Used primarily as a sulfonating agent in organic synthesis, enabling the introduction of sulfonyl groups into various substrates. It is particularly effective in the preparation of sulfonate esters and sulfonamides, which are key intermediates in pharmaceuticals and agrochemicals. Its high reactivity makes it suitable for modifying complex molecules under controlled conditions. Commonly employed in the development of active pharmaceutical ingredients where sulfonyl functionalities enhance biological activity or metabolic stability. Also utilized in polymer chemistry to modify resin properties and improve thermal or chemical resistance. Requires careful handling due to its moisture sensitivity and corrosive nature.