Nitration is a common reaction of benzene involving the substitution of a hydrogen atom in the benzene ring with a nitro group (NO2). The process typically requires a mixture of concentrated nitric acid (HNO3) and concentrated sulfuric acid (H2SO4) as a nitrating agent and catalyst, respectively. Below is a detailed note on the nitration reaction of benzene:
Nitration Reaction of Benzene
1. Â Conditions for Nitration
Reagents: Concentrated nitric acid (HNO3) and sulfuric acid (H2SO4).
Catalyst: Sulfuric acid catalyzes by providing the nitronium ion (NO2+), the electrophile involved in the substitution.
Temperature: The reaction is carried out at a moderately elevated temperature, usually around 50-55°C.
2. Â Reaction Mechanism
The nitration reaction involves the following steps:
Formation of Nitronium Ion (NO2+):
HNO3​+H2​SO4​​H2​NO3+​+HSO4−​
Generation of the Electrophile (NO2+):
H2​NO3+​​NO2+​+H2​O
Electrophilic Substitution:
C6​H6​+NO2+​​C6​H5​NO2​+H+
3. Â Formation of Nitrobenzene
The final product of the nitration of benzene is nitrobenzene (C6H5NO2).
The nitro group (NO2) is introduced at the position originally occupied by a hydrogen atom on the benzene ring.
4. Â Isomer Formation
Benzene is highly symmetrical, and all the hydrogen atoms are equivalent. Therefore, the nitration of benzene produces only one product – nitrobenzene.
Due to its symmetry, there are no positional isomers in the product.
5. Â Regioselectivity
Benzene is highly regioselective in nitration, meaning that the substitution predominantly occurs at one specific position.
The electrophile (NO2+) tends to attack the benzene ring at the ortho and para positions, with para being the major product.
6. Â Reaction Outcome
The overall balanced chemical equation for the nitration of benzene is:
C6​H6​+HNO3​​C6​H5​NO2​+H2​O
Significance
– Nitrobenzene is a crucial intermediate in synthesizing various organic compounds, including dyes, pharmaceuticals, and agrochemicals.
– The regioselectivity and the absence of side products make the nitration of benzene a valuable tool in organic synthesis.
– This reaction is part of a broader class of electrophilic aromatic substitution reactions, which benzene and its derivatives frequently undergo.
