Dichloromethane (DCM, methylene chloride, or methylene bichloride) is an organochlorine compound 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 betwe ...

. This colorless, volatile liquid with a

chloroform Chloroform, or trichloromethane (often abbreviated as TCM), is an organochloride with the formula and a common solvent. It is a volatile, colorless, sweet-smelling, dense liquid produced on a large scale as a precursor to refrigerants and po ...

-like, sweet odor is widely used as a

solvent A solvent (from the Latin language, Latin ''wikt:solvo#Latin, solvō'', "loosen, untie, solve") is a substance that dissolves a solute, resulting in a Solution (chemistry), solution. A solvent is usually a liquid but can also be a solid, a gas ...

. 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). Such substances are said to be miscible (etymologically ...

with water, it is slightly polar, and miscible with many organic

s.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 scale, macroscopic, Multicellular organism, multicellular, ocean, marine algae. The term includes some types of ''Rhodophyta'' (red), ''Brown algae, Phaeophyta'' (brown) and ...

, wetlands, and volcanoes. However, the majority of dichloromethane in the environment is the result of industrial emissions.

Production

DCM is produced by

treating In law and politics, treating is the act of serving food, drink, and other refreshments to influence people for political gain, often shortly before an election. In various countries, treating is considered a form of corruption, and is illegal ...

either chloromethane or

methane Methane ( , ) is a chemical compound with the chemical formula (one carbon atom bonded to four hydrogen atoms). It is a group-14 hydride, the simplest alkane, and the main constituent of natural gas. The abundance of methane on Earth makes ...

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,

, and

carbon tetrachloride Carbon tetrachloride, also known by many other names (such as carbon tet for short and tetrachloromethane, also IUPAC nomenclature of inorganic chemistry, recognised by the IUPAC), is a chemical compound with the chemical formula CCl4. It is a n ...

as well as hydrogen chloride as a byproduct. These compounds are separated by

distillation Distillation, also classical distillation, is the process of separating the component substances of a liquid mixture of two or more chemically discrete substances; the separation process is realized by way of the selective boiling of the mixt ...

. DCM was first prepared in 1839 by the French chemist

Henri Victor Regnault Henri Victor Regnault (21 July 1810 – 19 January 1878) was a French chemist and physicist best known for his careful measurements of the thermal properties of gases. He was an early thermodynamicist and was mentor to William Thomson in ...

(1810–1878), who isolated it from a mixture of chloromethane and

chlorine Chlorine is a chemical element; it has Symbol (chemistry), symbol Cl and atomic number 17. The second-lightest of the halogens, it appears between fluorine and bromine in the periodic table and its properties are mostly intermediate between ...

that had been exposed to

sunlight Sunlight is the portion of the electromagnetic radiation which is emitted by the Sun (i.e. solar radiation) and received by the Earth, in particular the visible spectrum, visible light perceptible to the human eye as well as invisible infrare ...

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, traditional, ...

, it is used to decaffeinate

coffee Coffee is a beverage brewed from roasted, ground coffee beans. Darkly colored, bitter, and slightly acidic, coffee has a stimulating effect on humans, primarily due to its caffeine content, but decaffeinated coffee is also commercially a ...

and

tea Tea is an aromatic beverage prepared by pouring hot or boiling water over cured or fresh leaves of '' Camellia sinensis'', an evergreen shrub native to East Asia which probably originated in the borderlands of south-western China and nor ...

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 whic ...

and other flavourings. Its volatility has led to its use as an aerosol spray propellant and as a blowing agent for

polyurethane foam Polyurethane foam is a solid polymeric foam based on polyurethane chemistry. As a specialist synthetic fibre, synthetic material with highly diverse applications, polyurethane foams are primarily used for thermal insulation and as a cushioning mat ...

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 envi ...

allows the chemical to function in a

heat engine A heat engine is a system that transfers thermal energy to do mechanical or electrical work. While originally conceived in the context of mechanical energy, the concept of the heat engine has been applied to various other kinds of energy, pa ...

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 A jukebox is a partially automated music-playing device, usually a coin-operated machine, that plays a user-selected song from a self-contained media library. Traditional jukeboxes contain records, compact discs, or digital files, and allow user ...

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 Civil engineering is a regulation and licensure in engineering, professional engineering discipline that deals with the design, construction, and maintenance of the physical and naturally built environment, including public works such as roads ...

; specifically it is used during the testing of bituminous materials as a solvent to separate the binder from the aggregate of an

asphalt Asphalt most often refers to: * Bitumen, also known as "liquid asphalt cement" or simply "asphalt", a viscous form of petroleum mainly used as a binder in asphalt concrete * Asphalt concrete, a mixture of bitumen with coarse and fine aggregates, u ...

macadam Macadam is a type of road construction pioneered by Scottish engineer John Loudon McAdam , in which crushed stone is placed in shallow, convex layers and compacted thoroughly. A binding layer of stone dust (crushed stone from the original mat ...

to allow the testing of the materials. Dichloromethane extract of '' Asparagopsis taxiformis'', 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 ...

for cattle, has been found to reduce their

methane emissions Increasing methane emissions are a major contributor to the rising concentration of greenhouse gases in Earth's atmosphere, and are responsible for up to one-third of near-term global heating. During 2019, about 60% (360 million tons) of methane r ...

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 Benzyl alcohol (also known as α-cresol) is an aromatic alcohol with the formula C6H5CH2OH. The benzyl group is often abbreviated "Bn" (not to be confused with "Bz" which is used for benzoyl), thus benzyl alcohol is denoted as BnOH. Benzyl a ...

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 ''tert''-Butyllithium is a chemical compound with the Chemical formula, formula (CH3)3CLi. As an organolithium compound, it has applications in organic synthesis since it is a strong base (chemistry), base, capable of deprotonation, deprotonating ...

deprotonates DCM: :

Methyllithium Methyllithium is the simplest organolithium reagent, with the empirical formula LiCH3. This s-block organometallic compound adopts an oligomeric structure both in solution and in the solid state. This highly reactive compound, invariably used i ...

reacts with methylene chloride to give chlorocarbene: : 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 In organic chemistry, the Menshutkin reaction converts a tertiary amine into a quaternary ammonium salt by reaction with an alkyl halide. Similar reactions occur when tertiary phosphines are treated with alkyl halides. The reaction is the m ...

. 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. At increased temperatures,

pyridine Pyridine is a basic (chemistry), basic heterocyclic compound, heterocyclic organic compound with the chemical formula . It is structurally related to benzene, with one methine group replaced by a nitrogen atom . It is a highly flammable, weak ...

s 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 Triethylamine is the chemical compound with the formula N(CH2CH3)3, commonly abbreviated Et3N. Like triethanolamine and the tetraethylammonium ion, it is often abbreviated TEA. It is a colourless volatile liquid with a strong fishy odor remini ...

, forming

acetal In organic chemistry, an acetal is a functional group with the connectivity . Here, the R groups can be organic fragments (a carbon atom, with arbitrary other atoms attached to that) or hydrogen, while the R' groups must be organic fragments n ...

Toxicity

Serious health risks are associated with DCM, despite being one of the least

toxic Toxicity is the degree to which a chemical substance or a particular mixture of substances can damage an organism. Toxicity can refer to the effect on a whole organism, such as an animal, bacterium, or plant, as well as the effect on a subst ...

simple chlorohydrocarbons. Its high volatility makes it an inhalation hazard. It can also be absorbed through the skin. Symptoms of acute overexposure to dichloromethane via inhalation include difficulty concentrating,

dizziness Dizziness is an imprecise term that can refer to a sense of disorientation in space, vertigo, or lightheadedness. It can also refer to Balance disorder, disequilibrium or a non-specific feeling, such as giddiness or foolishness. Dizziness is a ...

fatigue Fatigue is a state of tiredness (which is not sleepiness), exhaustion or loss of energy. It is a signs and symptoms, symptom of any of various diseases; it is not a disease in itself. Fatigue (in the medical sense) is sometimes associated wit ...

nausea Nausea is a diffuse sensation of unease and discomfort, sometimes perceived as an urge to vomit. It can be a debilitating symptom if prolonged and has been described as placing discomfort on the chest, abdomen, or back of the throat. Over 30 d ...

headache A headache, also known as cephalalgia, 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 (mood), depression in those with severe ...

s, numbness, weakness, and irritation of the upper respiratory tract and

eye An eye is a sensory organ that allows an organism to perceive visual information. It detects light and converts it into electro-chemical impulses in neurons (neurones). It is part of an organism's visual system. In higher organisms, the ey ...

s. More severe consequences can include suffocation,

loss of consciousness Unconsciousness is a state in which a living individual exhibits a complete, or near-complete, inability to maintain an awareness of self and environment or to respond to any human or environmental stimulus. Unconsciousness may occur as the re ...

coma A coma is a deep state of prolonged unconsciousness in which a person cannot be awakened, fails to Nociception, respond normally to Pain, painful stimuli, light, or sound, lacks a normal Circadian rhythm, sleep-wake cycle and does not initiate ...

, and death. DCM is also metabolized to

carbon monoxide Carbon monoxide (chemical formula CO) is a poisonous, flammable gas that is colorless, odorless, tasteless, and slightly less dense than air. Carbon monoxide consists of one carbon atom and one oxygen atom connected by a triple bond. It is the si ...

potentially leading to

carbon monoxide poisoning Carbon monoxide poisoning typically occurs from breathing in carbon monoxide (CO) at excessive levels. Symptoms are often described as " flu-like" and commonly include headache, dizziness, weakness, vomiting, chest pain, and confusion. Large ...

. 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 Hepatitis is inflammation of the liver parenchyma, liver tissue. Some people or animals with hepatitis have no symptoms, whereas others develop yellow discoloration of the skin and whites of the eyes (jaundice), Anorexia (symptom), poor appetite ...

. 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

carcinogen A carcinogen () is any agent that promotes the development of cancer. Carcinogens can include synthetic chemicals, naturally occurring substances, physical agents such as ionizing and non-ionizing radiation, and biologic agents such as viruse ...

ic, as it has been linked to

cancer Cancer is a group of diseases involving Cell growth#Disorders, abnormal cell growth with the potential to Invasion (cancer), invade or Metastasis, spread to other parts of the body. These contrast with benign tumors, which do not spread. Po ...

of the

lungs The lungs are the primary organs of the respiratory system in many animals, including humans. In mammals and most other tetrapods, two lungs are located near the backbone on either side of the heart. Their function in the respiratory syste ...

liver The liver is a major metabolic organ (anatomy), organ exclusively found in vertebrates, which performs many essential biological Function (biology), functions such as detoxification of the organism, and the Protein biosynthesis, synthesis of var ...

, and

pancreas The pancreas (plural pancreases, or pancreata) is an Organ (anatomy), organ of the Digestion, digestive system and endocrine system of vertebrates. In humans, it is located in the abdominal cavity, abdomen behind the stomach and functions as a ...

in laboratory animals. Other animal studies showed

breast cancer Breast cancer is a cancer that develops from breast tissue. Signs of breast cancer may include a Breast lump, lump in the breast, a change in breast shape, dimpling of the skin, Milk-rejection sign, milk rejection, fluid coming from the nipp ...

and salivary gland cancer. Research is not yet clear as to what levels may be carcinogenic to humans. DCM crosses the

placenta The placenta (: placentas or placentae) is a temporary embryonic and later fetal organ that begins developing from the blastocyst shortly after implantation. It plays critical roles in facilitating nutrient, gas, and waste exchange between ...

but

fetal A fetus or foetus (; : fetuses, foetuses, rarely feti or foeti) is the unborn offspring of a viviparous animal that develops from an embryo. Following the embryonic stage, the fetal stage of development takes place. Prenatal development is a ...

toxicity in women who are exposed to it during

pregnancy Pregnancy is the time during which one or more offspring gestation, gestates inside a woman's uterus. A multiple birth, multiple pregnancy involves more than one offspring, such as with twins. Conception (biology), Conception usually occurs ...

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 caused by ...

effects were seen. In people with pre-existing heart problems, exposure to DCM can cause abnormal heart rhythms and/or

heart attack A myocardial infarction (MI), commonly known as a heart attack, occurs when Ischemia, blood flow decreases or stops in one of the coronary arteries of the heart, causing infarction (tissue death) to the heart muscle. The most common symptom ...

s, sometimes without any other symptoms of overexposure. People with existing

nervous system In biology, the nervous system is the complex system, highly complex part of an animal that coordinates its behavior, actions and sense, sensory information by transmitting action potential, signals to and from different parts of its body. Th ...

, or

skin Skin is the layer of usually soft, flexible outer tissue covering the body of a vertebrate animal, with three main functions: protection, regulation, and sensation. Other animal coverings, such as the arthropod exoskeleton, have different ...

problems may worsen after exposure to methylene chloride.

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. In the

European Union The European Union (EU) is a supranational union, supranational political union, political and economic union of Member state of the European Union, member states that are Geography of the European Union, located primarily in Europe. The u ...

, 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 The European Parliament (EP) is one of the two legislative bodies of the European Union and one of its seven institutions. Together with the Council of the European Union (known as the Council and informally as the Council of Ministers), it ...

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 The Occupational Safety and Health Administration (OSHA; ) is a regulatory agency of the United States Department of Labor that originally had federal visitorial powers to inspect and examine workplaces. The United States Congress established ...

(OSHA) and the

National Institute for Occupational Safety and Health The National Institute for Occupational Safety and Health (NIOSH, ) is the List of United States federal agencies, United States federal agency responsible for conducting research and making recommendations for the prevention of work-related occ ...

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.

Environmental effects & US Regulations

Dichloromethane is not classified as an ozone-depleting substance by the

Montreal Protocol The Montreal Protocol on Substances That Deplete the Ozone Layer is an international treaty designed to protect the ozone layer by phasing out the production of numerous substances that are responsible for ozone depletion. It was agreed on 16 ...

. The US Clean Air Act does not regulate dichloromethane as an ozone depleter. 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. The EPA (Environmental Protection Agency) finalized a ban on most uses of methylene chloride (also known as 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.

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 Refrigerants Halogenated solvents IARC Group 2A carcinogens Fetotoxicants Testicular toxicants Chlorine-containing natural products GABAA receptor positive allosteric modulators Sweet-smelling chemicals Ozone depletion