Sulfonaation

Sulfonation is a chemical reaction in which a sulfonic acid group (-SO3H) is introduced onto a substrate. This reaction is most commonly applied to organic compounds, but can also occur with inorganic molecules. The most typical sulfonating agent is sulfur trioxide (SO3), often used in combination with concentrated sulfuric acid (H2SO4) to form oleum. Other sulfonating agents include chlorosulfonic acid (ClSO3H) and sulfuryl chloride (SO2Cl2).

The mechanism of sulfonation generally involves an electrophilic attack on the substrate by sulfur trioxide. For aromatic compounds, this is an electrophilic aromatic substitution reaction. The sulfonic acid group is electron-withdrawing and can deactivate the aromatic ring towards further electrophilic substitution. The reversibility of sulfonation is an important characteristic; under acidic conditions and with heating, the sulfonic acid group can be removed. This reversibility is often exploited in organic synthesis, for example, to direct other substitutions on an aromatic ring.

Sulfonation has numerous industrial applications. It is used in the production of detergents and surfactants, where the sulfonic acid group imparts water solubility. Sulfonic acids are also intermediates in the synthesis of dyes and pharmaceuticals. Sulfonation is also employed in the petroleum industry to remove undesirable aromatic compounds. The properties of sulfonic acids, such as their strong acidity and solubility, make them versatile reagents and functional groups.