Benzene Hexachloride
BHC is one of various stereoisomers of 1,2,3,4,5,6-hexachlorocyclohexane. It is formed by the light-induced addition of chlorine to benzene. One of these isomers is the insecticide lindane, also known as Gammexane.
- The insecticidal properties of benzene hexachloride were identified in 1944 with the -isomer.
- -isomer is 1,000 times more toxic than any of the other diastereomers formed in the reaction.
- The orientations of the chlorine atoms with respect to the carbon ring are the structural variations between these individuals.
- When chlorine is added to benzene, it produces a mixture of several stereoisomers of 1,2,3,4,5,6-hexachlorocyclohexane.
- The -isomer (20–25 percent of this mixture), is more soluble in certain solvents than the other isomers and can thus be separated from them.
- Benzene hexachloride, which is more volatile as compared to DDT, kills insects faster but for a shorter timespan.
Benzene Hexachloride Preparation
- In the presence of sunlight and in the absence of oxygen and substitution catalysts, chlorine combines with benzene to form hexachlorocyclohexane.
- Photochlorination can be used to create lindane from benzene and chlorine.
- The resulting product, benzene hexachloride, contains isomers, of which only the -isomer is desired.
- The gamma-isomer is obtained by treating the reaction mixture with methanol or acetic acid, which dissolves only the alpha and beta isomers easily.
Properties of Benzene Hexachloride
Benzene hexachloride
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Properties
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Molar mass/molecular mass
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290.814 g/mol
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Density
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1.89 at 66°F
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Boiling point
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323°C
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Melting point
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113°C
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Harmful effects of Benzene Hexachloride
- Lindane has been found to build up in the food chain.
- Animals and humans consume foods grown in soils contaminated with lindane.
- Fish and other marine life are exposed to waters contaminated with lindane.
- Exposure to high levels of lindane in fish and mammals can result in acute poisoning and dysfunction of the nervous system.
- Chronic exposure may have a negative effect on liver functions of humans.
- Lindane is no longer permitted to be used as smoke fumigators inside closed spaces, and its use as an insecticide is prohibited in many countries.
- Although, the use of BHC as topical lice-fighting ointments is permitted.
Adverse effects
- A wide range of adverse reactions to lindane pharmaceuticals have been reported, such as skin irritation,seizures and, in rare cases, death.
- Burning sensations, dryness, itching, and rash are the most common side effects.
- While serious side effects are uncommon and almost always the result of misuse, adverse reactions have occurred when used properly.
- As a result, the FDA requires a so-called black box warning on lindane products, which explains the risks of lindane products and how to use them properly.
- The black box warning emphasises that lindane should not be used on premature infants or individuals with known uncontrolled seizure disorders
- It should be used with caution in infants, children, the elderly, and people with other skin conditions (e.g., psoriasis, dermatitis), as they may be at risk of serious neurotoxicity.
Isomers
- The gamma isomer of hexachlorocyclohexane ("-HCH") is lindane.
- Aside from lindane pollution, there are some concerns about the other isomers of HCH, i.e. alpha-HCH and beta-HCH, which are significantly more toxic than lindane, lack its insecticidal properties, and are byproducts of lindane production.
- In the 1940s and 1950s, lindane producers piled these isomers in open heaps, contaminating the ground and water.
- Since then, the International HCH and Pesticide Forum has been formed to bring experts together to address the containment of these sites.
- Modern lindane manufacturing practises include the treatment and conversion of waste isomers to less toxic industrial chemicals. This process is known as "cracking."
- Today, only a few production plants remain operational around the world to accommodate lindane's public-health applications and declining agricultural needs.
- Lindane has not been produced in the United States since the mid-1970s, but it is still imported.