Chloroprene
Chemical compound
From Wikipedia, the free encyclopedia
Chloroprene (IUPAC name 2-chlorobuta-1,3-diene) is a chemical compound with the molecular formula CH2=CCl−CH=CH2.[5] Chloroprene is a colorless volatile liquid, almost exclusively used as a monomer for the production of the polymer polychloroprene, better known as neoprene, a type of synthetic rubber.
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| Names | |||
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| Preferred IUPAC name
2-Chlorobuta-1,3-diene | |||
Other names
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| Identifiers | |||
3D model (JSmol) |
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| 741875 | |||
| ChEBI | |||
| ChEMBL | |||
| ChemSpider | |||
| ECHA InfoCard | 100.004.381 | ||
| EC Number |
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| 277888 | |||
| KEGG | |||
PubChem CID |
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| RTECS number |
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| UNII | |||
| UN number | 1991 | ||
CompTox Dashboard (EPA) |
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| Properties | |||
| C4H5Cl | |||
| Molar mass | 88.53 g·mol−1 | ||
| Appearance | Colorless liquid | ||
| Odor | Pungent, ether-like | ||
| Density | 0.9598 g/cm3 | ||
| Melting point | −130 °C (−202 °F; 143 K)[1] | ||
| Boiling point | 59.4 °C (138.9 °F; 332.5 K)[1] | ||
| 0.026 g/100 mL | |||
| Solubility in diethyl ether | miscible[1] | ||
| Solubility in acetone | miscible[1] | ||
| Solubility in benzene | miscible[1] | ||
| Solubility in ethanol | soluble | ||
| Vapor pressure |
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Refractive index (nD) |
1.4583 | ||
| Hazards | |||
| Occupational safety and health (OHS/OSH): | |||
Main hazards |
Highly flammable, irritant, toxic | ||
| GHS labelling:[1] | |||
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| Danger | |||
| H225, H302, H315, H319, H332, H335, H350, H373 | |||
| P203, P210, P233, P240, P241, P242, P243, P260, P264, P264+P265, P270, P271, P280, P281, P301+P317, P302+P352, P303+P361+P353, P304+P340, P305+P351+P338, P308+P313, P317, P318, P319, P321, P330, P332+P317, P337+P313, P362+P364, P370+P378, P403+P233, P403+P235, P405, P501 | |||
| NFPA 704 (fire diamond) | |||
| Flash point | −4 °C (25 °F; 269 K)[1] | ||
| Explosive limits | 1.9%–20.0%[1] | ||
Threshold limit value (TLV) |
10 ppm (skin)[1] (TWA) | ||
| Lethal dose or concentration (LD, LC): | |||
LD50 (median dose) |
450 mg/kg (rat, oral) | ||
LC50 (median concentration) |
3207 ppm (rat, 4 hr)[3] | ||
LCLo (lowest published) |
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| NIOSH (US health exposure limits):[4] | |||
PEL (Permissible) |
25 ppm (90 mg/m3, TWA, skin) | ||
REL (Recommended) |
1 ppm (3.6 mg/m3, Ca C, [15-minute]) | ||
IDLH (Immediate danger) |
300 ppm (1086 mg/m3) | ||
| Related compounds | |||
Related Dienes |
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Related compounds |
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Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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History
Although it may have been discovered earlier, chloroprene was largely developed by DuPont during the early 1930s, specifically with the formation of neoprene in mind.[6] The chemists Elmer K. Bolton, Wallace Carothers, Arnold Collins and Ira Williams are generally accredited with its development and commercialisation although the work was based upon that of Julius Arthur Nieuwland, with whom they collaborated.[7]
Only one facility in the United States produces the chemical, the Pontchartrain Works in Reserve, Louisiana.[8] In 2015, the United States Environmental Protection Agency identified chloroprene as causing cancer.[9]
Production
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:[5]
- CH2=CHCH=CH2 + Cl2 → ClCH2CH=CHCH2Cl
- ClCH2CH=CHCH2Cl → ClCH2CHClCH=CH2
- ClCH2CHClCH=CH2 → CH2=CClCH=CH2 + HCl
The chief impurity in chloroprene prepared in this way is 1-chlorobuta-1,3-diene, which is usually separated by distillation.[5] In 1983, approximately 2 million kilograms (2,200 short tons) were produced in this manner.
Acetylene process
Until the 1960s, chloroprene production was dominated by the "acetylene process," which was modeled after the original synthesis of vinylacetylene.[6] 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 copper(I) chloride, rearranges to the targeted 2-chlorobuta-1,3-diene:[5]
The acetylene process is energy-intensive and has high investment costs. Furthermore, the intermediate vinyl acetylene is unstable. This "acetylene process" has been replaced by the chlorination of 1,3-butadiene.
Hazards
Chloroprene may explosively polymerize. The peroxide catalyzes this.[10]
Occupational exposure limits
A table of occupational exposure limits (OELs) from various jurisdictions follows. In general, the OELs range from 0.55 to 25 ppm.[11]
| Occupational exposure limits for chloroprene[citation needed] | |
|---|---|
| Organization | Concentration |
| NIOSH REL | 1 ppm |
| ACGIH TLV 8-hour TWA | 10 ppm |
| OSHA PEL 8-hour TWA | 25 ppm |
| Mine Safety and Health Administration | 25 ppm |
| Austria OEL MAK-TMW | 5 ppm |
| Belgium OEL TWA | 10 ppm |
| Denmark OEL ceiling concentration | 1 ppm |
| Finland OEL TWA | 1 ppm |
| France OEL VME | 10 ppm |
| Hungary OEL TWA | 5 ppm |
| Iceland OEL Short Term Exposure Limit (STEL) | 1 ppm |
| Korea OEL TWA | 10 ppm |
| Mexico OEL TWA | 10 ppm |
| New Zealand OEL TWA | 10 ppm |
| Norway OEL TWA | 1 ppm |
| Peru OEL TWA | 10 ppm |
| Poland OEL MAC TWA | 0.55 ppm |
| Sweden OEL TWA | 1 ppm |
| Switzerland OEL MAK-week | 5 ppm |
| The Netherlands OEL MAC-TGG | 5 ppm |
Environment
The fate of chloroprene in the environment has been examined.[12] Due to its volatility and extreme reactivity, it is not expected to bioaccumulate.[13]
Health
Chloroprene is toxic. Chloroprene is potentially carcinogenic, can cause temporary hair loss on the exposed area, and can cause damage to the eyes and skin.[14]
The Environmental Protection Agency designated chloroprene as likely to be carcinogenic to humans based on evidence from studies that showed a statistically significant association between occupational chloroprene exposure and the risk of lung cancer.[13] There are criticisms of this report that indicate that the unsafe exposure levels may have been exaggerated badly based on levels for known carcinogens.[15]
Chronic exposure to chloroprene may have the following symptoms: liver function abnormalities, disorders of the cardiovascular system, and depression of the immune system.[1]
One fatality as a result of chloroprene intoxication has been recorded, which was a result of cleaning a container used for chloroprene.[16]