halocarbons

Halocarbons are chemical compounds that contain carbon and at least one halogen atom—fluorine, chlorine, bromine, or iodine. The term typically refers to organohalogens, organic molecules in which carbon is bonded to one or more halogens, though some inorganic carbon–halogen species exist. Halocarbons are produced by substituting halogen atoms for hydrogen in hydrocarbons or by direct halogenation of hydrocarbon frameworks.

Classification and examples: They range from haloalkanes (alkyl halides) and haloarenes (aryl halides) to fluorinated, chlorinated, or brominated hydrocarbons. Notable groups include chlorofluorocarbons (CFCs), hydrochlorofluorocarbons (HCFCs), hydrofluorocarbons (HFCs), halons, chlorinated solvents such as trichloroethylene, and fluorinated refrigerants. Perhalogenated compounds, where all hydrogens are replaced by halogens, also exist.

Uses and properties: Halocarbons are often liquids or gases at room temperature, chemically stable, and diverse in applications. They serve as solvents, refrigerants, propellants, blowing agents for foams, plasticizers, pesticides, and chemical intermediates. Health and environmental hazards vary; some are toxic or carcinogenic (for example vinyl chloride), while others pose little acute risk but may contribute to atmospheric pollution.

Environmental impact and regulation: Certain halocarbons have ozone depletion potential, notably CFCs and halons, leading to phaseouts under the Montreal Protocol. Even less ozone-depleting compounds can have high global warming potential. Regulatory frameworks promote safer substitutes (such as HCFCs replaced by HFCs or hydrofluoroolefins) and require controlled handling or destruction at end of life.

Industrial and historical notes: The widespread use of halocarbons expanded in the 20th century with refrigeration, solvents, and manufacturing. Ongoing efforts focus on reducing emissions, improving end-of-life destruction, and developing non-halogenated alternatives.