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

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.Advantages of DESs compared to pure ILs include easy preparation and therefore low production costs, increased biocompatibility in case of certain components, and bigger variety for customization concerning acidity, hydrophobicity, or polarity. DES systems have demonstrated their practical use in several applications, such as interfacial polymerizations [7], electrochemistry [8], and organic reactions [9].So far, the published research describing IL mixtures has mainly focused on imidazolium [10,11], pyrrolidinium [12], and pyridinium [13] ILs. In these works, significant melting point suppression effects were found for the respective eutectic mixtures. However, imidazolium, pyrrolidinium, and pyridinium ILs and their mixtures face some limitations when it comes to large-scale applications in contact with microorganisms or living matter [14]. Challenges include toxicity aspects and the cost for the organic cation synthesis. This is why a more detailed investigation of choline salts is highly interesting. Based on the available literature, choline salts are characterized by their low toxicity for different cell-lines [15,16], bacteria [17], and other organisms [18]. Moreover, choline salts are industrially available on a large scale.The most widely studied choline salt used in eutectic mixtures is choline chloride [19][20][21][22][23][24][25][26]. One of the first reported DESs was a mixture of choline chloride (liquefaction temperature 302 • C), and urea (melting point 134 • C) that resulted in a 2:1 molar mixture with a remarkable melting point suppression to 12 • C [4]. The typical strategy was to combine choline ILs with molecular compounds such as carboxylic acids, alcohols, and urea derivates [27], and such choline-based DESs have been used in various applications, e.g., as drug solubilization vehicles [28][29][30]. Note, however, that by mixing a choline IL with molecular substances, some of the very attractive IL properties, e.g., non-volatility, non-flammability, and high ionic conductivity can get lost to a large extent. This is why the mixing of two choline ILs is ...

Tin molybdenum mixed metal oxides catalyst for oxidative desulfurization of model diesel

“…In the low-temperature range, spanning from 100 to 156°C, a weight loss of 3.4% is observed. This can be attributed to the removal of physically adsorbed water molecules within the sample, as well as the decomposition of carboxylate ions (COO -); this finding aligns with previous reports in the literature regarding similar phenomena Elhi et al (2020). The middle-temperature region from 156 to 532°C with a 27.6 % weight loss, is attributed to NO emissions, SnO2 crystallization, and polymorphic transition of h-MoO3 to α -MoO3 (Il'in et al, 2017;Poyraz et al, 2013).…”

Binary Mixtures of Choline Acetate and Tetrabutylammonium Acetate with Natural Organic Acids by Vibrational Spectroscopy and Molecular Dynamics Simulations

“…In this framework, with the aim of understanding the mechanism governing the formation of the deep eutectic solvents, we conducted a systematic study of the chemical–physical properties of mixtures composed of choline acetate (ChAc) or tetrabutylammonium acetate (TBAAc) with three different natural organic acids containing different numbers and typologies of acidic functions. It is worth noting that both acetate salts present cations commonly applied in the formulation of DESs. − The three chosen natural organic acids, namely, l -ascorbic acid (AA), citric acid (CA), and maleic acid (MA) (see Figure ), are molecules involved in many biological processes; skipping over their biochemical functions, it is more compelling to concentrate on the chemical distinctions between the three acids: AA, CA, and MA differ not only in the chemical structures but also in the number and type of acidic groups, which can act as a hydrogen bond donor (HBD). In particular, AA is the only one that has a noncarboxylic acidic function and contains three different hydroxyl groups.…”

Bulk Nanostructure of Mixtures of Choline Arginate, Choline Lysinate, and Water

“…Mixtures of two ILs, sharing the same cation but with different anions (or vice versa ), provide additional control over pure ILs. − Properties may be tuned by varying both the chemical structure and the mole ratio of the components in the mixture. For mixed cation or anion ILs, the mole ratio influences the repeat spacing, local ion structure, viscosity, interfacial adsorption, and eutectic behavior. ,,− Sensitive solvent tuning improves the selective extraction of petrochemical solutes from biomass feedstocks or the dissolution of biopolymers like cellulose or nucleic acids. , …”