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| Dichloromethane | |
|---|---|
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| IUPAC name | Dichloromethane |
| Other names | Methylene chloride, methylene dichloride, Solmethine, Narkotil, Solaesthin, Di-clo, Freon 30, R-30, DCM, UN 1593, MDC |
| Identifiers | |
| CAS number | 75-09-2 |
| PubChem | |
| EINECS number | |
| KEGG | |
| ChEBI | |
| RTECS number | PA8050000 |
| SMILES |
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| InChI |
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| Properties | |
| Molecular formula | CH2Cl2 |
| Molar mass | 84.93 g/mol |
| Appearance | Colorless liquid |
| Density | 1.3266 g/cm³, liquid |
| Melting point |
-96.7 °C (175.7 K) |
| Boiling point |
40 °C (312.8 K) |
| Solubility in water | 13 g/l at 20 °C |
| Vapor pressure | 47 kPa at 20 °C |
| Hazards | |
| MSDS | External MSDS |
| Main hazards | Harmful (Xn), Carc. Cat. 2B |
| NFPA 704 |
 0
2
0
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| R-phrases | R40 |
| S-phrases | S23, S24/25, S36/37 |
| Flash point | None |
| Supplementary data page | |
| Structure and properties |
n, εr, etc. |
| Thermodynamic data |
Phase behaviour Solid, liquid, gas |
| Spectral data | UV, IR, NMR, MS |
| Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa) Infobox references |
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Dichloromethane (DCM) or methylene chloride is the chemical compound with the formula CH2Cl2. It is a colorless, volatile liquid with a moderately sweet aroma. It is widely used as a solvent, the general view being that it is one of the less harmful of the chlorocarbons. Although it is not miscible with water, it will dissolve in most organic solvents. Approximately 500,000 tons were produced in 1995.1
Dichloromethane was first prepared in 1840 by the French chemist Henri Victor Regnault, who isolated it from a mixture of chloromethane and chlorine that had been exposed to sunlight.
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Production
Industrially, dichloromethane is produced by reacting either methyl chloride or methane with chlorine gas at 400–500 °C. At these temperatures, both methane and methyl chloride undergo a series of reactions producing progressively more chlorinated products.1
- CH4 + Cl2 → CH3Cl + HCl
- CH3Cl + Cl2 → CH2Cl2 + HCl
- CH2Cl2 + Cl2 → CHCl3 + HCl
- CHCl3 + Cl2 → CCl4 + HCl
The output of these processes is a mixture of methyl chloride, dichloromethane, chloroform, and carbon tetrachloride. These compounds are separated by distillation.
Uses
Dichloromethane's volatility and ability to dissolve a wide range of organic compounds makes it an ideal solvent for many chemical processes. Concerns about its health effects have led to a search for alternatives in many of these applications.1
It is widely used as a paint stripper and a degreaser. In the food industry, it is used to decaffeinate coffee and to prepare extracts of hops and other flavorings.2 Its volatility has led to its use as an aerosol spray propellant and as a blowing agent for polyurethane foams.
Speciallized uses
Dichloromethane chemically welds certain plastics (for example, it is used to seal the casing of electric meters). Often sold under the brand name of "EMA Plastic Weld" it is also used extensively in the modelmaking industry for joining plastic components together - it is commonly referred to as "Di-clo."
Its volatility is exploited in novelty items - drinking birds, bubble lights, and jukebox displays.
Toxicity
Dichloromethane is the least toxic of the simple chlorohydrocarbons, but it is not without its health risks as its high volatility makes it an acute inhalation hazard. Dichloromethane is also metabolised by the body to carbon monoxide potentially leading to carbon monoxide poisoning.3 Prolonged skin contact can result in the dichloromethane dissolving some of the fatty tissues in skin, resulting in skin irritation or chemical burns.4
It may be carcinogenic, as it has been linked to cancer of the lungs, liver, and pancreas in laboratory animals.5 Dichloromethane crosses the placenta. Fetal toxicity in women who are exposed to it during pregnancy however has not been proven.6 In animal experiments it was fetotoxic at doses that were maternally toxic but no teratogenic effects were seen.5
In many countries products containing dichloromethane must carry labels warning of its health risks.
References
- ^ a b c M. Rossberg et al. “Chlorinated Hydrocarbons” in Ullmann’s Encyclopedia of Industrial Chemistry 2006, Wiley-VCH, Weinheim. doi:10.1002/14356007.a06 233.pub2
- ^ Office of Environmental Health Hazard Assessment (September 2000). "Dichloromethane". Public Health Goals for Chemicals in Drinking Water. California Environmental Protection Agency.
- ^ Fagin J, Bradley J, Williams D (1980). "Carbon monoxide poisoning secondary to inhaling methylene chloride". Br Med J 281 (6253): 1461. PMID 7437838.
- ^ Wells G, Waldron H (1984). "Methylene chloride burns". Br J Ind Med 41 (3): 420. PMID 6743591.
- ^ a b USDHHS. "Toxicological Profile for Methylene Chloride" (PDF). Retrieved on 2006-09-10.
- ^ Bell B, Franks P, Hildreth N, Melius J (1991). "Methylene chloride exposure and birthweight in Monroe County, New York". Environ Res 55 (1): 31–9. doi:. PMID 1855488.
External links
- NIOSH Pocket Guide to Chemical Hazards 0414
- National Pollutant Inventory - Dichloromethane Fact Sheet
- MSDS at Oxford University
- Dichloromethane at National Toxicology Program
- IARC Summaries & Evaluations Vol. 71 (1999)
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- This page was last modified on 22 November 2008, at 22:55.
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