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Haloalkanes and Haloarenes – Definition, Classification, Uses, Effects

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  • Last Updated : 11 Feb, 2022

Haloalkanes and haloarenes are hydrocarbons that have had one or more hydrogen atoms replaced with halogen atoms. The major distinction between haloalkanes and haloarenes is that the former are formed from open-chain hydrocarbons (alkanes), whilst the latter are derived from aromatic hydrocarbons.

Haloalkanes are typically known as alkyl halides, whereas haloarenes are known as aryl halides. Multiple halogen atoms can be found in these substances. In general, halogen atoms are connected to sp3 hybridised carbon atoms in haloalkanes, whereas sp2 hybridised carbon atoms are attached to haloarenes. The variation in the hybridization state of the carbon atom in the C-X bond is responsible for the two families’ distinct properties. Haloalkanes and haloarenes are more chemically reactive than parent alkanes and aromatic compounds due to the presence of halogens. These chemicals have a variety of medical applications as well.

Classification of Haloalkanes and Haloarenes

They can be classed as follows:

  1. The number of halogen atoms on a molecule of alkyl or aryl halide.
  2. Carbon atom types
  3. Hybridization of a carbon atom with a halogen atom.

Haloalkanes and haloarenes are categorised into two categories based on the number of halogen atoms on an alkyl or aryl halide molecule –

  1. Mono Haloalkanes and Mono Haloarenes: These are molecules with only one halogen atom.
  2. Poly Haloalkanes and Poly Haloarenes: These are molecules that include two or more halogen atoms. These are further classified into the three types listed below:
    1. Di Haloalkanes and Di Haloarenes: These compounds contain two Halogens.
    2. Tri Haloalkanes and Tri Haloarenes: These compounds contain three Halogens.
    3. Tetra Haloalkanes and Tetra Haloarenes: These compounds contain four Halogens.

Di Haloalkanes

Tri Haloalkanes

Carbon atoms can be categorized into three categories based on their chemical composition –

  1. Primary Alkyl Halide: a halogen atom is joined to a primary carbon atom.
  2. Secondary Alkyl Halide: a halogen atom linked to a secondary carbon atom.
  3. Tertiary Alkyl Halide: a halogen atom joined to a tertiary carbon atom.

Haloalkanes and Haloarenes are categorised into two categories based on the hybridization of the Carbon atom to which Halogen is bonded.

  • Attachment of halogen to sp3 hybridised carbon: On this basis, Alkyl Halide and Aryl Halide can be divided into three types:
    1. Alkyl Halide: Halogen connected to an alkyl chain is referred to as an alkyl halide.
    2. Allylic Halide: A halogen linked to the sp3 hybridised carbon next to C=C.
    3. Benzylic Halide: Halogen linked to the benzene ring via the sp3 hybridised carbon.

Alkyl Halide

Allylic Halide

  • Attachment of halogen to sp2 hybridised carbon: On this basis, alkyl halide and aryl halide can be divided into three types:
    1. Vinyl Halide is a halogen that has been bonded to sp2 hybridised carbon.
    2. Aryl Halide is an aromatic ring with halogen linked to sp2 hybridised carbon.

Vinyl Halide

Uses of Haloalkanes and Haloarenes

These chemicals have a variety of useful applications, which are described below.

  1. Because these organic compounds may dissolve non-polar substances, they are utilised as solvents.
  2. Many alkyl and aryl halide compounds are employed in medicine. One such example is the antibiotic chloramphenicol, which is used to treat typhoid fever.
  3. Another example is chloroquine, which is extremely effective in treating malaria.
  4. Dichlorodiphenyltrichloroethane (commonly known as DDT) is a pesticide.
  5. Some haloalkanes and haloarenes have negative environmental impacts and are classified as contaminants. One such example is chlorofluorocarbons (or CFCs), which contribute to the depletion of the ozone layer, which shields the Earth from dangerous solar radiation.

Environmental Effects

These chemicals are widely used in commercial applications. However, halocarbons have been connected to major pollutants and poisons that have a negative impact on the ecosystem. CFC (chlorofluorocarbon), for example, is a well-known contributor to ozone depletion in the atmosphere. Methyl bromide is another highly debated fumigant that has been connected to numerous negative environmental impacts. Because of their destructive effects, these chemicals have repeatedly been shown to be a severe hazard to the environment. However, other chemicals, such as methyl iodide, have no ozone-depleting impacts on the environment. Furthermore, the molecule has been designated as a non-ozone layer depleter by the USEPA (United States Environmental Protection Agency).

Sample Problems

Question 1: What is the difference between haloalkanes and Haloarenes?

Answer: 

Haloalkanes are chemicals created when hydrogen atoms in aliphatic hydrocarbons (alkanes) are replaced by halogen atoms. The compounds generated when hydrogen atoms linked to benzene rings are replaced by halogen atoms are known as haloarenes.

Question 2: Which is the example of Haloarenes?

Answer: 

Haloarenes are chemicals that are generated when hydrogen atoms linked to benzene rings are replaced by halogen atoms. Chlorobenzene, bromobenzene, iodobenzene, 2-Chlorotoluene, and other haloarenes are examples.

Question 3: What are the uses of Haloarenes?

Answer:

DDT, Picric acid, Phenol, and other chemicals containing haloarenes were developed. DDT was employed as an insecticide to kill anopheles mosquitos that spread malaria, but it was prohibited in 1973 due to its toxicity. Picric acid is used in the manufacture of explosives, matches, electric batteries, coloured glass making, and dye synthesis. Phenol is a chemical that is used to make nylon and other synthetic textiles.

Question 4: What are haloalkanes reactions?

Answer: 

Grignard reagents are formed when haloalkanes react with magnesium metal in the presence of fully anhydrous ether to generate organomagnesium halide. In the presence of an aqueous alkali solution or a moist silver oxide solution, haloalkane undergoes a nucleophilic substitution process, forming alcohols.

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