Abstract
Ionic liquids are organic salts with melting points typically below ambient or reaction temperature. The unique combination of physical properties of ionic liquids, such as lack of measurable vapor pressure, high thermal and chemical stability, make them ideal to be used as reusable homogenous support for catalysts. In addition, the solubility of ionic liquids in various reaction media can be controlled and easily fine-tuned by modification of the structures of their cations and anions. As a result, ionic liquid immobilized organocatalysts are very effective in aqueous media and can be separated easily from organic solvents, as well as aqueous phases by simply adjusting the polarity of the media. Ionic liquid immobilized organocatalysts are not only very versatile compounds that are effective catalysts for a wide spectrum of reactions, but are also environmentally friendly and recyclable organocatalysts. Herein, we provide a summary of the past decade in the area of asymmetric catalysis in aqueous media for a wide variety of reactions in which ionic liquid and related ammonium salt immobilized organocatalysts are used.
Highlights
Introduction and BackgroundRecently, organocatalysis has emerged as the third pillar of asymmetric catalysis together with transition-metal and biocatalysis [1,2,3,4,5,6,7,8]
We present recent exciting progress in ionic liquid and related ammonium salt immobilized organocatalysis in aqueous media
This short review focuses on the application and recyclability of recently developed ionic liquid and related ammonium salt immobilized organocatalysts in asymmetric reactions
Summary
Organocatalysis has emerged as the third pillar of asymmetric catalysis together with transition-metal and biocatalysis [1,2,3,4,5,6,7,8]. Ionic liquids are non-flammable, lack measurable vapor pressure, and have high thermal and chemical stabilities; they are perfect solvents for polar compounds [27,28,29,30] Another attractive property of ILs is their enormous diversity. When ionic liquid immobilized catalysts are used to induce organic reactions, such reactions are usually carried out in polar solvents, which can form a homogeneous system. Water holds some unique physical and chemical properties, such as high surface tension, hydrogen bonding capability, high dielectric constant and high cohesive energy density [44,45,46] In nature, both type I and type II aldolases catalyze the direct aldol reaction in an aqueous environment [47]. We present recent exciting progress in ionic liquid and related ammonium salt immobilized organocatalysis in aqueous media
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