Conversion Of Carbon Dioxide To Organic Carbonates Under Low Pressure

Excessive emission of carbon dioxide（CO₂）is well known as one of the major factors for the global greenhouse effect.Meanwhile,CO₂ is a non-toxic,naturally ample,nonflammable and economical C1 source.Therefore,the effective use of CO₂ for the benefit of mankind has always been the focuses of scientists.Organic carbonates are an important class of compounds with high polarity,low viscosity,low toxicity and easy degradation.They can replace hazardous reagents in certain organic processes selectively and effectively.The conversion of CO₂ to organic carbonates has important application value.Dimethyl carbonate（DMC）is the simplest carbonate.One-pot synthesis of DMC from epoxide,methanol and CO₂ and direct synthesis of DMC from methanol and CO₂ are both important methods.In this dissertation,many efforts have been made on the reduction of reaction pressure and the optimization of reaction conditions to realize the efficient transformation of CO₂ to organic carbonates under mild conditions.The one-pot synthesis of DMC and the direct synthesis of DMC have been investigated systematically,and the efficient synthesis of symmetric and asymmetric organic carbonates has also been studied in detail.The main research contents of this dissertation include the following three parts:（1）Six hydroxyl-functionalized ionic liquids（HFILs）IL1-IL6 were designed and synthesized.A bi-component catalytic system composed of an HFIL and an alkali carbonate has been developed,which can efficiently convert epoxides,CO₂ and methanol into DMC under low initial pressure.The bi-component catalyst can be reused for 4 runs.Under the optimized reaction conditions,a 64%gas chromatography（GC）yield of DMC from propylene oxide and an 81%GC yield of DMC from ethylene oxide were obtained,respectively.（2）A mild and efficient reaction system has been developed for the transformation of CO₂and methanol into DMC under low initial pressure in the presence of CH₂Br₂,1,8-diazabicyclo[5.4.0]undec-7-ene（DBU）and ionic liquid.Under the optimized reaction conditions,DMC was obtained with a high GC yield of 81%at the initial pressure of 0.25 MPa.The reaction can be carried out under a CO₂ balloon condition in the presence of CH₂Br₂ and DBU,providing a 23%GC yield of DMC.In this case,after the reaction,DBU is proved to be recyclable after the residue obtained from the reaction mixture has been treated with KOH.（3）A mild and highly efficient reaction system under low initial pressure has been developed for the one-pot synthesis of organic carbonate from CO₂,alcohol and alkyl bromide using DBU as the activator.The reaction conditions were screened systematically,and 24symmetrical and unsymmetrical organic carbonates were prepared successfully,showing a broad substrate scope.Taking the synthesis of ethyl methyl carbonate（EMC）as an example,after the reaction,DBU is proved to be recyclable after the residue obtained from the reaction mixture has been treated with KOH.