Water Solubility Trends in Ionic Liquids: The Quantitative Structure-Property Relationship Model versus Molecular...

Area of Science:

• Physical Chemistry
• Computational Chemistry
• Materials Science

Background:

• Water solubility in ionic liquids (ILs) is vital for applications like purification and decontamination.
• Predictive models for IL water solubility can reduce costly experimental efforts.
• Understanding IL-water interactions is key to designing efficient separation processes.

Purpose of the Study:

• To compare water solubility predictions from a quantitative structure-property relationship (QSPR) model with molecular dynamics (MD) simulation results.
• To investigate the influence of different cation-anion combinations on IL water miscibility.
• To elucidate the molecular mechanisms governing water solubility in ILs.

Main Methods:

• Development and application of a quantitative structure-property relationship (QSPR) model for IL water solubility prediction.
• Conducting molecular dynamics (MD) simulations with aggregation studies to analyze IL-water interactions.
• Testing ILs composed of 1-butyl-1-methylpyrrolidinium and 1-butyl-1-methylmorpholinium cations with bis(pentafluoroethylsulfonyl)imide (BETI^-), trifluoromethanesulfonate (TF^-), and tetrafluoroborate (BF₄^-) anions.

Main Results:

• Both QSPR and MD methods showed cation type has minimal impact on water solubility at 298.15 K.
• Hydrophobic anions, like BETI^-, significantly decrease water solubility compared to TF^- and BF₄^-.
• MD simulations revealed that anion-water interactions, forming H₂O-solvated anion networks, drive phase separation and limit solubility.

Conclusions:

• Anion hydrophobicity is the primary determinant of water solubility in the studied ILs.
• The formation of anion-water clusters hinders water-water interactions, leading to reduced miscibility.
• QSPR models and MD simulations provide complementary insights into IL-water solubility phenomena.