Influence of Carboxylate Anions on Phase Behavior of Choline Ionic Liquid Mixtures.

Fred Elhi,Alvo Aabloo,Peter Wasserscheid,Gunnar Nurk,Kaija Põhako-Esko,Mikhail Gantman,Peter S Schulz

doi:10.3390/molecules25071691

Fred Elhi, Alvo Aabloo + Show 5 more

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https://doi.org/10.3390/molecules25071691

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Abstract

Mixing ionic liquids is a suitable strategy to tailor properties, e.g., to reduce melting points. The present study aims to widen the application range of low-toxic choline-based ionic liquids by studying eight binary phase diagrams of six different choline carboxylates. Five of them show eutectic points with melting points dropping by 13 to 45 °C. The eutectic mixtures of choline acetate and choline 2-methylbutarate were found to melt at 45 °C, which represents a remarkable melting point depression compared to the pure compounds with melting points of 81 (choline acetate) and 90 °C (choline 2-methylbutarate), respectively. Besides melting points, the thermal stabilities of the choline salt mixtures were investigated to define the thermal operation range for potential practical applications of these mixtures. Typical decomposition temperatures were found between 165 and 207 °C, with choline lactate exhibiting the highest thermal stability.

Highlights

Ionic liquids (ILs), salts liquid below a generally agreed 100 ◦ C limit, are important in many research fields, such as chemical synthesis, cost efficiency of production, reduction of waste, and toxic reagents
A comparison with previously published data indicates a certain underestimation of the melting points of choline ionic liquids (ILs) in the literature
The measurement conditions and interpretation of the differential scanning calorimetry (DSC) curves might lead to different results, too: determination of melting points as peak onsets had lower reproducibility compared to the top values reported in our study

Summary

Introduction

Ionic liquids (ILs), salts liquid below a generally agreed 100 ◦ C limit, are important in many research fields, such as chemical synthesis, cost efficiency of production, reduction of waste, and toxic reagents. ILs are known for their attractive properties such as high chemical and thermal stability, negligible vapor pressure and interesting electrochemical as well as solvating properties. These properties can be tailored by variation of the composition of cations and anions [1]. Even more variability is offered by using mixtures of ILs, an option that is considered the fourth evolution of ILs [2] In this contribution, we deal with mixtures of choline carboxylate ILs. In this contribution, we deal with mixtures of choline carboxylate ILs We anticipate that these mixtures will widen the application range of this class of ILs. We see potential applications in the medical [3] and environmental fields [1] where these systems offer a combination of low toxicity, adjustable solvation properties, and tunable ionic conductivity [2]

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