Synthesis Of Novel Br(?)nsted Acidic Heteropolyacid Ionic Liquids With Carboxyl And Study On Properties

Currently,the functionalization of ionic liquids is receiving a great deal of attention in the field of research.Designing and synthesizing ionic liquids with special functional groups to meet various reaction requirements is an important way for ionic liquids to function in green chemistry.The ionic liquid with specific acid functionalization has been widely used in organic synthesis,catalysis and other fields due to its advantages of high catalytic activity,good thermal stability and recycling.Currently,the study of the acidic functionalization of ionic liquids is mainly focused on the introduction of sulfonic acid groups in the cations and acidifying them with inorganic strong acids to improve the acidity,but some inorganic strong acids have strong oxidizing and corrosive properties.From the perspective of design and green chemistry,the functionalization of ionic liquids needs to be further expanded.The introduction of a wide variety of carboxylic acid groups in cations is an effective way to extend the types of acidic functionalized ionic liquids.However,systematic and deep synthesis methods on carboxylic acid functionalized ionic liquids have seldom been studied.Moreover,obtaining high-purity and high-stability acid-functional ionic liquids and their application in large-scale industrial production are still the main problems in this field.Therefore,it is of great significance to design and research new carboxylic acid functionalized ionic liquids with high purity to achieve a virtuous cycle of basic-application-industrial development.In this paper,through the exploration of the synthesis process of1-carboxymethyl-3-methylimidazolium chloride ionic liquid and the optimization of reaction conditions,the relationship between the nucleophilic addition reaction mechanism and the reaction conditions in the synthesis of carboxylic acid functionalized ionic liquids was clarified,and the synthesis method of carboxylic acid functionalized ionic liquids was extended based on this.?1?Six kinds of functionalized ionic liquids containing carboxylic acid functional groups were designed and synthesized by using N-methylimidazole as the main body.The structures were characterized by ¹H NMR,¹³C NMR and IR spectroscopy.The physical properties such as Br???nsted acidity and solubility of the ionic liquid were measured.?2?The carboxylic acid functionalized ionic liquid with the most acidity was selected as the substrate,and anion exchange was carried out with H₃PW₁₂O₄₀,H₃PMo₁₂O₄₀0 and H₄SiW₁₂O₄₀0 with Keggin structure.Six kinds of functionalized carboxylic acids with Br???nsted acid catalytic properties were synthesized.The structure was characterized by FT-IR,NMR and TG.The acid strength of several heteropolyacid salts was determined by UV vis-Hammett method.Combined with experiment,some rules of acid enhancement were summarized,which guided the synthesis of acid ionic liquid and acid intensity modulation,and improved the catalytic performance of acidic ionic liquid.?3?The catalytic activity of several heteropolyacid ionic liquids was investigated bycatalyticsynthesisofn-butylacetate.Itwasfoundthatthe1-carboxymethyl-3-methylimidazolium phosphotungstic ionic liquid with the most acidity exhibited the highest catalytic efficiency,and it was used as a catalyst to optimize the reaction conditions using an orthogonal variable method.The results indicated that the yield of butyl acetate was 93.3%and the esterification selectivity was more than 99%after 0.5 h,even at very low catalyst loadings only 0.5%?based on n-butanol,molar ratio?.Moreover,the catalyst and the product were liquid-solid two-phase systems,which can be separated by simple decantation;this solved problems that acid catalysts are difficult to separate.The catalyst still exhibited high catalytic activity after repeated use for many times.It was an environmentally friendly novel solid acid catalyst,and the research results were expected to provide a new idea and opportunity for the improvement of existing large-scale production processes.