Chloroprene
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2008-07-09T13:31:36Z
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{{Chembox new
| Name = Chloroprene
| ImageFileL1 = Chloroprene-2D-skeletal.png
| ImageSizeL1 = 120px
| ImageNameL1 = Chloroprene
| ImageFileR1 = Chloroprene-3D-vdW.png
| ImageSizeR1 = 120px
| ImageNameR1 = Chloroprene
| IUPACName = 2-Chloro-1,3-butadiene
| OtherNames = Chloroprene
| Section1 = {{Chembox Identifiers
| SMILES = C=C(Cl)C=C
| 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-chloro-1,3-butadiene''', which has the [[chemical 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 [[DuPont]] gave it when the company first developed it and currently used by DuPont Performance Elastomers.
==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) [[Dehydrohalogenation|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-chloro-1,3-butadiene. 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-chloro-1,3-butadiene, 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 [[vinyl acetylene]].<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 combine with [[hydrogen chloride]] to afford in succession vinyl acetylene, 3-chloro-1,2-butadiene, which, finally in the presence of [[cuprous chloride]], rearranges to the targeted 2-chloro-1,3-butadiene.<ref name=Ross/> The conversion is shown here:
[[Image:Chloroprene synthesis.png|400px]]
This process had disadvantages in that it is very energy-intensive and has high investment costs. Furthermore, the intermediate vinyl acetylene is unstable.
==References==
<references/>
*[http://www.iisrp.com/WebPolymers/04FinalPolychloropreneIISRP.pdf Polychloroprene (CR), chloroprene rubber]
==External links==
*{{ICSC|0133|01}}
*{{PGCH|0133}}
*{{ecb}}
*[[IARC]] Monograph "[http://www-cie.iarc.fr/htdocs/monographs/vol71/003-chloroprene.html Chloroprene.]"
[[Category:Dienes]]
[[Category:Monomers]]
[[Category:Organochlorides]]
[[Category:Hazardous air pollutants]]
[[Category:IARC Group 2B carcinogens]]
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