Definition and Uses :
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. Although not miscible with water, it is miscible with many organic solvents. One of the best-known applications of dichloromethane is the drinking bird heat engine.
Natural sources of dichloromethane include ocean sources, macroalgae, wetlands, and volcanoes. However, the majority of dichloromethane in the environment is a result of industrial emissions.
DCM is produced by treating either chloromethane or methane with chlorine gas at 400-500 °C. At these temperatures, both methane and chloromethane undergo a series of reactions that produce increasingly chlorinated products. Approximately 400,000 tons were produced in this way in the United States, Europe, and Japan in 1993.
CH4 + Cl2 → CH3Cl + HCl
CH3Cl + Cl2 → CH2Cl2 + HCl
CH2Cl2 + Cl2 → CHCl3 + HCl
CHCl3 + Cl2 → CCl4 + HCl
These processes produce a mixture of chloromethane, dichloromethane, chloroform and carbon tetrachloride. These compounds are separated by distillation.
DCM was first prepared in 1839 by the French chemist Henri Victor Regnault (1810-1878) and isolated from a mixture of chloromethane and chlorine that had been exposed to sunlight.