Chloroprene
| Chloroprene | |
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2-Chlorobuta-1,3-diene |
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Other names
Chloroprene, 2-chloro-1,3-butadiene |
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| Identifiers | |
| CAS number | 126-99-8  |
| ChemSpider | 29102 |
| KEGG | C19208 |
| ChEBI | CHEBI:39481 |
| ChEMBL | CHEMBL555660 |
| RTECS number | EL9625000 |
| Jmol-3D images | Image 1 |
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| 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. |
| Hazards | |
| R-phrases | R45, R11, R20/22, R36/37/38, R48/20 |
| S-phrases | S53, S45 |
| Main hazards | Highly flammable, toxic. |
| NFPA 704 |
 3
2
0
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| Flash point | -15.6°C |
| Related compounds | |
| Related Dienes | Butadiene Isoprene |
| Related compounds | Vinyl chloride |
 (verify) (what is:  / ?)Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa) |
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| 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.
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[edit] 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.
[edit] 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.
This "acetylene process" has been replaced by a process which adds Cl2 to one of the double bonds in 1,3-butadiene instead, and subsequent elimination produces HCl instead, as well as chloroprene.
[edit] References
- ^ a b 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
- ^ 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 (11): 4203–4225. doi:10.1021/ja01362a042.
