Chloroprene
Encyclopedia
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
.
, (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. The chief impurity in chloroprene prepared in this way is
1-chlorobuta-1,3-diene, which is usually separated by distillation
.
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:
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This "acetylene process" has been replaced by a process which adds Cl2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.
Organic compound
An organic compound is any member of a large class of gaseous, liquid, or solid chemical compounds whose molecules contain carbon. For historical reasons discussed below, a few types of carbon-containing compounds such as carbides, carbonates, simple oxides of carbon, and cyanides, as well as the...
2-chlorobuta-1,3-diene, which has the formula
Chemical formula
A chemical formula or molecular formula is a way of expressing information about the atoms that constitute a particular chemical compound....
CH2=CCl-CH=CH2. This colorless liquid is the monomer
Monomer
A monomer is an atom or a small molecule that may bind chemically to other monomers to form a polymer; the term "monomeric protein" may also be used to describe one of the proteins making up a multiprotein complex...
for the production of the polymer
Polymer
A polymer is a large molecule composed of repeating structural units. These subunits are typically connected by covalent chemical bonds...
polychloroprene, a type of synthetic rubber
Synthetic rubber
Synthetic rubber is is any type of artificial elastomer, invariably a polymer. An elastomer is a material with the mechanical property that it can undergo much more elastic deformation under stress than most materials and still return to its previous size without permanent deformation...
. Polychloroprene is better known to the public as Neoprene
Neoprene
Neoprene or polychloroprene is a family of synthetic rubbers that are produced by polymerization of chloroprene. Neoprene in general has good chemical stability, and maintains flexibility over a wide temperature range...
, the trade name given by DuPont
DuPont
E. I. du Pont de Nemours and Company , commonly referred to as DuPont, is an American chemical company that was founded in July 1802 as a gunpowder mill by Eleuthère Irénée du Pont. DuPont was the world's third largest chemical company based on market capitalization and ninth based on revenue in 2009...
.
Production of chloroprene
Chloroprene is produced in three steps from 1,3-butadiene: (i) chlorinationChlorination
Chlorination is the process of adding the element chlorine to water as a method of water purification to make it fit for human consumption as drinking water...
, (ii) isomerization of part of the product stream, and (iii) dehydrochlorination of 3,4-dichloro-1-butene.
Chlorine
Chlorine
Chlorine is the chemical element with atomic number 17 and symbol Cl. It is the second lightest halogen, found in the periodic table in group 17. The element forms diatomic molecules under standard conditions, called dichlorine...
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
Atom
The atom is a basic unit of matter that consists of a dense central nucleus surrounded by a cloud of negatively charged electrons. The atomic nucleus contains a mix of positively charged protons and electrically neutral neutrons...
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
Distillation
Distillation is a method of separating mixtures based on differences in volatilities of components in a boiling liquid mixture. Distillation is a unit operation, or a physical separation process, and not a chemical reaction....
.
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, acetyleneAcetylene
Acetylene is the chemical compound with the formula C2H2. It is a hydrocarbon and the simplest alkyne. This colorless gas is widely used as a fuel and a chemical building block. It is unstable in pure form and thus is usually handled as a solution.As an alkyne, acetylene is unsaturated because...
is dimerized to give vinyl acetylene, which is then combined with hydrogen chloride
Hydrogen chloride
The compound hydrogen chloride has the formula HCl. At room temperature, it is a colorless gas, which forms white fumes of hydrochloric acid upon contact with atmospheric humidity. Hydrogen chloride gas and hydrochloric acid are important in technology and industry...
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
Chlorine
Chlorine is the chemical element with atomic number 17 and symbol Cl. It is the second lightest halogen, found in the periodic table in group 17. The element forms diatomic molecules under standard conditions, called dichlorine...
to one of the double bonds in 1,3-butadiene instead, and subsequent elimination produces HCl
Hydrogen chloride
The compound hydrogen chloride has the formula HCl. At room temperature, it is a colorless gas, which forms white fumes of hydrochloric acid upon contact with atmospheric humidity. Hydrogen chloride gas and hydrochloric acid are important in technology and industry...
instead, as well as chloroprene.
External links
- IARCInternational Agency for Research on CancerThe International Agency for Research on Cancer is an intergovernmental agency forming part of the World Health Organisation of the United Nations....
Monograph "Chloroprene." - Polychloroprene (CR), chloroprene rubber