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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

Properties 

Molar mass/molecular mass

290.814 g/mol

Density 

1.89 at 66°F

Boiling point

323°C

Melting point 

113°C


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.
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