Polyhalogen Compounds

Description:

Polyhalogen compounds − are those compounds containing more than 1 halogen atoms.

Dichloromethane CH₂Cl₂

• Used as a solvent as a paint remover, propellant in aerosols.
• Used as process solvent in the manufacture of drugs.
• Used as a metal cleaning and finishing solvent.

Harmful Effects

• Harms the central nervous system
• Exposure to higher levels causes nausea, dizziness, numbness etc.
• Direct contact with eyes burn the cornea.

Trichloromethane CHCl₃

• Used as a solvent for fats, alkaloids and iodine.
• Major use is in the production of Freon refrigerant R − 22.
• Was previously used as an anesthetic as chloroform vapours depress the CNS.

Harmful Effects

• Chronic exposure can lead to kidneys and lever failure.

• Chloroform is stored in dark brown bottles as is it gets slowly oxidized by air to give a poisonous gas COCl₂, phosgene (carbonyl chloride).

Triiodomethane CHI₃

• It was used previously as an antiseptic due to the liberation of free iodine.

• Due to its unpleasant smell, it has now been replaced by other formulations that give iodine.

Tetrachloromethane CCl₄

• Carbon tetrachloride is used in the manufacture of refrigerants and propellants for aerosol cans.

• Also used as feedstock in the synthesis of chlorofluorocarbons, pharmaceutical manufacturing and as a solvent.

• Used as a cleaning fluid, as a degreasing agent, spot remover, and as a fire extinguisher.

Harmful Effects

• Dizziness, nausea, vomiting, and permanent damage to nerve cells.

• In severe cases, it can lead to stupor, coma, unconsciousness or death.

• When CCl₄ is released into the atmosphere, it results in depletion of ozone layer and thus increasing the exposure to harmful UV −rays  leading to skin cancer, eye diseases, disruption of immune system etc.

Freons

• The chlorofluorocarbon compounds of methane and ethane are called freons.

• They are stable, unreactive, non-toxic, non-corrosive and easily liquefiable gases.

• Freon − 12 (CCl₂F₂) is the most common freons used in industries.

• It is manufactured from CCl₄ via Swartz Reaction.

• Used in aerosol propellants, refrigeration, and air conditioning.

• When these freons reach the atmosphere, it initiates a radical chain reaction that affects the ozone layer balance.

p,p′ − Dichlorodiphenyltrichloroethane (DDT)

• It is the first chlorinated organic insecticides and was prepared by Paul Muller, who was awarded the Nobel Prize in Medicine and Physiology for this discovery.

• It is used as an insecticide and was mainly effective against mosquito (that caused malaria) and lice (that caused typhus).

Harmful Effects

• Due to its extensive use, many species of insects developed resistance to DDT.

• It was also found to have high toxicity towards fish.

• Due to its high chemical stability, DDT was not easily metabolized by animals and was deposited and stored in the fatty tissues.