Functionalized Ionic Liquids,Inorganic Salts Catalyzed Synthesis Of Organic Carbonates

Organic carbonates are important organic compounds with the label of‘‘green chemicals’’due to their low vapor pressure,moderate toxicity,biodegradability for human health and environment.The global demand for organic carbonates is growing at an annual rate of 6.9%,mainly used as feedstocks for manufacturing polycarbonates,electrolytes for lithium-ion batteries,low-volatile solvents,and fuel additives.The transesterification of ethylene carbonate with alcohols can yield dialkyl carbonate in high yield under relatively mild conditions,which is an important method for the synthesis of linear organic carbonates.Carboxylic cyclization of CO₂ with propargylic alcohols is an important method for the synthesis of cyclic carbonates,which has the advantage of 100%atom utilization and direct resource utilization of CO₂.Therefore,it is of great significance to develop green and efficient catalysts for transesterification and cyclization reactions.This dissertation is devoted to the catalytic synthesis of organic carbonates.Urea-functionalized swelling poly（ionic liquid）s and inorganic salt Na Cl were designed and synthesized for catalyzing transesterification of ethylene carbonate to dimethyl carbonate.Azaphosphatrane ionic liquids and Ag₂O catalytic system were designed and synthesized for catalyzing carboxylic cyclization of CO₂ with propargylic alcohols toα-alkylidene cyclic carbonates,and further synthesizingβ-carbonyl carbonate by transesterification.The specific research content and results are as follows:1.Urea-functionalized swelling poly（ionic liquid）s as efficient catalysts for the transesterification and hydrolysis of ethylene carbonateUrea-functionalized poly（ionic liquid）s catalysts with high swelling ability in methanol were designed and synthesized for the transesterification of ethylene carbonate to dimethyl carbonate.The swelling ability of poly（urea-IL）-n in methanol enabled active urea sites accessible for ethylene carbonate and methanol,resulting in a quasi-homogeneous catalytic system.Poly（urea-IL）-5%showed excellent catalytic activity,which was similar to that of corresponding homogeneous ionic liquid catalysts.The catalyst can be reused and recycled five times with stable activity.The reaction mechanism was investigated by NMR analysis.The urea tethered imidazolium in poly（urea-IL）-5%acted as hydrogen-bonding donor to activate ethylene carbonate for enhancing catalytic activity.The conversion of intermediate 2-hydroxyethyl methyl carbonate（HEMC）in the transesterification reaction was systematically investigated,and it was found that the complete conversion of ethylene carbonate was limited by reversible reaction between ethylene carbonate and HEMC.In addition,poly（urea-IL）-5%also exhibited high catalytic activity for the hydrolysis of ethylene carbonate.2.Na Cl catalyzed transesterification and hydrolysis of ethylene carbonateSodium chloride（Na Cl）was used as catalyst for the transesterification of ethylene carbonate with methanol first time in high activity with a TON of 770.Other inorganic chlorine salts including Li Cl,KCl,Cs Cl,Mg Cl₂,Sr Cl₂,Ba Cl₂,Ca Cl₂ and edible salt also exhibit similar high catalytic activity.The influences of feed molar ratio of methanol,catalyst dosage,temperature and time on catalytic activity were thoroughly studied.Mechanism studies by kinetic isotope effect measurements and DFT calculations indicated that Na Cl catalyze transesterification via the S_N2 mechanism.Na Cl can also efficiently catalyze the reaction of ethylene carbonate with ethanol and propanol to diethyl carbonate and dipropyl carbonate,respectively.Moreover,Na Cl was demonstrated to be an effective catalyst for the hydrolysis of ethylene carbonate,99%yield of ethylene glycol was obtained under optimized reaction conditions.Interestingly,seawater was successfully used instead of pure water without other additives for the hydrolysis of ethylene carbonate.3.Azaphosphatrane/Ag₂O catalyzed carboxylative reaction of CO₂ and propargyl alcohols for the synthesis of organic carbonatesAzaphosphatrans/Ag₂O catalyst system was designed and synthesized for the carboxylative cyclization of CO₂and propargylic alcohols,resulting inα-alkylidene cyclic carbonates in excellent yields（>99%）under room temperature.The influences of catalyst structures,various solvents,reaction temperature,and rection time on catalytic activity were thoroughly studied.PMB-AZAP/Ag₂O catalyst system showed excellent activities for numerous substrates.NMR studies indicated that azaphosphatrane played an important role in the activation of hydroxyl group of propargylic alcohols.The（proazaphosphatrane）silver complexes（PAP-Ag）generated from azaphosphatrans and Ag₂O could effectively activate carbon-carbon triple bond,which played a synergistic catalytic role.In addition,PMB-AZAP/Ag₂O catalyst system was further applied to the one-pot two-step rection of CO₂,propargylic alcohol and methanol,resulting in 80%yield of methyl 2-methyl-3-oxobutan-2-yl carbonate under optimized reaction conditions.