Catalytic Mechanism Of Cycloaddition Of CO₂ In Ionic Liquids

The reaction of carbon dioxide?CO₂?with epoxides to synthesize cyclic carbonates is an atomic economical reaction that can effectively fix CO₂.CO₂ is a widespread C1resource.Although there are some studies on the mechanism of catalyzed CO₂conversion of carbonates by ionic liquids,the detailed understanding of the microscopic mechanisms is still insufficient.This thesis discusses the reaction mechanism through the combination of experiment and simulation.The innovative work and achievements of this thesis are as follows:?1?The reaction mechanism of CO₂ converted to cyclic carbonates was studied using ionic liquids as catalysts.The results show that the anions and cations have a substantial effect on the conversion rate of the reaction.It is proposed that the ionic liquid plays a dual electrophilic and nucleophilic activating role in catalysis.The possible reaction mechanism was predicted.It was found that the formation of ion clusters due to hydrogen bonding of ionic liquids and the addition of trace amounts of water to the reaction system facilitated the reaction.?2?The Kamlet-Taft method was used to characterize the hydrogen bond acidity???and hydrogen bond basicity???of ionic liquids.The results show that the conversion rate has a certain relationship with the hydrogen bonding ability.1-hydr-oxyethyl-3-methylimidazolium bromide and 1-butyl-3-methylimidazolium bromide was selected to measure the products at different reaction time,and the products were characterized by GC,¹H NMR and UPLC-QTOF.The C₂-H cation of the ionic liquid was found to form hydrogen bond with O atom of propylene oxide?PO?,and the anion was also form the hydrogen bond with C-H of the PO,finally effort from both anion and cation led to PO ring opening.As the reaction proceeded,the conversion rate gradually decreased,and the amount of intermediates decreased correspondingly,and the structure of the intermediate was detected by MS.?3?In order to verify the experimental results,density functional theory?DFT?was used to calculate the interaction energy and second-order stabilization energy of ionic liquids,finding hydrogen bonds is one of the key factors in the reaction.And the reaction pathway for the 1-butyl-3-methylimidazolium bromide catalyst was calculated.Ring opening was found to be the controlling step for the entire reaction.The activation energies and transition states of ring opening for other ionic liquids were further calculated.The calculated energy barrier and experimental conversion rate have a certain relationship,and the mechanism of the reaction was clarified.The role of water in the reaction was studied.