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
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]
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.
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]
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
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:[19]
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.[20] Tertiary amines can react with DCM to form quaternary chloromethyl chloride salts via the Menshutkin reaction.[21] 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.[22] At increased temperatures, pyridines including DMAP, react with DCM to form methylene bispyridinium dichlorides.[23]Hydroxybenzotriazole and related reagents used in peptide coupling react with DCM in the presence of triethylamine, forming acetals.[24]
It may be carcinogenic, as it has been linked to cancer of the lungs, liver, and pancreas in laboratory animals.[32] 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][27] DCM crosses the placenta but fetal toxicity in women who are exposed to it during pregnancy has not been proven.[33] In animal experiments, it was fetotoxic at doses that were maternally toxic but no teratogenic effects were seen.[32]
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.[27] People with existing liver, nervous system, or skin problems may worsen after exposure to methylene chloride.[9]
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.[12][34]
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.[40] 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.[41]
The EPA (Environmental Protection Agency) finalized a ban on most uses of dichloromethane in April 2024. This ban, which took effect on July 8, 2024, prohibits most industrial and commercial uses of the chemical, including its use in paint removers for consumer use.
New U.S. Environmental Protection Agency (EPA) regulations under the Toxic Substances Control Act (TSCA) have significantly lowered permissible exposure limits for methylene chloride to 2 ppm TWA and 16 ppm STEL, far below OSHA's existing standard (29 CFR 1910.1052). For remaining permitted uses, this necessitates a Workplace Chemical Protection Program (WCPP) requiring initial and periodic exposure monitoring at these much stricter levels to protect worker health. This EPA Final Rule (89 FR 39806) drives the new compliance requirements for monitoring.
Environmental effects
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.[42] The US Clean Air Act does not regulate dichloromethane as an ozone depleter.[43] 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.[44] Atmospheric abundances of dichloromethane have been increasing in recent years.
^ abcdeMethylene 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)
^ abcdRossberg, M. et al. (2006) "Chlorinated Hydrocarbons" in Ullmann's Encyclopedia of Industrial Chemistry, Wiley-VCH, Weinheim. doi:10.1002/14356007.a06_233.pub2.
^ abGribble, Gordon W. (2009). Naturally Occurring Organohalogen Compounds. Springer. ISBN978-3211993248.
^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:
^ abcdeHall, Ronald M. (4 February 2013). "Dangers of Bathtub Refinishing". National Institute for Occupational Safety and Health. Retrieved 21 January 2015.
^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. PMID19049266.
