Study On Cycloaddition Reaction Of Carbon Dioxide And Epoxides

Carbon dioxide is a cheap and abundant C1 resource,which can be used as a raw material for the synthesis of value-added chemicals.The cycloaddition of epoxides with CO₂ is a green route to synthesize cyclocarbonates,which has been paid much attention in recent years.In this thesis,three kinds of catalytic systems wih high green features and high efficiency were developed for synthesis of cyclocarbonates from CO₂ and epoxides.The main contents and results are listed as follows.1.Using biomass macromolecular chitosan,phytic acid and Fe Cl₃ as raw materials,through hydrogen bonding and metal coordination,a mesoporous metal organic hybrid material（CS-Fe）with multifunctional groups was prepared in aqueous solution.With assistance of alkali metal halides（such as KI,KBr,KCl）,the resultant CS-Fe showed high activity for the cycloaddition of epoxides with carbon dioxide.Especially,under the catalysis of KI/CS-Fe the cycloaddition of propane oxide with CO₂ afforded carbonate in a yield of 96%and selectivity of98%at 120℃and 2.0 MPa.The KI/CS-Fe catalytic system showed good stability and wide substrate scope.The possible catalytic mechanism of KI/CS-Fe was explored.2.Using polyethylene glycol 400（PEG 400）as the solvent and catalyst,the cycloaddition of epoxides with carbon dioxide was achieved in the presence of the co-catalyst KI.Under the optimized reaction conditions（e.g.,100°C,2.0 MPa and 1.0 h）,the yield of PC reached98%with the selectivity of 99%.It was indicated that KI/PEG400 had high activity for catalyzing the reaction of epoxides with CO₂,especially for catalyzing the cycloaddition of styrene oxide with carbon dioxide,producing corresponding carbonate in excellent yield.3.Ionic liquid[DBU][Im]was synthesized based on the reaction of imidazole and organic base DBU.Combined with KI as a cocatalyst,[DBU][Im]showed high efficiency for catalysing the cycloaddition of epoxides with CO₂ under the optimized conditions（i.e.,120°C,2.0MPa,4.0 h,the molar ratio of KI/[DBU][Im]of 1:2）,with the PC yield of 96%and selectivity of98%.It was indicated that the KI/[DBU][Im]catalytic system displayed good stability and wide substrate scope.Especially,it could efficiently catalyze the reaction of CO₂ with epoxides with larger steric hindrance,affording corresponding carbonates with high selectivity（e.g.,96%）.Based on the experimental results,the possible reaction mechanism was proposed.