Preparation Of ?-diketone-based Catalysts And Their Catalytic Cycloaddition Of CO₂ And Epoxides

Carbon dioxide(CO₂)is not only a major greenhouse gas,but also a carbon resource with abundant reserves,easy availability and low cost.With the increasing shortage of global resources,the conversion of CO ₂ into high value-added chemical products has become a research topic in the field of green chemistry.The way which utilizing CO₂ as a resource to synthesize cyclic carbonates by the ring-opening addition of CO₂ and epoxides is an important.However,due to the inert nature of CO₂,there is an urgent need to develop high-performance catalysts to promote the ring-opening addition reaction of CO₂.The structure of?-diketone compounds contains multiple functional groups such as carbonyl groups,hydroxyl groups,unsaturated double bonds,and?-position active hydrogen atoms because of structural interconversion.Therefore,?-diketone compound could participate in many types of reactions such as metal coordination,dynamic crosslinking and amino condensation.In this paper,a series of high-efficiency non-metal homogeneous catalysts were synthesised by?-diketone compounds to synthesize high value-added cyclic carbonates by chemical methods with epoxides and CO₂.The main contents of the research are as follows:(1)A series of non-metal homogeneous catalysts with different structures were successfully prepared by one-step reflux method referring to the Schiff base reaction between 2,4-pentanedione and amine compounds of different structures in this paper.On basis,the most stable state of different catalysts at the molecular or atomic level was studied by theoretical means,and the optimal structure of the catalyst was obtained by density functional theory(DFT)calculations.(2)The Pentane-I catalyst was used in the cycloaddition reaction of CO₂ and epichlorohydrin(ECH)to synthesize 3-chloropropene carbonate which prepared by the reaction of tetraethylenepentamine and2,4-pentanedione.The optimal catalytic parameters of the reaction were obtained through single factor investigation and response surface optimization method(RSM):the reaction temperature was 100?,the reaction time was 6.5 h,the CO₂ pressure was 0.7 MPa,and the product yield reached 97.3%.In addition,the effect of the reaction temperature,pressure,time and the pairwise interaction between different factors on the yield of the cycloaddition product is also obtained:reaction temperature>CO₂ pressure>reaction time.The interaction between reaction temperature and reaction time possesses the most significant influence on the product yield.Under the optimal reaction conditions,it is concluded that,Pentane-I has the highest catalytic activity due to the combined action of-OH and-NH-among the five catalysts.(3)Finally,the Arrhenius equation and Eyring equation were used to study the reaction kinetics and thermodynamics of CO₂ with ECH catalyzed by Pentane-I.Studies have shown that the activation energy of the reaction is E_a=49.71 k J mol^-1,the value of the former factor A is 5.09×10⁶,and the kinetic equation of the reaction is:R=5.093×10⁶c_(ECH)e^-49.71/RT.The thermodynamic study shows that the thermodynamic activation enthalpy change(?H)and thermodynamic activation entropy change(?S)of the catalytic reaction are 54.24 k J mol^-1 and 0.1035 J·mol^-1·K^-1,respectively.DFT was used to simulate the interaction between five catalysts and CO₂and ECH.The results show that the simultaneous presence of-OH and-NH-in the Pentane catalyst can generate strong hydrogen bonding with ECH to activate ECH.Based on various studies,the possible mechanism of Pentane-I catalyzing the ring-opening addition of CO₂ and ECH is proposed.