Chloroprene

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Chloroprene
style="background: #F8EABA; text-align: center;" colspan="2" | Identifiers
CAS number 126-99-8 YesY
RTECS number EL9625000
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style="background: #F8EABA; text-align: center;" colspan="2" | Properties
Molecular formula C4H5Cl
Molar mass 88.5365 g/mol
Appearance Colorless liquid.
Density 0.9598 g/cm3, liquid.
Melting point

-130 °C, 143 K, -202 °F

Boiling point

59.4 °C, 333 K, 139 °F

Solubility in water 0.026 g/100 mL, liquid.
style="background: #F8EABA; text-align: center;" colspan="2" | Hazards
R-phrases R45, R11, R20/22,
R36/37/38, R48/20
S-phrases S53, S45
NFPA 704
3
2
0
Flash point -15.6°C
style="background: #F8EABA; text-align: center;" colspan="2" | Related compounds
Related Dienes Butadiene
Isoprene
Related compounds Vinyl chloride
 YesY (what is this?)  (verify)
Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
Infobox references

Chloroprene is the common name for the organic compound 2-chlorobuta-1,3-diene, which has the formula CH2=CCl-CH=CH2. 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 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.[1] 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.[2] 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:[1]

HC≡C-CH=CH2 + HCl → H2C=C=CH-CH2Cl
H2C=C=CH-CH2Cl → H2C=CCl-CH=CH2

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

References

  1. 1.0 1.1 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
  2. Wallace H. Carothers, Ira Williams, Arnold M. Collins, and James E. Kirby (1937). "Acetylene Polymers and their Derivatives. II. A New Synthetic Rubber: Chloroprene and its Polymers". J. Am. Chem. Soc. 53: 4203–4225. doi:10.1021/ja01362a042. 

External links

cs:Chloropren de:Chloropren et:Kloropreen es:Cloropreno it:Cloroprene nl:Chloropreen ja:クロロプレン pl:Chloropren pt:Cloropreno ru:Хлоропрен sk:Chloroprén fi:Kloropreeni sv:Kloropren vi:Cloropren zh:氯丁二烯