Chemical Formation Of C-O\C-N Bonds With Carbon Dioxide As Synthetic Sub Catalyzed By New Catalyst Systems

Carbon dioxide（CO₂）is the greenhouse gas that contributes the most to global warming.At the same time,it is also an environmentally friendly,non-toxic,and abundant C1 resource.Through chemical activation to realize the chemical utilization of carbon dioxide,various high value-added chemical products can be obtained,which can be used in industrial production,medical treatment and food production,and are of great significance in environmental protection and resource utilization.In this study,a variety of new imidazole-based ionic liquid catalysts were designed and synthesized,and their structures were characterized by modern instrumental analysis methods such as NMR,FTIR and elemental analysis.Tests have found that the ionic liquid catalytic system can efficiently catalyze the cycloaddition reaction of propylene oxide（PO）and CO₂ without co-catalysts and solvents,and produce propylene carbonate（PC）with high selectivity（>99%）.Through the systematic discussion of reaction parameters such as reaction temperature,CO₂ pressure,reaction time and catalyst dosage,the optimal reaction conditions are:120℃,1 MPa,3 h,and catalyst dosage 0.25 mol%.Under the optimal reaction conditions,the PC yield is as high as 93%,and the selectivity is close to 100%.At the same time,the catalyst ILs4shows good substrate applicability and can catalyze the cycloaddition reaction of carbon dioxide with a variety of epoxides.In particular,the coupling reaction of carbon dioxide and some difficult-to-react bicyclic glycidyl ether epoxy compounds can be realized.In addition,the effects of different groups on the activity of this type of catalytic reaction were compared,including groups such as halogen,hydroxyl,and carboxyl.Under the same conditions,the catalyst modified with glycine had the highest yield.We also found that the catalyst also showed excellent catalytic activity and good substrate applicability under normal pressure conditions.Finally,a possible catalytic mechanism of intramolecular synergy is proposed.Further studies have found that the catalyst ILs4 can not only catalyze the cycloaddition reaction of carbon dioxide and epoxides to build C-O bonds,but also catalyze the reaction of carbon dioxide and nitrogen heterocyclic compounds to form oxazolidinones under the condition of no co-catalyst and solvent-free to realize the construction of C-N bonds.Using carbon dioxide and aziridine as a template reaction,under normal pressure conditions,the influence of the catalyst dosage,reaction time and reaction temperature on the reaction activity was explored,and the optimal reaction conditions were obtained:catalyst dosage 2 mol%,reaction time 12 h,the reaction temperature was 80℃.Under the optimal reaction conditions,the catalyst ILs4 shows good substrate applicability,and can react with 10 different nitrogen heterocyclic substrates synthesized in the laboratory to produce 5-substituted oxazolidinones and4-substituted oxazolidinones with high selectivity.Further studies have found that under high pressure（1 MPa）,the reaction temperature is reduced to room temperature,the amount of catalyst is reduced by half,and it takes only 3 hours to obtain excellent yield and good substrate applicability with high selectivity.Finally,a reasonable reaction mechanism is proposed based on the experimental results and related literature.The cheap and easily available Michler’s ketone is used as the main catalyst to catalyze the cycloaddition reaction of carbon dioxide and epoxides under solvent-free conditions.Use tetrabutylammonium iodide（TBAI）as a co-catalyst under normal pressure,and carbon dioxide and epichlorohydrin as a template to react.The reaction time,reaction temperature,the amount of catalyst and co-catalyst,and the reaction time reaction parameters are explored to obtain The best reaction conditions are:reaction time 24 h,reaction temperature 100℃,catalyst dosage 1 mol%,catalyst dosage:co-catalyst dosage=1:1.Under the optimal reaction conditions,the catalytic system showed good substrate applicability,high yield and good selectivity.Replace the co-catalyst TBAI with tetra butyl ammonium chloride（TBAC）or tetra butyl ammonium bromide（TBAB）to obtain excellent catalytic activity.High-pressure catalysis studies have shown that the reaction time is shortened to 3 hours,and the catalytic system composed of three co-catalysts and Michler’s ketones all show good substrate applicability,and can be highly efficient and selective（>99%）.Carbon dioxide and epoxides are converted into corresponding cyclic carbonates.