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Polyhalogen Compounds

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Polyhalogen Compounds - Lesson Summary

Polyhalogen compounds are carbon compounds containing more than one halogen atom. Many polyhalogen compounds are useful in the industry and in agriculture.


Dichloromethane, also called methylene chloride, is a colourless volatile liquid with a moderately sweet aroma.

Dichloromethane is used as a propellant in aerosols and also as a paint remover. Dichloromethane is also used as a process solvent in the manufacture of drugs. It has additional uses as a metal cleaning and finishing solvent.

It harms the central nervous system. Exposure to even low levels in the air can lead to slightly impaired hearing and vision. Exposure to higher levels in the air may cause dizziness, nausea, and tingling or numbness in the fingers and toes. If dichloromethane comes in direct contact with the eyes, it may burn the cornea.


Trichloromethane (or) chloroform, is a colourless, volatile, non-flammable liquid with a sweet odour. It is also used in the synthesis of Freon, a refrigerant. Chloroform was once used as a general anaesthetic in surgery. However, this use has been discontinued, as there are a number of safer alternatives.

Breathing in chloroform vapours depresses the central nervous system. Breathing chloroform even for a short time can cause dizziness, fatigue and headache. Chronic chloroform exposure may cause damage to the kidneys and liver. In the liver, chloroform is metabolised to form phosgene, a deadly gas.

Chloroform is slowly oxidised by air in the presence of light into deadly phosgene gas. Therefore, chloroform is stored in dark bottles to prevent exposure to light. The bottles are filled completely to keep air out.


Triiodomethane (or) iodoform, is a pale yellow, crystalline solid, has a pungent, medicine-like odour.

Iodoform has uses as an antiseptic. Iodoform is used in medical applications. The antiseptic properties are due to the liberation of free iodine.

Carbon tetrachloride:

Carbon tetrachloride is a clear liquid with a sweet smell.

It is used in the manufacture of refrigerants and aerosol propellants also in the synthesis of chlorofluorocarbons.

The health risks associated with carbon tetrachloride are very serious, as the substance is a suspected carcinogen. Chronic exposure to carbon tetrachloride may cause liver cancer in humans. Kidney damage is also a risk. Carbon tetrachloride has been linked to the depletion of the ozone layer.


Freons are chlorofluorocarbon derivatives of methane and ethane. They are non-toxic, non-corrosive and easily liquefiable gases.

Freon-12 was one of the most commonly used Freons in the industry. Freon-12 useful in aerosol propellants, refrigeration and air conditioning.

Freon-12 and other chlorofluorocarbons are known to initiate radical chain reactions that lead to the destruction of the ozone layer.


DDT has been used to prevent insect-transmitted human diseases, such as malaria, spread by mosquitoes, and typhus, spread by lice.

DDT is toxic to many species of fish. For certain species of birds, such as ospreys, eagles, pelicans, falcons and hawks, DDT exposure leads to thinning of eggshells, causing serious population declines. DDT is stored in the fatty tissues of the body and is metabolised very slowly. The use of DDT in agriculture has lead to measurable DDT levels in humans.


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