Bis-ammonium immobilized polystyrenes with co-catalyzing functional end groups as efficient and reusable heterogeneous catalysts for synthesis of cyclic carbonate from CO2 and epoxides†
Abstract
A series of novel bis-ammonium ionic liquid immobilized polystyrene (BisAm-i-PS) heterogeneous catalysts with co-catalyzing functional end groups of –CH2COOH, –CH2CH2OH, and –CH2CH2NH2 were synthesized for the cycloaddition reaction of CO2 and epoxides without any additional co-catalyst and organic solvent. All the ammonium immobilized catalysts showed high selectivity. Bis-ammonium immobilized catalysts were more efficient than single-ammonium ones. The yield was further increased by introducing the functional end groups. Both –CH2COOH and –CH2CH2OH terminated BisAm-i-PS catalysts achieved high activities (yield: >99%), while the –NH2 terminated one had a slightly lower activity (yield: 97.3%) under the same reaction conditions. The effects of different parameters, such as the halide anions of the catalysts, reaction temperature, initial pressure and reaction time were also investigated with –CH2CH2OH terminated BisAm-i-PS (BisAm-OH-i-PS) as the catalyst. Under optimal reaction conditions (1.2 MPa, 130 °C and 2.5 h), BisAm-OH-i-PSs with 2Br− and 2I− showed very high efficiencies. For each of them, propylene carbonate selectivity and yield were more than 99% and 99%, respectively. In addition, the catalyst possessed good stability, and both catalytic activity and selectivity were always more than 99% for 5 times of recycle tests.