Haloalkanes and Haloarenes - Polyhalogen Compounds

Polyhalogen compounds are carbon compounds containing more than one halogen atom. Many of these are industrially important but have significant environmental and health impacts.

Dichloromethane ($CH_2Cl_2$): Widely used as a solvent in paint strippers, propellants in aerosols, and process solvent in pharmaceuticals. High levels in air cause dizziness, nausea, and numbness.

Trichloromethane ($CHCl_3$): Also known as Chloroform. It was used as an anesthetic but is now primarily used in the production of Freon refrigerant $R-22$. It is oxidized by air in the presence of light to an extremely poisonous gas called Phosgene ($COCl_2$).

Triiodomethane ($CHI_3$): Also known as Iodoform. It is used as an antiseptic, though its antiseptic properties are due to the liberation of free iodine ($I_2$) rather than the $CHI_3$ molecule itself. It has a characteristic unpleasant smell.

Tetrachloromethane ($CCl_4$): Also known as Carbon tetrachloride. Used in the manufacture of refrigerants and as a cleaning fluid. It is a major contributor to ozone depletion and can cause liver cancer in humans.

Freons: Chlorofluorocarbon ($CFC$) derivatives of methane and ethane. They are extremely stable, unreactive, non-toxic, and non-corrosive. $CCl_2F_2$ (Freon-12) is common. In the stratosphere, they trigger radical chain reactions that deplete the ozone layer.

p,p'-Dichlorodiphenyltrichloroethane ($DDT$): The first chlorinated organic insecticide. It is highly effective against mosquitoes and lice but is chemically stable and fat-soluble, leading to bioaccumulation in the food chain and harmful effects on wildlife.