Due to its unique properties, ionic liquids are widely used in various fields of chemical research. Ionic liquids have been used as solvents for many types of reactions.
There have been a large number of reports on the application of ionic liquids to hydrogenation reactions. The advantage of using ionic liquids instead of ordinary solvents in the reaction is that the reaction rate is several times faster than in conventional solvents; the mixture of ionic liquid and catalyst used can be reused. Studies have shown that ionic liquids act as both a solvent and a catalyst during the process.
Since ionic liquids can dissolve part of the transition metal, the most widely used ionic liquids in hydrogenation reactions are the homogeneous reaction systems using transition metal complexes as catalysts. In addition, compared with the conventional solvent, the ionic liquid is applied to the hydrogenation reaction of diesel oil (mainly for the aromatic hydrocarbon contained therein), and the product has the advantages of easy separation, easy purification, and no environmental pollution.
The Friedel-Crafts reaction includes Friedel-Craft acylation and Friedel-Crafts alkylation reactions, both of which play a pivotal role in organic chemicals. More mature catalysts include zeolites, solid acids and molecular sieves. However, due to green synthesis and cost considerations, many chemists have changed the traditional solvent for ionic liquids for related research.
For example, Seddon et al. studied the alkylation of two nucleophilic hydrazines and 2-naphthol using ionic liquids. The method is simple, the product is easy to separate, and the regioselective alkylation yield on heteroatoms is 90%. Above, and the solvent can be recycled and reused, showing the advantages of the ionic liquid as a solvent for the alkylation reaction.
In 1972, Parshall studied the carbonylation of ethylene in tetrahexylamine trichlorostannate. In recent years, chemists have made more efforts in this regard. For example, Chinese chemical worker Deng Youquan and other related research on the carbonylation of alkanes. They reported for the first time the direct carbonylation of several alkanes with CO in a super acidic room temperature ionic liquid composed of a halogenated 1-alkylpyridine and 1-methyl-3-alkylimidazolium salt and anhydrous AlCl3. The product is a ketone.
The Heck reaction is the reaction of an olefin and a halogenated aromatic hydrocarbon or aromatic anhydride under the action of a catalyst such as metal palladium to form an aromatic olefin, which is an important carbon-carbon binding reaction in organic synthesis. The use of ionic liquids in such reactions can better overcome the problems of catalyst loss in the conventional reaction and the volatilization of the organic solvent used. In 2000, Vincenzo et al. reported that after the ionic liquid was applied to the Heck reaction, the reaction rate of the reaction was fast, and the yield was increased to over 90%. The research group of Seddon et al. in the three-phase system [BMIM (1-butyl-3-) The Heck reaction was studied in methylimidazole)]PF6/water/hexane. The catalyst used was left in the ionic liquid and can be recycled. The product was dissolved in the organic layer, and the by-product formed by the reaction was extracted into the aqueous phase. Medium, easy to separate.
The Diels-Alder reaction is an important reaction in organic chemistry. The attention of the reaction is not only its yield and rate, but more importantly its stereoselectivity. There have been a lot of reports on the application of ionic liquids to Diels-Alder reaction studies. For example, the research team at Howarth reported the reaction of cyclopentadiene with alkenals in an imidazolium salt solution at room temperature. It has been found that the stereoselectivity of the reaction is better when it is carried out in an ionic liquid, that is, the ratio of the obtained internal and external products is about 95:5. Studies have found that the reaction carried out in the ionic liquid not only has a fast reaction rate, a high reaction yield, a good stereoselectivity of the reaction, and the ionic liquid can be recycled and reused. This shows that the ionic liquid has a greater advantage than the ordinary solvent in the Diels-Alder reaction.
Studies have shown that the application of ionic liquids to asymmetric catalytic reactions, the selectivity of enantiomers is greatly improved compared to common solvents, and solves the problem that products in traditional methods are not easily separated from the system. There have been a large number of reports on the application of ionic liquids to asymmetric catalytic reactions. For example, the Chen research group reported the application of ionic liquids to asymmetric allylic alkylation reactions; the Song research group applied ionic liquids to asymmetric rings. In the oxidation reaction; Wasserschied et al. reported the synthesis and properties of novel chiral ionic liquids derived from "chiral pools". We believe that the synthesis of these chiral ionic liquids is especially useful for studying asymmetric catalytic reactions. The synthesis of drugs will be of great significance.
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