Chloroprene

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. 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. Only one facility in the United States produces the chemical, the Pontchartrain Works in Reserve, Louisiana. In 2015, the United States Environmental Protection Agency identified chloroprene as causing cancer. ==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: In 1983, approximately 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. 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: : 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 This "acetylene process" has been replaced by the chlorination of 1,3-butadiene.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. Occupational exposure limits A table of occupational exposure limits (OELs) from various jurisdictions follows. In general, the OELs range from . Environment The fate of chloroprene in the environment has been examined. Due to its volatility and extreme reactivity, it is not expected to bioaccumulate. 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. There are criticisms of this report that indicate that the unsafe exposure levels may have been exaggerated badly based on levels for known carcinogens. Chronic exposure to chloroprene may have the following symptoms: liver function abnormalities, disorders of the cardiovascular system, and depression of the immune system. ==References==