:Dichloromethane

Natural sources of dichloromethane include oceanic sources, macroalgae, wetlands, and volcanoes.{{cite book | author = Gribble, Gordon W. | title = Naturally Occurring Organohalogen Compounds |date=2009 | publisher = Springer|isbn=978-3211993248}} However, the majority of dichloromethane in the environment is the result of industrial emissions.

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.

:{{chem2|CH4 + Cl2 → CH3Cl + HCl}}

:{{chem2|CH3Cl + Cl2 → CH2Cl2 + HCl}}

:{{chem2|CH2Cl2 + Cl2 → CHCl3 + HCl}}

:{{chem2|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.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: [https://archive.today/20131023140514/http://babel.hathitrust.org/cgi/pt?id=nyp.33433062741982;view=1up;seq=385 "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:

• {{cite journal | last1 = Regnault | first1 = V. | title = Ueber die Einwirkung des Chlors auf die Chlorwasserstoffäther des Alkohols und Holzgeistes und über mehrere Punkte der Aethertheorie | journal = Annalen der Chemie und Pharmacie | volume = 33 | issue = 3 | pages = 310–334 | year = 1840 | doi = 10.1002/jlac.18400330306 | url = https://books.google.com/books?id=4Uw9AAAAcAAJ&pg=PA310 }} See p. 328.
• {{cite journal | last1 = Regnault | first1 = V. | title = Ueber die Wirkung des Chlors auf den Chlorwasserstoffäther des Alkohols und des Holzgeistes, so wie über mehrere Puncte der Aethertheorie | journal = Journal für Praktische Chemie | volume = 19 | pages = 193–218 | year = 1840 | doi = 10.1002/prac.18400190134 | url = https://zenodo.org/record/1427780 }} See p. 210.

DCM's volatility and ability to dissolve a wide range of organic compounds makes it a useful solvent for many chemical processes. In the food industry, it is used to decaffeinate coffee and tea as well as to prepare extracts of hops and other flavourings.{{cite web|url=http://oehha.ca.gov/media/downloads/pesticides/report/dcm.pdf |title=Dichloromethane |date=September 2000 |publisher=California Environmental Protection Agency |access-date=June 5, 2016 |author=Office of Environmental Health Hazard Assessment |work=Public Health Goals for Chemicals in Drinking Water }}{{dead link|date=December 2016 |bot=InternetArchiveBot |fix-attempted=yes }}{{cite web |last1=James2014-04-09T00:00:00+01:00 |first1=Emily |title=Dichloromethane |url=https://www.chemistryworld.com/podcasts/dichloromethane/7254.article |website=Chemistry World |language=en}} Its volatility has led to its use as an aerosol spray propellant and as a blowing agent for polyurethane foams.

Image:Dichloromethane near IR spectrum.png 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.{{cite book |last=Perelman |first=Yakov |url=https://archive.org/details/PhysicsForEntertainmentBook2 |title=Physics for Entertainment |date=1972 |publisher=Hyperion Books |isbn=978-1401309213 |volume=2 |pages=175–178 |orig-year=1936}} [https://archive.org/download/PhysicsForEntertainmentBook2] [http://booksnote.com/phydownload?bdn=PhysicsforEntertainmentBook2.pdf] 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.{{cite book|author = Shell Bitumen|title = The Shell Bitumen Handbook|url = https://books.google.com/books?id=bA1tIkRJL8kC&pg=PA277|isbn = 978-0-7277-3220-0|date = 2003-09-25| publisher=Thomas Telford |author-link = Royal Dutch Shell}}

Dichloromethane extract of Asparagopsis taxiformis, a seaweed fodder for cattle, has been found to reduce their methane emissions by 79%.{{cite journal|title=Identification of bioactives from the red seaweed Asparagopsis taxiformis that promote antimethanogenic activity in vitro|first1=Lorenna |last1=Machado|first2=Marie |last2=Magnusson|first3=Nicholas |last3=Paul|first4=Nigel |last4=Tomkins|year=2016|journal=Journal of Applied Phycology|volume=28|issue=5|pages=3117–3126|doi=10.1007/s10811-016-0830-7|doi-access=free|bibcode=2016JAPco..28.3117M }}

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.

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:{{cite journal |doi=10.1021/om50005a008|title=Homologation of boronic esters to .alpha.-chloro boronic esters |year=1983 |last1=Matteson |first1=Donald S. |last2=Majumdar |first2=Debesh |journal=Organometallics |volume=2 |issue=11 |pages=1529–1535 }}

:{{Chem2|H2CCl2 + RLi -> HCCl2Li + RH}}

Methyllithium reacts with methylene chloride to give chlorocarbene:{{cn|date=May 2024}}

:{{chem2|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.{{Cite journal |last1=Mills |first1=John E. |last2=Maryanoff |first2=Cynthia A. |last3=Cosgrove |first3=Robin M. |last4=Scott |first4=Lorraine |last5=McComsey |first5=David F. |title=The Reaction of Amines with Methylene Chloride. A Brief Review |date=1984 |url=http://www.tandfonline.com/doi/abs/10.1080/00304948409356172 |journal=Organic Preparations and Procedures International |language=en |volume=16 |issue=2 |pages=97–114 |doi=10.1080/00304948409356172 |issn=0030-4948|url-access=subscription }} Tertiary amines can react with DCM to form quaternary chloromethyl chloride salts via the Menshutkin reaction.{{Cite journal |last1=Dunlap |first1=Lee E. |last2=Olson |first2=David E. |date=2018-05-31 |title=Reaction of N , N -Dimethyltryptamine with Dichloromethane Under Common Experimental Conditions |journal=ACS Omega |language=en |volume=3 |issue=5 |pages=4968–4973 |doi=10.1021/acsomega.8b00507 |issn=2470-1343 |pmc=5981293 |pmid=29876537}} 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.{{Cite journal |last1=Mills |first1=John E. |last2=Maryanoff |first2=Cynthia A. |last3=McComsey |first3=David F. |last4=Stanzione |first4=Robin C. |last5=Scott |first5=Lorraine |date=1987 |title=Reaction of amines with methylene chloride. Evidence for rapid aminal formation from N-methylenepyrrolidinium chloride and pyrrolidine |url=https://pubs.acs.org/doi/abs/10.1021/jo00385a038 |journal=The Journal of Organic Chemistry |language=en |volume=52 |issue=9 |pages=1857–1859 |doi=10.1021/jo00385a038 |issn=0022-3263|url-access=subscription }} At increased temperatures, pyridines including DMAP, react with DCM to form methylene bispyridinium dichlorides.{{Cite journal |last1=Rudine |first1=Alexander B. |last2=Walter |first2=Michael G. |last3=Wamser |first3=Carl C. |date=2010-06-18 |title=Reaction of Dichloromethane with Pyridine Derivatives under Ambient Conditions |url=https://pubs.acs.org/doi/10.1021/jo100276m |journal=The Journal of Organic Chemistry |language=en |volume=75 |issue=12 |pages=4292–4295 |doi=10.1021/jo100276m |pmid=20469919 |issn=0022-3263|url-access=subscription }} Hydroxybenzotriazole and related reagents used in peptide coupling react with DCM in the presence of triethylamine, forming acetals.{{Cite journal |last1=Ji |first1=Jian-guo |last2=Zhang |first2=De-yi |last3=Ye |first3=Yun-hua |last4=Xing |first4=Qi-yi |date=1998 |title=Studies on the reactions of HOBt, HOOBt, HOSu with dichloroalkane solvents |url=https://linkinghub.elsevier.com/retrieve/pii/S0040403998014063 |journal=Tetrahedron Letters |language=en |volume=39 |issue=36 |pages=6515–6516 |doi=10.1016/S0040-4039(98)01406-3|url-access=subscription }}

Serious health risks are associated with DCM, despite being one of the least toxic simple chlorohydrocarbons. Its high volatility makes it an inhalation hazard.{{cite journal |vauthors=Rioux JP, Myers RA | title = Methylene chloride poisoning: a paradigmatic review | journal = J Emerg Med | volume = 6 | issue = 3 | pages = 227–238 | year = 1988 | pmid = 3049777 | doi = 10.1016/0736-4679(88)90330-7 }}{{cite journal|author = CDC |title = Fatal Exposure to Methylene Chloride Among Bathtub Refinishers — United States, 2000–2011 |journal = MMWR|volume = 61|issue = 7|pages = 119–122|year = 2012|pmid = 22357403 |url=https://www.cdc.gov/mmwr/preview/mmwrhtml/mm6107a2.htm}} It can also be absorbed through the skin.{{cite web |url = http://blogs.cdc.gov/niosh-science-blog/2013/02/04/bathtub-refinishing/ |title = Dangers of Bathtub Refinishing |date = 4 February 2013 |first = Ronald M. |last = Hall |access-date = 21 January 2015 |publisher = National Institute for Occupational Safety and Health}}

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.{{PGCH|0414}}

DCM is also metabolized to carbon monoxide potentially leading to carbon monoxide poisoning.{{cite journal |vauthors=Fagin J, Bradley J, Williams D | title = Carbon monoxide poisoning secondary to inhaling methylene chloride | journal = Br Med J | volume = 281 | issue = 6253 | pages = 1461 | year = 1980 | pmid = 7437838 | pmc = 1714874 | doi = 10.1136/bmj.281.6253.1461 }} Acute exposure by inhalation has resulted in optic neuropathy{{cite journal |vauthors=Kobayashi A, Ando A, Tagami N, Kitagawa M, Kawai E, Akioka M, Arai E, Nakatani T, Nakano S, Matsui Y, Matsumura M | title = Severe optic neuropathy caused by dichloromethane inhalation | journal = J Ocul Pharmacol and Ther | volume = 24 | issue = 6 | pages = 607–612 | year = 2008 | pmid = 19049266 | doi = 10.1089/jop.2007.0100 }} and hepatitis.{{cite journal |vauthors=Cordes DH, Brown WD, Quinn KM | title = Chemically induced hepatitis after inhaling organic solvents | journal = West J Med | volume = 148 | issue = 4 | pages = 458–460 | year = 1988 | pmid = 3388849 | pmc = 1026148 }} Prolonged skin contact can result in DCM dissolving some of the fatty tissues in skin, resulting in skin irritation or chemical burns.{{cite journal |vauthors=Wells GG, Waldron HA | title = Methylene chloride burns | journal = Br J Ind Med | volume = 41 | issue = 3 | pages = 420 | year = 1984 | pmid = 6743591 | pmc = 1009322 | doi = 10.1136/oem.41.3.420 }}

It may be carcinogenic, as it has been linked to cancer of the lungs, liver, and pancreas in laboratory animals.{{cite web|author=USDHHS|title=Toxicological Profile for Methylene Chloride|url=http://www.atsdr.cdc.gov/toxprofiles/tp14.pdf|access-date=2006-09-10}} Other animal studies showed breast cancer and salivary gland cancer. Research is not yet clear as to what levels may be carcinogenic to humans. DCM crosses the placenta but fetal toxicity in women who are exposed to it during pregnancy has not been proven.{{cite journal |vauthors=Bell BP, Franks P, Hildreth N, Melius J | title = Methylene chloride exposure and birthweight in Monroe County, New York | journal = Environ Res | volume = 55 | issue = 1 | pages = 31–9 | year = 1991 | pmid = 1855488 | doi = 10.1016/S0013-9351(05)80138-0 | bibcode = 1991ER.....55...31B }} In animal experiments, it was fetotoxic at doses that were maternally toxic but no teratogenic effects were seen.

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. People with existing liver, nervous system, or skin problems may worsen after exposure to methylene chloride.

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.{{cite web |title=Summary of Regulations Controlling Air Emissions from Paint Stripping and Miscellaneous Surface Coating Operations |work=NESHAP (Subpart HHHHHH) |date=April 2008 |publisher=US Environmental Protection Agency |url=http://www.epa.gov/ttn/atw/area/paint_stripb.pdf |archive-url=https://web.archive.org/web/20161123143224/https://www3.epa.gov/ttn/atw/area/paint_stripb.pdf |archive-date=2016-11-23}}

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.{{cite report |url=https://echa.europa.eu/documents/10162/35144386/099_dichloromethane_oel_en.pdf |title=Recommendation from the Scientific Committee on Occupational Exposure Limits for methylene chloride (dichloromethane) |date=June 2009 |website=European Chemicals Agency |access-date=2023-09-07}} The European Parliament voted in 2009 to ban the use of DCM in paint-strippers for consumers and many professionals,{{cite web |url=https://www.paintsquare.com/news/view/?7328 |title=EU Banning Most DCM Paint Strippers |author= |date=2012-03-09 |website=PaintSquare News |access-date=2023-09-07}} with the ban taking effect in December 2010.{{cite web |url=http://eur-lex.europa.eu/LexUriServ/LexUriServ.do?uri=OJ:L:2010:086:0007:0012:EN:PDF |title=COMMISSION REGULATION (EU) No 276/2010 (Official Journal of the European Union, L 86/7) |date=2010-04-01 |access-date=2012-02-07}}

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.{{cite web |url = http://www.osha.gov/dts/hazardalerts/methylene_chloride_hazard_alert.html |title = Methylene Chloride Hazards for Bathtub Refinishers |work = OSHA-NIOSH Hazard Alert 2013-110 |publisher = OSHA and NIOSH |access-date = 22 January 2015}}[http://www.osha.gov/as/opa/quicktakes/qt02012013.html OSHA QuickTakes], February 1, 2013; OSHA has since then issued a DCM standard.[https://www.osha.gov/pls/oshaweb/owadisp.show_document?p_table=STANDARDS&p_id=10094 Methylene Chloride]. Occupational Safety & Health Administration. osha.gov

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.{{cite web|url= https://www.epa.gov/newsreleases/epa-proposes-ban-all-consumer-most-industrial-and-commercial-uses-methylene-chloride|title=EPA Proposes Ban on All Consumer, Most Industrial and Commercial Uses of Methylene Chloride to Protect Public Health|date=2023-04-20}} 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.{{cite web|url= https://www.epa.gov/newsreleases/biden-harris-administration-finalizes-ban-most-uses-methylene-chloride-protecting|title=Biden-Harris Administration Finalizes Ban on Most Uses of Methylene Chloride, Protecting Workers and Communities from Fatal Exposure |date=2024-04-30}}

File:CH2Cl2_mm.png) 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.{{cite web|url=https://www.epa.gov/ozone-layer-protection/ozone-depleting-substances|author=United States Environmental Protection Agency|title=Ozone-Depleting Substances|date=2015-07-17|access-date=April 20, 2018}} The US Clean Air Act does not regulate dichloromethane as an ozone depleter.{{cite web|url=https://nepis.epa.gov/Exe/tiff2png.cgi/50000S6R.PNG?-r+75+-g+7+D%3A%5CZYFILES%5CINDEX%20DATA%5C95THRU99%5CTIFF%5C00000344%5C50000S6R.TIF|author=United States Environmental Protection Agency|title=Questions and Answers on Ozone-Depleting Solvents and Their Substitutes|date=October 1995|access-date=April 20, 2018}} 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.{{cite web|url=https://public-old.wmo.int/en/resources/library/scientific-assessment-of-ozone-depletion-2018|archive-url=https://web.archive.org/web/20231218174345/https://public-old.wmo.int/en/resources/library/scientific-assessment-of-ozone-depletion-2018|url-status=dead|archive-date=December 18, 2023|author=World Meteorological Organization, United Nations Environmental Program|title=Scientific Assessment of Ozone Depletion: 2018|date=15 April 2020 }} Atmospheric abundances of dichloromethane have been increasing in recent years.

• Deuterated dichloromethane
• Chloromethane
• Trichloromethane
• Tetrachloromethane
• List of organic compounds
• Carbon monoxide-releasing molecules

{{reflist|30em}}

{{Commons category|Dichloromethane}}

• {{ICSC|0058|00}}
• {{PGCH|0414}}
• [http://www.npi.gov.au/substances/dichloromethane/index.html National Pollutant Inventory – Dichloromethane Fact Sheet]
• [https://web.archive.org/web/20121014171614/http://ntp.niehs.nih.gov/ntp/htdocs/LT_rpts/tr306.pdf Dichloromethane at National Toxicology Program]
• [http://www.inchem.org/documents/iarc/vol71/004-dichloromethane.html IARC Summaries & Evaluations Vol. 71 (1999)]
• [http://www.hc-sc.gc.ca/ewh-semt/alt_formats/hecs-sesc/pdf/pubs/contaminants/psl1-lsp1/dichloromethane/dichloromethane-eng.pdf Canadian Environmental Protection Act Priority Substances List Assessment Report]
• [http://www.colby.edu/chemistry/cmp/cmp.html Organic Compounds Database]
• [http://www.chlorinated-solvents.eu Sustainable uses and Industry recommendations]

{{Halomethanes}}

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