Fact sheet: Pentachlorobenzene

From: Public Services and Procurement Canada

Discover a list of a contaminant's important chemical properties, how it will react in the environment, main sources of contamination related, and a brief overview of health and safety issues.

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General information

CAS number


Molecular formula


Formula weight

250.3 g/mol



Properties (at room temperature where applicable)

Compound properties list
Melting/boiling point85 °CSolid
Relative density1.83 g/cm3Sinks in water
Vapour pressure0.006 mm HgVery low volatility
Vapour density0N/A
Solubility in water0.5 mg/LVery low solubility
Henry's law constant6 x 10-4atm·m3/molModerately volatile when dissolved
log Koc (Depending on soil or sediment characteristics)4.1 - 6.3*Very strong adsorption to organic matter

Environmental behaviour

At 20 0C, pentachlorobenzene is a solid with very low volatility and solubility. Once it is dissolved, it is moderately volatile and adsorbs very strongly to organic matter. When present in the soil, it volatilizes and dissolves very slowly. In the dissolved phase, pentachlorobenzene can reach the water table or drain into a waterway where it will be diluted before partially volatilizing. Fragments of pentachlorobenzene can also be carried into waterways where they will be deposited at the bottom and dissolve very slowly. Once the source has been removed, the adsorbed phase will take a very long time to disappear, liberating contamination in either the gaseous or dissolved state. The resulting plumes (gaseous and dissolved) are generally small in size.

Health and safety

In Canada, pentachlorobenzene is considered "toxic", as defined under Paragraph 64(a) of CEPA 1999, and has been added to Schedule 1.

Principal resources

Pentachlorobenzene is not currently produced or used in its pure form in Canada. The principal current commercial use of pentachlorobenzene is as a chemical intermediate in the formation of pentachloronitrobenzene (also known as quintozene), a fungicide which is currently used, but not produced, in Canada. Pentachlorobenzene is present as an impurity in this and other herbicides, pesticides and fungicides currently in use in Canada. Pentachlorobenzene is also present as an impurity in pentachlorophenol, one of the five main wood treatment chemicals that are used in Canada.

Pentachlorobenzene may be present as an undesirable by-product in the manufacture of hexachlorobenzene, pentachloronitrobenzene, tetrachlorobenzenes, tetrachloroethylene, trichloroethylene, and 1,2-dichloroethane.

Pentachlorobenzene was a component of a mixture of chlorobenzenes added to products containing polychlorinated biphenyls (transformer dielectric fluids) in order to reduce viscosity. In Canada, approximately 200,000 kg of pentachlorobenzene are present in transformer dielectric fluids either in use or stored before disposal. Pentachlorobenzene has also been used as a fire retardant.


Canadian Council of Ministers of the Environment. 1999. Canadian water quality guidelines for the protection of aquatic life: Chlorinated benzenes-Pentachlorobenzene. In: Canadian environmental quality guidelines, 1999. Canadian Council of Ministers of the Environment, Winnipeg. Canada. (Viewed December 2013)

Environment Canada. 2009. CEPA Environmental Registry: Toxic Substances List-Updated Schedule 1 as of December 27, 2006. (Viewed December 2013)

Environment Canada. 2009. Management of Toxic Substances: Pentachlorobenzenes (QCB). (Viewed December 2013)

Montgomery, John H. 2007. Groundwater Chemicals, Desk Reference, Fourth Edition, CRC Press, Taylor and Francis Group, Florida, U.S.A.