Efficient SO₂ Capture and Fixation to Cyclic Sulfites by Dual Ether-Functionalized Protic Ionic Liquids without Any Additives

The capture of SO 2 with ionic liquids (ILs) has attracted much attention in recent years; however, the examples involving SO 2 capture and utilization (SCU) in the same medium are scarce. Here, we demonstrated an innovative strategy for SO 2 capture and fixation to cyclic sulfites in dual ether-functionalized protic ionic liquids (PILs) for the first time. These dual ether-functionalized PILs exhibited low viscosities and remarkable SO 2 loading capacities (up to 6.12 mol of SO 2 per mol of IL and 1.34 g of SO 2 per g of IL at 1.0 bar) that is conducive to conversion of SO 2 absorbed in situ. The mechanism of absorption was proposed which includes both chemical and physical absorptions from the spectral results and theoretical calculations. Particularly, the SO 2 absorbed in the PILs was directly transformed into cyclic sulfites without any additives; meanwhile, these PILs were also used as efficient catalysts for the synthesis of a series of cyclic sulphites using equimolar SO 2 and epoxides. Good to excellent yields of cyclic sulfites were obtained for varied substrates. The dual roles of PILs as both absorbents and catalysts as well as the recyclability of the PILs are examined in detail in this paper. This innovative strategy not only eliminated the traditional intensive energy input for SO 2 desorption but also enabled the production of value-added cyclic sulfites.