Vinylhalide

Vinylhalide refers to a class of organohalide compounds that contain a vinyl group (CH2=CH–) bonded to a halogen. In common usage the term designates vinyl halides with the halogen on the vinylic carbon, i.e., compounds of the form CH2=CHX where X is F, Cl, Br, or I. The most widely encountered member is vinyl chloride (chloroethene, CH2=CHCl), followed by vinyl fluoride (CH2=CHF), vinyl bromide (CH2=CHBr), and vinyl iodide (CH2=CHI).

Production and occurrence: The most important vinyl halide is vinyl chloride, a monomer for polyvinyl chloride (PVC). Commercial vinyl chloride is produced primarily by dehydrochlorination of 1,2-dichloroethane (ethylene dichloride), which is formed from ethylene and chlorine. An older route used hydrochlorination of acetylene to yield vinyl chloride directly. Other vinyl halides are prepared by halogenation of alkenes or by various synthetic methods in organic chemistry. They are typically gases or low-boiling liquids at room temperature and require appropriate containment.

Uses and applications: As monomers, vinyl halides polymerize to form halogenated polymers; vinyl chloride monomer yields PVC, a major plastic used in construction, packaging, and electrical insulation. Vinyl halides also serve as versatile intermediates in organic synthesis, enabling cross-coupling reactions and various substitutions, and act as precursors to other halogenated compounds and specialty polymers.

Safety and handling: Many vinyl halides are hazardous. Vinyl chloride is a known human carcinogen and is flammable and toxic. Other vinyl halides can irritate eyes, skin, and lungs. They may polymerize under certain conditions, so storage typically requires stabilizers, proper ventilation, and adherence to safety regulations.

See also: PVC; vinyl chloride monomer; halogenated alkenes; cross-coupling chemistry.