Pentachlorobenzene (PeCB) is a chemical compound with the molecular formula C₆HCl₅ which is a chlorinated

aromatic hydrocarbon Aromatic compounds, also known as "mono- and polycyclic aromatic hydrocarbons", are organic compounds containing one or more aromatic rings. The parent member of aromatic compounds is benzene. The word "aromatic" originates from the past grouping ...

. It consists of a

benzene Benzene is an organic chemical compound with the molecular formula C6H6. The benzene molecule is composed of six carbon atoms joined in a planar ring with one hydrogen atom attached to each. Because it contains only carbon and hydrogen atoms, ...

ring substituted with five

chlorine Chlorine is a chemical element with the Symbol (chemistry), symbol Cl and atomic number 17. The second-lightest of the halogens, it appears between fluorine and bromine in the periodic table and its properties are mostly intermediate betwee ...

atoms. PeCB was once used industrially for a variety of uses, but because of environmental concerns there are currently no large scale uses of PeCB.Pentachlorobenzene – Sources, environmental fate and risk characterization
, Robert E. Bailey, EuroChlor, July 2007 Pentachlorobenzene is a known

persistent organic pollutant Persistent organic pollutants (POPs), sometimes known as "forever chemicals", are organic compounds that are resistant to environmental degradation through chemical, biological, and photolytic processes. They are toxic chemicals that adversely ...

(POP) and banned globally by the

Stockholm Convention on Persistent Organic Pollutants Stockholm Convention on Persistent Organic Pollutants is an international environmental treaty, signed on 22 May 2001 in Stockholm and effective from 17 May 2004, that aims to eliminate or restrict the production and use of persistent organic ...

in 2009.Press Release – COP4 – Geneva, 8 May 2009: Governments unite to step-up reduction on global DDT reliance and add nine new chemicals under international treaty
2009.

Production

PeCB can be produced as a byproduct of the manufacture of

carbon tetrachloride Carbon tetrachloride, also known by many other names (such as tetrachloromethane, also IUPAC nomenclature of inorganic chemistry, recognised by the IUPAC, carbon tet in the cleaning industry, Halon-104 in firefighting, and Refrigerant-10 in HVAC ...

and benzene. It is extracted by

distillation Distillation, or classical distillation, is the process of separation process, separating the components or substances from a liquid mixture by using selective boiling and condensation, usually inside an apparatus known as a still. Dry distilla ...

and

crystallization Crystallization is the process by which solid forms, where the atoms or molecules are highly organized into a structure known as a crystal. Some ways by which crystals form are precipitating from a solution, freezing, or more rarely deposi ...

. The direct production of pure PeCB is not practical because of the simultaneous production of other chlorinated compounds. Since PeCB is generally produced in small quantities in the chlorination of benzene, it is also contained in other chlorobenzenes (

dichlorobenzene There are three distinct chemical compounds which are dichlorobenzenes: * 1,2-Dichlorobenzene or ''ortho''-dichlorobenzene; *1,3-Dichlorobenzene or ''meta''-dichlorobenzene; *1,4-Dichlorobenzene or ''para''-dichlorobenzene. All three isomers are co ...

trichlorobenzene Trichlorobenzene (TCB) may refer to any of three isomeric chlorinated derivatives of benzene with the molecular formula C6H3Cl3. Trichlorobenzenes are man-made chemical compounds that occur in three different forms. Even though the forms have the ...

s etc.) Today, a majority of the PeCB released into the environment is a result of backyard trash burning and municipal waste incineration.

Uses

PeCB was used as an intermediate in the manufacture of pesticides, particularly the

fungicide Fungicides are biocidal chemical compounds or biological organisms used to kill parasitic fungi or their spores. A fungistatic inhibits their growth. Fungi can cause serious damage in agriculture, resulting in critical losses of yield, quality, ...

pentachloronitrobenzene Pentachloronitrobenzene, typically abbreviated PCNB, is a registered fungicide formally derived from nitrobenzene. It is either an off-white or yellow solid, depending on its purity, with a musty odor. Preparation PCNB was originally synthesized ...

. Pentachloronitrobenzene is now made by the chlorination of

nitrobenzene Nitrobenzene is an organic compound with the chemical formula C6H5 NO2. It is a water-insoluble pale yellow oil with an almond-like odor. It freezes to give greenish-yellow crystals. It is produced on a large scale from benzene as a precursor t ...

in order to avoid the use of PeCB. PeCB was a component of a mixture of chlorobenzenes added to products containing

polychlorinated biphenyl Polychlorinated biphenyls (PCBs) are highly carcinogenic chemical compounds, formerly used in industrial and consumer products, whose production was banned in the United States by the Toxic Substances Control Act in 1979 and internationally by t ...

s in order to reduce

viscosity The viscosity of a fluid is a measure of its resistance to deformation at a given rate. For liquids, it corresponds to the informal concept of "thickness": for example, syrup has a higher viscosity than water. Viscosity quantifies the inte ...

. PeCB has also been used as a fire retardant.

Safety and regulation

PeCB is a

, allowing an accumulation in the food chain. Consequently, pentachlorobenzene was added in 2009 to the list of chemical compounds covered by the

Stockholm Convention Stockholm Convention on Persistent Organic Pollutants is an international environmental treaty, signed on 22 May 2001 in Stockholm and effective from 17 May 2004, that aims to eliminate or restrict the production and use of persistent organic ...

, an international treaty which restricts the production and use of persistent organic pollutants.Adding the 'Nasty Nine' to the 'Dirty Dozen'
thedailygreen.com PeCB has been banned in the European Union since 2002. PeCB is very toxic to aquatic organisms, and decomposes on heating or on burning with the formation of toxic, corrosive fumes including

hydrogen chloride The compound hydrogen chloride has the chemical formula and as such is a hydrogen halide. At room temperature, it is a colourless gas, which forms white fumes of hydrochloric acid upon contact with atmospheric water vapor. Hydrogen chloride ga ...

. Combustion of PeCB may also result in the formation of

polychlorinated dibenzodioxins Polychlorinated dibenzodioxins (PCDDs), or simply dioxins, are a group of long-lived polyhalogenated compound, polyhalogenated organic compounds that are primarily anthropogenic, and contribute toxic, Persistent organic pollutant, persistent org ...

("dioxins") and

polychlorinated dibenzofuran More thorough treatise of all groups with similar actions and binding to aryl hydrocarbon receptor is given in Dioxins and dioxin-like compounds. Polychlorinated dibenzofurans (PCDFs) are a family of organic compounds with one or several of the ...

References

{{reflist Chloroarenes Persistent organic pollutants under the Stockholm Convention

Production

Uses

Safety and regulation

See also

References