Catalysis Today, Vol.330, 76-84, 2019
Chemical fixation of CO2 to cyclic carbonate catalyzed by new environmental- friendly bifunctional bis-beta-cyclodextrin derivatives
In present work, three amino-bridged biomass bis-beta-cyclodextrins (bis-beta-CDs) and eight bifunctionalized bis-beta-CDs derivatives were designed and synthesized as environmental friendly catalysts to fix CO2. Both the bridged bis-beta-CDs 1a-3a/potassium halide and haloalkane functionalized bis-beta-CDs 1b-8b were poven to be efficient catalytic systems for the solvent-free coupling reaction of CO2 and epoxides. After systematic investigation, the optimized conditions of (120 degrees C, 4 MPa, 0.14mol% 1a, 1.25mol% KI, 2 h) have been established for dual catalytic system 1a/ KI and the excellent yield (94%) with high selectivity (99%) can be achieved for the cycloaddition of CO2 and propylene oxide. Furthermore, after functionalization with alkyl halides, bis-beta-CD derivative 1b-8b as sigle bifunctional catalyst exhibited better activity under milder optimal conditions of (110 degrees C, 2 MPa, 0.125mol% 1b and 4 h). Moreover, these bifunctional catalysts are also applicable to a variety of epoxides (including diepoxides) and good catalytic performances were abtained for producing the corresponding cyclic carbonates in most cases. Furthermore, this catalyst can be reused at least for five times without significant activity decrease. Finally, a possible mechanism including the activation of both epoxide and CO2 was proposed based on the literatures and experimental results.