SO2 Transfer Enabled by an Easy-to-Handle Ionic Liquid.

Herein, the ionic liquid [NEt3Me][Cl(SO2)n] is reported as a reversible sulfur dioxide storage medium and transfer reagent for organic synthesis. Vapor pressure measurements revealed that the ionic liquid can store up to 3.66 equivalents of SO2 at room temperature, which can be released in a controlled manner upon heating or depressurization. The physicochemical properties were investigated, and long-term stability was demonstrated, as no decomposition was observed for more than six months. Based on its solid-state structure, the bonding analysis indicated a covalent sulfur-chlorine interaction, which is consistent with conducted Raman studies and quantum chemical calculations. Atom economy and cost estimates are compared with those of commonly used SO2 surrogates, highlighting the developed transfer reagent as an inexpensive and (atom-)economic alternative for laboratory-scale applications. The synthetic utility of [NEt3Me][Cl(SO2)n] is further demonstrated, enabling the synthesis of valuable organosulfur compounds such as 3-sulfolenes, sulfonamides, sulfones, and sulfonyl fluorides in good to excellent yields. Importantly, the incorporation of SO2 is scalable, rendering [NEt3Me][Cl(SO2)n] as a safe and user-friendly SO2 transfer reagent for synthetic applications.