Tris(2-hydroxyethyl)ammonium-Based Protic "Ionic Liquids": Synthesis and Characterization.

Area of Science:

• Materials Science
• Chemical Synthesis
• Physical Chemistry

Background:

• Protic ionic liquids (PILs) synthesis is frequently incomplete, resulting in coexisting parent compounds and ionic species.
• The term "ionic liquid" is often applied to PILs without rigorous ionicity assessment, potentially impacting their application.
• Tris(2-hydroxyethyl)ammonium-based PILs with specific anions are of interest due to low toxicity and biopolymer interaction capabilities.

Purpose of the Study:

• To investigate the ionicity and thermal properties of tris(2-hydroxyethyl)ammonium-based protic ionic liquids.
• To propose improved synthesis methods for PILs, focusing on solvent-free conditions and moderate temperatures.
• To evaluate the suitability of the term "ionic liquid" for these synthesized systems.

Main Methods:

• Nuclear Magnetic Resonance (NMR) spectroscopy was employed to determine the ionicity of the synthesized PILs.
• Thermal characterization, including isothermal thermogravimetric analysis, was performed.
• Solvent-free synthesis at moderate temperatures was explored to minimize reactant decomposition.

Main Results:

• The ionicity of the studied tris(2-hydroxyethyl)ammonium-based PILs ranged from 20% to 86%, indicating significant coexisting un-ionized species.
• Mass loss for these PILs commenced around 350 K, with minimal influence of the anion on thermal stability.
• The proposed solvent-free synthesis method aimed to reduce impurities from reactant decomposition.

Conclusions:

• The term "ionic liquid" should be used with caution for systems with partial ionicity, as un-ionized species coexist with ionic forms.
• The findings necessitate consideration of both ionic and neutral species in applications involving these PILs.
• The synthesis approach offers potential improvements for producing PILs with reduced impurities.