Used as an intermediate in the synthesis of sulfa drugs and other pharmaceuticals, particularly in the development of anti-inflammatory and antimicrobial agents. Its reactive chlorosulfonyl group allows for easy attachment to amines, forming sulfonamide derivatives, which are key structural motifs in many bioactive molecules. Also employed in the preparation of dyes and functional organic materials due to its ability to undergo electrophilic substitution and coupling reactions. Its carboxylic acid functionality enables further derivatization, such as esterification or amidation, making it valuable in multi-step organic syntheses.