Morpholinium ionic liquid is a class of compound with morpholinium ring. Generally, morpholinium in this compound contains two R groups on the N atom, and the changes of the groups can impart different functions and properties to the ionic liquid. As a member of the ionic liquid family, it is increasingly favored by scientists because of its unique physical and chemical properties. A variety of functionalized morpholinium ionic liquids with different physical and chemical properties such as liquid range, polarity, acidity, chirality, coordination ability and solubility can be obtained by design.
Figure 1. The structure of morpholinium ionic liquids
Applications
Organic chemistry: In the organic reaction, ionic liquids used as the reaction medium can obtain higher yield and better selectivity than conventional solvents. When ionic liquids are applied as catalysts, the rate of many reactions can be accelerated, and the ionic liquid catalyst system is simple in post-treatment process and can be reused after recovery. For example, [MMPPA][HSO4] (N-methylmorpholinium propanesulfonic acid ammonium hydrogensulfate) is a highly efficient, chemoselective and reusable catalyst for the acetylation of alcohols, phenols and acetic anhydride at room temperature in the absence of solvents. [MMPPA][HSO4] is also a promising alternative to traditional catalyst in terms of environmental and economic factors. After removing water, it can be recycled and reused.
Material science: In the preparation of metal and non-metal nanomaterials, the use of ionic liquid is an effective and green method. Morpholinium ionic liquids can be used to prepare gold nanoparticles, and nanoparticles of different sizes can be obtained by controlling the structure of morpholinium ionic liquid cations, thereby forming dispersed and selective gold nanoparticles. The hydroxyl group-containing Morpholinium ionic liquid acts as a reducing agent to reduce Au3+ to Au0 and -CH2OH- to -CHO-.
Electrochemistry: Ionic liquids are often studied as electrolytes in electrochemical devices. For example, butyl-methyl-morpholinyl bis(trifluoromethanesulfonyl)imide [ButMetMor][TFSI] and ethyl-methyl-morpholinium bis(trifluoromethanesulfonyl)imide [EtMetMor][TFSI] and their mixture with propylene carbonate have been investigated as potential electrolyte layer capacitors in electrochemical double electrolytes for their good conductivity.
Figure 2. The acetylation of alcohols and phenols with acetic anhydride
Figure 3. Synthesis scheme of [EtMetMor][TFSI] and [ButMetMor][TFSI]
References
1. Yue, C. B.; et al. (2010). “Acetylation of alcohols and phenols with acetic anhydride under solvent-free conditions using an ionic liquid based on morpholine as a recoverable and reusable catalyst.” Monatsh.Chem 141, 975–978.
2. Kim, K. S.; et al. (2006). “Facile one-pot synthesis of gold nanoparticles using alcohol ionic liquids.” J.Med.Chem 16,1315-1317.
3. Galinski, M.; Stepniak, I. (2009). “Morpholinium-based ionic liquid mixtures as electrolytes in electrochemical double layer capacitors.” Journal of applied electrochemistry 39(10), 1949.
