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.