Research On The Applications Of Functional Ionic Liquids In Condensation Reactions

The Green Chemistry movement-the designing of chemical processes and products that reduce or eliminate the use and generation of hazardous substances-has become a new paradigm in many aspects of pure and applied chemistry. One aspect of the Green Chemistry focus involved the development and use of benign solvents, such as water, supercritical fluids, or ionic liquids (ILs), to replace volatile organic compounds (VOCs). The ILs have been the subject of considerable interest in the context of Green Chemistry because of their relatively benign character, very low volatility, thermal stability, efficiency as a catalyst, solvent and promoter and reusability. Therefore, ILs were extensively used in electronic absorption spectroscopy, liquid-liquid extraction processes, organic and organometallic syntheses, catalytic cracking of polyethylene, radical polymerization, analytical and physical chemistry, lubricant, etc. From both economic and environmental points of view, researching on the new chemical functionality and application area of ILs is very attractive.In this research, kinds of functional ILs were synthesized and used as catalysts in three condensations. It was composed with three sections. The first section was about Claisen-Schmidt condensation catalyzed by basic functional ILs. The second section was about SO3H-functionalized ILs as efficient and recyclable catalysts for the synthesis of pentaerythritol diacetals and diketalsacid. The third section was that the synthesis of 2-phenyl benzimadazole in a variety of Brφnsted acidic ILs. The details are given as follows.1. Claisen-Schmidt conddensation catalyzed by basic functional ILsAn efficient, environmentally friendly procedure was developed for the Claisen-Schmidt condensation. Several basic functional ILs [Bmim]OH, [Emim]OH, [Bmim]HCO3, [Bmim]PhCOO, [Bmim]OAc, [Aemim]BF4 were synthesized and used in Claisen-Schmidt condensation as benign catalysts. The reaction was proceeded without organic solvent in room temperature. This method is highly effective, selective and environmentally benign. Furthermore, [Bmim]OH was conveniently separated with the products and easily recycled to catalyze Claisen-Schmidt condensation again with excellent yields.2. SO3H-functionalized ILs as efficient and recyclable catalysts for the synthesis of pentaerythritol diacetals and diketalsThe efficient, simple and environmentally friendly synthesis of pentaerythritol diacetals and diketals using SO3H-functionalized ILs as catalysts was reported. The ILs showed high catalytic activities and reusabilities with good to excellent yields of the desired products. H0 (Hammett function) values and the minimum-energy geometries of SO3H-functionalized ILs were determined and the results revealed that the acidities and catalytic activities of ILs in acetalization were related to their structures. The IL [PSPy] [OTf] with the shortest H-O bond distance had the strongest acidity and the highest catalytic activity in the synthesis of pentaerythritol diacetals and diketals.3. Bronsted acidic ILs as efficient and environmentally benign medium for the synthesis of 2-phenylbenzimidazole2-Substituted benzimidazoles have been synthesized in excellent yields under solvent-free conditions using a series of Brφnsted acidic ILs as catalysts. The results indicate that SO3H-functionalized ILs show higher catalytic activities than other acidic ILs. The effects of reaction conditions such as the amounts of ILs, the ratio of reactants were investigated. A Hammett method was used to determine the acidity order of these ILs and the results were found to be relevant to the catalytic activities observed in the synthesis reaction. Besides, the reaction mechanism was stimulated using DFT method.