Low-melting mixtures based on choline ionic liquids

Abstract

In this article a strategy is proposed for the design of low toxic, room temperature liquid low-melting mixtures (LMMs) which are entirely composed of natural materials. From literature it is well known that, in general, deep eutectic solvents based on choline chloride and dicarboxylic acids are LMMs, but not liquids at room temperature, with one exception: a 1 : 1 molar mixture of malonic acid and choline chloride. Therefore, the starting point of this study was the decrease of the melting point of one of the components, namely the dicarboxylic acid, which is succinic, glutaric or adipic acid. For this purpose, one of the two protons of the acidic group was exchanged by a bulky unsymmetrical choline cation. The resulting ionic liquids (ILs) were still solid at room temperature, but have a reduced melting temperature compared to the corresponding acids. In the second step, mixtures of these ILs with choline chloride were prepared. It turned out that choline glutarate-choline chloride mixtures are liquids at room temperature at compositions containing 95-98 wt% of choline glutarate. Finally, urea was added as another hydrogen bond donor. Density, conductivity and viscosity measurements were performed for all obtained mixtures. Moreover, a Walden plot was drawn which indicates that all mixtures are liquids with fully dissociated ions moving independently. Therefore, they are considered as "good" ionic liquids and, thus, for example they can be used to exchange more toxic or less biodegradable ILs in application processes. A brief outlook containing application possibilities is given. It is demonstrated that choline dodecylsulfate is readily soluble in these mixtures, forming aggregates in the LMM at temperatures exceeding 55 °C.

Deep eutectic solvents: designer fluids for chemical processes

“…Rengstl et al examined the thermal stability of ChCl-based DESs. 63 They found that the decomposition temperatures of ChCl-based DESs (269-280 ∘ C) are higher than those of HBDs and pure ILs. Thermal decomposition of DESs containing urea takes place in two steps, while a singular step mechanism is observed for DESs not containing urea.…”

“…Rengstl et al . examined the thermal stability of ChCl‐based DESs . They found that the decomposition temperatures of ChCl‐based DESs (269–280 °C) are higher than those of HBDs and pure ILs.…”

Review on Carbon Dioxide Absorption by Choline Chloride/Urea Deep Eutectic Solvents

“…Moreover, the thermal stability of choline-based DES was studied by Rengstl et al [18] who reported that the decomposition temperature of these solvents is in the range of 269-290 ∘ C which is higher than those reported for ionic liquids [11]. …”

Deep eutectic solvent an efficient reaction medium for the synthesis of chromeno pyrazolo and indazolo phthalazine derivatives

“…However, there are some limitations to use these solvents because of the low solubility of organic compounds, high cost and long reaction time. In the recent years, scientists received a lot of attention towords the DES beacuse of its unique properties such as high polarity, low toxicity, nonvolatility, biodegradability, low cost, thermal stability and ready availability from bulk renewable resources . Due to such environmental benign properties of DES, it is used in many organic transformations .…”

“…In the recent years, scientists received a lot of attention towords the DES beacuse of its unique properties such as high polarity, low toxicity, nonvolatility, biodegradability, low cost, thermal stability and ready availability from bulk renewable resources. [8][9][10][11] Due to such environmental benign properties of DES, it is used in many organic transformations. [12,13] DES is a mixture of hydrogen bond acceptors (HBAs) [14] such as choline chloride (ChCl), proline and hydrogen bond donors (HBDs) [15] such as tartaric acid, oxalic acid, urea, inorganic salts, alcohols and amines or carbohydrates.…”