Reactions

Benzene undergoes electrophilic aromatic substitution (EAS) rather than simple addition reactions, because addition would disrupt its aromatic stability.

đŸ”č Substitution Reactions on Benzene (EAS)

Here are the common substitution reactions and their reagents:

Reaction Type

Reagents

Product Formed

Nitration

HNO₃ + H₂SO₄ (conc.)

Nitrobenzene (–NO₂)

Sulfonation

Fuming H₂SO₄ (or SO₃ + H₂SO₄)

Benzenesulfonic acid (–SO₃H)

Halogenation

Cl₂ or Br₂ + FeCl₃ or FeBr₃ catalyst

Chlorobenzene or Bromobenzene

Friedel–Crafts Alkylation

R–Cl + AlCl₃

Alkylbenzene (e.g., methylbenzene)

Friedel–Crafts Acylation

R–COCl + AlCl₃

Acylbenzene (e.g., acetophenone)

All of these are substitution reactions, where a hydrogen on the ring is replaced by another group.

🔾 Why Not Addition?

  • Benzene is aromatic—a highly stable structure due to delocalized π electrons.

  • Addition reactions would break this aromaticity, making them unfavorable.

  • Only under extreme conditions can you force benzene into addition.

đŸ”č Addition Reactions (Rare/Forced Conditions)

Type

Reagents

Notes

Hydrogenation

H₂ + Ni or Pt (high T, P)

Benzene → cyclohexane (loses aromaticity)

Chlorination

Cl₂ + UV or heat (free radical)

Non-selective, destroys ring

Birch Reduction

Na/NH₃ + alcohol (in liquid NH₃)

Produces 1,4-cyclohexadiene

✅ Summary:

  • Substitution reactions are preferred for benzene due to aromatic stability.

  • Reagents for substitution usually involve electrophiles + Lewis acids (e.g., AlCl₃, FeBr₃).

  • Addition reactions are rare and typically need harsh conditions.