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. 2024 Apr 24;69(10):3427-3434.
doi: 10.1021/acs.jced.4c00024. eCollection 2024 Oct 10.

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

Emilia Tojo  1 , Alexandra Cáceres  2 , Alba Somoza  2 , Carlos A Pena  2 , Ana Soto  2
Affiliations

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

Emilia Tojo et al. J Chem Eng Data. .

Abstract

The proton transfer associated with the synthesis of protic ionic liquids (PILs) is often incomplete, meaning that the parent compounds may coexist with the ionic species. However, PILs are proposed for many applications as pure compounds without analysis of their ionicity. This work focuses on tris(2-hydroxyethyl)ammonium-based PILs with lactate, hydrogen succinate, hydrogen malate, and dihydrogen citrate anions. The interest of these anions lies in their low toxicity and capacity to disrupt the hydrogen-bonding network inherent to biopolymers. To improve current synthesis methods of this kind of PILs, which frequently lead to impurities derived from decomposition of reactants, working in the absence of solvents and at moderate temperatures is proposed. Through NMR studies, the ionicity of these systems was found to be low, from 20% to 86%, so the widely used term "ionic liquid" is not rigorous and must be used with caution. The un-ionized acid and base species coexist with the corresponding ionic forms, and this has to be considered in the studies involving these chemicals. The thermal characterization of the PILs was carried out. The influence of the anion on the thermal stability was found to be low. Isothermal thermogravimetric analysis showed that mass loss of these PILs starts at temperatures close to 350 K.

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Conflict of interest statement

The authors declare no competing financial interest.

Figures

Figure 1
Figure 1
Structure of the salts synthesized. 1: [TEA][LAC]; 2: [TEA][HSUC]; 3: [TEA][HMAL]; [TEA][DHCIT]; and 5: [TEA]Cl.
Figure 2
Figure 2
DSC thermograms of synthesized compounds: First run (- - - -), Third run (—).
Figure 3
Figure 3
TGA thermograms of synthesized compounds.
Figure 4
Figure 4
Isothermal TGA curves of synthesized compounds.
See this image and copyright information in PMC

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