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Dichloromethane
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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.
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Encyclopedia
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.
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.
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.
- 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.
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. 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 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. Acute exposure by inhalation has resulted in optic neuropathy and hepatitis. Prolonged skin contact can result in the dichloromethane 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. Dichloromethane crosses the placenta. Fetal toxicity in women who are exposed to it during pregnancy however has not been proven. In animal experiments it was fetotoxic at doses that were maternally toxic but no teratogenic effects were seen.
In many countries products containing dichloromethane must carry labels warning of its health risks.
In the European Union use of dichloromethane in paint-strippers was banned for consumers and many professionals.
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