Study On The Synthesis Of Diethyl Carbonate Catalyzed By Self-derived Strong Basic Salts In The Syste

Diethyl carbonate is an important organic synthesis intermediate.It can be used as carbonylation and alkylation reagents,solvents,electrolytes for lithium-ion batteries,fuel additives for gasoline and diesel,and is widely used in chemical and pharmaceutical industries.And other fields.Among the many synthetic methods,the method of transesterification to synthesize diethyl carbonate is considered to be the most promising synthetic route at present due to the advantages of green pollution-free,simple operation,and high yield.At present,the catalysts in the transesterification reaction reported in the literature are mainly divided into two categories:homogeneous catalysts and heterogeneous catalysts.However,there are problems such as poor repeatability,fast deactivation,and low catalytic efficiency.In this paper,aiming at the two routes for the transesterification reaction to synthesize diethyl carbonate（EC/PC and ethanol transesterification synthesis method）,two homogeneous strong basic alkoxide catalysts with high catalytic efficiency and reusable have been developed from the system.In the reaction of EC and ethanol,the reaction product ethylene glycol and potassium hydroxide were used to synthesize potassium ethylene glycol（EGK）catalyst.The structure was proved by thermogravimetric,infrared and nuclear magnetic characterization,and the Hammett indicator method was used to determine The alkali strength of EGK is15.0<H_-<18.4,and its alkali content determined by benzoic acid titration is 6.18 mmol/g.The EGK catalyst reacted at 0℃for only 5 minutes,the EC conversion rate reached33.67%,the DEC selectivity exceeded 99%,the DEC yield was 33.34%,and the TOF value reached 456.66 mol_DEC·mol^-1_cat·h^-1,showing extreme Good catalytic effect.As the reaction temperature,time,initial ratio of Et OH and EC and catalyst content increase,the yield of the target product DEC gradually increases.After repeated use of EGK for 5 times,no obvious inactivation occurred,indicating that it has good stability and reusability.EGK also has good general applicability for catalyzing the exchange reaction between EC and a variety of lower alcohol ester alcohols.The conversion rate of EC and the yield of target carbonates gradually decrease with the growth of the carbon chain of C₁～C₄ normal alcohols,but the catalysis is different.The reactivity of constitutive alcohols is relatively low.According to the analysis results of gas chromatography-mass spectrometry（GC-MS）,the reaction mechanism is inferred.The process starts with ethylene glycol oxygen anion activating Et OH to generate ethoxy anion.The kinetic data proves that the transesterification process is a first-order reaction,and Ea is only 10.996 k J·mol^-1,which is far lower than the value reported in the known literature.In the transesterification of PC and ethanol to synthesize diethyl carbonate,starting from the reaction system,the product 1,2-propanediol was used as the reaction material to prepare a homogeneous strong basic 1,2-propanediol salt catalyst.Its structure was characterized by thermogravimetry,infrared and nuclear magnetism.And explored its catalytic activity,through experiments,it is concluded that the 1,2-propanediol salt catalyst with K⁺as the cation is the best catalyst in the reaction of PC and ethanol;the reaction temperature of PGK is 82℃,and the molar ratio of PC to ethanol is 1:10.The amount of catalyst added is 3%of the mass of PC,and the reaction equilibrium is reached when the reaction time is 60min.At this time,the DEC yield is 63.65%and the TOF value is 23.73 mol_DEC·mol^-1_cat·h^-1.Moreover,PGK has good reusability and universal applicability.PGK still has a high catalytic effect after repeated use for 5 times,and no obvious deactivation phenomenon occurs.