CHAPTER 6: Aryl Halides and Aralkyl Halides
B.sc 1st year Book Organic Chemistry (Page 3)
BHC | Benzenehexachloride or Gammaxene or 666 |
Molecular Formula : C6H6Cl6
Introduction: BHC is an organochlorine insecticide that can be sold under the name Gammaxene or indane. It was first prepared in 1825, and the insecticidal properties were identified in 1944 with the γ-isomer gamma-isomer), which is about 1,000 times more toxic than any of the other diastereomers formed in the reaction. The structural differences between these individuals are in the orientations of the chlorine בloms with respect to the ring of carbon atoms. The chemical addition of chlorine to benzene produces a mixture of several stereoisomers of 1,2,3,4,5,6-hexachlorocyclohexane. One of these isomers is an insecticide called lindane, or gammaxene. The γ-isomer, which makes up 20−25% of this mixture, is more soluble than the other isomers in certain solvents and can be separated from them. More volatile than DDT, BHC has a faster but less protracted action upon insects.
Lindane has been shown to accumulate in the food chain. This occurs because animals, including -humans, eat foods grown in lindane-contaminated soils, and fishes and other marine life are exposed to indane-contaminated waters. In fishes and mammals, exposure to high levels of lindane may cause acute poisoning, which is evidenced by nervous system dysfunction. Chronic exposure may adversely affect liver function in humans.
Technical BHC and the α,β,γ and δ-isomers of BHC are carcinogenic for the liver of mice and rats. Among the three BHC isomers, β-isomer was the most stable and bio-concentrated in all of the organisms. a- and γ – isomers were moderately persistent and degraded to some extent during the 33-day period.
Method of Preparation of BHC:
BHC is prepared by the addition of chlorine molecules to benzene in presence of ultraviolet light.
Mechanism of BHC:
The above reaction is carried out through a free radical mechanism. It involves the following steps –
Alpha( α)−HCH and beta( (β)−HCH are the isomers of hexachlorocyclohexane (HCH), They are by-production. the production of the insecticide lindane (γ−HCH). They are still contained in commercial-grade lindens as insecticides. As of 2009, the Stockholm Convention on Persistent Organic Pollutants classified ( α and (β−HCH) as Persistent Organic Pollutants(POPs), due to their chemical ability to persist an environment., bioaccumulative.
Animal studies show that organochlorine pesticides, including β−HCH, are neurotoxic, cause oxidative stress and damage the brain’s dopaminergic system. Human studies show that exposure to β−HCH is linked to Parkinson’s and Alzheimer’s disease.
Lindane is also known as gamma (γ)−HCH, gammaxene, gammallin, and benzene hexachloride(BHC). It -as been used both as an agricultural insecticide and as a pharmaceutical treatment for lice. It also affects the nervous system, liver, and kidneys and may be carcinogenic(generates cancer).