Structure-property relationships in protic ionic liquids: a study of solvent-solvent and solvent-solute interactions

Area of Science:

• Chemistry
• Materials Science

Background:

• Protic ionic liquids (PILs) are salts formed by proton transfer between acid and base.
• Understanding the ionic nature of functionalized PILs is crucial for their applications.

Purpose of the Study:

• To investigate how functional groups on the cation affect the ionic nature of tertiary ammonium acetate PILs.
• To explore the relationship between ionic nature and physicochemical properties.

Main Methods:

• Synthesis of tertiary ammonium acetate PILs with varying cation functional groups (hydroxyl, alkyl, amino).
• Analysis of proton transfer extent (equilibrium ionicity).
• Evaluation of solvent-solute and solvent-solvent interaction parameters.
• Measurement of physicochemical properties, including viscosity.

Main Results:

• The ionic nature of PILs is not solely determined by acid-base dissociation constants.
• Introducing a hydroxyl functional group on the cation significantly increases the equilibrium ionicity compared to alkyl or amino groups.
• Increased ionicity correlates with altered solvent-solute and solvent-solvent interactions.
• Physicochemical properties, such as viscosity, are influenced by the cation's functional group and resulting ionicity.

Conclusions:

• Cation functionalization, particularly with hydroxyl groups, is a key factor in tuning the ionic nature of protic ionic liquids.
• The observed changes in ionic nature are linked to intermolecular interactions and macroscopic properties.
• This study provides insights into the design of PILs with tailored properties for specific applications.