Chapter 12 :  Reactions of Arenes. Electrophilic Aromatic Substitution

Nitration of Benzene

Summary

• Overall transformation :  Ar-H to Ar-NO₂
• Reagent : for benzene, HNO₃ in H₂SO₄ / heat
• Electrophilic species :  the nitronium ion (i.e. NO₂⁺) formed by the loss of water from the nitric acid

MECHANISM FOR NITRATION OF BENZENE
Step 1: An acid / base reaction. Protonation of the hydroxy group of the nitric acid. This provides a better leaving group.....
Step 2: Loss of the leaving group, a water molecule provides the nitronium ion, the reactive electrophile.
Step 3: The electrophilic nitronium ion reacts with the nucleophilic C=C of the arene. This is the rate determining step as it destroys the aromaticity of the arene.
Step 4: Water functions as a base to remove the proton from the sp3 C bearing the nitro- group and reforms the C=C and the aromatic system.

© Dr. Ian Hunt, Department of Chemistry