Vinyl chloride

Vinyl chloride
Name	Vinyl chloride
IUPACName	Chloroethene
OtherNames	Chloroethylene, VCM

Vinyl chloride is a colorless, flammable gas with a faint, sweet odor. It is a crucial industrial chemical, primarily serving as the monomer for the production of polyvinyl chloride, one of the most widely used synthetic polymers globally. The compound is a haloalkene, characterized by the presence of a chlorine atom bonded to one of the carbon atoms in an ethene (ethylene) framework. Its industrial importance is matched by significant health and environmental concerns, leading to stringent regulatory controls.

Chemical properties and structure

Vinyl chloride is a simple organochloride with the chemical formula C₂H₃Cl. Its molecular structure consists of a double bond between two carbon atoms, with one carbon bonded to two hydrogen atoms and the other to a single hydrogen and a chlorine atom. This structure makes it an alkene and a vinyl compound. The presence of the electron-withdrawing chlorine atom influences the reactivity of the double bond, making it susceptible to addition reactions, most notably free-radical polymerization. It is highly volatile, with a low boiling point, and is only slightly soluble in water but miscible with most common organic solvents like ethanol, diethyl ether, and carbon tetrachloride. Under certain conditions, it can form explosive mixtures with air.

Production and synthesis

The dominant industrial method for producing vinyl chloride is through a two-step process known as balanced VCM process. This involves the direct chlorination of ethylene with chlorine to produce ethylene dichloride, followed by the catalytic cracking of this intermediate to yield vinyl chloride and hydrogen chloride. The hydrogen chloride produced is then used in an oxychlorination reaction with additional ethylene and oxygen, forming more ethylene dichloride and closing the loop. Historically, it was first prepared in a laboratory setting by the French chemist Henri Victor Regnault and later by the German chemist Fritz Klatte while working for Griesheim-Elektron.

Uses and applications

Over 95% of all vinyl chloride produced is used in the manufacture of polyvinyl chloride resins. Polyvinyl chloride is an extremely versatile plastic used in a vast array of applications, including construction materials like piping, siding, and window frames, as well as in consumer goods such as credit cards, packaging, and medical devices. A small fraction is used as a chemical intermediate in the synthesis of other organochlorine compounds. Before its carcinogenicity was fully understood, it was also used briefly as a refrigerant and as an ingredient in aerosol spray propellants.

Health effects and safety

Vinyl chloride is a known human carcinogen, classified as such by agencies including the International Agency for Research on Cancer and the United States Environmental Protection Agency. Chronic occupational exposure is strongly linked to a rare form of liver cancer known as hepatic angiosarcoma, as well as cancers of the brain, lung, and lymphatic system. Acute exposure can cause central nervous system effects, including dizziness, headache, and at very high concentrations, loss of consciousness and death. Due to these risks, workplace exposure limits are strictly enforced by organizations like the Occupational Safety and Health Administration in the United States.

Environmental impact and regulation

Vinyl chloride can enter the environment from industrial emissions, improper waste disposal, and leaching from polyvinyl chloride products in landfills. It is a volatile organic compound and a groundwater contaminant of major concern. In the atmosphere, it contributes to the formation of ground-level ozone. Major regulatory actions, such as the Toxic Substances Control Act and the Clean Air Act in the United States, strictly control its production, use, and disposal. The Environmental Protection Agency sets maximum contaminant levels for it in drinking water, and its release is reportable under the Emergency Planning and Community Right-to-Know Act.

History and discovery

Vinyl chloride was first synthesized in 1835 by the French chemist Henri Victor Regnault, who produced it by treating ethylene dichloride with a potassium hydroxide solution. It remained a laboratory curiosity for nearly a century. Its potential for polymerization was discovered in the early 20th century, with significant early work conducted by German chemist Fritz Klatte at Griesheim-Elektron, who patented a process using sunlight to initiate polymerization. Large-scale commercial production and use of polyvinyl chloride began in the 1930s and expanded rapidly after World War II. The link between vinyl chloride exposure and hepatic angiosarcoma was definitively established in the 1970s, leading to a dramatic overhaul of industrial hygiene standards worldwide.

Category:Organochlorides Category:IARC Group 1 carcinogens Category:Industrial gases