Dichloromethane (DCM or methylene chloride, methylene bichloride) is an organochlorine compound with the formula . This colorless, volatile liquid with a

chloroform Chloroform, or trichloromethane, is an organic compound with formula C H Cl3 and a common organic solvent. It is a colorless, strong-smelling, dense liquid produced on a large scale as a precursor to PTFE. It is also a precursor to various ...

-like, sweet odour is widely used as a

solvent A solvent (s) (from the Latin '' solvō'', "loosen, untie, solve") is a substance that dissolves a solute, resulting in a solution. A solvent is usually a liquid but can also be a solid, a gas, or a supercritical fluid. Water is a solvent for ...

. Although it is not miscible 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 cli ...

, 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, multicellular, marine algae. The term includes some types of '' Rhodophyta'' (red), ''Phaeophyta'' (brown) and ''Chlorophyta'' (green) macroalgae. Seaweed species such as ...

, 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 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 relative abundance of 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,

, and carbon tetrachloride as well as hydrogen chloride as a byproduct. These compounds are separated by

distillation Distillation, or classical distillation, is the process of separating the components or substances from a liquid mixture by using selective boiling and condensation, usually inside an apparatus known as a still. Dry distillation is the he ...

. 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 A chemist (from Greek ''chēm(ía)'' alchemy; replacing ''chymist'' from Medieval Latin ''alchemist'') is a scientist trained in the study of chemistry. Chemists study the composition of matter and its properties. Chemists carefully describe th ...

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

chlorine Chlorine is a chemical element with the 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 them. Chlorine i ...

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 ...

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, it is used to decaffeinate

coffee Coffee is a drink prepared from roasted coffee beans. Darkly colored, bitter, and slightly acidic, coffee has a stimulating effect on humans, primarily due to its caffeine content. It is the most popular hot drink in the world. Seeds of ...

and tea as well as to prepare extracts of hops and other

flavouring A flavoring (or flavouring), also known as flavor (or flavour) or flavorant, is a food additive used to improve the taste or smell of food. It changes the perceptual impression of food as determined primarily by the chemoreceptors of the gus ...

s. Its volatility has led to its use as an aerosol spray propellant and as a

blowing agent A blowing agent is a substance which is capable of producing a cellular structure via a foaming process in a variety of materials that undergo hardening or phase transition, such as polymers, plastics, and metals. They are typically applied wh ...

for polyurethane foams.

Hydrogen bonding

Methylene chloride is a Lewis acid that can hydrogen bond 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 allows the chemical to function in a

heat engine In thermodynamics and engineering, a heat engine is a system that converts heat to mechanical energy, which can then be used to do mechanical work. It does this by bringing a working substance from a higher state temperature to a lower stat ...

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 adhesives, 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 mod ...

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 professional engineering discipline that deals with the design, construction, and maintenance of the physical and naturally built environment, including public works such as roads, bridges, canals, dams, airports, sewa ...

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

asphalt Asphalt, also known as bitumen (, ), is a sticky, black, highly viscous liquid or semi-solid form of petroleum. It may be found in natural deposits or may be a refined product, and is classed as a pitch. Before the 20th century, the term ...

or macadam 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 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 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 sub ...

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

, fatigue,

nausea Nausea is a diffuse sensation of unease and discomfort, sometimes perceived as an urge to vomit. While not painful, it can be a debilitating symptom if prolonged and has been described as placing discomfort on the chest, abdomen, or back of th ...

, headaches, numbness, weakness, and irritation of the upper respiratory tract and eyes. 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 ...

loss of consciousness Loss may refer to: Arts, entertainment, and media Music * ''Loss'' (Bass Communion album) (2006) * ''Loss'' (Mull Historical Society album) (2001) *"Loss", a song by God Is an Astronaut from their self-titled album (2008) * Losses "(Lil Tjay son ...

, coma, and death. DCM is also metabolized by the body to

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

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 tissue. Some people or animals with hepatitis have no symptoms, whereas others develop yellow discoloration of the skin and whites of the eyes ( jaundice), poor appetite, vomiting, tiredness, abdominal ...

. 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 substance, radionuclide, or radiation that promotes carcinogenesis (the formation of cancer). This may be due to the ability to damage the genome or to the disruption of cellular metabolic processes. Several radioactive sub ...

ic, as it has been linked to

cancer Cancer is a group of diseases involving abnormal cell growth with the potential to invade or spread to other parts of the body. These contrast with benign tumors, which do not spread. Possible signs and symptoms include a lump, abnormal b ...

of the

lungs The lungs are the primary organs of the respiratory system in humans and most other animals, including some snails and a small number of fish. In mammals and most other vertebrates, two lungs are located near the backbone on either si ...

liver The liver is a major organ only found in vertebrates which performs many essential biological functions such as detoxification of the organism, and the synthesis of proteins and biochemicals necessary for digestion and growth. In humans, it i ...

, and

pancreas The pancreas is an organ of the digestive system and endocrine system of vertebrates. In humans, it is located in the abdomen behind the stomach and functions as a gland. The pancreas is a mixed or heterocrine gland, i.e. it has both an ...

in laboratory animals. Other animal studies showed

breast cancer Breast cancer is cancer that develops from breast tissue. Signs of breast cancer may include a lump in the breast, a change in breast shape, dimpling of the skin, milk rejection, fluid coming from the nipple, a newly inverted nipple, or ...

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

placenta The placenta 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 the physically separate mate ...

but fetal toxicity in women who are exposed to it during

pregnancy Pregnancy is the time during which one or more offspring develops ( gestates) inside a woman's uterus (womb). A multiple pregnancy involves more than one offspring, such as with twins. Pregnancy usually occurs by sexual intercourse, but ...

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 ...

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 blood flow decreases or stops to the coronary artery of the heart, causing damage to the heart muscle. The most common symptom is chest pain or discomfort which ma ...

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

nervous system In biology, the nervous system is the highly complex part of an animal that coordinates its actions and sensory information by transmitting signals to and from different parts of its body. The nervous system detects environmental changes ...

, 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. In February 2013, the U.S.

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

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

, the

European Parliament The European Parliament (EP) is one of the Legislature, legislative bodies of the European Union and one of its seven Institutions of the European Union, institutions. Together with the Council of the European Union (known as the Council and in ...

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 Montreal Protocol 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 September 1987, and entered into force ...

. The U.S. Clean Air Act does not regulate dichloromethane as an ozone depleter. 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 Caprico ...

from the ground up through the stratosphere from 1998 to 2016 have declined by 2.2 Dobson units, 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.

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