Skeletal formula
Ball-and-stick model of hexachlorocyclopentadiene
IUPAC name
Other names
graphlox, perchlorocyclopentadiene
77-47-4 YesY
3D model (Jmol) Interactive image
ChemSpider 6233 YesY
ECHA InfoCard 100.000.937
PubChem 6478
Molar mass 272.76 g·mol−1
Appearance Pale-yellow to amber-colored liquid
Odor Pungent, unpleasant[1]
Density 1.702 g/cm3
Melting point −10 °C (14 °F; 263 K)
Boiling point 239 °C (462 °F; 512 K)
0.0002% (Reacts, 25°C)[1]
Vapor pressure 0.08 mmHg
Main hazards Teratogen
Flash point 100 °C (212 °F; 373 K)
US health exposure limits (NIOSH):
PEL (Permissible)
REL (Recommended)
TWA 0.01 ppm (0.1 mg/m3)[1]
IDLH (Immediate danger)
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Infobox references

Hexachlorocyclopentadiene, also known as C-56, 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 pollutants. 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 Chemical Corporation in the US and by Jiangsu Anpon Electrochemicals Co. in China. [2]

Synthesis and applications

Hexachlorocyclopentadiene is prepared by chlorination of cyclopentadiene to give 1,1,2,3,4,5-octachlorocyclopentane, which in a second step undergoes dehydrochlorination:[3]

C5H6 + 6 Cl2 → C5H2Cl8 + 4 HCl
C5H2Cl8 → C5Cl6 + 2 HCl

Hexachlorocyclopentadiene readily undergoes the Diels-Alder reaction to give a variety of adducts 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.


Almost all derivatives have been banned or are under consideration for banning, according to the deliberations of the Stockholm Convention on Persistent Organic Pollutants.

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 lindane approached 300 by 1989.[2]


  1. 1 2 3 4 5 "NIOSH Pocket Guide to Chemical Hazards #0315". National Institute for Occupational Safety and Health (NIOSH).
  2. 1 2 Robert L. Metcalf “Insect Control” in Ullmann’s Encyclopedia of Industrial Chemistry” Wiley-VCH, Wienheim, 2002. doi:10.1002/14356007.a14_263
  3. Dieter Hönicke, Ringo Födisch, Peter Claus, Michael Olson “Cyclopentadiene and Cyclopentene” Ullmann's Encyclopedia of Industrial Chemistry 2002, Wiley-VCH, Weinheim. doi:10.1002/14356007.a08_227
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