Synthesis of 1,2-glycerol carbonate from carbon dioxide: the role of methanol in fluid phase equilibrium

The effect of methanol on the synthesis of 1,2-glycerol carbonate from CO₂ and glycerol is studied in the presence of Bu ₂Sn(OCH₃)₂, n-Bu₂SnO, and tert-Bu₂SnO. At 423 K, up to 2.7 mol% yield in glycerol carbonate, based on glycerol, could be obtained in the pressure range 14-20 MPa. Addition of acetonitrile promotes notably the yield to 7 mol%. Fluid phase equilibrium experiments with the ternary mixture CO₂/glycerol/methanol show that the reaction takes place in a liquid phase where methanol dissolves glycerol, CO₂, and the tin complexes. Above ∼0.6 mole fraction, CO ₂ behaves as an anti-solvent, separating methanol from glycerol, thus inhibiting the formation of 1,2-glycerol carbonate. Dimethyl carbonate is a sideproduct of glycerol carbonation resulting mainly from transesterification between glycerol carbonate and methanol. Glycerol coordination to tin center is evidenced by the isolation of di-tert-Bu₂Sn(1,2-glycerolate) complex. Its structure determination by single-crystal X-ray diffraction shows that the remaining OH group of glycerol promotes the formation of onedimensional polymeric chain.