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.
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]
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 2million 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 This "acetylene process" has been replaced by the chlorination of 1,3-butadiene.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 25ppm.[11]
Occupational exposure limits for chloroprene[citation needed]
Organization
Concentration
NIOSH REL
1ppm
ACGIH TLV 8-hour TWA
10ppm
OSHA PEL 8-hour TWA
25ppm
Mine Safety and Health Administration
25ppm
Austria OEL MAK-TMW
5ppm
Belgium OEL TWA
10ppm
Denmark OEL ceiling concentration
1ppm
Finland OEL TWA
1ppm
France OEL VME
10ppm
Hungary OEL TWA
5ppm
Iceland OEL Short Term Exposure Limit (STEL)
1ppm
Korea OEL TWA
10ppm
Mexico OEL TWA
10ppm
New Zealand OEL TWA
10ppm
Norway OEL TWA
1ppm
Peru OEL TWA
10ppm
Poland OEL MAC TWA
0.55ppm
Sweden OEL TWA
1ppm
Switzerland OEL MAK-week
5ppm
The Netherlands OEL MAC-TGG
5ppm
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]
12Carothers, Wallace H.; Williams, Ira.; Collins, Arnold M.; Kirby, James E. (November 1931). "Acetylene Polymers and their Derivatives. II. A New Synthetic Rubber: Chloroprene and its Polymers". Journal of the American Chemical Society. 53 (11): 4203–4225. doi:10.1021/ja01362a042.
↑Smith, John K. (January 1985). "The Ten-Year Invention: Neoprene and Du Pont Research, 1930-1939". Technology and Culture. 26 (1): 34–55. doi:10.2307/3104528. JSTOR3104528. S2CID113234844.
↑"Template Package 4". Centers for Disease Control and Prevention. Retrieved 2018-11-24.
↑National Institute of Environmental Health Sciences. National Toxicology Program (2016). Report on Carcinogens, fourteenth edition. ISBN978-1-5231-0852-7. OCLC990561140.
