The Application Of Deep Eutectic Solvent In The Synthesis Of Propylene Carbonate

Propylene carbonate?PC?is an important organic chemical which has been widely applied into chemical,textile and battery field.For example,propylene carbonate commonly used as plasticizer,adhesive,extractant and electrolyte for secondary lithium battery.For the moment,one of the most green and important methodologies to obtian propylene carbonate is the cycloaddition of CO₂ and propylene oxide?PO?.In the past decades,numerous of catalysts have been developed for the cycloaddition reaction,such as alkali metals,quaternary ammonium salts and phosphine salts,ion exchange resins and ionic liquids.However,in many cases,these catalysts are unsuitable for industry scales due to some drawbacks,such as low catalyst activity,expensive cost,harsh reaction conditions?high pressure or temperature?and the need of organic solvent.Therefore,it is urgent to explore a novel catalytic system for the cycloaddition reaction.As a new type of universal alternatives to ILs,DESs not only retain the similar physicochemical properties of traditional ILs,but also have some excellent nature,such as easily prepared,low cost and environmental benign.Nowadays,DESs have been employed in many fields due to their excellent properties.In this paper,we reported a series of deep eutectic solvents?DESs?as catalyst for the cycloaddition of CO₂ under solvent and metal free condition.The reaction mechanism was also studied.The major work and innovative results for this dissertation are summarized as follows:A series of DESs based on amino acids?AAs?and dicarboxylic acids were prepared for the cycloaddition of CO₂ and epoxides with additive ZnBr₂.These DESs both have amino and carboxyl,which would activate PO and CO₂.The eutectic mixture of L-proline?L-Pro?/propanedioic acid?PA?system exhibited high activity and selectivity for cycloaddition of CO₂ and PO among the prepared DESs.The PC yield of the L-Pro/PA system can reach as high as 98%under optimal conditions.Furthermore,the L-Pro/PA system was readily recovered and reused over 9 times without noticeable decrease in yield and selectivity of PC.For the cycloaddition of CO₂ and other epoxides,the L-Pro/PA system also showed good activity.We have proposed a plausible catalytic mechanism that fully explains the main reason in DES and discussed the effect of the lengths of carbon chain of dicarboxylic acids for the cycloaddition reaction.However,ZnBr₂ as the co-catalyst was essential for the catalyst system.The toxicity of ZnBr₂ and the adverse effects of bromide on the environment were against the principle of green chemistry.The choline chloride-based DESs were prepared to catalyze the cycloaddition of CO₂ and epoxides without any additive.The Cl^-of choline chloride-based DESs accelerate the conversion of PO and enhance the PC yield.The CHCl/PEG₂₀₀system exhibited the highest catalytic activity that the PC yield reached 98%at 150^?C and0.8 MPa in 5 h.The CHCl/PEG₂₀₀00 system was readily recovered and reused over 5 times without noticeable decrease of PC yield.In addition,high yields over a wide scope of substrates were also obtained.A possible reaction mechanism elucidating the excellent catalytic activity of the choline-based DESs was proposed.During the L-Pro/PA system and CHCl/PEG₂₀₀00 system,the reaction temperature and pressure were both harsh?the reaction temperature was 150^oC and the reaction pressure was>0.8 MPa?.According to this,in this part,we prepared the choline chloride-sugar DESs catalytic for the cycloaddition of CO₂ and epoxides under milder conditions.