SO3Hryhmä

The SO3H ryhmä, commonly written as the sulfonic acid group, is a functional group in organic chemistry represented by the formula R-SO3H. It consists of a sulfur atom in the oxidation state +6 bonded to three oxygens, one of which bears a hydrogen atom. When attached to a carbon framework, the group is often written as R-SO3H, forming sulfonic acids such as benzenesulfonic acid or p-toluenesulfonic acid.

The sulfonic acid group is a strong Brønsted acid. In water, most aryl and alkyl sulfonic acids dissociate completely, producing the sulfonate anion (RSO3−) and a hydronium ion. The group is highly electron withdrawing, which makes rings substituted with SO3H less reactive toward electrophilic substitution and typically directs new substituents to the meta position on aromatic rings.

Synthesis and occurrence: the SO3H group is commonly introduced into substrates by sulfonation using sulfur trioxide or fuming sulfuric acid (oleum). It also appears in various industrial and natural products as part of sulfonic acid derivatives. The acidic group is often converted into salts, known as sulfonates, which are water-soluble and useful in applications ranging from detergents to catalysis.

Applications: sulfonic acids and their salts are widely used in detergents (alkylbenzene sulfonates), in organic synthesis as strong acid catalysts (for example p-toluenesulfonic acid), and in pharmaceuticals and dyes to improve water solubility and chemical properties. The SO3H ryhmä is valued for its stability, acidity, and ability to form diverse sulfonate derivatives.