Synthesis And Application Of Novel Alkylimidazolium Ionic Liquids

Recently, ionic liquids research has become a new field of green chemistry. Due to their favorable properties such as negligible vapour pressure, non-inflammability, reusability, high thermal stability and favorable and easily tunable physical and chemical properties, ionic liquids technology has been successfully applied to many areas of organic synthesis, biocatalysis reaction, separation process, electrochemistry etc.. However, the select of ionic liquids for special application is also very limited now. At present, main ionic liquids used in various biocatalysis reactions are 1-alkyl-3-methylimidazolium hexafluorophosphate abbreviated as [Cxmim][PF6]. Howener, the defaults of strong polarity, hydrophobicity and poor organic property has limited its application. Herefore, 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.13 novel alkylimidazolium ionic liquids were designed and synthesized and the results of the IR,1H-NMR and ESI-MS analysis confirmed the structure and composition of the ionic liquids. The cations mainly consist of 1,3-dialkylimidazolium [D(R)Im], the anions mainly consist of PF6ˉand NTf2ˉ. The modified two-step method using temperature programmed technologies was developed for improving the synthetic yields. After the crude products were diluted by acetone, it was decolored with activated carbon and almost colorless ionic liquids were obtained. There was no obvious absorption peak in the wavelength range of 400～800 nm. Moreover, Mechanism study showed that synthesis of 1,3-dialkylimidazolium bromide was the key rate-determining step. Polarity of ionic liquid was determined by pyrene fluorescence probe and was smaller than traditional ionic liquid; We determined the solubility of ionic liquids in water by ultraviolet absorption spectrum method firstly. And found water content and solubility in water were lower than 1-2 orders of magnitude. Besides, the physical properties containing thermal stability, density, viscosity and surface tension were determined. The relationship between structures and properties of ionic liquids were also studied. The results showed the properties were decided by both cations and anions of ionic liquids and exhibited how melting point, viscosity, density and surface tension were affected by changes in alkyl chain length and configuration. In the series of ionic liquids studied here, changes in spatial configuration of the alkyl had a more dramatic effect on melting point and viscosity of ionic liquids than changes in alkyl chain length, while the latter change had a stronger influence on water content existed in dried ionic liquids, densities and surface tension of them. All these ionic liquids exhibited excellent thermal stability of 320℃; density was of 1.1～1.3g.cm-3; surface tension lower than water and higher than hexane.The application of ionic liquid in enzymatic synthesis of flavors and fragrances was examized. The synthesis of phenylethyl acetate catalyzed by Pseudomonas cepacial lipase was selected as mode reaction to investigate effect of different medium containing structure and property on catalysis performance of the lipase. It was found activity and reactivity of the lipase affected by configuration structure, polarity and anion species of ionic liquids. Among ionic liquid isomers medium, lipase exhibited higher catalysis activity in these ionic liquids containing branched chains. Fluorescence spectrum exhibited the lipase showed higher activity with the decreasing of polarity. Higher initial reaction rate and yield of the reaction were exhibited in ionic liquids containing PF6ˉand NTf2ˉthan BF4ˉand Clˉ. By investigating the influence of various factors on the yield of product, [D(2-mb)Im][PF6] was the best. The optimal conditions for synthesis of phenylethyl acetate were obtained. These were reaction temperature of 35℃, the amounts of lipase of 30 mg, the ionic liquid of 1.0 g, reaction time of 48 h and water content of 1.44%. Under the optimal conditions, the yield and initial reaction rate was up to 92.3% and 0.0138μmol·h-1·mgprot-1. Also, the stability of the lipase in the [D(2-mb)Im][PF6] medium were 522h and as same as 7.4-fold that in hexane. The lipase in the [D(2-mb)Im][PF6] medium was recycled 10 times without substantial diminution in activity.The application of ionic liquid in enzymatic resolution of secondary alcohol was examized. The resolution of (R,S)-1-phenylethanol by Pseudomonas cepacial lipase in six isomer ionic liquids was chosen as the model reaction to study on effects of the reaction medium, water content and temperature on the reaction. The results showed the activity of lipase in the ionic liquid 1,3-di-isobutylimidazolium hexafluorophosphate abbreviated as [D(i-C4)Im][PF6] had obviously better activity and reactivity than those in other ionic liquids and hexane. Accordingly, the ionic liquid [D(i-C4)Im][PF6] was chosen as the medium for the reaction. Under optimal condition, initial rate of lipase, the conversion of 1-phenylethanol, ee value of (R)-1-phenylethyl acetate and half life time of the lipase were 1.93μmol.mg-1.min-1, 50%,99% and 348 h, respectively. Moreover, optical microscope analysis demonstrated lipase existing as native ball enzyme conformation in ionic liquids, and having a higher activity and thermal stability. Fluorescence spectrum showed that after the incubation of lipase in the ionic liquid [D(i-C4)Im][PF6] for six days, the lipase exhibited an slightly increasing exposure level of amino-acid residue, however, its secondary structure is of excellent stability than hexane medium. Circular dichroism pointed the activity and stability was mainly influenced by the content of (3-sheet.Immobilization of lipase from PCLwas also investigated because of the difficulties in lipase recycle in ionic liquids. Superparamagnetic particles Fe3O4 were used as immobilization support both in physical and chemical modified methods:Fe3O4 covalent modification, Fe3O4/CS covalent modification and Fe3O4/CS coated with chitosan. Optically active of 1-phenylethanol was examined in ionic liquid using immobilized PCL as a biocatalyst. Fe3O4/CS coated with chitosan was chosen as the best due to its highest initioal reaction rate and conversion. Under optimal condition, the conversion of 1-phenylethanol, ee value of (R)-1-phenylethyl acetate and half life time of the lipase were 49.7%,99% and 373 h, respectively. The immobilized lipase in the [D(i-C4)Im][PF6] medium was recycled 15 times without substantial diminution in activity.The application of ionic liquid in extraction was examized. A simple and reliable procedure was developed for preconcentraion of ultratrace lead ion in water sample using room temperature ionic liquids [D(n-C4)Im][PF6],[D(n-C5)Im][PF6],[D(n-C8)Im][PF6] and [n-C4MIm][PF6] as novel solvents. Lead ion reacted with dithizone to form neutral lead-dithizone complex in 0.03 mol.L-1 ammonia solution, then the complex was extracted into the ionic liquid from aqueous phase and back-extracted with 5 ml of 1.0 mol.L-1 nitric acid rapidly, and the solution was directly used to determine lead concentration by graphite furnace atomic absorption spectrometry(GFAAS). It was found that [D(C4-8)Im][PF6] all gave an excellent solvent characterists in the extraction of ultratrace lead due to its good hydrophobic character and lower melting point and selected, its extraction and back-extraction efficiencies were 98.7 and 99.9% for 20μg standard lead ion in 1000 ml of water sample, respectively. The calibration graph using the preconcentration system for lead was linear with a correlation coefficient of 0.999 at levels near the detection limits up to at least 0.1μg 1-1. The detection limit, calculated using three times the standard error of estimate of the calibration graph, is 1.0 ng of lead per liter water sample. Proposed procedure allows the rapid lead determination at 100 ng.L"1 level in environmental water with satisfactory results. The interference study indicated the determination of lead was free from the interference of almost all positive and negative ions found in water. Lead recoveries between 97 and 102% for spiked samples proof the accuracy of the proposed method. Moreover, the reuse of ionic liquid was up to 5 times. The extraction mechanism of system was combination of ions pairs theory and similar dissolve mutually theory in aqueous solvent.On account of the kind polarity, strong hydrophobicity and favorable organic properties, this new class of ionic liquids has found a place as suitable alternatives to volatile organic solvents in nonaqueous biocatalysis and liquid/liquid extraction. Besides, the study will have wide application perspective in biomimetic synthesis, microreactor technology, biomacromolecule extraction and separation.