Used primarily as an intermediate in organic synthesis, especially in the pharmaceutical and agrochemical industries. It serves as a sulfonylating agent to introduce the 4-cyanobenzenesulfonyl group into various compounds, enhancing their stability or altering biological activity. Commonly employed in the preparation of sulfonamide derivatives, which are key structural motifs in many active pharmaceutical ingredients (APIs). Its nitrile group allows further functionalization, enabling versatile derivatization for drug discovery and development. Also utilized in the synthesis of dyes and functional polymers where sulfonyl chloride reactivity is required.