Synthesis, Characterization And Catalytic Activity Of Rhenium-Containing Epoxidation Catalysts For Olefins

Epoxides such as propylene oxide, epoxy cyclohexane, styrene oxide, etc. belong to the significant Organic Chemicals, and in terms of organic synthesis, are important intermediates. For years epoxides received special interest due to their vast applications in various industries, including petrochemical, high-polymer synthesis, fine chemicals, organic synthesis, pharmaceutical, etc. An important means to the synthesis of epoxides is the epoxidation of olefin. Therefore the research of the environment-friendly process of catalyze oxidation of olefin became dominant in the research and development of catalysis, and furthermore, the development of the ideal catalysis reaction system that having higher catalytic activity, that being more convenient for separating catalyst from reaction products and that suitable for recycling is highly expected. Up to now, the competitive candidates include, one, the catalytic system that composed of Methyltrioxorhenium (MTO) which according to reports is so far one of the most universally applicable and highest active organometallic catalysts, and hydrogen peroxide(H2O2), and the other, the room temperature ionic liquid system, a "green solvent", which, comparing with traditional solvent, are nontoxic, non-volatile, capable for recycling, having higher thermo stability and fitting for solving most kind of organics. Thus, it is very meaningful to carry out research on the application of the combination of the high-selective organometallic catalyst and the "green solvent", in terms of the epoxidation of olefin. More importantly, it is inestimably valuable for the development of a green chemical process. The research and tests on the application of the combination of the Re-based organometallic catalysts and the room temperature ionic liquids are discussed in this thesis, including six chapters.In chapter 1, firstly the references are reviewed, including the characters of MTO and the methods of the synthesis of MTO, as well as the current condition of the research of the coordination compounds of MTO and the application of it in terms of the organic synthesis. Secondly the room temperature ionic liquid is introduced in terms of its characters, synthesis method and application on organic synthesis. At the end of chapter 1, the development of the research on MTO as catalyst or the cocatalyst in room temperature ionic liquids is summarized.In chapter 2, the synthesises of eight types of Schiff base MTO complexes under standard Schlenk operation technology in water and oxygen free condition, which were not publicly reported, are introduced, including:N-salicylidene-aniline derived Schiff base complex of MTO(C13H11NO-CH3Re03)(A-MTO), N-salicylidene-p-chloroaniline derived Schiff base MTO complexes (C13H10ClNO-CH3Re03) (B-MTO), N-salicylidene-p-toluidine derived Schiff base complex of MTO(C14H13NO·CH3ReO3) (C-MTO), N-salicylidene-p-methoxy-aniline derived Schiff base complex of MTO (C14H13NO2-CH3ReO3)(D-MTO), N-salicylidene-o-toluidine derived Schiff base complex of MTO (C14H13NO-CH3Re03)(E-MTO), N-salicylidene-o-chloroaniline derived Schiff base MTO complexes (C13H10ClNO-CH3Re03)(F-MTO), N-salicylidene-p-hydroxyaniline derived Schiff base complex of MTO (C13H11NO2·CH3ReO3)(G-MTO), N-Salicylidene-p-oxyethylaniline derived Schiff base complex of MTO (C15H15NO2-CH3ReO3)(H-MTO). All of the eight complexes have high stability as they can remain in-decomposed for several weeks in the air. In addition, the eight complexes are characterized by IR,'H-NMR and elemental analysis, etc. The crystal structures were determined by single-crystal X-ray diffraction. The results show that the coordination mode of all the mentioned complexes is the coordination of phenolic hydroxyl oxygen atoms in Schiff base ligand and the center rhenium atom in MTO, displaying distorted trigonalbipyramidal structures in the solid state.Chapter 3 introduced that four types of Schiff base MTO complexes, E-MTO, F-MTO, G-MTO, E-MTO are used as catalyst respectively, together with hydrogen peroxide(H2O2) as oxidant and CH2Cl2 as solvent, in the epoxidation reaction of three various olefin(cyclohexene, styrene and cyclooctene). The respect effects of the quantities of the catalyst, the solvent and the ligand on each one of the three olefins are studied. Reaction products are analyzed quantitatively and qualitatively by instruments as gas chromatograph (GC), gas chromatography-mass spectrometry (GC MS), etc. The effect of substituent of aniline to the activity of the epoxidation of olefin catalyzed by MTO complexes is also discussed. The results show that, using cyclohexene as substrate, olefin turns into epoxide first, and gradually into diol, and the final reaction product is diol; as using styrene as substrate the yield of epoxide is not higher than 70%, and the final reaction product is diol. When using cyclooctene as substrate, olefin turns only into epoxide, which can stably exist, and no diol generated during the reaction process. Furthermore, from the results of olefin being catalyzed by the mentioned four complexes, conclusion can be made that the catalysts have a higher activity when the substituent of aniline is the electron-withdrawing group or weak electron-donating group, such as-Cl or-CH3; conversely, when the substituent of aniline is a strong electron-donating group, such as-OH or-OCH2CH3, or this kind of larger groups, the catalysts shows a relatively lower activity as the deactivation of the catalyst occurs.Chapter 4 discussed that six types of Schiff base MTO complexes, A-MTO, B-MTO, C-MTO, D-MTO, E-MTO, G-MTO are used as catalyst respectively, together with carbamide peroxide (UHP) as Oxidant and [Emi]SE as solvent, in the epoxidation reaction of cyclopentene, cyclohexene and cyclooctene. Respective effects of the quantities of the catalyst, the solvent and the ligand on the reactions are studied and the optimizing conditions of each of the three olefins are confirmed. The results show that the reaction occurs continuously towards epoxidation without any byproduct generated. The reaction product is divided by column chromatography and characterized by 1H-NMR to be purified epoxide. Thus the results indicate that, the substitution of [Emi]SE for the traditional organic solvent CH2Cl2 in the epoxidation of olefin enhanced the selectivity of the reaction and provide the catalyst system the advantages as higher catalytic activity, convenient to separate the products, environment friendly, etc. In chapter 5, the synthesises of six types of room temperature Re ionic liquids using N-methylimidazole and ammonium perrhenate with the two-step technique are discussed, including 1-ethyl-3-methylimidazolium perrhenate, 1-butyl-3-methylimidazolium perrhenate, 1-amyl-3-methylimidazolium perrhenate, 1-hexyl-3-methylimidazolium perrhenate, 1-octyl-3-methylimidazolium perrhenate, 1-dodecyl-3-methylimidazolium perrhenate, which have not been reported. The new types of ion liquids are characterized by measure techniques including IR, EA, NMR, ESI-MS, DSC, Raman Spectroscopy, etc. and the characterizations of the ion liquids, such as structure, density, electrical conductivity, are confirmed.In chapter 6, the application of the six Re room temperature ionic liquid mentioned above, being both catalyst and medium of reaction, and carbamide peroxide (UHP) being oxidant, on the epoxidation of cyclooctene is discussed. The effects of the quantities of the ion liquid and the oxidant and temperature to the reaction are investigated, and the optimum reaction condition is required:substrate, 1mmol, oxidant,2.5mmol, ion liquid, 0.6mL, temperature 70℃, reaction time 4h, namely, the molar ratio of substrate and oxidant is 1:2.5, and ionic liquid is 0.6mL. The selectivity of 1,2-epoxy cyclooctane is higher than 99% in this condition. The research indicate that, the remarkable character of the catalytic system is that the Re ion liquid acts both the catalyst and solvent; therefore the operation and post treatment are easy to implement. The separated ion liquid can be reused after the organic solvent and water being removed by a simple vacuum drying process. The catalytic system can be reused many times without losing its catalytic activity. Tests have proved that, after cycling for 12 times, the selectivity of the product is still high as over 99%. Due to the fact that Re ionic liquid is a non-volatile, non-corrosive, environment friendly catalyst and the application of it avoided the use of volatile organic solvent, Re ionic liquid is an ideal catalytic reaction system of epoxidation of olefin.