Chloromethane

Chloromethane
	Stereo, skeletal formula of chloromethane with all explicit hydrogens added
Ball and stick model of chloromethane	Spacefill model of chloromethane
Names
	Preferred IUPAC name Chloromethane
	Other names Refrigerant-40; R-40; Methyl chloride; Monochloromethane;
Identifiers
CAS Number	74-87-3 ;
3D model (JSmol)	Interactive image;
Beilstein Reference	1696839
ChEBI	CHEBI:36014 ;
ChEMBL	ChEMBL117545 ;
ChemSpider	6087 ;
ECHA InfoCard	100.000.744
EC Number	200-817-4;
Gmelin Reference	24898
KEGG	C19446 ;
MeSH	Methyl+Chloride
PubChem CID	6327;
RTECS number	PA6300000;
UNII	A6R43525YO ;
UN number	1063
CompTox Dashboard (EPA)	DTXSID0021541 ;
	InChI InChI=1S/CH3Cl/c1-2/h1H3 Key: NEHMKBQYUWJMIP-UHFFFAOYSA-N ;
	SMILES CCl;
Properties
Chemical formula	CH3Cl
Molar mass	50.49 g·mol−1
Appearance	Colorless gas
Odor	Faint, sweet odor
Density	1.003 g/mL (-23.8 °C, liquid) 2.3065 g/L (0 °C, gas)
Melting point	−97.4 °C (−143.3 °F; 175.8 K)
Boiling point	−23.8 °C (−10.8 °F; 249.3 K)
Solubility in water	5.325 g/L
log P	1.113
Vapor pressure	506.09 kPa (at 20 °C (68 °F))
Henry's law; constant (kH)	940 nmol/(Pa⋅kg)
Magnetic susceptibility (χ)	−32.0·10−6 cm3/mol
Structure
Coordination geometry	Tetragonal
Molecular shape	Tetrahedron
Dipole moment	1.9 D
Thermochemistry
Std molar; entropy (S⦵298)	234.36 J/(K⋅mol)
Std enthalpy of; formation (ΔfH⦵298)	−83.68 kJ/mol
Std enthalpy of; combustion (ΔcH⦵298)	−764.5–−763.5 kJ/mol
Hazards
	GHS labelling:
Pictograms
Signal word	Danger
Hazard statements	H220, H351, H373
Precautionary statements	P210, P281, P410+P403
NFPA 704 (fire diamond)	2 4 0
Flash point	−20 °C (−4 °F; 253 K)
Autoignition; temperature	625 °C (1,157 °F; 898 K)
Explosive limits	8.1–17.4%
	Lethal dose or concentration (LD, LC):
LD50 (median dose)	150–180 mg/kg (oral, rat); 5.3 mg/L (4 h, inhalation, rat)
LC50 (median concentration)	72,000 ppm (rat, 30 min); 2200 ppm (mouse, 6 h); 2760 ppm (mammal, 4 h); 2524 ppm (rat, 4 h)
LCLo (lowest published)	20,000 ppm (guinea pig, 2 h); 14,661 ppm (dog, 6 h)
	NIOSH (US health exposure limits):
PEL (Permissible)	TWA 100 ppm C 200 ppm 300 ppm (5-minute maximum peak in any 3 hours)
REL (Recommended)	Ca
IDLH (Immediate danger)	Ca [2000 ppm]
Related compounds
Related alkanes	Chloroiodomethane; Bromochloromethane; Dibromochloromethane;
Related compounds	2-Chloroethanol
Supplementary data page
	Chloromethane (data page)
	Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). verify (what is ?) Infobox references

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]

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.^[10] 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.^[10]^[11]

Sugarcane and the emission of methyl chloride

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]}

Production

Chloromethane (originally called "chlorohydrate of methylene") was among the earliest organochlorine compounds to be discovered when it was synthesized by French chemists Jean-Baptiste Dumas and Eugène-Melchior Péligot in 1835 by boiling a mixture of methanol, sulfuric acid, and sodium chloride.^[15] This method is the forerunner for that used today, which uses hydrogen chloride instead of sulfuric acid and sodium chloride.^[16]

Chloromethane is produced commercially by treating methanol with hydrochloric acid or hydrogen chloride, according to the chemical equation:^[5]

CH₃OH + HCl → CH₃Cl + H₂O

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]

Uses

Large scale use of chloromethane is for the production of dimethyldichlorosilane and related organosilicon compounds.^[5] These compounds arise via the direct process. The relevant reactions are (Me = CH₃):

x MeCl + Si → Me₃SiCl, Me₂SiCl₂, MeSiCl₃, Me₄Si₂Cl₂, ...

Dimethyldichlorosilane (Me₂SiCl₂) is of particular value as a precursor to silicones, but trimethylsilyl chloride (Me₃SiCl) and methyltrichlorosilane (MeSiCl₃) are also valuable. 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, e.g. the production of methylcellulose. 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.

Obsolete applications

Chloromethane was widely used as a refrigerant during the 1920s and 1930s, before being replaced by safer alternatives such as chlorofluorocarbons and hydrofluorocarbons. In the late 1920s, some manufacturers promoted methyl chloride as a safer and less odorous option compared to sulfur dioxide and ammonia.^[24]^[25]^[26] However, a series of fatal leaks in 1928 and 1929 raised serious concerns related to its toxicity and flammability. Although chloromethane has a faint sweet odor, its subtle scent made leaks difficult to detect. To address this issue, acrolein was later added as a nasal-irritating tracer, enhancing leak detection and serving as a warning mechanism.^[24]^[25]

Chloromethane was also once used for producing the lead-based gasoline additives tetramethyllead and tetraethyllead.^[27]^[28]^[29]

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]

References

^ ^a ^b ^c ^d ^e ^f ^g ^h ⁱ ^j ^k Record in the GESTIS Substance Database of the Institute for Occupational Safety and Health
^ International Union of Pure and Applied Chemistry (2014). Nomenclature of Organic Chemistry: IUPAC Recommendations and Preferred Names 2013. The Royal Society of Chemistry. p. 1033. doi:10.1039/9781849733069. ISBN 978-0-85404-182-4.
^ ^a ^b ^c ^d ^e NIOSH Pocket Guide to Chemical Hazards. "#0403". National Institute for Occupational Safety and Health (NIOSH).
^ ^a ^b "Methyl chloride". Immediately Dangerous to Life or Health Concentrations (IDLH). National Institute for Occupational Safety and Health (NIOSH).
^ ^a ^b ^c ^d ^e Rossberg, 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.
^ Scarratt MG, Moore RM (1996). "Production of Methyl Chloride and Methyl Bromide in Laboratory Cultures of Marine Phytoplankton". Mar Chem. 54 (3–4): 263–272. Bibcode:1996MarCh..54..263S. 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): 311–320. Bibcode:1998MarCh..59..311S. 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): 103–108. Bibcode:2001ESPR....8..103L. doi:10.1007/BF02987302. PMID 11400635. S2CID 570389.
^ ^a ^b 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. Bibcode:1998PNAS...9512866N. 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. 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.
^ "ALMA and Rosetta Detect Freon-40 in Space".
^ "ALMA and Rosetta Detect Freon-40 in Space - Dashing Hopes that Molecule May be Marker of Life". eso.org. Retrieved 3 October 2017.
^ Crochard (París); Arago, François; Gay-Lussac, Joseph Louis (1835). Annales de chimie et de physique (in French). Chez Crochard.
^ "Chloromethane". American Chemical Society. Retrieved 2022-05-13.
^ Fabian P, Borchers R, Leifer R, Subbaraya BH, Lal S, Boy M (1996). "Global stratospheric distribution of halocarbons". Atmospheric Environment. 30 (10/11): 1787–1796. Bibcode:1996AtmEn..30.1787F. doi:10.1016/1352-2310(95)00387-8.
^ 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.
^ Carpenter LJ, Reimann S, Burkholder JB, Clerbaux C, Hall BD, Hossaini R, Laube JC, Yvon-Lewis SA (2014). "Update on ODSs and Other Gases of Interest to the Montreal Protocol". WMO (World Meteorological Organization), Scientific Assessment of Ozone Depletion: 2014, Global Ozone Research and Monitoring Project.
^ Lyman, Warren; Rosenblatt, David; Reehl, William (1982). Handbook of chemical property estimation methods. McGraw-Hill. ISBN 9780070391758.
^ Agency for Toxic Substances and Disease Registry (1990). Toxicological profile for chloromethane. Agency for Toxic Substances and Disease Registry (ATSDR) Toxicological Profiles. Agency for Toxic Substances and Disease Registry (US). PMID 38412209.
^ Borchers R, Gunawardena R, Rasmussen RA (1994). "Long term trend of selected halogenated hydrocarbons". Ozone in the Troposphere and Stratosphere. NASA: 259–262. 19950004240.
^ Crutzen PJ, Gidel LT (1983). "The tropospheric budgets of the anthropogenic chlorocarbons CO, CH4, CH3Cl and the effect of various NOx sources on tropospheric ozone". Journal of Geophysical Research. 88: 6641–6661. doi:10.1029/JC088iC11p06641.
^ ^a ^b Hand, Greg (4 April 2023). "Refrigeration Was A Wonderful Invention When It Wasn't Trying To Kill You". Cincinnati Magazine. Retrieved 15 May 2025.
^ ^a ^b "Toxicological Profile for Chloromethane". Agency for Toxic Substances and Disease Registry. September 2023. Retrieved 15 May 2025.
^ https://archive.org/details/sim_consumer-reports_1936-07_1_3/page/5/mode/1up Consumers Union Reports, Vol. 1, No. 3, July 1936, p. 5.
^ "Technical Bulletin - Health Effects Information Methyl Chloride" (PDF). Oregon Department of Human Services. March 1992. Retrieved 3 August 2025.
^ Seyferth, Dietmar (1 December 2003). "The Rise and Fall of Tetraethyllead. 2". Organometallics. 22 (25): 5154–5178. doi:10.1021/om030621b. ISSN 0276-7333. Retrieved 3 August 2025.
^ "Acute Exposure Guideline Levels for Selected Airborne Chemicals: Volume 12 - Methyl Chloride: Acute Exposure Guideline Levels". National Academies Press. 27 April 2012. Retrieved 3 August 2025.