10. HALOGEN DERIVATIVES - part 08 - Uses and Environmental effects of some polyhalogen compounds

10. HALOGEN DERIVATIVES - part 08 - Uses and Environmental effects of some polyhalogen compounds

Uses and Environmental effects of some polyhalogen compounds :
1 Dichloromethane/ methylene chloride (CH2Cl2) :
  • Colourless volatile liquid with moderately sweet aroma. 
  • Used as a solvent, and used as a propellant in aerosols.
  • Over exposure to dichloromethane causes dizziness, fatigue, nausea, headaches, numbness, weakness. 
  • Highly dangerous if it comes in direct contact with eyes as it damages cornea.
2 Chloroform / trichloromethane (CHCl3) : 
  • Colourless liquid with peculiar sweet smell. 
  • Used to prepare chlorofluromethane, a refrigerant R-22. 
  • Used as a solvent for extraction of natural products like gums, fats, resins. 
  • Used as a source of dichlorocarbene. 
  • Causes depression of central nervous system. 
  • Inhaling chloroform for a short time causes fatigue, dizziness and headache. 
  • Long exposure to chloroform may affect liver. 
  • Chloroform when exposed to air and light forms a poisonous compound phosgene so it is stored in dark coloured air tight bottles.
3 Carbon tetrachloride / tetrachloromethane (CCl4) :
  • Colourless liquid with sweet smell. 
  • Very useful solvent for oils, fats, resins. 
  • Serves as a source of chlorine. 
  • Used as a cleaning agent. 
  • Highly toxic to liver. 
  • Exposure to high concentration of CCl4 can affect central nervous system and it is suspected to be carcinogenic. 
  • Prolonged exposure may cause death. 
  • It is a green house gas.
4 Idoform or triiodomethane (CHI3):
  • Yellow crystalline substance with disagreeable smell.used in medicine as a healing agent and antiseptic in dressing of wounds.
  • Causes irritation to skin and eyes. 
  • May cause respiratory irritation or breathing difficulty, dizziness, nausea, depression of central nervous system, visual disturbance.
5 Freons : 
  • These are organic compounds of chlorine and fluorine, chlorofluorocarbons, CFC's are commonly used as refrigerants.
  • Most common representative is dichlorodifluromethane (Freon-12) others include chlorodifluromethane (R-22), trichlorofluromethane (R-11) and so on.
  • Used as refrigerants in fridge and airconditioning, propellants in aerosol and solvents. 
  • Used as blowing agents in making foams and packing materials.
  • Chloroflurocarbons are responsible for ozone depletion of ozone in stratosphere. 
  • Regular large inhalation of freons results in breathing problems, organ damage, loss of consciousness.

6 Dichlorodiphenyltrichloroethane (DDT) : 

  • Colourless, tasteless and odorless crystalline compound havinginsecticidal property.
  • Kills insects such as houseflies, mosquitoes and body lice. 
  • Used for controlling maleria and typhus.
  • Exposure to high doses of DDT may cause vomiting, tremors or shakiness. 
  • Laboratory animal studies showed adverse effect of DDT on liver and reproduction. 
  • DDT is a pressistent organic pollutant, readily absorbed in soils and tends to accumulate in the ecosystem.
  • When dissolved in oil or other lipid, it is readily absorbed by the skin. 
  • It is resistant to metabolism. 
  • It accumulates in fatty tissues.
  • There is a ban on use of DDT due to all these adverse effects .

Do U Know?
  • When ultraviolet radiation (UV) strikes CFC (CFCl3) molecules in the upper atmosphere, the carbon-chlorine bond breaks and produces highly reactive chlorine atom (Cl).
                                 CFCl3 → CFCl2 + Cl
  • This reactive chlorine atom decomposes ozone (O3) molecule into oxygen molecule (O2).
                                O3 + Cl → O2 + ClO
                               ClO + O → O2 + Cl

  • One atom of chlorine can destroy upto 100,000ozone molecules.

Do you know ?

  • DDT, the first chlorinated organic insecticides, was originally prepared in 1873, but it was not until 1939 that Paul Muller of Geigy Pharmaceuticals in Switzerland discovered the effectiveness of DDT as an insecticide. 
  • Paul Muller was awarded the Nobel Prize in Medicine and Physiology in 1948 for this discovery.
  • The use of DDT increased enormously on a worldwide basis after World War II, primarily because of its effectiveness against the mosquito that spreads malaria and lice that carry typhus. 
  • Many species of insects developed resistance to DDT, and it was also discovered to have a high toxicity towards fish. 
  • DDT is not metabolised very rapidly by animals; instead, it is deposited and stored in the fatty tissues. 
  • Use of DDT was banned in the United States in 1973, although it is still in use in some other parts of the world.

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