Study On Preparation Of Imidazolium-based Ionic Liquids And Its Application On Diels-Alder Reactions

Room temperature ionic liquids are composed of organic cation and inorganic anion or organic anion and are liquid state at room temperature.They possess of many perfect physical properties and are the substitutes of conventional organic solvents.Also,they are very important orientation of the development of green chemistry.In this paper,intermediate product 1-butyl-3-methylimidazolium chloride was prepared by n-C₄H₉Cl and N-methylimidazole.Then the ionic liquid 1-butyl-3-methyl-imidazolium tetrafluoroborate[BMIM]BF₄ and the ionic liquid 1-butyl-3-methyl-imidazolium hexafluorophosphate[BMIM]PF₆ were prepared by[BMIM]Cl and NaBF₄ or KPF₆ through replacement reaction,respectively.These compounds have been characterized and analyzed by IR spectra and ¹H-NMR.At the same time,the optimum processing conditions of preparing the intermediate product[BMIM]Cl were studied by monofactorial experiment:materiel ratio of n-C₄H₉Cl and N-methylimidazole was 1:1.1, reaction temperature was 90℃,and reaction time was 12h.Microwave radiation was used to improve the synthesis of[BMIM]Cl.It was showed that when microwave power was 240W,yield of[BMIM]Cl was the highest which was 73.3%.Ultrasonic was used to improve the synthesis of[BMIM]BF₄ and[BMIM]PF₆.As the result of the use of ultrasonic,the preparation times of[BMIM]BF₄ and[BMIM]PF₆ were shorten to 2h and 0.5h,respectively.At last,physical properties such as bibulous ability and solubility of [BMIM]Cl,[BMIM]BF₄ and[BMIM]PF₆ were determined.In addition,Diels-Alder reaction of cyclopentadiene with acrylonitrile was studied in[BMIM]BF₄ ionic liquid and the optimum processing conditions were described (temperature,0℃;molar ratio,cyclopentadiene:acrylonitrile=1:1.1;volume dosage: [BMIM]BF₄,20%;[BMIM]PF₆,15%;time,20h).Finally,Diels-Alder reaction of cyclopentadiene with methyl acrylate or ethyl acrylate was studied under the optimum conditions which were discussed above.The influences on yields and endo selectivity of Diels-Alder reaction for different dienophiles in ionic liquids were studied.It was found that with the addition of ionic liquids,Diels-Alder reactions of different dienophiles had remarkable promotion in yield and endo-selectivity.