A Mechanistic Study on the Synthesis Reaction of Glycerol Sulfite─A Key Intermediate for Novel Electrolyte Additives

Using SO₂ as a sulfinic-acid building block to synthesize valuable sulfur-based electrolyte additives is an important issue in the field of green and sustainable chemistry. Glycerol sulfite, as a key intermediate for the design and synthesis of sulfite-based electrolyte additives, clarifying its synthesis mechanism is of great significance for the design and synthesis of sulfite-based additives. Herein, the reaction mechanisms of synthesizing glycerol sulfite were explored by density functional theory (DFT) calculations, based on an analysis of glycerol sulfite's structures and properties. The results show that the reaction of SOCl₂ with glycerol proceeds through two steps and removes two molecules of HCl, generating glycerol sulfite. The first step of removing HCl is the rate-determining step, with an activation energy barrier of 36.97 kcal/mol. Based on this, we proposed an innovative green synthetic strategy for the atom-economical synthesis of glycerol sulfite by the direct reaction of SO₂ with glycerol. The reaction of the SO₂ with glycerol involves three steps and removes one molecule of H₂O to form glycerol sulfite. The formation of the S-O bond in the second step is the rate-determining step. The activation energy barrier was reduced to 29.75 kcal/mol, which is better than the reaction of SOCl₂ with glycerol to form glycerol sulfite. Further exploration of the three-molecule synergistic reaction of 2-cyanopyridine, SO₂, and glycerol revealed that glycerol sulfite was generated through four steps. The second step, where the cyano group of 2-cyanopyridine was transformed into an imide group, was identified as the rate-determining step, with an activation energy barrier as low as 25.51 kcal/mol, which was better than the reactions of SOCl₂ with glycerol and SO₂ with glycerol to form glycerol sulfite. These results provide a new avenue for the design and synthesis of sulfur-based electrolyte additives.