Chloroprene

Chloroprene
Names
IUPAC name
2-Chlorobuta-1,3-diene
Other names
Chloroprene, 2-chloro-1,3-butadiene, Chlorobutadiene, beta-Chloroprene
Identifiers
126-99-8 Yes
ChEBI CHEBI:39481 Yes
ChEMBL ChEMBL555660 Yes
ChemSpider 29102 Yes
Jmol-3D images Image
KEGG C19208 Yes
PubChem 31369
RTECS number EL9625000
Properties
C4H5Cl
Molar mass 88.5365 g/mol
Appearance Colorless liquid
Odor pungent, ether-like
Density 0.9598 g/cm3
Melting point −130 °C (−202 °F; 143 K)
Boiling point 59.4 °C (138.9 °F; 332.5 K)
0.026 g/100 mL
Solubility soluble in alcohol, diethyl ether
miscible in ethyl ether, acetone, benzene
Vapor pressure 188 mmHg (20°C)[1]
1.4583
Hazards
Main hazards Highly flammable, toxic.
R-phrases R45, R11, R20/22,
R36/37/38, R48/20
S-phrases S53, S45
NFPA 704
Flammability code 3: Liquids and solids that can be ignited under almost all ambient temperature conditions. Flash point between 23 and 38 °C (73 and 100 °F). E.g., gasoline) Health code 2: Intense or continued but not chronic exposure could cause temporary incapacitation or possible residual injury. E.g., chloroform Reactivity code 0: Normally stable, even under fire exposure conditions, and is not reactive with water. E.g., liquid nitrogen Special hazards (white): no codeNFPA 704 four-colored diamond
3
2
0
Flash point −15.6 °C (3.9 °F; 257.5 K)
Explosive limits 1.9%-11.3%[1]
450 mg/kg (rat, oral)
US health exposure limits (NIOSH):
TWA 25 ppm (90 mg/m3) [skin][1]
Ca C 1 ppm (3.6 mg/m3) [15-minute][1]
300 ppm[1]
Related compounds
Related Dienes
Butadiene
Isoprene
Related compounds
 Vinyl chloride
Except where noted otherwise, data is given for materials in their standard state (at 25 °C (77 °F), 100 kPa)
 Yes verify (what is: Yes/?)
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.[2] 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.[3] 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:[2]

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.

Transportation regulations

Transportation of uninhibited chloroprene has been banned in the United States by the US Department of Transportation. Stabilized chloroprene is in hazard class 3 (flammable liquid). Its UN number is 1991 and is in packing group 1.

References

  1. ↑ 1.0 1.1 1.2 1.3 1.4 "NIOSH Pocket Guide to Chemical Hazards #0133". National Institute for Occupational Safety and Health (NIOSH).
  2. ↑ 2.0 2.1 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
  3. ↑ 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.

External links