Limited ionicity in poor protic ionic liquids: Association Gibbs energies

Area of Science:

• Physical Chemistry
• Materials Science

Background:

• Protic ionic liquids (PILs) can exhibit limited ionicity, particularly when using carboxylic acids.
• Ion-pair association, rather than incomplete proton transfer, is a key factor in low-ionicity PILs.

Purpose of the Study:

• To develop improved electrostatic equations for predicting ion pairing in anhydrous amine/carboxylic acid mixtures.
• To provide a more accurate model than the Fuoss equation for association phenomena in PILs.

Main Methods:

• Development of new electrostatic equations incorporating induced dipoles to model ion-pair association.
• Determination of association Gibbs energies (ΔG_A) as functions of mixing ratio, proton-transfer strength, and dielectric constant.
• Fitting parameter values using quantum chemistry data and predicting autoionization Gibbs energies (ΔG_ioniz).

Main Results:

• New equations accurately predict association Gibbs energies (ΔG_A) and ion-pair formation.
• Predicted autoionization Gibbs energies (ΔG_ioniz) show excellent agreement with experimental data for carboxylic acid/amine mixtures.
• The models successfully link fundamental properties to ion association behavior.

Conclusions:

• The developed electrostatic equations offer improved predictive power for ion pairing in protic ionic liquids.
• These findings advance the understanding and design of PILs with desired ionic properties.
• The approach provides a valuable tool for studying complex equilibria in non-aqueous mixtures.