The ammonium ionic liquid is a compound in which hydrogen atoms in the ammonium ion are substituted by alkyl groups, and its general formula is R4NX, and the four alkyl groups may be the same or different groups. X may represent a halogen anion (F-, Cl-, Br-, I-), or an acid ion (RCOO-, HSO4-).
Figure 1. The structure of ammonium ionic liquids
Organic chemistry: Ammonium ionic liquids have proven to be valuable and useful in many different organic reactions, both as catalysts and as environmentally friendly solvents. For example, in the hydrolytic reaction of 1,1,1,3-tetrachloro-3-phenylpropane using ammonium ionic liquid, a volatile organic solvent and an additional catalyst are not required. In quaternary ammonium ionic liquids, the acrylic acid can be obtained with high conversion and yield. Good conversion and high yield of cinnamic acid can also be obtained by using ammonium ionic liquid [Et3NH][HSO4]. These ionic liquids provide a good alternative to the industrial synthesis of cinnamic acid.
Figure 2. Hydrolytic reaction in ionic liquids
Polymer science: Ionic liquids are continued to be studied as important media for achieving various polymerizations. In polymer science, the ionic liquids can be used not only as solvents, but also as functional additives for polymer chains or hybrid materials. For example, poly(ionic liquid) made with ammonium ionic liquid can be used for CO2 adsorption. Poly(p-vinylbenzyltrimethyl ammonium tetrafluoroborate) has a high CO2 solubility, indicating that different cationic polymerized ionic liquids have different effects on CO2 adsorption. Therefore, poly(ionic liquid) has been successfully used as a gas separation membrane for CO2 separation by using this property.
Electrochemistry: Ammonium ionic liquids with stable cations, such as tetraalkylammonium, have a broad electrochemical window (typically more than 5V). Lithium electrochemical intercalation of carbon materials in these ionic liquids has shown better prospects. The possibility of electrochemical formation of lithium graphite intercalation compounds in trimethyl-n-hexylammonium bis(trifluoromethanesulfone) imide (TMHATFSI) ionic liquids has also been reported.
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