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Hexachlorobenzene
Hexachlorobenzene, or perchlorobenzene, is an aryl chloride and a six-substituted chlorobenzene with the molecular formula C6Cl6. It is a fungicide formerly used as a seed treatment, especially on wheat to control the fungal disease bunt. Its use has been banned globally under the Stockholm Convention on Persistent Organic Pollutants.
Hexachlorobenzene is a stable, white, crystalline chlorinated hydrocarbon. It is sparingly soluble in organic solvents such as benzene, diethyl ether and alcohol, but practically insoluble in water with no reaction. It has a flash point of 468 °F and it is stable under normal temperatures and pressures. It is combustible but it does not ignite readily. When heated to decomposition, hexachlorobenzene emits highly toxic fumes of hydrochloric acid, other chlorinated compounds (such as phosgene), carbon monoxide, and carbon dioxide.
Hexachlorobenzene was first known as "Julin's chloride of carbon" as it was discovered as a strange and unexpected product of impurities reacting in Johan Jacob von Julin's nitric acid factory. In 1864, Hugo Müller synthesised the compound by the reaction of benzene and antimony pentachloride, he then suggested that his compound was the same as Julin's chloride of carbon. Müller previously also believed it was the same compound as Michael Faraday's "perchloride of carbon" (Hexachloroethane), obtained a small sample of Julin's chloride of carbon to send to Richard Phillips and Faraday for investigation. In 1867, Henry Bassett proved that the compound produced from benzene and antimony was the same as Julian's carbon chloride and named it "hexachlorobenzene".
Leopold Gmelin named it "dichloride of carbon" and claimed that the carbon was derived from cast iron and the chlorine was from crude saltpetre.
Victor Regnault obtained hexachlorobenzene from the decomposition of chloroform and tetrachloroethylene vapours through a red-hot tube.
The crystal structure of hexachlorobenzene was determined by Kathleen Lonsdale who showed the molecule to be planar and hexagonal.
Large-scale manufacture for use as a fungicide was developed by using the residue remaining after purification of the mixture of isomers of hexachlorocyclohexane, from which the insecticide lindane (the γ-isomer) had been removed, leaving the unwanted α- and β- isomers. This mixture is produced when benzene is reacted with chlorine in the presence of ultraviolet light (e.g. from sunlight). However, manufacture is no longer practiced following the compound's ban.
Hexachlorobenzene has been made on a laboratory scale since the 1890s, by the electrophilic aromatic substitution reaction of chlorine with benzene or chlorobenzenes. A typical catalyst is ferric chloride. Much milder reagents than chlorine (e.g. dichlorine monoxide, iodine in chlorosulfonic acid) also suffice, and the various hexachlorocyclohexanes can substitute for benzene as well.
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Hexachlorobenzene
Hexachlorobenzene, or perchlorobenzene, is an aryl chloride and a six-substituted chlorobenzene with the molecular formula C6Cl6. It is a fungicide formerly used as a seed treatment, especially on wheat to control the fungal disease bunt. Its use has been banned globally under the Stockholm Convention on Persistent Organic Pollutants.
Hexachlorobenzene is a stable, white, crystalline chlorinated hydrocarbon. It is sparingly soluble in organic solvents such as benzene, diethyl ether and alcohol, but practically insoluble in water with no reaction. It has a flash point of 468 °F and it is stable under normal temperatures and pressures. It is combustible but it does not ignite readily. When heated to decomposition, hexachlorobenzene emits highly toxic fumes of hydrochloric acid, other chlorinated compounds (such as phosgene), carbon monoxide, and carbon dioxide.
Hexachlorobenzene was first known as "Julin's chloride of carbon" as it was discovered as a strange and unexpected product of impurities reacting in Johan Jacob von Julin's nitric acid factory. In 1864, Hugo Müller synthesised the compound by the reaction of benzene and antimony pentachloride, he then suggested that his compound was the same as Julin's chloride of carbon. Müller previously also believed it was the same compound as Michael Faraday's "perchloride of carbon" (Hexachloroethane), obtained a small sample of Julin's chloride of carbon to send to Richard Phillips and Faraday for investigation. In 1867, Henry Bassett proved that the compound produced from benzene and antimony was the same as Julian's carbon chloride and named it "hexachlorobenzene".
Leopold Gmelin named it "dichloride of carbon" and claimed that the carbon was derived from cast iron and the chlorine was from crude saltpetre.
Victor Regnault obtained hexachlorobenzene from the decomposition of chloroform and tetrachloroethylene vapours through a red-hot tube.
The crystal structure of hexachlorobenzene was determined by Kathleen Lonsdale who showed the molecule to be planar and hexagonal.
Large-scale manufacture for use as a fungicide was developed by using the residue remaining after purification of the mixture of isomers of hexachlorocyclohexane, from which the insecticide lindane (the γ-isomer) had been removed, leaving the unwanted α- and β- isomers. This mixture is produced when benzene is reacted with chlorine in the presence of ultraviolet light (e.g. from sunlight). However, manufacture is no longer practiced following the compound's ban.
Hexachlorobenzene has been made on a laboratory scale since the 1890s, by the electrophilic aromatic substitution reaction of chlorine with benzene or chlorobenzenes. A typical catalyst is ferric chloride. Much milder reagents than chlorine (e.g. dichlorine monoxide, iodine in chlorosulfonic acid) also suffice, and the various hexachlorocyclohexanes can substitute for benzene as well.