Nitration of Benzene
The nitration of benzene mechanism is a classic example of electrophilic aromatic substitution. This reaction produces nitrobenzene, an important intermediate in the synthesis of many organic compounds.
Vocabulary: Nitration - The process of introducing a nitro group −NO2 into an organic compound.
The nitration of benzene equation can be summarized as:
C₆H₆ + HNO₃ → C₆H₅NO₂ + H₂O
The reaction conditions and mechanism are as follows:
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Conditions:
Concentrated sulfuric acid H2SO4 acts as a catalyst
Concentrated nitric acid HNO3 provides the nitro group
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Mechanism Steps:
Step 1: H₂SO₄ + HNO₃ → HSO₄⁻ + NO₂⁺ + H₂O
Step 2: The nitronium ion NO2+ acts as the electrophile
Step 3: Benzene attacks the electrophile, forming a resonance-stabilized carbocation
Step 4: Loss of a proton restores aromaticity, yielding nitrobenzene
Highlight: The benzene HNO₃ H₂SO₄ mechanism showcases the importance of sulfuric acid as both a catalyst and a dehydrating agent, facilitating the formation of the nitronium ion.
Halogenation of Benzene
The halogenation of benzene mechanism involves the substitution of a hydrogen atom with a halogen typicallychlorineorbromine. This reaction is crucial in the synthesis of various aromatic compounds.
Example: The halogenation of benzene with FeBr₃ catalyst example demonstrates the role of Lewis acids in activating the halogen molecule.
The halogenation of benzene with FeBr₃ catalyst equation is:
C₆H₆ + Br₂ → C₆H₅Br + HBr
The mechanism proceeds as follows:
- Step 1: Br₂ + FeBr₃ → Br⁺ + FeBr₄⁻
- Step 2: The bromonium ion Br+ acts as the electrophile
- Step 3: Benzene attacks the electrophile, forming a resonance-stabilized carbocation
- Step 4: Loss of a proton restores aromaticity, yielding bromobenzene
Highlight: The halogenation of benzene electrophilic substitution mechanism demonstrates the importance of Lewis acid catalysts in generating the electrophilic species.
Alkylation of Benzene
The alkylation of benzene is a Friedel-Crafts reaction that introduces an alkyl group onto the benzene ring. This reaction is vital in the synthesis of various alkylbenzenes.
The mechanism involves the following steps:
- Step 1: CH₃Cl + AlCl₃ → CH₃⁺ + AlCl₄⁻
- Step 2: The carbocation CH3+ acts as the electrophile
- Step 3: Benzene attacks the electrophile, forming a resonance-stabilized carbocation
- Step 4: Loss of a proton restores aromaticity, yielding methylbenzene toluene
Definition: Friedel-Crafts alkylation is a type of electrophilic aromatic substitution reaction used to alkylate aromatic rings using an alkyl halide and a Lewis acid catalyst.
