Chlorination of methane proceeds via free radical mechanism. Conversion of methyl chloride to methyl alcohol proceeds via nucleophilic substitution. Formation of ethylene from ethyl alcohol proceeds via dehydration reaction. Nitration of benzene is electrophilic substitution reaction.

Electrophilic Substitution Reaction: Nitration of Benzene

Introduction:
Electrophilic substitution reactions are a type of organic reaction in which an electrophile replaces a functional group or atom in a molecule. These reactions are commonly observed in aromatic compounds, such as benzene. One such example is the nitration of benzene.

Nitration of Benzene:
The nitration of benzene involves the substitution of a hydrogen atom in the benzene ring with a nitro group (-NO2) in the presence of a strong nitrating agent, usually concentrated nitric acid (HNO3), and a catalyst, such as concentrated sulfuric acid (H2SO4).

Reaction Mechanism:
The nitration of benzene proceeds through a stepwise mechanism, which involves the following steps:

1. Generation of the electrophile: The concentrated sulfuric acid acts as a catalyst and protonates the nitric acid, forming a strong electrophile, known as the nitronium ion (NO2+).
HNO3 + H2SO4 → NO2+ + HSO4- + H2O

2. Formation of the arenium ion: The electrophilic nitronium ion attacks the π electron cloud of the benzene ring, forming a resonance-stabilized intermediate called the arenium ion or sigma complex.
NO2+ + C6H6 → C6H5NO2+

3. Rearrangement of the arenium ion: The arenium ion undergoes a rearrangement, shifting the positive charge from the carbon atom to one of the adjacent carbon atoms. This intermediate is also stabilized by resonance.
C6H5NO2+ ⇌ C6H4(NO2)C+

4. Regeneration of aromaticity: The aromaticity of the benzene ring is restored by the loss of a proton from the arenium ion, leading to the formation of the final product, nitrobenzene.
C6H4(NO2)C+ + H2O → C6H5NO2 + H+

Key Points:
- Electrophilic substitution reactions involve the substitution of a functional group or atom in a molecule by an electrophile.
- Nitration of benzene is an example of an electrophilic substitution reaction.
- The reaction involves the substitution of a hydrogen atom in the benzene ring with a nitro group (-NO2).
- The reaction proceeds through a stepwise mechanism, involving the generation of the electrophile, formation of the arenium ion, rearrangement of the arenium ion, and regeneration of aromaticity.
- The nitration of benzene is catalyzed by concentrated sulfuric acid and requires concentrated nitric acid as the nitrating agent.

Conclusion:
The nitration of benzene is an example of an electrophilic substitution reaction, where a hydrogen atom in the benzene ring is replaced by a nitro group. This reaction is an important method for the synthesis of nitroaromatic compounds and is widely used in the production of various chemicals, dyes, and pharmaceuticals.