Vinyl chloride, also known as chloroethene in IUPAC nomenclature, is an important industrial chemical chiefly used to produce its polymer, polyvinyl chloride (PVC). At room temperature, it is a toxic, colorless gas with a sweet odor.

History

Vinyl chloride was first produced in 1835 by Justus von Liebig and his student Henri Victor Regnault. They obtained it by treating ethylene dichloride with a solution of potassium hydroxide in ethanol.

In 1912, Fritz Klatte, a German chemist working for Griesheim-Elektron, patented a means to produce vinyl chloride from acetylene and hydrogen chloride using mercuric chloride as a catalyst. While this method was widely used during the 1930's and 1940's, it has since been superseded by more economical processes.

Production

Vinyl chloride is manufactured on the industrial scale from ethylene and chlorine. In the presence of ferric chloride as a catalyst, these compounds react to produce ethylene dichloride according to the chemical equation

CH₂=CH₂ + Cl₂ → ClCH₂CH₂Cl

Typically, this reaction is conducted in a bath of boiling ethylene dichloride. When then heated to 500°C at 15_30 atm pressure, the ethylene dichloride decomposes to produce vinyl chloride and hydrogen chloride.

ClCH₂CH₂Cl → CH₂=CHCl + HCl

In industrial practice, the hydrogen chloride produced in this step is mixed with oxygen and then reacted with additional ethylene on a cupric chloride catalyst to produce even more ethylene dichloride via the reaction

CH₂=CH₂ + 2 HCl + ½ O₂ → ClCH₂CH₂Cl + H₂O

The hydrogen chloride consumed in this step exactly balances that produced in the second step, and the resulting balanced process neither requires hydrogen chloride as an input nor produces it as a waste. Due to the economical advantages of this process, most vinyl chloride has been produced via this technique since the late 1950's.

Uses

By far the most important use of vinyl chloride is its polymerization to make PVC. Much smaller amounts are used to produce other chlorinated hydrocarbons including ethylidene chloride, 1,1,1-trichloroethane, trichloroethylene, tetrachloroethylene, and vinylidene chloride.

Vinyl chloride's toxicity limits its use in consumer goods, though it has been historically (until 1974) utilized as an aerosol propellant; carcinogenic potential has long been established and the prospective legal liability is comparable to that of mesothelioma). Accumulation of vinyl chloride vapor in hair salons readily exceeded the NOAEL (NO Adverse Effect Level) exposure guidelines, its high index of mutagenicity possibly responsible for an increase of an order of magnitude of the occurrence of cancer in the most severely effected occupations.

It was briefly used as an anesthetic, in a similar vein to ethyl chloride, though its toxicity forced this practice to be abandoned.

Health effects

Vinyl chloride depresses the central nervous system, and inhaling its vapors produces symptoms similar to alcohol intoxication. These include headache, dizziness, and loss of coordination, and in severe cases may progress to hallucination, unconsciousness, and death by respiratory failure.

In laboratory animals, exposure to vinyl chloride during pregnancy has produced miscarriages and birth defects. Its effect on human reproduction is unknown.

Long_term exposure to vinyl chloride can cause chronic skin irritations and has also been linked to a painful inflammation of the extremities called Raynaud's syndrome. Vinyl chloride is considered to be a carcinogen and has in particular been linked to certain cancers of the liver - chiefly, hepatocellular carcinoma.

External Links

• Information on the aerosol propellant controversy (http://www.chemicalindustryarchives.org/dirtysecrets/vinyl/5.asp)