Synthesis Of Cyclic Carbonate Catalyzed By Nitrogen-containing Heterocyclic Ionic Liquids

Carbon dioxide?CO₂?is a rich,renewable,non-toxic and non-flammable C raw material.It can be used to synthesize a variety of organic compounds.The synthesis of cyclic carbonates from epoxy compounds and CO₂ is an effective CO₂ fixation method.At present,catalysts for synthesizing cyclic carbonates still have problems such as corrosion equipment and environmental pollution.A series of N-heterocyclic carbenes catalysts were investigated from the perspective of green and safety in this paper,which could convert CO₂ to valuable products efficiently and relieve the greenhouse effect.According to the research,the catalyst of[DBU-CH2CONH2]Br has achieved a very good catalytic effect and reusable stability.The optimum reaction condition was investigated and the proposal mechanism was confirmed by simulation and experiment.The innovative and major achievements of the paper are as follows:1.A series of N-heterocyclic carbenes derived ionic liquids?ILs?was synthesized and used to catalyze the cycloaddition reactions under solvent-free and metal-free condition.In this paper,different functional group has been substituted into DBUIDBN/MIM-deri-ved ionic liquids.After tested these ILs catalysts,it is said that the catalytic performance of acylamino-based ILs is better than alkyl-based ILs.The activity of each bromine-based ILs is following the order:[DBU-CH2CONH2]Br>[DBN-CH2CONH2]Br>[MMIM-CH2CONH2]Br.The reaction conditions?including temperature,pressure and reaction time?on the reaction of CO₂ to propylene oxide?PO?catalyzed by[DBU-CH2CONH2]Br were studied.It showed that the best condition is under 120 ?,1 MPa,2.5 h catalyzed by 2 mol%DBU-derived bromide ionic liquid,the conversion of PO and the selectivity of propylene carbonate?PC?reached 99%and 99%,respectively.Under the optimum reaction conditions,the ionic liquid system could be reused at least five times without decrease of selectivity and conversion.Further,CO₂ with several kinds of epoxides to form cyclic carbonates was studied.It is suggested that[DBU-CH2CONH2]Br have a better catalytic performance in different epoxy compounds.The catalytic mechanism is proposed in this paper:ILs would attack on PO by electrophile and nucleophile.The H atom from amide-ILs would promote the ring-opening of PO,that add to CO₂ forming the PC.This mechanism has been confirmed by NMR spectroscopy and DFT calculations to reveal the hydrogen-bond interaction between ionic liquids and reagent.It is suggested that the hydrogen-bond affect the reactivity of ILs catalysts?[DBU-CH2CONH2]Br>[DBN-CH2CONH2]Br>[MMIM-CH2CONH2]Br?.The shift of 1HNMR is very agree with H-bond simulation.The stronger hydrogen-bond of ILs,the shift of 1HNMR and the length of hydrogen-bond simulation is larger.2.Nano-sized resin beads were prepared in this paper.Ionic liquids?[DBU-CH2CONH2]Br,[DBN-CH2CONH2]Br and[MMIM-CH2CONH2]Br?are loaded on resin beads for the catalytic synthesis of cyclic carbonates.In order to obtain optimal catalytic performance of the catalyst,a variety of ionic liquids are immobilized on the resin.Based on the experiment,the resin pellet loading[DBU-CH2CONH2]Br have a better catalytic activity.In order to explore the effect of ionic liquid loading on the catalytic activity,a series of different amount of[DBU-CH2CONH2]Br loading resin catalysts were synthesized and the best catalysts is the 30%-loading[DBU-CH2CONH2]Br to resin.The reaction of loaded[DBU-CH2CONH2]Br ionic liquids for different epoxy compounds and CO₂ was studied.It shows that the loaded[DBU-CH2CONH2]Br ionic liquid has a wide range of applications.