Reactions

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

🔹 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.

🔹 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.