Synthesis And Characterization Of Vinylidene Carbonate

Vinylidene carbonate（VC）is an important pharmaceutical intermediate and is of vital research importance,both in theory and in practical application.This paper reviews the current status and problems of VC research,in particular the environmental problems associated with the synthesis of vinylidene carbonate by conventional processes that generate large amounts of waste acid.In this paper,we propose to adopt the theory of direct dehydrogenation to achieve the conversion from a"two-step"to a"one-step"direct dehydrogenation,to gain an in-depth understanding of the mechanism of ethylene carbonate（EC）dehydrogenation,to combine the energy of each compound in the reaction path with Gaussian calculations,and to screen for functional catalysts.The design of the Ag/K-ZSM-5 catalyst as a dehydrogenation catalyst was used to investigate the direct dehydrogenation of EC under high temperature conditions in a fixed bed,and this idea was experimentally explored.This thesis is a detailed study of（1）the traditional synthesis process of vinylidene carbonate;（2）the density flooding theory（DFT）study of vinylidene carbonate;and（3）the preparation of ZSM-5 molecular sieve carrier and its modification.The specific results are as follows:（1）Traditional synthesis process of vinylidene carbonate:This paper investigated the effects of material ratio,reaction temperature,reaction time and initiator dosage on chlorination under water-bath heating conditions,and applied orthogonal tests to optimize the conditions of n（EC）:n（AIBN）=600:1,n（EC）:n（SO₂Cl₂）=1:1.3,the reaction temperature was 90℃,the reaction time was 60 min,and the yield of monochlorinate was 65.8%.The optimum experimental conditions were n（CLEC）:n（triethylamine）=1:1.5,reaction temperature of 60℃,reaction time of 1.5 h,n（CLEC）:n（EC）=1:2,and the yield of the monochlorinated substituent was 65.8%.The yield of the product was 75.9%and the overall yield was 49.9%.（2）Density flooding theory study of vinylidene carbonate:In this paper,density flooding theory was used to perform thermodynamic and kinetic calculations for the dehydrogenation and decarboxylation of vinylidene carbonate using the Gaussian 09software package.The calculations are based on the M06-2X/def2-TZVP density flooding theory with quasi-resonant oscillator-rigid rotor thermochemical corrections to calculate the Gibbs free energy of each compound,which concludes that the dehydrogenation and decarboxylation of vinyl carbonate are entropy-increasing reactions and thermodynamically controlled;the dehydrogenation reaction to produce vinylidene carbonate is easier to carry out,and the reaction absorbs heat and needs to be warmed up to about 650℃to carry out the reaction autonomously.The DSC results show that vinylidene carbonate decomposes at this temperature,so the reaction needs to be controlled by a catalyst to reduce the activation energy of the reaction.（3）Preparation of ZSM-5 molecular sieve carrier and its modification:In this paper,the method of hydrothermal synthesis was used to prepare ZSM-5（20:1,50:1,80:1,100:1）mesoporous molecular sieves with different silica-alumina ratios,then XRD,FTIR,SEM,BET,NH₃-TPD and other means were used to characterize the molecular sieves.The ZSM-5-80 molecular sieve catalyst had good catalytic performance and recycling performance,and its optimum yield was 4.6%.The effect of single promoter K and double promoter Ag-K and their ratios on the reaction yield was investigated,in which the highest yield of 5.9%was obtained for Ag/K-ZSM-5catalyst with a loading ratio of 0.7 potassium and 8 silver.The state of the optimum catalyst before and after use was characterised by XRD,SEM,TEM,BET,NH₃-TPD,XPS and TG-DTG.In summary,this paper explores a green route to VC synthesis through direct dehydrogenation that not only helps prevent pollution,but also promotes a balanced industrial ecology.The implementation of the direct dehydrogenation route not only breaks with the traditional synthesis method,reduces waste emissions and facilitates environmental protection,but also greatly simplifies the operational process.The deepening of the route will provide a new way of thinking for subsequent research and development,and provide basic research for the realisation of industrialisation.