Do all the protic ionic liquids exist as molecular aggregates in the gas phase?

Area of Science:

• Physical Chemistry
• Materials Science

Background:

• Protic ionic liquids (PILs) are salts that are liquid at room temperature and formed by proton transfer.
• The gas-phase behavior of PILs is crucial for understanding their properties and applications.

Purpose of the Study:

• To investigate the gas-phase aggregation states of 1,1,3,3-tetramethylguanidium-based protic ionic liquids.
• To determine if PILs exist solely as molecular aggregates or if ionic aggregates are also present in the gas phase.

Main Methods:

• Electron ionization mass spectrometry (EI-MS) was employed to study the gas-phase composition of PILs.
• Analysis of mass-to-charge ratios (m/z) to identify molecular and ionic species.

Main Results:

• The study found that not all PILs exist as molecular aggregates in the gas phase.
• For 1,1,3,3-tetramethylguanidinium trifluoromethylsulfonate (TMGS), both molecular and ionic aggregates were detected in the gas phase.
• The gas-phase structure of PILs was shown to be dependent on the acidity and basicity of the constituent acid and base.

Conclusions:

• PILs can exist as both molecular and ionic aggregates in the gas phase.
• TMGS can evaporate via ionic aggregates, similar to aprotic ionic liquids.
• The acid-base properties of the components significantly influence the gas-phase structure of PILs.