sulfonating

Sulfonating is a chemical process that introduces a sulfonic acid group (-SO3H) into a substrate. It is most commonly used to describe electrophilic sulfonation of aromatic or unsaturated compounds, typically using sulfuric acid, sulfur trioxide (SO3), oleum, or chlorosulfonic acid as the sulfonating agent. In aromatic systems, sulfonation proceeds by electrophilic substitution: Ar-H + SO3 → Ar-SO3H, often carried out in concentrated acids at modest temperatures. The reaction is reversible under certain conditions; heating sulfonic acids can lead to desulfonation and regeneration of the parent hydrocarbon.

Other substrates can undergo sulfonation with SO3 equivalents added to alkenes or activated rings to give sulfated products, which are then protonated to form sulfonic acids. Inorganic and polymer substrates can also be sulfonated to install sulfonic acid groups, creating ion-exchange resins and sulfonated polymers with hydrophilic properties.

Industrial relevance: sulfonation is widely used in the manufacture of alkylbenzene sulfonates—a class of detergents—via aggressive sulfonation of linear alkylbenzenes. It is also used to modify polymers for fuel-cell membranes and catalysis, such as sulfonated polystyrene or perfluorosulfonic acid polymers.

Safety and handling: sulfonation reactions are highly exothermic and involve corrosive reagents. Reactions are performed with appropriate controls to manage heat, moisture sensitivity, and formation of byproducts.