Chloromethane

Chloromethane, also called methyl chloride, Refrigerant-40, R-40 or HCC 40, is a chemical compound of the group of organic compounds called haloalkanes. It was once widely used as a refrigerant. It is a colorless extremely flammable gas with a mildly sweet odor, which is, however, detected at possibly toxic levels. Due to concerns about its toxicity, it is no longer present in consumer products. Chloromethane was first synthesized by the French chemists Jean-Baptiste Dumas and Eugene Peligot in 1835 by boiling a mixture of methanol, sulfuric acid, and sodium chloride. This method is similar to that used today.

Occurrence

Chloromethane is the most abundant organohalogen, anthropogenic or natural, in the atmosphere.

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.^[5]^[6] An extensive study of 30 species of polar macroalgae revealed the release of significant amounts of CH₃Cl in only Gigartina skottsbergii and Gymnogongrus antarcticus.^[7]

Biogenesis

The salt marsh plant Batis maritima contains the enzyme methyl chloride transferase that catalyzes the synthesis of CH₃Cl from S-adenosine-L-methionine and chloride.^[8] This protein has been purified and expressed in E. coli, and seems to be present in other organisms such as white rot fungi (Phellinus pomaceus), red algae (Endocladia muricata), and the ice plant (Mesembryanthemum crystallinum), each of which is a known CH₃Cl producer.^[8]^[9]

Production

Large amounts of chloromethane are produced naturally in the oceans by the action of sunlight on biomass and chlorine in sea foam. However, all chloromethane that is used in industry is produced synthetically.

Most chloromethane is prepared by reacting methanol with hydrogen chloride, according to the chemical equation

CH₃OH + HCl → CH₃Cl + H₂O

This can be carried out either by bubbling hydrogen chloride gas through boiling methanol with or without a zinc chloride catalyst, or by passing combined methanol and hydrogen chloride vapors over an alumina catalyst at 350 °C (662 °F).

A smaller amount of chloromethane is produced by heating a mixture of methane and chlorine to over 400 °C (752 °F). However, this method also results in more highly chlorinated compounds such as methylene chloride and chloroform and is usually only used when these other products are also desired.

Further reaction of chloromethane with chlorine can produce dichloromethane, trichloromethane (known as chloroform) and tetrachloromethane (also known as carbon tetrachloride).

Uses

Chloromethane was a widely used refrigerant, but its use has been discontinued due to its toxicity and flammability. Chloromethane was also once used for producing lead-based gasoline additives (tetramethyllead).

The most important use of chloromethane today is as a chemical intermediate in the production of silicone polymers. Smaller quantities are used as a solvent in the manufacture of butyl rubber and in petroleum refining.

Chloromethane is employed as a methylating and chlorinating agent in organic chemistry. It is also used in a variety of other fields: as an extractant for greases oils and resins, as a propellant and blowing agent in polystyrene foam production, as a local anesthetic, as an intermediate in drug manufacturing, as a catalyst carrier in low-temperature polymerization, as a fluid for thermometric and thermostatic equipment, and as a herbicide.

Safety

Inhalation of chloromethane gas produces central nervous system effects similar to drug intoxication. Exposure may cause drowsiness, dizziness, or confusion and difficulty breathing, walking or speaking may occur. At higher concentrations, paralysis, seizures, and coma can result.

In case of ingestion, nausea and vomiting may occur. Skin contact, when in the form of a refrigerated liquid, may result in frostbite. Contact with the eyes may result in dim vision, and widely dilated pupils that react slowly to changes in light.

Chronic exposure to chloromethane has been linked to birth defects in mice. In humans, exposure to chloromethane during pregnancy may cause the fetus' lower spinal column, pelvis, and legs to form incorrectly, but this has not been conclusively demonstrated.

References

↑ "Methyl Chloride - Compound Summary". PubChem Compound. USA: National Center for Biotechnology Information. 26 March 2005. Retrieved 23 June 2012.
1 2 3 4 5 6 7 8 9 10 11 Record in the GESTIS Substance Database of the IFA
1 2 3 4 5 "NIOSH Pocket Guide to Chemical Hazards #0403". National Institute for Occupational Safety and Health (NIOSH).
1 2 "Methyl chloride". Immediately Dangerous to Life and Health. National Institute for Occupational Safety and Health (NIOSH).
↑ Scarratt MG, Moore RM (1996). "Production of Methyl Chloride and Methyl Bromide in Laboratory Cultures of Marine Phytoplankton". Mar Chem 54 (3–4): 263. doi:10.1016/0304-4203(96)00036-9.
↑ Scarratt MG, Moore RM (1998). "Production of Methyl Bromide and Methyl Chloride in Laboratory Cultures of Marine Phytoplankton II". Mar Chem 59 (3–4): 311. doi:10.1016/S0304-4203(97)00092-3.
↑ Laturnus F (2001). "Marine Macroalgae in Polar Regions as Natural Sources for Volatile Organohalogens". Environ Sci Pollut Res 8 (2): 103. doi:10.1007/BF02987302.
1 2 Ni X, Hager LP (1998). "cDNA Cloning of Batis maritima Methyl Chloride Transferase and Purification of the Enzyme". Proc Natl Acad Sci USA 95 (22): 12866–71. doi:10.1073/pnas.95.22.12866. PMC 23635. PMID 9789006.
↑ Ni X, Hager LP (1999). "Expression of Batis maritima Methyl Chloride Transferase in Escherichia coli". Proc Natl Acad Sci USA 96 (7): 3611–5. doi:10.1073/pnas.96.7.3611. PMC 22342. PMID 10097085.

External links

Halomethanes

Monosubstituted	CH₃F CH₃Cl CH₃Br CH₃I

Disubstituted	CH₂F₂ CH₂ClF CH₂BrF CH₂FI CH₂Cl₂ CH₂BrCl CH₂ClI CH₂Br₂ CH₂BrI CH₂I₂

Trisubstituted	CHF₃ CHClF₂ CHBrF₂ CHF₂I CHCl₂F CHBrClF CHClFI CHBr₂F CHBrFI CHFI₂ CHCl₃ CHBrCl₂ CHCl₂I CHBr₂Cl CHBrClI CHClI₂ CHBr₃ CHBr₂I CHBrI₂ CHI₃

Tetrasubstituted	CF₄ CClF₃ CBrF₃ CF₃I CCl₂F₂ CBrClF₂ CClF₂I CBr₂F₂ CBrF₂I CF₂I₂ CCl₃F CBrCl₂F CCl₂FI CBr₂ClF C*BrClFI CClFI₂ CBr₃F CBr₂FI CBrFI₂ CFI₃ CCl₄ CBrCl₃ CCl₃I CBr₂Cl₂ CBrCl₂I CCl₂I₂ CBr₃Cl CBr₂ClI CBrClI₂ CClI₃ CBr₄ CBr₃I CBr₂I₂ CBrI₃ CI₄

* Chiral compound.

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