Question

The sulfonation of an aromatic ring with is reversible. That is, heating benzenesulfonic acid with H2SO4 yields benzene. Show the mechanism of the desulfonation reaction. What is the electrophile?

Short answer

It is a process of the addition of the sulphonic group in the presence of sulphuric acid it occurs by the removal of the one hydrogen from the sulphuric acid and addition of ${\mathbf{SO}}_{\mathbf{3}}\mathbf{H}$ to the benzene ring.

Step-by-step solution

Step-by-Step SolutionStep 1:  Sulphonation

It is a process of the addition of the sulphonic group in the presence of sulphuric acid it occurs by the removal of the one hydrogen from the sulphuric acid and addition of ${\mathbf{SO}}_{\mathbf{3}}\mathbf{H}$ to the benzene ring.

De- Sulphonation

It lead to removal of the sulphonic group by deportation and also leads to the regaining of aromaticity, again and again, benzene ring formation occurs.

Electrophile

Proton is the electrophile here having protons that are electropositive in nature.

Reaction occurs as

1. Sulphonation
2. De Sulphonation

Sulphonation and De-Sulphonation