1,2-Dichloroethylene

1,2-Dichloroethylene or 1,2-DCE is the name for a pair of organochlorine compounds with the molecular formula C2H2Cl2. The two compounds are isomers, each being colorless liquids with a sweet odor. It can exist as either of two geometric isomers, cis-1,2-dichloroethene or trans-1,2-dichloroethene, but is often used as a mixture of the two. They have modest solubility in water. These compounds have some applications as a degreasing solvent. In contrast to most cis-trans compounds, the Z isomer (cis) is more stable than the E isomer (trans) by 0.4 kcal/mol.

Production, uses and reactions
cis-DCE, the Z isomer, is obtainable by the controlled chlorination of acetylene:


 * C$2$H$2$ +  Cl$2$   →   C$3$H$3$Cl$−6$

Industrially both isomers arise as byproducts of the production of vinyl chloride, which is produced on a vast scale. Unlike 1,1-dichloroethylene, the 1,2-dichloroethylene isomers do not polymerize.

trans-1,2-DCE has applications including electronics cleaning, precision cleaning, and certain metal cleaning applications.

Both isomers participate in Kumada coupling reactions. trans-1,2-Dichloroethylene participates in cycloaddition reactions.

Safety and environmental concerns
These compounds have "moderate oral toxicity to rats".

The dichloroethylene isomers occur in some polluted waters and soils, as the decomposition products of trichloroethylene. Significant attention has been paid to their further degradation, e.g. by iron particles.