Hydroxyl Functionalized Ionic Liquids

Modifying the ionic liquid with hydroxyl as a functional group can increase the polarity of the ionic liquid and make it exhibit strong hydrogen bonds and surface tension. Hydroxy functionalized ionic liquid cations mainly include 1-hydroxyethyl-3-methylimidazole and hydroxyethyltrimethylammonium. The anions of hydroxyl functionalized ionic liquids mainly include Cl^-, Br^-, BF₄^- and so on. The introduction of hydroxyl groups in ionic liquids can increase the polarity and solvation effect of ionic liquids, and can replace traditional organic solvent alcohols in some fields. At the same time, the presence of hydroxyl will also affect the force between the solvent and the solute, enhance the activity of the enzyme, and improve the efficiency of the reaction. In the field of inorganic nanomaterials and electrochemistry, hydroxyl functionalized ionic liquids have also been widely used.

Figure 1. Common structure of hydroxyl functionalized ionic liquid

Applications:

• Preparation of nano-materials: Nano-scale precious metal materials have a higher specific surface area, which will greatly improve their catalytic performance. The hydroxyl functionalized ionic liquid can be used as a reducing agent and reaction medium to prepare nanoparticles. Utilizing the reducibility and ion conductivity of the hydroxyl ionic liquid itself, nanoparticles of different particle sizes can be prepared at a lower temperature, which increases the demand for catalysts of different particle sizes for the reaction. Moreover, the preparation method does not introduce impurities, the conditions are mild, and the pollution is small.
• Catalyst: Hydroxyl functionalized ionic liquids can be used as Lewis bases to catalyze many organic chemical reactions, such as Knoevenagel reaction, phenol alkylation, and Suzuki reaction. In some reactions, hydroxyl-functionalized ionic liquids can also be used as reaction solvents to improve reaction selectivity and raw material solubility.
• Biological field: In the biological field, hydroxyl functionalized ionic liquids have been widely used as green solvents. First, hydroxyl functionalized ionic liquid can be used as a benign solvent for cellulose and degummed silk, providing a reaction solvent for the recyclable and degradable biological materials. Secondly, hydroxyl functionalized ionic liquids can form hydrogen bonds with amino groups and carbonyl groups in proteins, which can be used to study enzyme activities in organisms. Finally, hydroxyl functionalized ionic liquids can be combined with two-phase extraction technology to efficiently and quickly achieve protein separation and purification under the premise of ensuring that the biological activity of the protein is not destroyed.

Reference

• Reza Fareghi-Alamdari, Mehri Nadiri Niri, Hassan Hazarkhani. Synthesis and characterization of a new hydroxyl functionalized diacidic ionic liquid as catalyst for the preparation of diester plasticizers [J]. Journal of Molecular Liquids 2017, 227, 153-160.