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Dichloromethane (DCM or methylene chloride, methylene bichloride) is an
organochlorine compound An organochloride, organochlorine compound, chlorocarbon, or chlorinated hydrocarbon is an organic compound containing at least one covalent bond, covalently bonded atom of chlorine. The chloroalkane class (alkanes with one or more hydrogens subst ...
with the
formula In science, a formula is a concise way of expressing information symbolically, as in a mathematical formula or a ''chemical formula''. The informal use of the term ''formula'' in science refers to the general construct of a relationship betwee ...
. This colorless, volatile liquid with a
chloroform Chloroform, or trichloromethane, is an organic compound with chemical formula, formula Carbon, CHydrogen, HChlorine, Cl3 and a common organic solvent. It is a colorless, strong-smelling, dense liquid produced on a large scale as a precursor to ...
-like, sweet odour is widely used as a solvent. Although it is not
miscible Miscibility () is the property of two substances to mix in all proportions (that is, to fully dissolve in each other at any concentration), forming a homogeneous mixture (a solution). The term is most often applied to liquids but also applies ...
with water, it is slightly
polar Polar may refer to: Geography Polar may refer to: * Geographical pole, either of two fixed points on the surface of a rotating body or planet, at 90 degrees from the equator, based on the axis around which a body rotates * Polar climate, the c ...
, and miscible with many organic solvents.Rossberg, M. ''et al.'' (2006) "Chlorinated Hydrocarbons" in Ullmann's Encyclopedia of Industrial Chemistry, Wiley-VCH, Weinheim. .


Occurrence

Natural sources of dichloromethane include oceanic sources,
macroalgae Seaweed, or macroalgae, refers to thousands of species of macroscopic, multicellular, marine algae. The term includes some types of ''Rhodophyta'' (red), ''Phaeophyta'' (brown) and ''Chlorophyta'' (green) macroalgae. Seaweed species such as k ...
, wetlands, and volcanoes. However, the majority of dichloromethane in the environment is the result of industrial emissions.


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. : : : : The output of these processes is a mixture of chloromethane, dichloromethane,
chloroform Chloroform, or trichloromethane, is an organic compound with chemical formula, formula Carbon, CHydrogen, HChlorine, Cl3 and a common organic solvent. It is a colorless, strong-smelling, dense liquid produced on a large scale as a precursor to ...
, and
carbon tetrachloride Carbon tetrachloride, also known by many other names (such as tetrachloromethane, also IUPAC nomenclature of inorganic chemistry, recognised by the IUPAC, carbon tet in the cleaning industry, Halon-104 in firefighting, and Refrigerant-10 in HVAC ...
as well as hydrogen chloride as a byproduct. These compounds are separated by distillation. DCM was first prepared in 1839 by the
French French (french: français(e), link=no) may refer to: * Something of, from, or related to France ** French language, which originated in France, and its various dialects and accents ** French people, a nation and ethnic group identified with Franc ...
chemist Henri Victor Regnault (1810–1878), who isolated it from a mixture of chloromethane and chlorine that had been exposed to
sunlight Sunlight is a portion of the electromagnetic radiation given off by the Sun, in particular infrared, visible, and ultraviolet light. On Earth, sunlight is scattered and filtered through Earth's atmosphere, and is obvious as daylight when t ...
.


Uses

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 The food industry is a complex, global network of diverse businesses that supplies most of the food consumed by the world's population. The food industry today has become highly diversified, with manufacturing ranging from small, traditiona ...
, it is used to
decaffeinate Decaffeination is the removal of caffeine from coffee beans, cocoa, tea leaves, and other caffeine-containing materials. Decaffeinated drinks contain typically 1–2% of the original caffeine content, and sometimes as much as 20%. Decaffeinated ...
coffee and tea as well as to prepare extracts of
hops Hops are the flowers (also called seed cones or strobiles) of the hop plant ''Humulus lupulus'', a member of the Cannabaceae family of flowering plants. They are used primarily as a bittering, flavouring, and stability agent in beer, to whi ...
and other flavourings. Its volatility has led to its use as an aerosol spray propellant and as a blowing agent for polyurethane foams.


Hydrogen bonding

Methylene chloride is a
Lewis acid A Lewis acid (named for the American physical chemist Gilbert N. Lewis) is a chemical species that contains an empty orbital which is capable of accepting an electron pair from a Lewis base to form a Lewis adduct. A Lewis base, then, is any sp ...
that can
hydrogen bond In chemistry, a hydrogen bond (or H-bond) is a primarily electrostatic force of attraction between a hydrogen (H) atom which is covalently bound to a more electronegative "donor" atom or group (Dn), and another electronegative atom bearing a ...
to electron donors. It is classified as a hard acid and is included in the ECW model. It is a solvent that has been used in many thermodynamic studies of donor-acceptor bonding. The donor hydrogen-bonding corrections of methylene chloride in these thermodynamic studies has been reported.


Specialized uses

The chemical compound's low
boiling point The boiling point of a substance is the temperature at which the vapor pressure of a liquid equals the pressure surrounding the liquid and the liquid changes into a vapor. The boiling point of a liquid varies depending upon the surrounding envir ...
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.
/ref> 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 adhesive Plastic welding is welding for semi-finished plastic materials, and is described in ISO 472 as a process of uniting softened surfaces of materials, generally with the aid of heat (except solvent welding). Welding of thermoplastics is accomplishe ...
s, it is also used extensively by
model building Model building is a hobby and career that involves the creation of physical models either from kits or from materials and components acquired by the builder. The kits contain several pieces that need to be assembled in order to make a final mode ...
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 Macadam is a type of road construction, pioneered by Scottish engineer John Loudon McAdam around 1820, in which crushed stone is placed in shallow, convex layers and compacted thoroughly. A binding layer of stone dust (crushed stone from the o ...
to allow the testing of the materials. Dichloromethane extract of
Asparagopsis taxiformis ''Asparagopsis taxiformis'', (red sea plume or limu kohu) formerly ''A. sanfordiana'', is a species of red algae, with cosmopolitan distribution in tropical to warm temperate waters. Researchers have demonstrated that feeding ruminants a diet c ...
, a seaweed
fodder Fodder (), also called provender (), is any agriculture, agricultural foodstuff used specifically to feed domesticated livestock, such as cattle, domestic rabbit, rabbits, sheep, horses, chickens and pigs. "Fodder" refers particularly to food g ...
for cattle, has been found to reduce their methane emissions by 79%. It has been used as the principal component of paint stripper, but its use for this purpose is now prohibited in the United States and the European Union.


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: : Hydride reagents convert dichloromethane to methyl chloride.


Toxicity

Even though DCM is the least toxic of the simple chlorohydrocarbons, it has serious health risks. Its high volatility makes it an acute inhalation hazard. It can also be absorbed through the skin. Symptoms of acute overexposure to dichloromethane via inhalation include difficulty concentrating, dizziness,
fatigue Fatigue describes a state of tiredness that does not resolve with rest or sleep. In general usage, fatigue is synonymous with extreme tiredness or exhaustion that normally follows prolonged physical or mental activity. When it does not resolve ...
, nausea,
headache Headache is the symptom of pain in the face, head, or neck. It can occur as a migraine, tension-type headache, or cluster headache. There is an increased risk of depression in those with severe headaches. Headaches can occur as a result ...
s, numbness, weakness, and irritation of the upper respiratory tract and
eye Eyes are organs of the visual system. They provide living organisms with vision, the ability to receive and process visual detail, as well as enabling several photo response functions that are independent of vision. Eyes detect light and conv ...
s. More severe consequences can include
suffocation Asphyxia or asphyxiation is a condition of deficient supply of oxygen to the body which arises from abnormal breathing. Asphyxia causes generalized hypoxia, which affects primarily the tissues and organs. There are many circumstances that can i ...
, loss of consciousness,
coma A coma is a deep state of prolonged unconsciousness in which a person cannot be awakened, fails to respond normally to painful stimuli, light, or sound, lacks a normal wake-sleep cycle and does not initiate voluntary actions. Coma patients exhi ...
, and death. DCM is also metabolized by the body to carbon monoxide potentially leading to carbon monoxide poisoning. Acute exposure by inhalation has resulted in
optic neuropathy Optic neuropathy is damage to the optic nerve from any cause. The optic nerve is a bundle of millions of fibers in the retina that sends visual signals to the brain. Damage and death of these nerve cells, or neurons, leads to characteristic featu ...
and hepatitis. Prolonged skin contact can result in DCM dissolving some of the fatty tissues in skin, resulting in skin irritation or chemical burns. It may be carcinogenic, as it has been linked to cancer of the lungs, liver, 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. 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
teratogenic Teratology is the study of abnormalities of physiological development in organisms during their life span. It is a sub-discipline in medical genetics which focuses on the classification of congenital abnormalities in dysmorphology. The related t ...
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.


Regulation

In many countries, products containing DCM must carry labels warning of its health risks. In February 2013, the U.S. 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
In the European Union, the European Parliament voted in 2009 to ban the use of DCM in paint-strippers for consumers and many professionals."EU Banning Most DCM Paint Strippers,"
PaintSquare News, retrieved 1/5/14.
The ban took effect in December 2010. In Europe, the
Scientific Committee on Occupational Exposure Limit Values The Scientific Committee on Occupational Exposure Limit Values (SCOEL) is a committee of the European Commission established in 1995 to advise on occupational exposure limits for chemicals in the workplace within the framework of: * Directive 98/24 ...
(SCOEL) recommends for DCM an occupational exposure limit (8 h time-weighted average) of 100 ppm and a short-term exposure limit (15 min) of 200 ppm. Concerns about its health effects have led to a search for alternatives in many of these applications. On March 15, 2019, the U.S. Environmental Protection Agency (EPA) issued a final rule to prohibit the manufacture (including importing and exporting), processing, and distribution of methylene chloride in all paint removers for consumer use, effective in 180 days. However, it does not affect other products containing methylene chloride, including many consumer products not intended for paint removal.


Environmental effects


Ozone

Dichloromethane is not classified as an ozone-depleting substance by the Montreal Protocol. The U.S. Clean Air Act does not regulate dichloromethane as an
ozone depleter Ozone depletion consists of two related events observed since the late 1970s: a steady lowering of about four percent in the total amount of ozone in Earth's atmosphere, and a much larger springtime decrease in stratospheric ozone (the ozone lay ...
. Recent research shows that dichloromethane and other halogenated very short-lived substances (VSLSs), despite their short atmospheric lifetimes of less than 0.5 year, 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. Ozone concentrations measured at the
midlatitudes The middle latitudes (also called the mid-latitudes, sometimes midlatitudes, or moderate latitudes) are a spatial region on Earth located between the Tropic of Cancer (latitudes 23°26'22") to the Arctic Circle (66°33'39"), and Tropic of Capric ...
from the ground up through the stratosphere from 1998 to 2016 have declined by 2.2
Dobson unit The Dobson unit (DU) is a unit of measurement of the amount of a trace gas in a vertical column through the Earth's atmosphere. It originated, and continues to be primarily used in respect to, atmospheric ozone, whose total column amount, usually te ...
s, just under 1%. The reasons for this decline are unclear, but one unverified hypothesis is the presence of short-lived substances such as dichloromethane in the lower atmosphere.


See also

* Chloromethane * Trichloromethane * Tetrachloromethane * List of chemical compounds *
List of organic compounds This is a list of common chemical compounds with chemical formulae and CAS numbers, indexed by formula.This complements alternative listing at list of inorganic compounds. There is no complete list of chemical compounds since by nature the list ...
*
Carbon monoxide-releasing molecules Carbon monoxide-releasing molecules (CORMs) are chemical compounds designed to release controlled amounts of carbon monoxide (CO). CORMs are being developed as potential therapeutic agents to locally deliver CO to cells and tissues, thus overcomin ...


References


External links

* *
National Pollutant Inventory – Dichloromethane Fact Sheet

Dichloromethane at National Toxicology Program



Canadian Environmental Protection Act Priority Substances List Assessment ReportSustainable uses and Industry recommendations
{{Authority control Chloroalkanes Halomethanes Aerosol propellants Hazardous air pollutants Refrigerants Halogenated solvents IARC Group 2A carcinogens Fetotoxicants Testicular toxicants Halogen-containing natural products GABAA receptor positive allosteric modulators Sweet-smelling chemicals Ozone depletion