Study On The Ionic Liquid Promoted Nucleophilic Reaction

Chemistry industry is closely linked to our daily lives, which does not only create a variety of conveniences for us but also bring about numerous environmental pollutions and hazards. Based on this, green chemistry, which mainly develops new green medium and atomic economic reaction, has gradually become the subject of chemistry development. Ionic liquids, as a new green reaction medium or "soft" functional materials, owing to their distinctive physical properties and chemical properties, are suffering the wide attention from the researchers. Due to ionic liquids can be designed and they can provide unique ionic environment different from molecular solvent which plays an important role in stabilizing the reactive catalytic species or the reaction intermediates. Compared with molecular solvents, ionic liquids have an incomparable advantage. In this paper, synthesis of ionic liquids and their application in nucleophilic reactions were mainly studied. The relationship between properties and structure of the ionic liquids as well as the action mechanism of ionic liquid in organic nucleophilic reaction was investigated, and further developed a green, efficient and convenient method for organic reactions. This thesis consists of six main parts:In chapter one, the research progress and the main application fields of ionic liquids were reviewed. Combined with the classic example and the latest achievements of ionic liquid, the applications of ionic liquid in organic reactions, which mainly act as solvents, catalysts or solvent-catalysts, were discussed in detail. In addition, the important role of the ionic liquid in organic reactions was analyzed and the trends for their future were also prospected.In chapter two, based on the understanding to the mechanism of Knoevenagel reaction, the protic-ionic-liquid HMTA-AcOH was desigined and prepared. Then, the solvent-catalyst system HMTA-AcOH-H2O was developed and used in the Knoevenagel condensation reaction of aromatic aldehydes with ethyl 2-cyanoacetate. The results are as follows:(1) under the effect of HMTA-AcOH-H2O, shorter reaction time (20-50 min) and high reaction yield (87-96%) were obtained; (2) The work-up is ease and the pure products can be obtained through simple extraction, filtering and recrystallization; (3) the HMTA-AcOH-H2O can be recycled more than six times and the active almost remains the same.In chapter three, for the imidazolium ionic salts, incorporating a hydrogen substituent at the C-2 position, are deprotonated under mildly basic conditions, which may cause the undesired side reactions and lower the yield of M-B-H product. A series of phosphonium ionic liquids with different chains were prepared and applied in the Morita-Baylis-Hillman reaction. We found that the composite system of phosphonium ionic liquid with water can effectivly facilitate the M-B-H reaction. Not only the composite system is stable in alkaline medium, but aiso the reaction rate is fast and the reaction yield is high, which may be suitable for other base-catalyzed organic reactions.In chapter four, based on the understanding that the hydrogen bond plays a great role in organic reaction, a series of functional ionic liquids containing hydroxyl group were designed, synthesized and used in the Morita-Baylis-Hillman reaction. Experimental results showed that the solvent-catalyst system of N-2-hydroxy ethylpyridinium chloride with water is stable in alkaline conditions, and the solvent-catalyst system can effectivily accelerate the Morita-Baylis-Hillman reaction, fast reaction rate and high yield were obtained. For the reason, it may be attribut to the activation to the substrates by hydroxyl group as well as the stabilization effect on the intermediate provided by the unique ionic environment of ionic liquid, which may greatly promote the positive reaction.In chapter five, based on the development of green chemistry, environmental friendly solvent PEG-400 was used in the Rap-Stoermer reaction of salicylaldehydes with various a-haloketones. Owing to the presence of ether bond, hydroxyl group and soft chain in PEG-400 molecules, in the presence of the weak base K2CO3, it can effectivily accelerate the Rap-Stoermer reaction and 76- 92% yield of target product was obtained within 15-40 min. This work further enriches the green organic synthesis.In chapter six, a work summary was given and the main research direction in the next stage was prospected.