The guanidyl compound has high thermal and chemical stability, high catalytic activity, strong physiological activity, has been widely used. In the ionic liquid, the guanidyl group can enhance the stability, heat resistance and regulatibleity of ionic liquids as cations. For the guanidine-based ionic liquids, the special properties are manifested in the melting point, viscosity, density, solubility, stability, etc. For melting points, the hydrogen-censoon is conjugated in the salt cation, and the positive charge is distributed over three nitrogen and center carbon atoms such that the neutralized hydrazine salt has a lower melting point. For density, the density of the entire glyzed salt ion liquid is between 0.90-1.49 g / cm3. Regarding viscosity, due to the larger ion volume of the guanidine salt cation, the van der Waals force between molecules is enhanced, which increases the viscosity. Regarding the solubility, the increase of the guanidine salt cationic side chain will increase its solubility in non-polar solvents. For stability, the distribution of the positive charge of the guanidine salt cation makes it have good thermal and chemical stability. From the above aspects, the guanidine salt ionic liquid has excellent properties in all aspects, making it widely used in organic synthesis, electrochemistry and fuel gas treatment.
Figure 1. Chemical structure of hexaalkyl guanidine-based ionic liquids
- Organic synthesis: In organic synthesis, guanidine-based ionic liquids can be used as organic solvents and phase transfer catalysts in nucleophilic substitution reactions, oxidation reactions, condensation reactions, and catalytic olefin hydrogenation reactions. In the condensation reaction, the acidic guanidine-based ionic liquids can also be used as a catalyst for highly selective catalytic reactions, and the catalyst can be recycled for many times. In the catalytic hydrogenation of olefins, the guanidine-based ionic liquids can immobilize nano-Pd(0) on molecular sieves to catalyze the hydrogenation of olefins, achieving high catalytic activity and selectivity.
- Electrochemistry: The guanidine-based ionic liquids electrolyte made in the form of liquid and gel has the advantages of stability, non-volatility, high conductivity and long service life. In addition, the manufactured batteries and capacitors have the advantages of easy processing and not easy to leak. In practical applications, ionic liquids composed of open-chain, cyclic guanidine cations and anions such as trifluoromethanesulfonate, tetrafluoroborate, and hexafluorophosphate are used in the electrolyte of primary batteries, secondary batteries and capacitors.
- Fuel gas treatment: Guanidine-based ionic liquids can be used to absorb and desorb SO2 in fuel gas to achieve selective absorption of SO2 at lower temperature and lower pressure. Moreover, the recycling of ionic liquids can be realized by desorption.
- Christina M Geiselhart,Christian W Schmitt,Philipp Jöckle,Hatice Mutlu,Christopher Barner-Kowollik. A Guanidine-Based Superbase as Efficient Chemiluminescence Booster[J]. Scientific Reports 2019, 9, 14519.