Aromatic sulfonation
Abstract
Aromatic sulfonation is a reaction in which a hydrogen atom of an aromatic ring is replaced by a sulfonic group (–SO3H), yielding an aryl sulfonic acid. Like aromatic halogenation, it proceeds via electrophilic aromatic substitution (EAS).
Keywords
Aromatic, Aryl sulfonic acid, EAS
Category
Aromatic
Mechanism
First, the sulfuric acid protonates the sulfur trioxide (SO3), forming a highly electrophilic sulfonium ion. Then, the 𝜋 electrons of the aromatic ring attack the electrophilic sulfur of the sulfonium ion, forming an arenium ion (also called Wheland intermediate). At this stage, aromaticity is lost and the carbon bearing the sulfonic acid becomes sp3 hybridized. A base (HSO4- or H2O) abstracts the proton from the sp3 carbon, restoring aromaticity and yielding the aryl sulfonic acid product.
