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Vinylacetylene
Chemical compound From Wikipedia, the free encyclopedia
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Vinylacetylene is the organic compound with the formula C4H4 or H2C=CH−C≡CH. The colourless gas was once used in the polymer industry. It is composed of both alkyne and alkene groups and is the simplest enyne.
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Safety
Vinylacetylene is extremely dangerous because in high enough concentrations (typically > 30 mole percent, but pressure dependent) it can auto-detonate (explode without air being present) especially at elevated pressures, such as those seen in chemical plants processing C4 hydrocarbons (hydrocarbons with 4 carbon atoms).[2] An example of such an explosion occurred at a Union Carbide plant in Texas City in 1969.[3]
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Synthesis
Vinylacetylene was first synthesized by Hofmann elimination of the related quaternary ammonium salt:[4]
- [(CH3)3N+−CH2−CH=CH−CH2−N+(CH3)3](I−)2 → 2 [(CH3)3NH]+I− + H2C=CH−C≡CH
It is usually synthesized by dehydrohalogenation of 1,3-dichloro-2-butene Cl−CH2−CH=CCl−CH3.[5]
It also arises via the dimerization of acetylene, which is catalyzed by copper(I) chloride.[6]
Dehydrogenation of 1,3-butadiene is yet another route.[citation needed]
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Application
At one time, chloroprene (2-chloro-1,3-butadiene), an industrially important monomer, was produced via the intermediacy of vinyl acetylene.[7] In this process, acetylene is dimerized to give vinyl acetylene, which is then combined with hydrogen chloride to give 4-chloro-1,2-butadiene via 1,4-addition. This allene derivative which, in the presence of cuprous chloride, rearranges to 2-chloro-1,3-butadiene:[8]
- H2C=CH−C≡CH + HCl → H2ClC−CH=C=CH2
- H2ClC−CH=C=CH2 → H2C=CH−CCl=CH2
References
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