Ionic Liquids/Organic Bases Synergistically Catalyze The Cycloaddition Of Carbon Dioxide And Epoxides

The carbon dioxide(CO2)concentration in the atmosphere has increased continuously because of the combustion of huge amounts of fossil fuels.As a main greenhouse gas,it has caused some serious environmental problems.On the otherhand,CO2 is one of the abundant,non-toxic,economic and renewable Cl feedstock,it can be used as raw material to synthesize a variety of chemicals.Accordingly,reducing CO2 emissions and transforming it to high value-added chemicals has attracted many attentions from academia and industry.Ionic liquids exhibit unique advantages for transformation of CO2,due to their excellent properties including low melting point,negligible vapor pressure,high stability and tunable structure.Meanwhile,organic bases have been widely applied in capture and fixation of CO2,ascribe to their advantages such as easy obtainment,economic and tunable structure.This dissertation focuses on the conversion of CO2 to cyclic carbonate catalyzed by synergistic catalytic system consisting of ionic liquid and organic base under mild conditions.The main works are as follows:1.A concise of introduction of significance and the researching advances of CO2 cycloaddition reaction.2.An intermolecular synergistic catalytic combination of ionic liquids and organic bases has been applied to the cycloaddition of CO2 and epoxides.The influence of the type and amount of ionic liquids,the type and amount of bases,the reaction temperature and reaction time on the reaction have been systemically investigated.It showed that the optimum catalysts are 1-benzyl-3-butylimidazolium bromide(BnBimBr)and diethylamine(DEA)/N,N-Diethylbenzylamine(DEBA).Under the the optimum reaction conditions,excellent reactivities were obtained by BnBimBr/DEA or BnBimBr/DEBA,and various 5-membered cyclic carbonates were synthesized.In the BnBimBr/DEA catalytic system,NMR,FT-IR spectroscopy and DFT calculations demonstrate the intermediate which formed from CO2 and DEA.In addition,C2-H of imidazolium as a hydrogen bond donor can activate the substrate by inducing hydrogen bond.Based on these results,a plausible ionic liquids andsecondary amines intermolecular synergistically catalyzed mechanism is proposed and further confirmed by more detail DFT calculations including reaction pathways and energy profiles.In the BnBimBr/DEBA catalytic system,adventitious water can promote the reaction effectively.DFT calculations demonstrate that organic base activate CO2 with the assistance of water to form bicarbonate.Accordingly,a possible reaction mechanism on the synergistic catalysis of BnBimBr and DEB A is proposed.3.An intramolecular synergistic catalytic system of amine functionalized ionic liquids have been designed and synthesized.The catalytic system was applied to catalyze the cycloaddition of CO2 and epichlorohydrin.The effect of reaction time,reaction temperature and catalyst amount on the reaction have been systemically investigated.Similarly,adventitous water could accelerate the reaction effectively.Base on these results,a plausible ionic liquid and organic base intramolecular synergistically catalyzed mechanism are proposed.Furthermore,when the butyl group in the functionalized ionic liquid is replaced by ethenyl group,it presented excellent catalytic activity as well.