Reaction mechanism of desulphonation of benzene ring using dil. #"HCl"# and, #"H"_2"SO"_4//150^@c# "?"
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The sulfonation of benzene is a reversible reaction.
Thus, we can remove a sulfonic acid group by heating the compound with an acid.
The reaction with steam alone is often sufficient for desulfonation.
The mechanism of desulfonation
Step 1. Attack by an electrophile
A hydronium ion protonates the aromatic ring and generates a resonance-stabilized carbocation intermediate.
Passo 2. Desulfonation
A base deprotonates the sulfonic acid, and the sulfur trioxide leaves, regenerating the aromatic ring.