Preparation And Characterization Of Novel Ionic Liquids And Their Widening Application In Organic Synthesis

Recently,ionic liquids research has become a new field of green chemistry.Due to their favorable properties such as non-inflammability,negligible vapour pressure, reusability and high thermal stability,ionic liquids technology has been successfully applied to many areas of chemistry including organic and inorganic synthesis, biphasic catalysis,separation processes,electrochemistry etc..With the development of ionic liquids,more and more ionic liquids with special function are required to satisfy the various demands and enrich the fundamental theory of ionic liquids.In order to keep up with the trend,we studied the preparation,characterization of novel ionic liquids and widening application of ionic liquids in organic reactions.The details are given as follows:1.Ionic liquids as initiators in cationic copolymerization of 1,3-pentadiene with styreneCationic copolymerization of 1,3-pentadiene with styrene using ionic liquids BmimCl-AlCl₃,PyHCl-AlCl₃,Et₃NHCl-AlCl₃,Et₃NHCl-FeCl₃ and Et₃NHCl-ZnCl₂ as initiators in toluene have been investigated for the first time.Among all the ionic liquids used,Et₃NHCl-AlCl₃ shows the best reactivity.The polymerization proceeds to high conversions,indicating high initiating reactivity of ionic liquids in the copolymerization systems,although molecular weights of the polymers are limited which are similar to polymerization initiated by Lewis acids such as TiCl₄,BF₃, BF₃·OEt₂.The polymers were analyzed using IR,¹H-NMR spectra in conjunction with gel permeation chromatography.2.Cationic ring-opening polymerization of 3,3-bis(chloromethyl) oxacyclobutane in ionic liquidsCationic ring-opening polymerization of 3,3-bis(chloromethyl)oxacyclobutane (BCMO)initiated by BF₃·OEt₂ was carried out in ionic liquids[Bmim]BF₄ and [Bmim]PF₆ for the first time.The influences of BCMO concentration and molar ratio of BCMO/ BF₃·OEt₂ on the molecular weights and yield of PBCMO were investigated.Cationic polymerization of BCMO in ionic liquids proceeds to high conversions,although molecular weights are limited,similar to polymerization in organic solvent.The DSC and TG analysis of polymers show that all of the polymers have good thermal stabilities.Follow a viewpoint of green chemistry,we feel ionic liquid[Bmim]BF₄ is superior to[Bmim]PF₆.Extracting[Bmim]PF₆ from the product using organic solvent as extractant limited its advantage as a green reaction media.3.Brφnsted acidic ionic liquids as reaction medium for cyclodehydration of diethylene glycolCyclodehydration of diethylene glycol using various Brφnsted acidic ionic liquids as dual solvent-catalysts was studied for the first time.Better results were obtained in the presence of 1-(3-sulfopropyl)-3-methylimidazolium hydrogen sulfate ([PSmim]HSO₄)comparing with other Brφnsted acidic ionic liquids.The effects of reaction conditions such as reaction temperature,reaction time and molar ratio of ionic liquid/ diethylene glycol were investigated.Good conversion rate and high selectivity were obtained in ionic liquid[PSmim]HSO₄ under the optimum conditions. Hammett method was used to determine the acidity order of these ionic liquids and the results were consistent with the order of catalytic activities observed in the cyclodehydration reaction.4.Preparation and characterization of benzimidazolium novel Bronsted acid ionic liquid[Hebim]BF₄ and its application in the synthesis of arylic estersA novel Brφnsted acid task specific ionic liquid 1-ethylbenzimidazolium tetrafluoroborate([Hebim]BF₄)with functional benzimidazolium cation was synthesized and characterized by ¹H-NMR,IR and elements analysis.This novel ionic liquid was successfully used as dual solvent-catalyst for the synthesis of arylic esters. Higher yields were obtained in the presence of[Hebim]BF₄ in comparison with other imidazolium ionic liquids,because of the good solubility of the aromatic alcohols and aromatic carboxylic acids in[Hebim]BF₄.The product could be separated conveniently from the reaction system,and the ionic liquid could be easily reused after removal of water under vacuum.After ten times reuse,the selectivity of the ester was still 100%.5.Synthesis and characterization of novel functional Brφnsted acidic ionic liquids based on benzimidazolium cationSix novel functional Brφnsted acidic ionic liquids based on benzimidazolium cation were prepared.They are[C₄ebim]HSO₄(1-butyl-3-ethylbenzimidazolium hydrogen sulfate),[C₄ebim]H₂PO₄(1-butyl-3-ethylbenzimidazolium dihydrogen phosphate), [C₅ebim]HSO₄(1-amyl-3-ethylbenzimidazolium hydrogen sulfate),[C₅ebim]H₂PO₄ (1-amyl-3-ethylbenzimidazolium dihydrogen phosphate),[PSebim]HSO₄ (1-ethyl-3-(3-sulfopropyl)-benzimidazolium hydrogen sulfate)and[PSebim]BF₄ (1-ethyl-3-(3-sulfopropyl)-benzimidazolium tetrafluoroborate).These novel ionic liquids are characterized by FT-IR,¹H-NMR,element analysis to make certain their molecular formulas.At the same time,the melting points of them and their other physical properties,such as conductivity,solubility and thermo stability were determined.6.Application of novel benzimidazolium ionic liquids as catalysts in acetalization of aromatic aldehydes with diolsThese novel benzimidazolium ionic liquids was used as environmentally benign catalysts for acetalization of aromatic aldehydes with diols.Hammett method has been used to determine the acidity order of these ionic liquids and the results are consistent with the order of catalytic activities observed in acetalization reaction. Maximum substrate conversion 98%and product selectivity 100%were observed on using[PSebim]HSO₄ as catalyst and it can be reused at least 10 times without obvious activity loss.