Uses of Haloalkanes and Haloarenes: The alkanes that have one or more halogens bonded to the \({\text{s}}{{\text{p}}^3}\) hybridised carbon atoms of the alkyl group are known as haloalkanes. These compounds are generally represented as \({\text{R-X,}}\) where \({\text{R}}\) represents the alkyl group, and \({\text{X}}\) denotes halogen atom, which can be fluorine \(\left({\text{F}} \right),\) chlorine \(\left({{\text{Cl}}} \right),\) bromine \(\left({{\text{Br}}} \right),\) or iodine \(\left({\text{I}} \right).\)

General Uses

1. Alkyl halides are used as solvents for relatively non-polar compounds.
2. Haloalkanes and haloarenes are used as starting materials for the synthesis of a wide range of organic compounds.
3. Chloramphenicol, a chlorine-containing antibiotic produced by soil microorganisms, is very effective for treating typhoid fever.
4. The deficiency of the iodine-based hormone thyroxine causes a disease called goitre.
5. Chloroquine, a synthetic halogen compound, is used to treat malaria; halothane is used as an anaesthetic during surgery.

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Uses of Halogen Derivatives

Carbon compounds that contain more than one halogen atom are known as Polyhalogen compounds. Many of these compounds are widely used in agriculture and industrial purposes. The uses of some polyhalogen compounds are discussed below.

Dichloro-methane, \({\text{C}}{{\text{H}}_2}{\text{C}}{{\text{l}}_2}\)

1. Dichloromethane, also known as Methylene chloride, is widely used as a solvent.
2. It is also used as a paint remover, as a propellant in aerosols, and as a metal cleaning agent.
3. In the manufacture of drugs, dichloromethane is used as a process solvent.
4. Methylene chloride damages the human central nervous system and affects the hearing and vision of individuals exposed to it. Higher levels of methylene chloride in the air cause dizziness, nausea, tingling, and numbness in the fingers and toes.
5. Methylene chloride causes intense burning and a mild redness when it comes in direct contact with the skin. Direct contact with the eyes can burn the cornea.

Trichloromethane, \({\text{CHC}}{{\text{l}}_3}\)

1. Chemically, trichloromethane is known as Chloroform and was once used as a general anaesthetic in surgery.
2. It is used as a solvent for fats, iodine, alkaloids, and other substances.
3. It is widely used in the production of the freon refrigerant \({\text{R}} – 22.\)
4. Its use as a general anaesthetic has been replaced by ether which is less toxic and safer.
5. Inhaling chloroform vapours depresses the central nervous system. Dizziness, fatigue, and headache are caused when inhaled about \(900\) parts of Chloroform per million parts of air (\(900\) parts per million) for a short time.
6. Continuous exposure to Chloroform may cause damage to the liver as Chloroform is metabolised to Phosgene.
7. Chloroform is stored in closed dark coloured bottles to keep it away from air and light. This is because Chloroform on slow oxidation forms Carbonyl chloride or Phosgene, an extremely poisonous gas. This reaction takes place in the presence of light and air.
8. Chloroform is used to detect primary amines during the isocyanide test, also known as the Carbylamine test. In this test, Chloroform is heated with a mixture of amines and alcoholic \({\text{NaOH}}{\text{.}}\) A foul-smelling isocyanide gas is formed in this reaction. This test is used for the identification of aliphatic and aromatic primary amines.

Triiodomethane, \({\text{CH}}{{\text{I}}_3}\)

Triiodomethane or iodoform is widely used as an antiseptic. Its antiseptic properties are due to the liberation of iodine. It has an offensive smell and hence is replaced by other formulations containing iodine.

Tetrachloromethane, \({\text{CC}}{{\text{l}}_4}\)

1. Carbon tetrachloride or Tetrachloromethane is widely used for the manufacture of refrigerants and propellants for aerosol cans.
2. \({\text{CC}}{{\text{l}}_4}\) is also used as a general solvent and as a feedstock in the synthesis of chlorofluorocarbons and other pharmaceutical manufacturing.
3. It is also used as a cleaning fluid, degreasing agent, spot remover, and fire extinguisher in the home.
4. Exposure to carbon tetrachloride causes liver cancer, dizziness, light-headedness, nausea, and vomiting. It can also cause permanent damage to nerve cells. It causes the heart to beat irregularly or stop. In extreme cases, these effects can be fatal or lead to coma. \({\text{CC}}{{\text{l}}_4}\) may cause eye irritation on contact.
5. When carbon tetrachloride is released into the atmosphere, it depletes the ozone layer. The ozone layer depletion increases human exposure to ultraviolet rays, resulting in skin cancer, eye diseases, and possible disruption of the immune system.

Freons

1. Freons are the chlorofluorocarbon compounds of methane and ethane. These compounds are extremely stable, non-reactive, non-corrosive, non-toxic, and easily liquefiable gases.
2. Freon \({\text{12}}\left({{\text{CC}}{{\text{l}}_2}{{\text{F}}_2}} \right)\) is one of the most common freons in industrial use. It is manufactured by Swarts reaction from Tetrachloromethane. These compounds are widely used for refrigeration and air conditioning purposes.
3. Most freon used in refrigeration eventually makes its way into the atmosphere, where it diffuses unchanged into the stratosphere, where it initiates radical chain reactions that can disturb the natural ozone balance.

\({\text{p,p’}}\)-Dichlorodiphenyltrichloroethane(DDT)

1. DDT or p,p’-Dichlorodiphenyltrichloroethane is the first chlorinated organic insecticide prepared in \(1873.\)
2. Its effectiveness against malaria-spreading mosquitoes and lice that carry typhus increased its use enormously on a worldwide basis after World War II. However, it is highly toxic to fish.
3. DDT is not easily metabolised by animals if consumed by animals; instead, it gets deposited and stored in the fatty tissues. If ingestion continues at a steady rate, DDT builds up within the animal over time.

Summary

Haloalkanes and haloarenes have a wide range of applications in our day-to-day life. From being used as a paint remover to treating malaria fever, the uses of haloalkanes and haloarenes are widespread.  Besides, polyhalogen compounds also find extensive use in our everyday lives, from antiseptics to insecticides. However, these compounds are found to pollute and deplete our ozone layer, such as freons. The use of air conditioners and refrigerators releases freons into the atmosphere, disturbing the ozone balance and posing environmental threats.

Classification of Haloalkanes and Haloarenes

Frequently Asked Questions

Q.1. Why are haloalkanes used as solvents?
Ans: Alkyl halides or haloalkanes are used as solvents because the nature of the \({\text{C-X}}\) bond makes alkyl halides polar, with carbon having a positive delta charge and halide having a negative delta charge. Hence, they effectively dissolve polar compounds as there will be more interactions between the compound and alkyl halide.

Q.2. What are freons?
Ans: Freons are chlorofluorocarbon compounds that contain only carbon, chlorine, and fluorine, produced as a volatile derivative of methane, ethane and propane.

Q.3. What are polyhalogen compounds?
Ans: Polyhalogen compounds are the carbon compounds that contain more than one halogen atom—for example, Chloroform, Carbon tetrachloride, etc.

Q.4. What is the full form of DDT?
Ans: The full form of DDT is Dichlorodiphenyltrichloroethane. In agriculture, DDT is used as an insecticide.

Q.5. What is the formula and use of iodoform?
Ans: The chemical formula of Iodoform is \({\text{CH}}{{\text{I}}_3}.\) It is a yellow, crystalline polyhalogeno compound. It is widely used as a disinfectant.