Page 228 - Chemical and process design handbook

Speight_Part II_C 11/7/01 3:08 PM Page 2.168

CHLOROPRENE

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Chloroprene (boiling point: 59.4 C, density: 0.9583) is, chemically, a
chlorovinyl ester of hydrochloric acid and can be manufactured by poly-
merizing acetylene to vinyl acetylene using a weak solution containing
ammonium chloride (NH Cl), cuprous chloride (Cu Cl ), and potassium
4 2 2
chloride (KCl) as catalyst. The off-gas from the reactor has its water con-
densed out and is then fractionated. Aqueous hydrochloric acid at 35 to
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45 C is then reacted with the vinyl acetylene in the presence of cupric chlo-
ride to give chloroprene (2-chloro-1,3-butadiene).
2HC≡CH → CH =CHC≡CH
2
CH =CHC≡CH + HCl → CH =CClC=CH
2 2 2
The contact time is about 15 seconds with a 20 percent conversion per
pass. An overall yield of approximately 65 percent can be achieved.
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Chloroprene is also made by chlorination of butadiene at 300 C fol-
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lowed by dehydrochlorination, using sodium hydroxide at 100 C. Addition
of the chlorine to the butadiene occurs at either 1,2 or 1,4 because the inter-
mediate allyl carbocation is delocalized.
CH =CHCH=CH + Cl → CH ClCH=CHCH Cl
2 2 2 2 2

CH ClCH=CHCH Cl + Cl → CH =CHC(Cl)=CH
2 2 2 2 2
The 1,4-dichloro isomer can be isomerized to the 1,2-dichloro isomer by
heating with cuprous chloride.
CH ClCH=CHCH Cl + → CH CH CCl=CHCl
2 2 3 2

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