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Dichloromethane ( DCM, methylene chloride, or methylene bichloride) is an organochlorine compound with the chemical formula . 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 .Rossberg, M. et al. (2006) "Chlorinated Hydrocarbons" in Ullmann's Encyclopedia of Industrial Chemistry, Wiley-VCH, Weinheim. .
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: "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.,), 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.
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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 Bitumen or macadam to allow the testing of the materials.
Dichloromethane extract of Asparagopsis taxiformis, a seaweed fodder for cattle, has been found to reduce their methane emissions by 79%.
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.
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. Tertiary amines can react with DCM to form quaternary chloromethyl chloride salts via the Menshutkin reaction. 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 . At increased temperatures, including DMAP, react with DCM to form methylene bispyridinium dichlorides. Hydroxybenzotriazole and related reagents used in peptide coupling react with DCM in the presence of triethylamine, forming .
DCM is also metabolized to carbon monoxide potentially leading to carbon monoxide poisoning. Acute exposure by inhalation has resulted in optic neuropathy and hepatitis. Prolonged skin contact can result in DCM dissolving some of the Adipose tissue in skin, resulting in skin irritation or chemical burns.
It may be , as it has been linked to cancer of the Lung cancer, Liver cancer, and pancreas in laboratory animals. 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. In animal experiments, it was fetotoxic at doses that were maternally toxic but no teratology effects were seen.
In people with pre-existing heart problems, exposure to DCM can cause Heart arrhythmia and/or , sometimes without any other symptoms of overexposure. People with existing liver, nervous system, or skin problems may worsen after exposure to methylene chloride.
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. The European Parliament voted in 2009 to ban the use of DCM in paint-strippers for consumers and many professionals, with the ban taking effect in December 2010.
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. OSHA QuickTakes, February 1, 2013; OSHA has since then issued a DCM standard. 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. 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.
Regulation
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.
Environmental effects
Dichloromethane is not classified as an ozone-depleting substance by the Montreal Protocol. The US Clean Air Act does not regulate dichloromethane as an ozone depletion. 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. Atmospheric abundances of dichloromethane have been increasing in recent years.
See also
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