Chloroprene

Chloroprene

Chloroprene Chloroprene
Names
IUPAC name 2-Chlorobuta-1,3-diene
Other names Chloroprene, 2-chloro-1,3-butadiene, Chlorobutadiene, beta-Chloroprene
Identifiers
CAS Number	126-99-8 Y
ChEBI	CHEBI:39481 Y
ChEMBL	ChEMBL555660 Y
ChemSpider	29102 Y
Jmol 3D model	Interactive image
KEGG	C19208 Y
PubChem	31369
RTECS number	EL9625000
InChI InChI=1S/C4H5Cl/c1-3-4(2)5/h3H,1-2H2 Y Key: YACLQRRMGMJLJV-UHFFFAOYSA-N Y InChI=1/C4H5Cl/c1-3-4(2)5/h3H,1-2H2 Key: YACLQRRMGMJLJV-UHFFFAOYAQ
SMILES Cl/C(=C)/C=C
Properties
Chemical formula	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)
Solubility in water	0.026 g/100 mL
Solubility	soluble in alcohol, diethyl ether miscible in ethyl ether, acetone, benzene
Vapor pressure	188 mmHg (20°C)
Refractive index (nD)	1.4583
Vapor pressure	{{{value}}}
Related compounds
Related Dienes	Butadiene Isoprene
Related compounds	Vinyl chloride
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 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.

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-dichlorobut-1-ene.

Chlorine adds to 1,3-butadiene to afford a mixture of 3,4-dichlorobut-1-ene and 1,4-dichlorobut-2-ene. The 1,4-dichloro 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. 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. 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:

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.

External links

• International Chemical Safety Card 0133
• IARC Monograph "Chloroprene."