Trihalogenmethane

Trihalogenmethane, or trihalomethane, refers to a class of organohalogen compounds in which three hydrogen atoms of methane are replaced by halogen atoms. The general formula is CHX3, where X is a halogen such as fluorine, chlorine, bromine, or iodine. The best-known members are chloroform (CHCl3), bromoform (CHBr3), and iodoform (CHI3); trifluoromethane (CHF3) is also regarded as a tri-halogenated derivative of methane.

These compounds vary in physical state at room temperature. Chloroform is a volatile liquid, bromoform is a dense liquid, iodoform is a pale yellow solid, and trifluoromethane is a gas. They are generally nonpolar and can act as solvents or reagents in organic synthesis, with some exhibiting characteristic reactions such as the iodoform test for methyl ketones (iodoform reaction).

Preparation and occurrence: tri-halogenated methanes are produced by halogenating methane or other methyl-containing substrates under radical or substitution conditions. They also arise as byproducts during chlorination or other halogenation processes of organic matter, including drinking-water treatment. In addition to laboratory and industrial uses, their formation is a concern in environmental and public health contexts due to their persistence and reactivity.

Uses and hazards: chloroform has historical use as a solvent and anesthetic; iodoform has antiseptic applications and is produced in the iodoform reaction; trifluoromethane is used as a refrigerant and industrial gas. All tri-halogen methanes can be toxic and environmentally hazardous; chloroform is hepatotoxic and suspected carcinogenic, while other members pose health and safety concerns. Some are potent greenhouse gases and ozone-depleting substances, necessitating careful handling and regulation.