Synthesis Of Halogenated Ionic Liquids, Supercritical Media And Its ¦Â-cyclodextrin Modified

Recently,much attention has been focused on the use of ionic liquids(ILs) as environmentally benign reaction media.This fact is attributed to some intriguing properties of ionic liquids,such as high thermal stability,negligible vapor pressure,high loading capacity,and tunable polarity.In view of these distinct advantages,ionic liquids have become an exciting area of research.While ILs are nonvolatile solvents,the processes to synthesize and separate ILs usually use many volatile organic solvents.Utilization of these volatile solvents causes environmental pollution and cross-contamination.Supercritical CO₂(scCO₂),an environmentally benign solvent,has received much attention because it is nontoxic,nonflammable,inexpensive,readily available in large quantities,and moderate critical parameters(31.1℃and 7.38 MPa).Supercritical CO₂ has been utilized in many chemical processes,such as extraction,chemical reactions and material processing.Accessible natural cyclodextrins and their derivatives have been found extensive applications in fine organic synthesis,for some practical applications inclusive.Unfortunately,the most accessible and inexpensive representative of this class of compounds,β-cyclodextrin,is poorly soluble in water(18.5 g/L at 25℃),which strongly limits its practical application.Homogeneous functionalization ofβ-cyclodextrin has been one focus for a long time.Sinceβ-cyclodextrin is soluble in organic solvents,such as DMSO,DMF,pyridine and their mixtures,traditional acetylation ofβ-cyclodextrin is carried out with acetic anhydride in pyridine.Due to the stiff molecule and close chain packing via numerous intermolecular and intramolecular hydrogen bonds,ramie fiber is extremely difficult to dissolve.The efficient dissolution of cellulose is a long-standing goal in cellulose research and development and still of great importance.Solvents are needed for dissolution that enable homogeneous phase reaction.The main contents of this thesis are as follows:The ILs of[bmim]Br and[amim]Cl were synthesized in scCO₂ at certain conditions.The prepared products were characterized through FF-IR and ¹H-NMR spectroscopy.The ¹H nuclear magnetic resonance(¹H-NMR) spectrum of the prepared 1-butyl-3-methylimidazolium bromide product was satisfactorily consistent with its standard structure.The Fourier transform infrared (FT-IR) spectroscopy results showed that the products were as pure as that made via the conventional reaction in the organic solvent/recrystallization method.The conversion of the reaction was dependent positively and strongly on the pressures.The residual reactants could be,in situ, removed completely using scCO₂ extraction after the required reaction time without any cross-contamination.The extracted reactants condensed in the cold trap can be recycled.The main advantage of the proposed procedure is that it does not need the excess butyl bromide as the solvent. It doesn't need any additional organic solvent for purification after reaction.The whole process is green and simple with high efficiency.We believe this green and effective route can be used to synthesize many other ILs with similar features.These advantages are highly favorable for producing large amount of ILs without producing waste or with minimum pollution.The combination of the renewable raw materialβ-cyclodextrin with the recyclable IL was investigated to yield a contribution to environment protection.The 1-butyl-3-methylimidzolium bromide([bmim]Br) was developed as a solvent for the dissolution and regeneration ofβ-cyclodextrin(β-CD).The acetylation ofβ-CD was carded out under acetic anhydride in [bmim]Br ionic liquid in the absence of any catalyst.The conditions of the acetylation,for example, reaction temperature,time,and the dosage of acetic anhydride were studied in detail.β-CD acetates with different degrees of substitution were obtained directly under the homogeneous reaction conditions.The reaction medium of IL applied can be easily recycled and reused after the synthesis ofβ-CD acetate.The recycled IL had the same efficiency to dissolveβ-CD compared to the starting IL.The acetylatedβ-CD samples were characterized by NMR,FT-IR and X-ray diffraction spectroscopy.We demonstrated for the first time that ILs could be used as an environmentally friendly solvent for the acetylation ofβ-CD.It makes it possible to prepare acetylatedβ-CD directly in only one reaction step by means of reacting nativeβ-CD with acetylating agents in the absence of a catalyst.The process is a simple process without any elaborate purification steps.This advantage makes ILs potentially attractive for industrial applications.The dissolution of cellulose in ionic liquid([bmim]C1) is described as a very recent subject for a direct dissolving process.The structural differences between ramie fiber and ramie fiber regenerated from the ionic liquid 1-butyl-3-methylimidazolium chloride([bmim]Cl) were investigated using Fourier transform infrared(FF-IR) and X-ray diffraction spectroscopy.The results show that the crystalline form of ramie fiber transforms completely from celluloseâ… to celluloseâ…¡after regeneration from[bmim]Cl solution.It is concluded that the ionic liquid[bmim]Cl is a good recyclable solvent to dissolve cellulose with considerable potential for application in the cellulose industry.