Electrophilic aromatic substitution

Introducing reactions of electrophilic aromatic substitution.

Sulfonation of benzene:

Steps:

1. π electrons on benzene attack sulfur trioxide to form a dearomatized σ-complex;
2. C-H bond on sulfur α position cleaves heterolytically, and then the proton leaves, recovering the aromaticity.
3. Sulfonate anion combines with proton to form benzenesulfonic acid.

Hydrolysis of benzenesulfonic acid:

Steps:

1. Protons dissociates from benzenesulfonic acid ;
2. Benzene is electrophilically added by proton, forming a dearomatized σ-complex;
3. C-S bond cleaves heterolytically, forming benzene and sulfur trioxide.