Chloromethane

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, odorless, flammable gas. Methyl chloride is a crucial reagent in industrial chemistry, although it is rarely present in consumer products.[5]

Chloromethane
Ball and stick model of chloromethane
Spacefill model of chloromethane
Names
IUPAC name
Chloromethane[1]
Other names
  • Refrigerant-40
  • R-40[2]
  • Methyl chloride[2]
  • Monochloromethane[2]
Identifiers
3D model (JSmol)
1696839
ChEBI
ChEMBL
ChemSpider
ECHA InfoCard 100.000.744
EC Number
  • 200-817-4
24898
KEGG
MeSH Methyl+Chloride
RTECS number
  • PA6300000
UNII
UN number 1063
Properties
CH3Cl
Molar mass 50.49 g·mol−1
Appearance Colorless gas
Odor Faint, sweet odor[3]
Density 1.003 g/mL (-23.8 °C, liquid)[2] 2.3065 g/L (0 °C, gas)[2]
Melting point −97.4 °C (−143.3 °F; 175.8 K)[2]
Boiling point −23.8 °C (−10.8 °F; 249.3 K)[2]
5.325 g L−1
log P 1.113
Vapor pressure 506.09 kPa (at 20 °C (68 °F))
940 nmol Pa−1 kg−1
-32.0·10−6 cm3/mol
Structure
Tetragonal
Tetrahedron
1.9 D
Thermochemistry
234.36 J K−1 mol−1
−83.68 kJ mol−1
−764.5–−763.5 kJ mol−1
Hazards
Main hazards carcinogen
Safety data sheet See: data page
GHS pictograms
GHS Signal word Danger
H220, H351, H373
P210, P281, P410+403
NFPA 704 (fire diamond)
Flammability code 4: Will rapidly or completely vaporize at normal atmospheric pressure and temperature, or is readily dispersed in air and will burn readily. Flash point below 23 °C (73 °F). E.g. propaneHealth code 2: Intense or continued but not chronic exposure could cause temporary incapacitation or possible residual injury. E.g. chloroformReactivity code 0: Normally stable, even under fire exposure conditions, and is not reactive with water. E.g. liquid nitrogenSpecial hazards (white): no code
4
2
0
Flash point −20 °C (−4 °F; 253 K)[2]
625 °C (1,157 °F; 898 K)[2]
Explosive limits 8.1%-17.4%[3]
Lethal dose or concentration (LD, LC):
1800 mg/kg (oral, rat)[2]
5.3 mg/L/4 h (inhalation, rat)[2]
72,000 ppm (rat, 30 min)
2200 ppm (mouse, 6 hr)
2760 ppm (mammal, 4 hr)
2524 ppm (rat, 4 hr)[4]
20,000 ppm (guinea pig, 2 hr)
14,661 ppm (dog, 6 hr)[4]
NIOSH (US health exposure limits):
PEL (Permissible)
 TWA 100 ppm C 200 ppm 300 ppm (5-minute maximum peak in any 3 hours)[3]
REL (Recommended)
 Ca[3]
IDLH (Immediate danger)
 Ca [2000 ppm][3]
Related compounds
Related alkanes
Related compounds
 2-Chloroethanol
Supplementary data page
Refractive index (n),
Dielectric constant (εr), etc.
Thermodynamic
data
 Phase behaviour
solid–liquid–gas
UV, IR, NMR, MS
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
N verify (what is YN ?)
Infobox references

Occurrence

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

Freon-40 has been detected in space.[14]

Production

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.

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]

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.[15][16][17]

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.[18][19]

The amount of methyl chloride in the stratosphere is estimated to be 2 x 106 tonnes per year, representing 20-25% of the total amount of chlorine that is emitted to the stratosphere annually.[20][21]

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 (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 a widely used refrigerant, but its use has been discontinued. 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]

References
  1. "Methyl Chloride - Compound Summary". PubChem Compound. USA: National Center for Biotechnology Information. 26 March 2005. Retrieved 23 June 2012.
  2. Record in the GESTIS Substance Database of the Institute for Occupational Safety and Health
  3. NIOSH Pocket Guide to Chemical Hazards. "#0403". National Institute for Occupational Safety and Health (NIOSH).
  4. "Methyl chloride". Immediately Dangerous to Life and Health Concentrations (IDLH). National Institute for Occupational Safety and Health (NIOSH).
  5. Rossberg, M.; Lendle, W.; Pfleiderer, G.; Tögel, A.; Dreher, E. L.; Langer, E.; Rassaerts, H.; Kleinschmidt, P.; Strack (2006). "Chlorinated Hydrocarbons". Ullmann's Encyclopedia of Industrial Chemistry. Weinheim: Wiley-VCH. doi:10.1002/14356007.a06_233.pub2.
  6. Lim, Y.-K.; Phang, S.-M.; Rahman, N. Abdul; Sturges, W. T.; Malin, G. (2017). "REVIEW: Halocarbon Emissions from Marine Phytoplankton and Climate Change". Int. J. Environ. Sci. Technol.: 1355–1370. doi:10.1007/s13762-016-1219-5. S2CID 99300836.
  7. 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. doi:10.1016/0304-4203(96)00036-9.
  8. 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. doi:10.1016/S0304-4203(97)00092-3.
  9. Laturnus F (2001). "Marine Macroalgae in Polar Regions as Natural Sources for Volatile Organohalogens". Environ Sci Pollut Res. 8 (2): 103–108. doi:10.1007/BF02987302. PMID 11400635. S2CID 570389.
  10. 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.
  11. 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.
  12. 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. Retrieved 11 March 2019.
  13. "ALMA and Rosetta Detect Freon-40 in Space".
  14. "ALMA and Rosetta Detect Freon-40 in Space - Dashing Hopes that Molecule May be Marker of Life". eso.org. Retrieved 3 October 2017.
  15. 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.
  16. 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.
  17. 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.
  18. Lyman, Warren; Rosenblatt, David; Reehl, Wiliam (1982). Handbook of chemical property estimation methods.
  19. Agency for Toxic Substances and Disease Registry (ATSDR) (1990). "Toxicological profile for chloromethane". Cite journal requires |journal= (help)
  20. Borchers R, Gunawardena R, Rasmussen RA (1994). "Long term trend of selected halogenated hydrocarbons": 259–262. Cite journal requires |journal= (help)
  21. 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.
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