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:

1. Conditions:

   • Concentrated sulfuric acid (H₂SO₄) acts as a catalyst
   • Concentrated nitric acid (HNO₃) provides the nitro group

2. 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 (typically chlorine or bromine). 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:

1. Step 1: Br₂ + FeBr₃ → Br⁺ + FeBr₄⁻
2. Step 2: The bromonium ion (Br⁺) acts as the electrophile
3. Step 3: Benzene attacks the electrophile, forming a resonance-stabilized carbocation
4. 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:

1. Step 1: CH₃Cl + AlCl₃ → CH₃⁺ + AlCl₄⁻
2. Step 2: The carbocation (CH₃⁺) acts as the electrophile
3. Step 3: Benzene attacks the electrophile, forming a resonance-stabilized carbocation
4. 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.