| Linear carbonates are valuable organic compounds in green chemistry due to the presence of functional groups such as methyl and carbonyl.Particularly,dimethyl carbonate(DMC)has been widely used as a solvent,gasoline additive,lithium battery electrolyte,and in the fields of medicine and pesticides.The ester exchange reaction of ethylene carbonate(EC)with methanol to prepare DMC has the advantages of being economical,low-carbon,and environmentally friendly.Although the homogeneous catalyst for the EC ester exchange reaction to produce ethylene carbonate has been industrialized,there are still problems such as side reactions and complex subsequent separation processes.Currently,most reported heterogeneous catalysts require harsh experimental conditions,such as high temperature or high pressure,to achieve moderate yields of DMC.Therefore,developing a highly active heterogeneous catalyst for the ester exchange reaction to produce DMC under mild reaction conditions is still a research focus.The porous ionic polymers(PIPs)are a new type of organic functional polymer with a cationic skeleton and a nucleophilic anion.They combine the advantages of ionic polymers and porous materials and have a wide range of applications in adsorption,gas separation,energy storage,and catalysis.Therefore,this article selects porous ionic polymers as the research object,and designs and synthesizes a series of bifunctional porous ionic polymers as heterogeneous catalysts for ester exchange reactions,exploring their catalytic effects on the production of dimethyl carbonate through the exchange reaction between ethylene carbonate and methanol.The structure of the synthesized polymers is characterized by 1HNMR,FT-IR,PXRD,and their gas adsorption properties,stability,and catalytic performance are tested to study the relationship between their structure and properties.The catalytic conditions are optimized,and the effects of different conditions such as temperature,time,alcohol/ester molar ratio,and catalyst dosage on the ester exchange reaction are explored.The research content of this paper is as follows:Four bifunctional porous ionic organic polymers PIP-Co,PIP-Cu,PIP-Zn,and CHX-PIP were synthesized using hexachlorocyclotriphosphazene as a ligand through Friedel-Crafts alkylation and quaternization reactions.Among the synthesized PIP-M,CHX-M acted as a Lewis acid,and the chloride of imidazolium cation acted as a Lewis base to synergistically promote ester exchange reaction,achieving good catalytic effect under relatively mild reaction conditions.It was found that these polymers not only showed good catalytic effect on ethylene carbonate but also catalyzed the production of dimethyl carbonate.In particular,the cyclic stability of PIP-Co was tested,and no significant decrease in catalytic activity was observed after five cycles.A Schiff base ligand,N,N’-bis(5-chloro-2-hydroxybenzyl)ethylenediamine,was synthesized by condensation reaction between 5-chlorosalicylaldehyde and ethylenediamine.Two bifunctional porous ionic organic polymers,PIP-Mn and Salen-PIP,were prepared by polymerization of N,N’-bis(5-chloro-2-hydroxybenzyl)ethylenediamine and a nitrogen-rich ligand TIT through quaternization and Friedel-Crafts alkylation reactions.Both catalysts were tested in the ester exchange reaction between ethylene carbonate and methanol,and PIP-Mn showed better catalytic effect than Salen-PIP due to the absence of a central metal as a Lewis acid active site.During the catalytic process,Salen-Mn in PIP-Mn acted as a Lewis acid,while Cl~-acted as a nucleophilic agent and a Lewis base to synergistically promote the ester exchange reaction.PIP-Mn exhibited good stability,and after 5 cycles of reaction,the catalytic effect in terms of selectivity and conversion rate remained essentially the same. |
