Ionic Liquid Based On Polyoxometalate And Its Application In Catalysis

Green chemistry is an important research area in chemistry. Ionic liquid as a new type of green solvent meets with many of the basic requirements of green chemistry. It's been seen that more and more new ionic liquids have been synthesized and applied in a wide field. In this thesis, a new class of polyoxometalte (POM)-based ionic liquids has been synthesized. Using different polymers such as polyether PEG2000, PEG300 and P123 to tether two alkylimidazole molecules yielded polymer-functionalized cations. Combining these cations with different kinds of POM anions like HPW12O402-and{PO4[WO(O2)2]4}3- produced the POM-based room temperature ionic liquids. Different characterization methods such as FT-IR,31PNMR, TEM et al. verified the successful synthesis of the ionic liquids. It also indicated that these ionic liquids have the general properties of common ionic liquids, such as low melting point and high viscosity and so on.Ionic liquid based on PEG2000 modified cation and Keggin polyoxometalate (HPW12O402-) effectively catalyzed esterification of different types of alcohol with acetic acid, with yields above 90%. During the reaction process, the system produced a novel emulsion in the presence of POM-based ionic liquids which was believed to promote the dispersion of the catalyst into the system. After the the reaction the catalyst can be separated by simply breaking the emulsion. The catalyst can also be used for oxidative esterification of aromatic aldehydes in methanol with H2O2 as the oxidant. For most of the substrates the yields are around 70%.31P NMR analysis indicated that the catalyst first degraded into different peoxo-species which were responsible for the oxidation of aldehydes. After H2O2 was consumed up these species can self-assembly into Keggin structure again.A higher activity for the esterification of alcohols with acetic acid was achieved when PEG2000 was replaced by P123. It is interesting that the ionic liquid was dissolved in the system forming a transparent solution in the beginning, with the reaction going on an emulsion was gradually observed which can be destroyed after the reaction by mechanical means to separate the catalyst. Dynamic light scattering studies showed that after the catalyst was added into the system, a colloidal system formed. The mean size of the colloidal particles is ca.600 nm. At the reaction conditions the particles gradually grew bigger and finally form emulsion. The difference in the dispersity of two POM-based ionic liquid may lead to the difference of activity.When PEG300 was used instead of PEG2000 coupling with imidazole with longer alkyl chain, a hydrophobic ionic liquid was produced to combine with?PO4[WO(O2)2]44?(Venturello anion) which is very active in epoxidation of olefins. The ionic liquid was a very effective catalyst in epoxidation of a variety of olefins with H2O2 as the oxygen in ethyl acetate. Yields were always over 90%. Allmost all the catalyst was precipited from the system after reaction, which led to easy separation of the catalyst.This work also extends the scope of application of P123. P123 stabilized Pd nanoparticles in the aqueous phase can be applied in selective hydrogenation of olefins under mild conditions with good activity and selectivity. Meanwhile, the P123-based ionic liquid can transfer different types of nano-objects from water to different organic solvents under certain conditions. It was also found that by replacing the organic solvents with the ones acting as hydrogen-bonding donors can make the phase transfer much more efficient.