Hexachlorocyclopentadiene
Encyclopedia
Hexachlorocyclopentadiene is an organochlorine compound that is a precursor to several pesticides. This colourless liquid is an inexpensive reactive diene
. Many of its derivatives proved to be highly controversial, as studies showed them to be persistent organic pollutant
s. Collectively, the pesticides derived from hexachlorocyclopentadiene are called the cyclodienes. An estimated 270,000 tons were produced until 1976, and some are still manufactured by Velsicol in the US and by Jiangsu Anpon Electrochemicals Co. in China.
to give 1,1,2,3,4,5-octachlorocyclopentane, which in a second step undergoes dehydrochlorination:
Hexachlorocyclopentadiene readily undergoes the Diels-Alder reaction
to give a variety of adduct
s that were commercialized as pesticides. The main derivatives are:
Additionally hexachlorocyclopentadiene is the precursor to the pesticides mirex
and kepone
, although these are not classified as cyclodienes.
.
approached 300 by 1989.
Diene
In organic chemistry a diene or diolefin is a hydrocarbon that contains two carbon double bonds.Conjugated dienes are functional groups, with a general formula of CnH2n-2. Dienes and alkynes are functional isomers...
. Many of its derivatives proved to be highly controversial, as studies showed them to be persistent organic pollutant
Persistent organic pollutant
thumb|right|275px|State parties to the Stockholm Convention on Persistent Organic PollutantsPersistent organic pollutants are organic compounds that are resistant to environmental degradation through chemical, biological, and photolytic processes...
s. Collectively, the pesticides derived from hexachlorocyclopentadiene are called the cyclodienes. An estimated 270,000 tons were produced until 1976, and some are still manufactured by Velsicol in the US and by Jiangsu Anpon Electrochemicals Co. in China.
Synthesis and applications
Hexachlorocyclopentadiene is prepared by chlorination of cyclopentadieneCyclopentadiene
Cyclopentadiene is an organic compound with the formula C5H6. This colorless liquid has a strong and unpleasant odor. At room temperature, this cyclic diene dimerizes over the course of hours to give dicyclopentadiene via a Diels–Alder reaction...
to give 1,1,2,3,4,5-octachlorocyclopentane, which in a second step undergoes dehydrochlorination:
- C5H6 + 6 Cl2 → C5H2Cl8 + 4 HCl
- C5H2Cl8 → C5Cl6 + 2 HCl
Hexachlorocyclopentadiene readily undergoes the Diels-Alder reaction
Diels-Alder reaction
The Diels–Alder reaction is an organic chemical reaction between a conjugated diene and a substituted alkene, commonly termed the dienophile, to form a substituted cyclohexene system. The reaction can proceed even if some of the atoms in the newly formed ring are not carbon...
to give a variety of adduct
Adduct
An adduct is a product of a direct addition of two or more distinct molecules, resulting in a single reaction product containing all atoms of all components. The resultant is considered a distinct molecular species...
s that were commercialized as pesticides. The main derivatives are:
- aldrinAldrinAldrin is an organochlorine insecticide that was widely used until the 1970s, when it was banned in most countries. It is a colourless solid. Before the ban, it was heavily used as a pesticide to treat seed and soil...
from norbornadieneNorbornadieneNorbornadiene is an organic compound. This bicyclic hydrocarbon is the most stable diolefin derived from the norbornane and norbornene. Norbornadiene is primarily of interest as a ligand in homogeneous catalysis, but it has been heavily studied due to its high reactivity and distinctive...
(the related dieldrinDieldrinDieldrin is a chlorinated hydrocarbon originally produced in 1948 by J. Hyman & Co, Denver, as an insecticide. Dieldrin is closely related to aldrin, which reacts further to form dieldrin. Aldrin is not toxic to insects; it is oxidized in the insect to form dieldrin which is the active compound...
is a metabolite of aldrin) - bromodan from allyl bromideAllyl bromideAllyl bromide is an organic halide. Its refractive index is 1.4697 . Allyl bromide is an alkylating agent used in synthesis of polymers, pharmaceuticals, allyls and other organic compounds. Physically, allyl bromide is a clear liquid with an intense, acrid, and persistent smell...
- chlordaneChlordaneChlordane, or chlordan, is an organochlorine compound that was used as a pesticide. This white solid was sold in the U.S. until 1983 as an insecticide for crops like corn and citrus and on lawns and domestic gardens.-Production and uses:...
from cyclopentadieneCyclopentadieneCyclopentadiene is an organic compound with the formula C5H6. This colorless liquid has a strong and unpleasant odor. At room temperature, this cyclic diene dimerizes over the course of hours to give dicyclopentadiene via a Diels–Alder reaction...
, followed by chlorination - endrinEndrinEndrin is an organochloride that was primarily used as an insecticide. It is a colourless odorless solid, although commercial samples are often off-white. It is also a rodenticide. This compound became infamous as persistent organic pollutant and for this reason is banned in many...
from acetyleneAcetyleneAcetylene 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...
, followed by cyclopentadiene, followed by epoxidation - heptachlorHeptachlorHeptachlor is an organochlorine compound that was used as an insecticide. Usually sold as a white or tan powder, heptachlor is one of the cyclodiene insecticides. In 1962, Rachel Carson's Silent Spring questioned the safety of heptachlor and other chlorinated insecticides. Due to its highly...
from cyclopentadiene, followed by monochlorination - isobenzanIsobenzanIsobenzan is a highly toxic organochloride insecticide. It was produced only in the period from 1958 to 1965 and its use has been since discontinued. It is a persistent organic pollutant that can remain in soil for 2 to 7 years, and the biological half-life of isobenzan in human blood is...
from dihydrofuran2,5-Dihydrofuran2,5-Dihydrofuran is a heterocyclic compound....
followed by chlorination - endosulfanEndosulfanEndosulfan is an off-patent organochlorine insecticide and acaricide that is being phased out globally. Endosulfan became a highly controversial agrichemical due to its acute toxicity, potential for bioaccumulation, and role as an endocrine disruptor...
from 1,4-dihydroxy-2-butene, followed by esterification with SOCl2
Additionally hexachlorocyclopentadiene is the precursor to the pesticides mirex
Mirex
Mirex is a chlorinated hydrocarbon that was commercialized as an insecticide and later banned because of its impact on the environment. This white crystalline odorless solid is a derivative of cyclopentadiene. It was popularized to control fire ants but by virtue of its chemical robustness and...
and kepone
Kepone
Kepone, also known as chlordecone, is a carcinogenic insecticide related to mirex, used between 1966 and 1975 in the USA for ant and roach baits.- Chemistry and toxicology :...
, although these are not classified as cyclodienes.
Regulation
Almost all derivatives have been banned or are under consideration for banning, according to the deliberations of the Stockholm Convention on Persistent Organic PollutantsStockholm Convention on Persistent Organic Pollutants
Stockholm Convention on Persistent Organic Pollutants is an international environmental treaty, signed in 2001 and effective from May 2004, that aims to eliminate or restrict the production and use of persistent organic pollutants .- History :...
.
Insect resistance
In addition to regulatory pressures, these pesticides became less effective owing to genetic mutations of the targeted insects. The number of insects resistant to cyclodienes and lindaneLindane
Lindane, also known as gamma-hexachlorocyclohexane, , gammaxene, Gammallin and erroneously known as benzene hexachloride , is an organochlorine chemical variant of hexachlorocyclohexane that has been used both as an agricultural insecticide and as a pharmaceutical treatment for lice and...
approached 300 by 1989.