chlorosulfonic

Chlorosulfonic acid, also referred to as chlorosulphonic acid, is a strong mineral acid with the formula ClSO3H. It is a colorless to yellowish liquid that fumes in air and is highly hygroscopic. The substance is extremely reactive with water and many organic materials, hydrolyzing to sulfuric acid and hydrogen chloride in a highly exothermic reaction. It is miscible with many organic solvents but requires dry, moisture-free handling.

Chemically, chlorosulfonic acid functions as a powerful sulfonating and chlorinating agent. It can introduce the sulfonyl group into substrates, making it useful for the preparation of sulfonic acid derivatives and sulfonate esters from alcohols. It can also participate in electrophilic sulfonation of aromatic rings under suitable conditions. Due to its reactivity, it is often used in situ or under tightly controlled, moisture-free conditions rather than being stored or handled in bulk.

Industrial production of chlorosulfonic acid typically involves chlorination of sulfuric acid or related sulfonation routes that generate ClSO3H under controlled conditions. Because of its high reactivity and corrosivity, it is handled with appropriate engineering controls, in fume hoods, and with materials compatible with strong acids. Storage requires moisture exclusion and suitable containment to prevent hydrolysis and venting of fumes.

Applications span organic synthesis, where it is employed to activate substrates for sulfonation or to form sulfonate esters, and in the manufacture of intermediates for detergents, dyes, and certain pharmaceutical chemicals. Caution is required due to its vigorous reaction with water and potential for releasing toxic fumes.