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, and it is miscible with most organic solvents.
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.
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.
Dichloromethane's volatility and ability to dissolve a wide range of organic compounds makes it an ideal solvent for many chemical processes. It is widely used as a paint stripper and a degreaser. In the food industry, it is still used to decaffeinate coffee and to prepare extracts of hops and other flavorings, .[1]. It is used to chemically weld certain plastics (for example, it is used to seal the casing of electric meters). Its volatility has led to its use as an aerosol spray propellant and as a blowing agent for polyurethane foams. It is also used as a fumigant pesticide for stored strawberries and grains. It is also the most common "active" component in Drinking Birds. Concerns about its health effects have led to a search for alternatives in many of these applications.
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.[2] Prolonged skin contact can result in the dichloromethane dissolving some of the fatty tissues in skin, resulting in skin irritation or chemical burns.[3]
It may be carcinogenic, as it has been linked to cancer of the lungs, liver, and pancreas in laboratory animals. [4] dichloromethane crosses the placenta. Fetal toxicity in women who are exposed to it during pregnancy however has not been proven. [5] in animal experiments it was fetotoxic at doses that were maternally toxic but no teratogenic effects were seen. [4]
In many countries products containing dichloromethane must carry labels warning of its health risks.
Large amounts of chloromethane are produced naturally in the oceans by the action of sunlight on biomass and chlorine in sea foam. However, all chloromethane that is used in industry is produced synthetically.
Most chloromethane is prepared by reacting methanol with hydrogen chloride, according to the chemical equation
CH3OH + HCl > CH3Cl + H2O
