Natural Deep Eutectic Solvents – Solvents for the 21st Century

Abstract

Green technology actively seeks new solvents to replace common organic solvents that present inherent toxicity and have high volatility, leading to evaporation of volatile organic compounds to the atmosphere. Over the past two decades, ionic liquids (ILs) have gained enormous attention from the scientific community, and the number of reported articles in the literature has grown exponentially. Nevertheless, IL "greenness" is often challenged, mainly due to their poor biodegradability, biocompatibility, and sustainability. An alternative to ILs are deep eutectic solvents (DES). Deep eutectic solvents are defined as a mixture of two or more components, which may be solid or liquid and that at a particular composition present a high melting point depression becoming liquids at room temperature. When the compounds that constitute the DES are primary metabolites, namely, aminoacids, organic acids, sugars, or choline derivatives, the DES are so called natural deep eutectic solvents (NADES). NADES fully represent green chemistry principles. Can natural deep eutectic solvents be foreseen as the next generation solvents and can a similar path to ionic liquids be outlined? The current state of the art concerning the advances made on these solvents in the past few years is reviewed in this paper, which is more than an overview on the different applications for which they have been suggested, particularly, biocatalysis, electrochemistry, and extraction of new data. Citotoxicity of different NADES was evaluated and compared to conventional imidazolium-based ionic liquids, and hints at the extraction of phenolic compounds from green coffee beans and on the foaming effect of NADES are revealed. Future perspectives on the major directions toward which the research on NADES is envisaged are here discussed, and these comprised undoubtedly a wide range of chemically related subjects.

Indirect assessment of the fusion properties of choline chloride from solid-liquid equilibria data

“…Usually, [Ch]Cl is combined with safe hydrogen bond donors such as polyols, urea, carboxylic acids or sugars [1,9,10], and their main applications include organic synthesis, biocatalysis and electrochemistry [2,7,11]. The knowledge of the fusion properties of [Ch]Cl is thus of utmost importance for a thermodynamic characterization of the choline-based DES, including the eutectic points and the complete description of the solid-liquid phase diagrams.…”

Development of a Method Based on Natural Deep Eutectic Solvents for Extraction of Flavonoids from Food Samples

“…These solvents have the following environmental and economic advantages: they are non-volatile, have a low toxicity, are biodegradable, sustainable, and inexpensive, and are made using simple preparation methods. They also show very good physicochemical properties: liquid state below 0°C, adjustable viscosity, a broad range of polarities, and ability to dissolve a wide range of compounds (Paiva et al 2014;Faggian et al 2006;Dai et al 2015). NADES therefore have good potential for the extraction of valuable secondary metabolites for use in the food and pharmaceutical industries.…”

Synthesis of a Novel Allyl-Functionalized Deep Eutectic Solvent to Promote Dissolution of Cellulose

“…Low viscosity benefited the accessibility of the solvent with hydrogen bonds in cellulose. Most of the DESs exhibited high viscosity, limiting their dissolving ability (Tang and Row 2013;Paiva et al 2014). The low viscosity of the allyl-functionalized DESs was expected based on previous reports on allyl-functionalized ILs.…”

“…They have been used as various media, such as extractants, electrolytes, catalysts, and solvents. This is due to their advantages of low environmental impact, high reactivity, and low cost (Tang and Row 2013;Paiva et al 2014;Juneidi et al 2015). The choline chloride (ChCl)-based DESs exhibit potential to dissolve various biopolymers, such as refined cork, starch, α-chitin, and microcrystalline cellulose (Garcia et al 2010;Hou et al 2012;Zhang et al 2012a;Xia et al 2014).…”