Dichloromethane

Dichloromethane
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 Y
PubChem	6344
EC number	200-838-9
KEGG	C02271
ChEBI	15767
RTECS number	PA8050000
SMILES C(Cl)Cl
InChI InChI=1/CH2Cl2/c2-1-3/h1H2
Properties
Molecular formula	CH2Cl2
Molar mass	84.93 g/mol
Appearance	Colorless liquid
Density	1.3266 g/cm3, liquid
Melting point	-96.7 °C, 176 K, -142 °F
Boiling point	40 °C, 313 K, 104 °F
Solubility in water	13 g/L at 20 °C
Vapor pressure	47 kPa at 20 °C
Hazards
R-phrases	R40
S-phrases	S23 S24/25 S36/37
NFPA 704	1 2 0
Flash point	None
Autoignition temperature	556 °C
Y (what is this?)  (verify) Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
Infobox references

Near IR absorption spectrum of dichloromethane showing complicated overlapping overtones of mid IR absorption features.

Dichloromethane (DCM or methylene chloride) is an organic compound with the formula CH₂Cl₂. This colorless, volatile liquid with a moderately sweet aroma is widely used as a solvent. More than 500,000 tons were produced in 1991. Although it is not miscible with water, it is miscible with many organic solvents.^[1] It 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.

Production

Dichloromethane is produced by treating 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 a useful 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 has been used to decaffeinate coffee and tea as well as 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.

Specialized uses

Dichloromethane 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 in the model-making industry for joining plastic components together — it is commonly referred to as "Di-clo."

Also used in the garment printing industry for removal of heat-sealed garment transfers. Usually sold in cans with methanol as the propellant gas. Its volatility is exploited in novelty items — drinking birds, bubble lights, and jukebox displays.

Dichloromethane is used within 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.^[3]

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.^[4] Dichloromethane is also metabolised by the body to carbon monoxide potentially leading to carbon monoxide poisoning.^[5] Acute exposure by inhalation has resulted in optic neuropathy^[6] and hepatitis.^[7] Prolonged skin contact can result in the dichloromethane dissolving some of the fatty tissues in skin, resulting in skin irritation or chemical burns.^[8]

It may be carcinogenic, as it has been linked to cancer of the lungs, liver, and pancreas in laboratory animals.^[9] Dichloromethane crosses the placenta. Fetal toxicity in women who are exposed to it during pregnancy however has not been proven.^[10] In animal experiments it was fetotoxic at doses that were maternally toxic but no teratogenic effects were seen.^[9]

In many countries products containing dichloromethane must carry labels warning of its health risks.

In the European Union, the European Parliament voted in 2009 to ban the use of dichloromethane in paint-strippers for consumers and many professionals.^[11] The ban will take effect by December 2010.

References

External links

• International Chemical Safety Card 0058
• 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)