarely present in consumer products,[5] and was formerly utilized as a refrigerant. Most chloromethane is biogenic.
Occurrence
Chloromethane is an abundant organohalogen, anthropogenic or natural, in the atmosphere. Natural sources produce an estimated 4,100,000,000 kg/yr.[6]
Marine
Laboratory cultures of marine phytoplankton (Phaeodactylum tricornutum, Phaeocystis sp., Thalassiosira weissflogii, Chaetoceros calcitrans, Isochrysis sp., Porphyridium sp., Synechococcus sp., Tetraselmis sp., Prorocentrum sp., and Emiliana huxleyi) produce CH3Cl, but in relatively insignificant amounts.[7][8] An extensive study of 30 species of polar macroalgae revealed the release of significant amounts of CH3Cl in only Gigartina skottsbergii and Gymnogongrus antarcticus.[9]
In the sugarcane industry, the organic waste is usually burned in the power cogeneration process. When contaminated by chloride, this waste burns, releasing methyl chloride in the atmosphere.[12]
Interstellar detections
Chloromethane has been detected in the low-mass Class 0 protostellar binary, IRAS 16293–2422, using the Atacama Large Millimeter Array (ALMA). It was also detected in the comet 67P/Churyumov–Gerasimenko (67P/C-G) using the Rosetta Orbiter Spectrometer for Ion and Neutral Analysis (ROSINA) instrument on the Rosetta spacecraft.[13] The detections reveal that chloromethane can be formed in star-forming regions before planets or life is formed.[citation needed]
A smaller amount of chloromethane is produced by treating a mixture of methane with chlorine at elevated temperatures. This method, however, also produces more highly chlorinated compounds such as dichloromethane, chloroform, and carbon tetrachloride. For this reason, methane chlorination is usually only practiced when these other products are also desired. This chlorination method also cogenerates hydrogen chloride, which poses a disposal problem.[5]
CH4 + Cl2 → CH3Cl + HCl
CH3Cl + Cl2 → CH2Cl2 + HCl
CH2Cl2 + Cl2 → CHCl3 + HCl
CHCl3 + Cl2 → CCl4 + HCl
Dispersion in the environment
Most of the methyl chloride present in the environment ends up being released to the atmosphere. After being released into the air, the atmospheric lifetime of this substance is about 10 months with multiple natural sinks, such as ocean, transport to the stratosphere, soil, etc.[17][18][19]
On the other hand, when the methyl chloride emitted is released to water, it will be rapidly lost by volatilization. The half-life of this substance in terms of volatilization in the river, lagoon and lake is 2.1 h, 25 h and 18 days, respectively.[20][21]
The amount of methyl chloride in the stratosphere is estimated to be 2×106 tonnes per year, representing 20–25% of the total amount of chlorine that is emitted to the stratosphere annually.[22][23]
Chloromethane was a widely used refrigerant, but its use has been discontinued. It was particularly dangerous among the common refrigerants of the 1930s due to its combination of toxicity, flammability and lack of odor as compared with other toxic refrigerants such as sulfur dioxide and ammonia.[24] Chloromethane was also once used for producing lead-based gasoline additives (tetramethyllead).
Safety
Inhalation of chloromethane gas produces central nervous system effects similar to alcohol intoxication. The TLV is 50 ppm and the MAC is the same. Prolonged exposure may have mutagenic effects.[5]
^ a b c d eRossberg, M.; Lendle, W.; Pfleiderer, G.; Tögel, A.; Dreher, E. L.; Langer, E.; Rassaerts, H.; Kleinschmidt, P.; Strack, H.; Cook, R.; Beck, U.; Lipper, K.-A.; Torkelson, T.R.; Löser, E.; Beutel, K.K.; Mann, T. (2006). "Chlorinated Hydrocarbons". Ullmann's Encyclopedia of Industrial Chemistry. Weinheim: Wiley-VCH. doi:10.1002/14356007.a06_233.pub2. ISBN 3527306730.
^Gribble, Gordon (2023). Kinghorn, A. Douglas.; Falk, Heinz; Gibbons, Simon; Asakawa, Yoshinori; Liu, Ji-Kai; Dirsch, Verena M. (eds.). Naturally Occurring Organohalogen Compounds. Progress in the Chemistry of Organic Natural Products. Switzerland: Springer Nature. ISBN 978-3-031-26629-4.
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^Ni X, Hager LP (1999). "Expression of Batis maritima Methyl Chloride Transferase in Escherichia coli". Proc Natl Acad Sci USA. 96 (7): 3611–5. Bibcode:1999PNAS...96.3611N. doi:10.1073/pnas.96.7.3611. PMC 22342. PMID 10097085.
^Lobert, Jurgen; Keene, Willian; Yevich, Jennifer (1999). "Global chlorine emissions from biomass burning: Reactive Chlorine Emissions Inventory". Journal of Geophysical Research: Atmospheres. 104 (D7): 8373–8389. Bibcode:1999JGR...104.8373L. doi:10.1029/1998JD100077.
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^Zhang W, Jiao Y, Zhu R, Rhew RC (2020). "Methyl Chloride and Methyl Bromide Production and Consumption in Coastal Antarctic Tundra Soils Subject to Sea Animal Activities". Environmental Science & Technology. 54 (20): 13354–13363. Bibcode:2020EnST...5413354Z. doi:10.1021/acs.est.0c04257. PMID 32935983. S2CID 221745138.
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