Acidity Scale in a Quaternary Phosphonium Ionic Liquid and Its Implication on Carbon Dioxide Absorption
Zhen Wang1, Qian-Hang Niu1, Wei Liu1
1School of Chemical and Environmental Engineering, Anyang Institute of Technology, Anyang 455000, China.
The Journal of Organic Chemistry
|August 15, 2025
Summary
A new acidity scale for 23 Brønsted acids was created in a quaternary phosphonium ionic liquid (QPIL). This QPIL demonstrated high CO2 absorption capacity, influenced by anion basicity.
Area of Science:
- Physical Chemistry
- Green Chemistry
Background:
- Ionic liquids (ILs) are tunable solvents with potential applications in catalysis and gas capture.
- Quaternary phosphonium ionic liquids (QPILs) offer unique solvation properties due to their structural characteristics.
Purpose of the Study:
- To establish an acidity scale for organic Brønsted acids in a specific QPIL.
- To investigate the CO2 absorption capabilities of anion-functionalized QPILs.
Main Methods:
- UV-vis spectroscopy was employed to determine the acidity scale of 23 organic Brønsted acids.
- Synthesis and characterization of anion-functionalized QPILs ([P4,4,4,16][X]) for CO2 absorption studies.
- Measurement of CO2 absorption capacities and kinetics in the synthesized QPILs.
Main Results:
- An acidity scale spanning 17 pK units (5.4–22.2) was established in [P4,4,4,16][OTf].
- The QPIL [P4,4,4,16][OTf] exhibited good stability towards strong bases.
- Anion-functionalized QPILs showed significantly higher CO2 absorption capacities than other ILs.
- Higher QPIL anion basicity correlated with faster CO2 absorption rates and increased capacity.
Conclusions:
- The counteranion's 'freeness' in [P4,4,4,16][OTf] influences solvation behavior, differing from imidazolium ILs.
- QPILs, particularly those with basic anions, are promising for efficient CO2 capture applications.
- The basicity of QPIL anions is a key factor governing CO2 absorption capacity and kinetics.
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