Wikipedia

Dichloromethane

(Redirected from Methylene Chloride)
"Di-clo" redirects here. For the anti-inflammatory drug trade named Diclo, see Diclofenac.

Dichloromethane (DCM, methylene chloride, or methylene bichloride) is an organochlorine compound with the formula CH2Cl2. This colorless, volatile liquid with a chloroform-like, sweet odor is widely used as a solvent. Although it is not miscible with water, it is slightly polar, and miscible with many organic solvents.[12]

Dichloromethane
Names
Preferred IUPAC name
Dichloromethane
Other names
Methylene bichloride; Methylene chloride gas; Methylene dichloride; Solmethine; Narkotil; Solaesthin; Di-clo; Refrigerant-30; Freon-30; R-30; DCM; MDC
Identifiers
3D model (JSmol)
ChEBI
ChEMBL
ChemSpider
ECHA InfoCard 100.000.763 Edit this at Wikidata
EC Number
  • 200-838-9
KEGG
RTECS number
  • PA8050000
UNII
UN number 1593
  • InChI=1S/CH2Cl2/c2-1-3/h1H2 checkY
    Key: YMWUJEATGCHHMB-UHFFFAOYSA-N checkY
  • InChI=1/CH2Cl2/c2-1-3/h1H2
    Key: YMWUJEATGCHHMB-UHFFFAOYAG
  • ClCCl
Properties
CH2Cl2
Molar mass 84.93 g·mol−1
Appearance Colorless liquid
Odor Faint, chloroform-like[1]
Density 1.3266 g/cm3 (20 °C)[2]
Melting point −96.7 °C (−142.1 °F; 176.5 K)
Boiling point 39.6 °C (103.3 °F; 312.8 K)
decomposes at 720 °C[3]
39.75 °C (103.55 °F; 312.90 K)
at 760 mmHg[4]
25.6 g/L (15 °C)
17.5 g/L (25 °C)
15.8 g/L (30 °C)
5.2 g/L (60 °C)[3]
Solubility Miscible in ethyl acetate, alcohol, hexanes, benzene, CCl4, diethyl ether, CHCl3
log P 1.19[5]
Vapor pressure 0.13 kPa (−70.5 °C)
2 kPa (−40 °C)
19.3 kPa (0 °C)
57.3 kPa (25 °C)[6]
79.99 kPa (35 °C)[3]
3.25 L·atm/mol[4]
−46.6·10−6 cm3/mol
1.4244 (20 °C)[4][7]
Viscosity 0.43 cP (20 °C)[4]
0.413 cP (25 °C)
Structure
1.6 D
Thermochemistry
102.3 J/(mol·K)[6]
174.5 J/(mol·K)[6]
−124.3 kJ/mol[6]
-454.0 kJ/mol (from standard enthalpies of formation)[6]
Hazards
Occupational safety and health (OHS/OSH):
Eye hazards
 Irritant
GHS labelling:[7]
GHS07: Exclamation mark GHS08: Health hazard
Warning
H315, H319, H335, H336, H351, H373
P261, P281, P305+P351+P338
NFPA 704 (fire diamond)
NFPA 704 four-colored diamondHealth 2: Intense or continued but not chronic exposure could cause temporary incapacitation or possible residual injury. E.g. chloroformFlammability 1: Must be pre-heated before ignition can occur. Flash point over 93 °C (200 °F). E.g. canola oilInstability 0: Normally stable, even under fire exposure conditions, and is not reactive with water. E.g. liquid nitrogenSpecial hazards (white): no code
2
1
0
Flash point None, but can form flammable vapor-air mixtures above ≈100 °C[8]
556 °C (1,033 °F; 829 K)
Explosive limits 13%-23%[1]
Lethal dose or concentration (LD, LC):
1.25 g/kg (rats, oral)
2 g/kg (rabbits, oral)[3]
24,929 ppm (rat, 30 min)
14,400 ppm (mouse, 7 h)[10]
5000 ppm (guinea pig, 2 h)
10,000 ppm (rabbit, 7 h)
12,295 ppm (cat, 4.5 h)
14,108 ppm (dog, 7 h)[10]
NIOSH (US health exposure limits):
PEL (Permissible)
 25 ppm over 8 hours (time-weighted average), 125 ppm over 15 minutes (STEL)[1][9]
REL (Recommended)
 Ca[1]
IDLH (Immediate danger)
 Ca [2300 ppm][1]
Legal status
Supplementary data page
Dichloromethane (data page)
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
checkY verify (what is checkY☒N ?)

Occurrence

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Natural sources of dichloromethane include oceanic sources, macroalgae, wetlands, and volcanoes.[13] However, the majority of dichloromethane in the environment is the result of industrial emissions.[13]

Production

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DCM is produced by treating either chloromethane or methane with chlorine gas at 400–500 °C. At these temperatures, both methane and chloromethane undergo a series of reactions producing progressively more chlorinated products. In this way, an estimated 400,000 tons were produced in the US, Europe, and Japan in 1993.[12]

CH4 + Cl2 → CH3Cl + HCl
CH3Cl + Cl2 → CH2Cl2 + HCl
CH2Cl2 + Cl2 → CHCl3 + HCl
CHCl3 + Cl2 → CCl4 + HCl

The output of these processes is a mixture of chloromethane, dichloromethane, chloroform, and carbon tetrachloride as well as hydrogen chloride as a byproduct. These compounds are separated by distillation.

DCM was first prepared in 1839 by the French chemist Henri Victor Regnault (1810–1878), who isolated it from a mixture of chloromethane and chlorine that had been exposed to sunlight.[14]

Uses

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DCM's volatility and ability to dissolve a wide range of organic compounds makes it a useful solvent for many chemical processes.[12] In the food industry, it is used to decaffeinate coffee and tea as well as to prepare extracts of hops and other flavourings.[15][16] Its volatility has led to its use as an aerosol spray propellant and as a blowing agent for polyurethane foams.

Specialized uses

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Near IR absorption spectrum of dichloromethane showing complicated overlapping overtones of mid IR absorption features

The chemical compound's low boiling point allows the chemical to function in a heat engine that can extract mechanical energy from small temperature differences. An example of a DCM heat engine is the drinking bird. The toy works at room temperature.[17] It is also used as the fluid in jukebox displays and holiday bubble lights that have a colored bubbling tube above a lamp as a source of heat and a small amount of rock salt to provide thermal mass and a nucleation site for the phase changing solvent.

DCM chemically welds certain plastics. For example, it is used to seal the casing of electric meters. Often sold as a main component of plastic welding adhesives, it is also used extensively by model building hobbyists for joining plastic components together. It is commonly referred to as "Di-clo".

It is used in the garment printing industry for removal of heat-sealed garment transfers.

DCM is used in the material testing field of civil engineering; specifically it is used during the testing of bituminous materials as a solvent to separate the binder from the aggregate of an asphalt or macadam to allow the testing of the materials.[18]

Dichloromethane extract of Asparagopsis taxiformis, a seaweed fodder for cattle, has been found to reduce their methane emissions by 79%.[19]

It has been used as the principal component of various paint and lacquer strippers, although its use is now restricted in the EU and many such products now use benzyl alcohol as a safer alternative.

Chemical reactions

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Dichloromethane is widely used as a solvent in part because it is relatively inert. It does participate in reactions with certain strong nucleophiles however. Tert-butyllithium deprotonates DCM:[20]

H2CCl2 + RLi → HCCl2Li + RH

Methyllithium reacts with methylene chloride to give chlorocarbene:[citation needed]

CH2Cl2 + CH3Li → CHCl + CH4 + LiCl

Although DCM is a common solvent in organic chemistry laboratories and is commonly assumed to be inert, it does react with some amines and triazoles.[21] Tertiary amines can react with DCM to form quaternary chloromethyl chloride salts via the Menshutkin reaction.[22] Secondary amines can react with DCM to yield an equilibrium of iminium chlorides and chloromethyl chlorides, which can react with a second equivalent of the secondary amine to form aminals.[23] At increased temperatures, pyridines including DMAP, react with DCM to form methylene bispyridinium dichlorides.[24] Hydroxybenzotriazole and related reagents used in peptide coupling react with DCM in the presence of triethylamine, forming acetals.[25]

Toxicity

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Serious health risks are associated with DCM, despite being one of the least toxic simple chlorohydrocarbons. Its high volatility makes it an inhalation hazard.[26][27] It can also be absorbed through the skin.[1][28] Symptoms of acute overexposure to dichloromethane via inhalation include difficulty concentrating, dizziness, fatigue, nausea, headaches, numbness, weakness, and irritation of the upper respiratory tract and eyes. More severe consequences can include suffocation, loss of consciousness, coma, and death.[1][28]

DCM is also metabolized to carbon monoxide potentially leading to carbon monoxide poisoning.[29] Acute exposure by inhalation has resulted in optic neuropathy[30] and hepatitis.[31] Prolonged skin contact can result in DCM dissolving some of the fatty tissues in skin, resulting in skin irritation or chemical burns.[32]

It may be carcinogenic, as it has been linked to cancer of the lungs, liver, and pancreas in laboratory animals.[33] Other animal studies showed breast cancer and salivary gland cancer. Research is not yet clear as to what levels may be carcinogenic to humans.[1][28] DCM crosses the placenta but fetal toxicity in women who are exposed to it during pregnancy has not been proven.[34] In animal experiments, it was fetotoxic at doses that were maternally toxic but no teratogenic effects were seen.[33]

In people with pre-existing heart problems, exposure to DCM can cause abnormal heart rhythms and/or heart attacks, sometimes without any other symptoms of overexposure.[28] People with existing liver, nervous system, or skin problems may worsen after exposure to methylene chloride.[9]

Regulation

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In many countries, products containing DCM must carry labels warning of its health risks. Concerns about its health effects have led to a search for alternatives in many of its applications.[12][35]

In the European Union, the Scientific Committee on Occupational Exposure Limit Values (SCOEL) recommends an occupational exposure limit for DCM of 100 ppm (8-hour time-weighted average) and a short-term exposure limit of 200 ppm for a 15-minute period.[36] The European Parliament voted in 2009 to ban the use of DCM in paint-strippers for consumers and many professionals,[37] with the ban taking effect in December 2010.[38]

In February 2013, the US Occupational Safety and Health Administration (OSHA) and the National Institute for Occupational Safety and Health warned that at least 14 bathtub refinishers have died since 2000 from DCM exposure. These workers had been working alone, in poorly ventilated bathrooms, with inadequate or no respiratory protection, and no training about the hazards of DCM.[9][28][39] OSHA has since then issued a DCM standard.[40]

On March 15, 2019, the US Environmental Protection Agency (EPA) issued a final rule to prohibit the manufacture (including importing and exporting), processing, and distribution of DCM in all paint removers for consumer use, effective in 180 days. However, it does not affect other products containing DCM, including many consumer products not intended for paint removal. On April 20, 2023, the EPA proposed a widespread ban on the production of DCM with some exceptions for military and industrial uses.[41] On April 30, 2024, the EPA finalized a ban on most commercial uses of DCM, which mainly banned its application for stripping paint and degreasing surfaces but allowed for some remaining commercial applications, such as chemical production.[42]

Environmental effects

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CH2Cl2 measured by the Advanced Global Atmospheric Gases Experiment (AGAGE) in the lower atmosphere (troposphere) at stations around the world. Abundances are given as pollution free monthly mean mole fractions in parts-per-trillion.

Dichloromethane is not classified as an ozone-depleting substance by the Montreal Protocol.[43] The US Clean Air Act does not regulate dichloromethane as an ozone depleter.[44] Dichloromethane has been classified as a very short-lived substance (VSLS). Despite their short atmospheric lifetimes of less than 0.5 year, VSLSs can contribute to stratospheric ozone depletion, particularly if emitted in regions where rapid transport to the stratosphere occurs.[45] Atmospheric abundances of dichloromethane have been increasing in recent years.

See also

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References

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  1. ^ a b c d e f g h NIOSH Pocket Guide to Chemical Hazards. "#0414". National Institute for Occupational Safety and Health (NIOSH).
  2. ^ Haynes, William M., ed. (2011). CRC Handbook of Chemistry and Physics (92nd ed.). Boca Raton, FL: CRC Press. p. 3.164. ISBN 1-4398-5511-0.
  3. ^ a b c d Properties of Dichloromethane. chemister.ru
  4. ^ a b c d CID 6344 from PubChem
  5. ^ "Dichloromethane_msds".
  6. ^ a b c d e Methylene chloride in Linstrom, Peter J.; Mallard, William G. (eds.); NIST Chemistry WebBook, NIST Standard Reference Database Number 69, National Institute of Standards and Technology, Gaithersburg (MD) (retrieved 2014-05-26)
  7. ^ a b Sigma-Aldrich Co., Dichloromethane. Retrieved on 2014-05-26.
  8. ^ "Real time measurement of dichloromethane containing mixtures" (PDF). Health & Safety Laboratory. Retrieved 5 August 2015.
  9. ^ a b c "Methylene Chloride Hazards for Bathtub Refinishers". OSHA-NIOSH Hazard Alert 2013-110. OSHA and NIOSH. Retrieved 22 January 2015.
  10. ^ a b "methylene chloride". Immediately Dangerous to Life or Health Concentrations (IDLH). National Institute for Occupational Safety and Health (NIOSH).
  11. ^ Anvisa (2023-03-31). "RDC Nº 784 - Listas de Substâncias Entorpecentes, Psicotrópicas, Precursoras e Outras sob Controle Especial" [Collegiate Board Resolution No. 784 - Lists of Narcotic, Psychotropic, Precursor, and Other Substances under Special Control] (in Brazilian Portuguese). Diário Oficial da União (published 2023-04-04). Archived from the original on 2023-08-03. Retrieved 2023-08-16.
  12. ^ a b c d Rossberg, M. et al. (2006) "Chlorinated Hydrocarbons" in Ullmann's Encyclopedia of Industrial Chemistry, Wiley-VCH, Weinheim. doi:10.1002/14356007.a06_233.pub2.
  13. ^ a b Gribble, Gordon W. (2009). Naturally Occurring Organohalogen Compounds. Springer. ISBN 978-3211993248.
  14. ^ Regnault, V. (1839) "De l'action du chlore sur les éthers hydrochloriques de l'alcool et de l'esprit de bois, et de plusieurs points de la théorie des éthers" (On the action of chlorine on the hydrochloric ethers of ethanol and methanol, and on several points of the theory of ethers), Annales de chimie et physique, series 2, 71 : 353–431; see especially: "Seconde partie. De l'action du chlore sur l'éther hydrochlorique de l'esprit de bois" (Second part. On the action of chlorine on the hydrochloric ether of methanol [i.e., chloromethane]), pages 377–380. Regnault gives dichloromethane the name éther hydrochlorique monochloruré (monochlorinated hydrochloric ether). Note: Regnault gives the empirical formula for dichloromethane as C2H4Cl4 because during that era, chemists used incorrect atomic masses.
    Reprinted in German in:
  15. ^ Office of Environmental Health Hazard Assessment (September 2000). "Dichloromethane" (PDF). Public Health Goals for Chemicals in Drinking Water. California Environmental Protection Agency. Retrieved June 5, 2016.[permanent dead link‍]
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  18. ^ Shell Bitumen (2003-09-25). The Shell Bitumen Handbook. Thomas Telford. ISBN 978-0-7277-3220-0.
  19. ^ Machado, Lorenna; Magnusson, Marie; Paul, Nicholas; Tomkins, Nigel (2016). "Identification of bioactives from the red seaweed Asparagopsis taxiformis that promote antimethanogenic activity in vitro". Journal of Applied Phycology. 28 (5): 3117–3126. Bibcode:2016JAPco..28.3117M. doi:10.1007/s10811-016-0830-7.
  20. ^ Matteson, Donald S.; Majumdar, Debesh (1983). "Homologation of boronic esters to .alpha.-chloro boronic esters". Organometallics. 2 (11): 1529–1535. doi:10.1021/om50005a008.
  21. ^ Mills, John E.; Maryanoff, Cynthia A.; Cosgrove, Robin M.; Scott, Lorraine; McComsey, David F. (1984). "The Reaction of Amines with Methylene Chloride. A Brief Review". Organic Preparations and Procedures International. 16 (2): 97–114. doi:10.1080/00304948409356172. ISSN 0030-4948.
  22. ^ Dunlap, Lee E.; Olson, David E. (2018-05-31). "Reaction of N , N -Dimethyltryptamine with Dichloromethane Under Common Experimental Conditions". ACS Omega. 3 (5): 4968–4973. doi:10.1021/acsomega.8b00507. ISSN 2470-1343. PMC 5981293. PMID 29876537.
  23. ^ Mills, John E.; Maryanoff, Cynthia A.; McComsey, David F.; Stanzione, Robin C.; Scott, Lorraine (1987). "Reaction of amines with methylene chloride. Evidence for rapid aminal formation from N-methylenepyrrolidinium chloride and pyrrolidine". The Journal of Organic Chemistry. 52 (9): 1857–1859. doi:10.1021/jo00385a038. ISSN 0022-3263.
  24. ^ Rudine, Alexander B.; Walter, Michael G.; Wamser, Carl C. (2010-06-18). "Reaction of Dichloromethane with Pyridine Derivatives under Ambient Conditions". The Journal of Organic Chemistry. 75 (12): 4292–4295. doi:10.1021/jo100276m. ISSN 0022-3263. PMID 20469919.
  25. ^ Ji, Jian-guo; Zhang, De-yi; Ye, Yun-hua; Xing, Qi-yi (1998). "Studies on the reactions of HOBt, HOOBt, HOSu with dichloroalkane solvents". Tetrahedron Letters. 39 (36): 6515–6516. doi:10.1016/S0040-4039(98)01406-3.
  26. ^ Rioux JP, Myers RA (1988). "Methylene chloride poisoning: a paradigmatic review". J Emerg Med. 6 (3): 227–238. doi:10.1016/0736-4679(88)90330-7. PMID 3049777.
  27. ^ CDC (2012). "Fatal Exposure to Methylene Chloride Among Bathtub Refinishers — United States, 2000–2011". MMWR. 61 (7): 119–122. PMID 22357403.
  28. ^ a b c d e Hall, Ronald M. (4 February 2013). "Dangers of Bathtub Refinishing". National Institute for Occupational Safety and Health. Retrieved 21 January 2015.
  29. ^ Fagin J, Bradley J, Williams D (1980). "Carbon monoxide poisoning secondary to inhaling methylene chloride". Br Med J. 281 (6253): 1461. doi:10.1136/bmj.281.6253.1461. PMC 1714874. PMID 7437838.
  30. ^ Kobayashi A, Ando A, Tagami N, Kitagawa M, Kawai E, Akioka M, Arai E, Nakatani T, Nakano S, Matsui Y, Matsumura M (2008). "Severe optic neuropathy caused by dichloromethane inhalation". J Ocul Pharmacol and Ther. 24 (6): 607–612. doi:10.1089/jop.2007.0100. PMID 19049266.
  31. ^ Cordes DH, Brown WD, Quinn KM (1988). "Chemically induced hepatitis after inhaling organic solvents". West J Med. 148 (4): 458–460. PMC 1026148. PMID 3388849.
  32. ^ Wells GG, Waldron HA (1984). "Methylene chloride burns". Br J Ind Med. 41 (3): 420. doi:10.1136/oem.41.3.420. PMC 1009322. PMID 6743591.
  33. ^ a b USDHHS. "Toxicological Profile for Methylene Chloride" (PDF). Retrieved 2006-09-10.
  34. ^ Bell BP, Franks P, Hildreth N, Melius J (1991). "Methylene chloride exposure and birthweight in Monroe County, New York". Environ Res. 55 (1): 31–9. Bibcode:1991ER.....55...31B. doi:10.1016/S0013-9351(05)80138-0. PMID 1855488.
  35. ^ "Summary of Regulations Controlling Air Emissions from Paint Stripping and Miscellaneous Surface Coating Operations" (PDF). NESHAP (Subpart HHHHHH). US Environmental Protection Agency. April 2008. Archived from the original (PDF) on 2016-11-23.
  36. ^ Recommendation from the Scientific Committee on Occupational Exposure Limits for methylene chloride (dichloromethane) (PDF). European Chemicals Agency (Report). June 2009. Retrieved 2023-09-07.
  37. ^ "EU Banning Most DCM Paint Strippers". PaintSquare News. 2012-03-09. Retrieved 2023-09-07.
  38. ^ "COMMISSION REGULATION (EU) No 276/2010 (Official Journal of the European Union, L 86/7)". 2010-04-01. Retrieved 2012-02-07.
  39. ^ OSHA QuickTakes, February 1, 2013;
  40. ^ Methylene Chloride. Occupational Safety & Health Administration. osha.gov
  41. ^ "EPA Proposes Ban on All Consumer, Most Industrial and Commercial Uses of Methylene Chloride to Protect Public Health". 2023-04-20.
  42. ^ "Biden-Harris Administration Finalizes Ban on Most Uses of Methylene Chloride, Protecting Workers and Communities from Fatal Exposure". 2024-04-30.
  43. ^ United States Environmental Protection Agency (2015-07-17). "Ozone-Depleting Substances". Retrieved April 20, 2018.
  44. ^ United States Environmental Protection Agency (October 1995). "Questions and Answers on Ozone-Depleting Solvents and Their Substitutes". Retrieved April 20, 2018.
  45. ^ World Meteorological Organization, United Nations Environmental Program (15 April 2020). "Scientific Assessment of Ozone Depletion: 2018". Archived from the original on December 18, 2023.
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