View source for Chloroprene

{{chembox
| verifiedrevid = 304939943
|   Name = Chloroprene
|   ImageFileL1 = Chloroprene-2D-skeletal.png
| ImageSizeL1 = 120px
|   ImageNameL1 = Chloroprene
|   ImageFileR1 = Chloroprene-3D-vdW.png
 | ImageSizeR1 = 120px 
|   ImageNameR1 = Chloroprene
|   IUPACName = 2-Chlorobuta-1,3-diene
|   OtherNames = Chloroprene, 2-chloro-1,3-butadiene
| Section1 = {{Chembox Identifiers
|   SMILES = C=C(Cl)C=C
|   CASNo_Ref = {{cascite}}
| CASNo = 126-99-8
|   RTECS = EL9625000
  }}
| Section2 = {{Chembox Properties
|   Formula = C<sub>4</sub>H<sub>5</sub>Cl
|   MolarMass = 88.5365 g/mol
|   Appearance = Colorless liquid.
|   Density = 0.9598 g/cm<sup>3</sup>, liquid.
|   Solubility = 0.026 g/100 mL, liquid.
|   MeltingPtC = -130
|   BoilingPtC = 59.4
|   Viscosity = 
  }}
| Section3 = {{Chembox Structure
|   MolShape = 
|   Dipole =
  }}
| Section7 = {{Chembox Hazards
|   ExternalMSDS =
|   MainHazards = Highly flammable, toxic.
|   NFPA-H = 2
|   NFPA-F = 3
|   NFPA-R =
|   FlashPt = -15.6°C
|   RPhrases = {{R45}}, {{R11}}, {{R20/22}},<br />{{R36/37/38}}, {{R48/20}}
|   SPhrases = {{S53}}, {{S45}}
  }}
| Section8 = {{Chembox Related
|   Function = [[Diene]]s
|   OtherFunctn = [[Butadiene]]<br />[[Isoprene]]
|   OtherCpds = [[Vinyl chloride]]
  }}
}}

'''Chloroprene''' is the common name for the [[organic compound]] 2-chlorobuta-1,3-diene, which has the [[chemical formula|formula]] CH<sub>2</sub>=CCl-CH=CH<sub>2</sub>. This colorless liquid is the [[monomer]] for the production of the [[polymer]] polychloroprene, a type of [[synthetic rubber]].  Polychloroprene is better known to the public as [[Neoprene]], the trade name given by [[DuPont]]. 

==Production of chloroprene==
Chloroprene is produced in three steps from [[Butadiene|1,3-butadiene]]: (i) [[chlorination]], (ii) isomerization of part of the product stream, and (iii) [[dehydrochlorination]] of 3,4-dichloro-1-butene.  

[[Chlorine]] adds to 1,3-butadiene to afford a mixture of 3,4-dichloro-1-butene and 2,3-dichloro-2-butene. The 2,3-chloro isomer is subsequently isomerized to 3,4 isomer, which in turn is treated with base to induce dehydrochlorination to 2-chlorobuta-1,3-diene. This dehydrohalogenation entails loss of a hydrogen [[atom]] in the 3 position and the chlorine atom in the 4 position thereby forming a double bond between carbons 3 and 4.  In 1983, approximately 2,000,000 kg were produced in this manner.<ref name=Ross>Manfred Rossberg, Wilhelm Lendle, Gerhard Pfleiderer, Adolf Tögel, Eberhard-Ludwig Dreher, Ernst Langer, Heinz Rassaerts, Peter Kleinschmidt, Heinz Strack, Richard Cook, Uwe Beck, Karl-August Lipper, Theodore R. Torkelson, Eckhard Löser, Klaus K. Beutel, “Chlorinated Hydrocarbons” in Ullmann’s Encyclopedia of Industrial Chemistry, 2006 John Wiley-VCH: Weinheim.DOI: 10.1002/14356007.a06_233.pub2</ref>  The chief impurity in chloroprene prepared in this way is
1-chlorobuta-1,3-diene, which is usually separated by [[distillation]].  

===Acetylene process===
Until the 1960s, chloroprene production was dominated by the “acetylene process,” which was modeled after the original synthesis of [[vinylacetylene]].<ref>{{cite journal | author = [[Wallace H. Carothers]], Ira Williams, Arnold M. Collins, and James E. Kirby | title = Acetylene Polymers and their Derivatives. II. A New Synthetic Rubber: Chloroprene and its Polymers | journal = [[J. Am. Chem. Soc.]]| year = 1937 | volume = 53 | pages = 4203–4225 | doi = 10.1021/ja01362a042}}</ref>  In this process, [[acetylene]] is dimerized to give vinyl acetylene, which is then combined with [[hydrogen chloride]] to afford 4-chloro-1,2-butadiene (an allene derivative), which in the presence of [[cuprous chloride]], rearranges to the targeted 2-chlorobuta-1,3-diene:<ref name=Ross/>
:HC&equiv;C-CH=CH<sub>2</sub>  +  HCl   →  H<sub>2</sub>C=C=CH-CH<sub>2</sub>Cl
: H<sub>2</sub>C=C=CH-CH<sub>2</sub>Cl →  H<sub>2</sub>C=CCl-CH=CH<sub>2</sub>

This process is very energy-intensive and has high investment costs. Furthermore, the intermediate vinyl acetylene is unstable.

==References==
<references/>

==External links==
* {{ICSC|0133|01}}
* {{PGCH|0133}}
* {{ecb}}
* [[IARC]] Monograph "[http://www-cie.iarc.fr/htdocs/monographs/vol71/003-chloroprene.html Chloroprene.]"
* [http://www.iisrp.com/WebPolymers/04FinalPolychloropreneIISRP.pdf Polychloroprene (CR), chloroprene rubber]

[[Category:Dienes]]
[[Category:Monomers]]
[[Category:Organochlorides]]
[[Category:Hazardous air pollutants]]
[[Category:IARC Group 2B carcinogens]]

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