Functionalized quaternary ammonium salt ionic liquids (FQAILs) as an economic and efficient catalyst for synthesis of glycerol carbonate from glycerol and dimethyl carbonate

A series of functionalized quaternary ammonium salt ionic liquids (FQAILs) with different functional groups, such as hydroxyl, carboxyl, ether group, and amino, were prepared and used as a catalyst for the synthesis of glycerol carbonate from transesterification of glycerol and dimethyl carbonate without any additional organic solvent and co-catalyst. The effects of functional groups, anions (Cl − , Br − , I − , OH − ), and reaction parameters were investigated in detail. It is found that both the cation and anion of FQAILs display an important effect on its catalytic activity. Among these FQAILs, hydroxyl functionalized ionic liquid, [HPTPA]OH possesses the highest activity because there are the strong interactions between hydroxyl and dimethyl carbonate molecular and between anion OH − and glycerol molecular, which were shown by FTIR spectra. The glycerol conversion of 96.2% and glycerol carbonate yield of 87.6% can be obtained over [HPTPA]OH under moderate conditions of reaction temperature of 80 °C, reaction time of 90 min, dimethyl carbonate/glycerol molar ratio of 3, and catalyst amount of 0.9 mol% based on glycerol amount. The [HPTPA]OH catalyst can be reused at least three cycles without significant reduction in its catalytic activity. Finally, a possible reaction mechanism for the synthesis of glycerol carbonate is also proposed.