Chlorosulfuric

Chlorosulfuric acid, also known as chlorosulfonic acid, is a strong, corrosive mineral acid with the chemical formula ClSO3H. It is a fuming liquid that reacts vigorously with water and many organic substrates, and it is highly reactive and moisture sensitive.

Preparation and properties

Chlorosulfuric acid is typically prepared by the reaction of sulfur trioxide with hydrogen chloride. The compound is highly hygroscopic and must be handled under strictly dry conditions. On contact with water, it hydrolyzes exothermically to sulfuric acid and hydrogen chloride, releasing heat and fumes. It is usually stored in dry, tightly closed containers and kept away from moisture, bases, reducing agents, and organic materials.

Uses

In organic synthesis, chlorosulfuric acid is a powerful sulfonating agent used to introduce sulfonyl groups (-SO3H) into substrates and to activate alcohols toward substitution by forming sulfate esters. It can also serve as a source of sulfonylating and related chlorinating species in certain reaction sequences and is a precursor to various chlorosulfonyl derivatives.

Safety and handling

Chlorosulfuric acid is highly corrosive and toxic. It reacts violently with water and many common materials, generating corrosive vapors. It should be handled in a well-ventilated fume hood with appropriate personal protective equipment. Storage should be in a dry, compatible container made of resistant material (often glass or certain fluorinated polymers) and kept away from moisture, bases, and organic oxidizers.

See also

Chlorosulfonic acid; Sulfonation; Sulfate esters.