Skeletal formula Ball-and-stick model
CAS number  YesY
ChemSpider  YesY
Jmol-3D images Image 1
Molecular formula C5Cl6
Molar mass 272.77 g mol−1
Appearance Pale-yellow to amber-colored liquid
Odor Pungent[1]
Density 1.702 g/cm3
Melting point −10 °C (14 °F; 263 K)
Boiling point 239 °C (462 °F; 512 K)
Vapor pressure 0.08 mmHg
Main hazards Teratogen
Flash point 100 °C (212 °F; 373 K)
Except where noted otherwise, data are given for materials in their standard state (at 25 °C (77 °F), 100 kPa)
 YesY   YesY/N?)

Hexachlorocyclopentadiene, also known as C-56, is an [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. ^ CDC - NIOSH Pocket Guide to Chemical Hazards
  2. ^ a b 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