Chlorosulfonic acid

Chlorosulfonic acid (CAS 7790-94-5), also known as chlorosulfuric acid or CSA, is a highly reactive sulfonating and chlorosulfonating agent used across chemical synthesis and industrial manufacturing.

It introduces sulfonic or sulfonyl chloride groups into organic molecules, enabling the production of a broad range of downstream intermediates and active ingredients for various sectors.

In agrochemical synthesis, CSA is used to manufacture herbicide and pesticide intermediates, particularly sulfonamide-class compounds where precise sulfonation is required for efficacy.

Pharmaceutical manufacturers rely on it to produce sulfonyl chloride intermediates that feed into APIs and specialty drug substances. It is a critical component in modern medicinal chemistry.

In the textile and leather industries, it functions as a precursor in the production of synthetic dyes and optical brighteners, where sulfonation determines solubility and fastness properties.

Polymer chemists also apply CSA in the sulfonation of polystyrene and similar backbones to produce ion-exchange resins and proton-exchange membranes for industrial filtration and energy applications.

Chlorosulfonic acid is supplied as a fuming liquid, typically in concentrations at or near 99% purity. Technical grade is the standard commercial offering for most industrial processes.

High-purity grades are available for pharmaceutical and specialty chemical synthesis. It is packaged in corrosion-resistant containers suited to its highly reactive and fuming nature.