Studies On The Synthesis And Application In Chemical Reactions Of Functional Choline-based Ionic Liquids

As new kind of reaction medium and functional materials, Ionic liquids (ILs) have received greatattention in organic synthesis and catalysis, utilization of biomass, energy storage, extraction and separationprocesses etc. The related studies have opened new perspectives to traditional chemistry and would bringbreakthroughs for the modern chemical industry facing with serious problems of environmental pollutionand crisis of survival.As a part of the project supported by the National Natural Science Foundation of China (No.20903037), in the work, we synthesized a series of choline derivative-based ionic liquids, discussed howthe difference in the cation as well as the anion influenced the properties of the ILs, and in the applicationsin chemical reactions. Furthermore, the choline-based ionic liquids in knoevenagel reactions, Henryreactions and the synthesis of benzoxanthenes were investigated, and the function of the ILs have also beendiscussed from the reaction mechanism.1. A series of choline derivative-based ionic liquids with halogen anions were synthesized using N, N’-dimethylaminoethanol and different carbon-chain halohydrocarbons. Followed by ionic exchangedmenthods, ILs with different anions were also synthesized. The thermostability of this kind of ILs have alsobeen detected by thermogravimetric analysis (TGA). The solution behaviors of these ILs in aqueoussolutions have also been investigated using conductance method, it was found that ionic liquids[Cncholine][Br] when n=4,6,8the critical aggregation concentration was lower than the quaternaryammonium ionic liquids and imidazolium-based ionic liquids, it probably due to the hydrophilicity of thehydroxyl group on the cation of ionic liquids.2. The polarity scale ET(30) and Kamlet-Taft paramethers (dipolarity or polarizability (π*), hydrogenbond donor acidity (), and hydrogen bond basicity (β)) of choline-based ionic liquids were determined byusing solvatochromic dyes, and the performances of this kind of ILs in catalyzing Knoevenagel reactionswere also investigated. It was found that the increasing of the hydrogen bond donor ability of the cationsand the increasing of the hydrogen bond acceptor ability of the anions will both increase the catalyticactivities, and then a dual activation mechanism that anion as hydrogen bond accepter activated the nucleopilic reagent and cation as hydrogen bond donor activated the electrophilic reagent were suggested.Used the optimized ionic liquid as catalyst, a large range of substrates can get high efficiency Knoevenagelreaction transformation at room temperature, and the work-up procedures is very simple, and the ionicliquid can be recycled and reused.3. Investigated the choline-based ionic liquids as reaction medium for the Henry reactions. Utilized theNMR external standard technology detected the1H-NMR and13C-NMR spectroscopies of electrophile andnucleophile in choline-based ionic liquid added to Henry reactions. When compared with that in pure stateor in non-polar solvent, it was found that the chemical shift of nucleophile in different ILs was moved tohigh strength field, and the chemical shift of electrophile was moved to low strength field. This findingexplained why both the nucleophilicity of nucleophile and the electrophilicity of electrophile can beimproved in choline-based ionic liquids. On the basis of results from NMR detected and the catalytic effectfor Henry reaction, the mechanism was discussed. It was believed that the interactions between thehydrogen on methylene of nitroalkanes and the anion of ILs, and the hydrogen bond formed between thecation of ILs and the C=O of aldehydes lead to collaborative catalytic effect, the optimized ionic liquidexhibit excellent performance in Henry reactions ar room temperature.4. The application of choline-based ILs in the preparation of benzoxanthenes. It was found that the ILshaving amphotericity anions can promote the reactin fluently and get the target product, while the ILs withbasic anions such as [AC] can get the intermediate product only. Therefore, the two steps reactionmechanism was proposed that at the first step, the anion of ILs as basic to attack the active hydrogenof naphthol and get the carbanion, which then reacted with the activated aldehyde by the cation of ILs toget the intermediate product, and then it was reacted with another naphthol to get target product under thecatalysis of the acidic anions. The substrate tolerance and the reusability of the ILs have also beeninvestigated.