Eutectic solvent

Related to ionic liquids are substances known as deep eutectic solvents or mixtures. A series of these materials based on choline chloride (HOCH2CH2NMe3Cl) and either zinc chloride or urea have been reported (Abbott et al., 2002 2003). The urea/choline chloride material has many of the advantages of more well-known ionic liquids (e.g. low volatility), but can be sourced from renewable feedstocks, is non-toxic and is readily biodegradable. However, it is not an inert solvent and this has been exploited in the functionalisation of the surface of cellulose fibres in cotton wool (Abbott et al, 2006). Undoubtedly, this could be extended to other cellulose-based materials, biopolymers, synthetic polymers and possibly even small molecules. 

It has recently been shown that the same principle can be applied to deep eutectic solvents by using small quaternary ammonium cations such as ethylammonium and fluorinated hydrogen bond donors such as trifluoroacetamide. However, there is only a limited benefit that can be achieved using this approach as the physical parameters cannot be varied totally independently of one another. For example there will be an optimum ion size too small and the lattice energy will increase the surface tension, too large and the ionic mobility will be impeded. 

Section 4.3 is devoted to electrodeposition in a special class of deep eutectic solvents/ionic liquids which are based on well-priced educts such as e.g. choline chloride. The impressive aspect of these liquids is their easy operation, even under air, as well as their large-scale commercial availability. One disadvantage has to be mentioned the choline chloride-based liquids especially are currently not yet... 

The electrodeposition of chromium in a mixture of choline chloride and chromium(III) chloride hexahydrate has been reported recently [39]. A dark green, viscous liquid is obtained by mixing choline chloride with chromium(III) chloride hexahydrate and the physical properties of this deep eutectic solvent are characteristic of an ionic liquid. The eutectic composition is found to be 1 2 choline chloride/chromium chloride. From this ionic liquid chromium can be electrode-posited efficiently to yield a crack-free deposit [39]. Addition of LiCl to the choline chloride-CrCl3-6H20 liquid was found to allow the deposition of nanocrystalline black chromium films [40], The use of this ionic liquid might offer an environmentally friendly process for electrodeposition of chromium instead of the current chromic acid-based baths. However, some efforts are still necessary to get shining... 

Abbott et al. [98-103] reported the synthesis and characterization of new moisture-stable, Lewis acidic ionic liquids made from metal chlorides and commercially available quaternary ammonium salts (see Chapter 2.3). They showed that mixtures of choline chloride (2-hydroxyethyltrimethylammonium chloride, [Me3NC2H40H]Cl and MCU (M=Zn, Sn) give conducting and viscous liquids at or around room temperature. These deep eutectic solvents/ionic liquids are easy to prepare, are water-and air-stable, and their low cost enables their use in large-scale applications. Furthermore, they reported [104] that a dark green, viscous liquid can be formed by mixing choline chloride with chromium(III) chloride hexahydrate and that the... 

Ethylene Clycol-based Deep Eutectic Solvent... 

Recently a novel class of deep eutectic solvents based on choline chloride have been developed. These can be handled easily under environmental conditions and circumvent many problems that occur in aqueous solutions. They also offer the first economically viable liquids that can be used on an industrial scale. As the interest of electrochemists and classical electroplaters in ionic liquids has risen strongly in the last few years we decided, in 2006, to collect the key aspects of the electrodeposition from ionic liquids in the present book. The book has been written by a panel of expert authors during late 2006 and the first half of 2007 and thus describes the state of the art as of that point in time. 

Since 1980s, a large number of studies on the electrodeposition of metals have been reported. Historically, the water-sensitive chloroaluminate first-generation ILs are the most intensively studied. However, in future, the focus will rather be on air-and water-stable ionic liquids due to their variety and the less strict conditions under which they can be handled. Several review articles, books, and book chapters on the electrodeposition of metals and alloys from ILs have already been published [27-183], Ionic liquids can be classified as water/air sensitive (first-generation ionic liquids based on AIX3 (X=C1, Br)) and water/air stable (discrete anions based and eutectic solvents/ionic liquids such as ZnCl, urea, ethylene glycol, and choline chloride). A selection of published examples of the electrodeposition of metals and alloys from ionic liquids is listed in Table 5.3 the original work for each metal can be found in Refs. [23, 29-183], In this section, we mainly focus on the electrodeposition of active metals such as Al, Mg, and Ti in ionic liquids. 

Abbott AP, Boothby D, Capper G et al (2004) Deep eutectic solvents formed between choline chloride and carboxylic acids versatile alternatives to ionic liquids. J Am Chem Soc 126 9142-9147... 

Abbott AP, Capper G, Davies DL et al (2006) Solubility of metal oxides in deep eutectic solvents based on choline chloride. J Chem Eng 51 1280-1282... 

In a small-scale test behind a safety shield pentaerythritol (mp 260°C) dissolved readily in (Li, K)NOa eutectic (41.2-58.8 mole%, mp 125°C) at 130°C to form a 16% by weight solution. A 10% solution showed no visual evidence of reaction at 200°C. DTA runs made with small samples of 10% pentaerythritol-90% (Li, K)NOa eutectic with heating rates of 10° per minute showed endothermic peaks at 123-125°C, corresponding to melting, and broad exothermic peaks about 375°C attributed to decomposition of the solvent. Essentially, identical DTA s were observed for the pure eutectic solvent. Evidently, a 10% solution of pentaerythritol is reasonably stable in this nitrate melt and therefore we made NMR measurements. A PMR spectrum of pentaerythritol in (Li, K)N03 eutectic at 130°C, taken with a Varian HA-100 NMR spectrometer, was quite analogous to those obtained for pentaerythritol dissolved in thiocyanate or acetate eutectics. Two singlet peaks were observed, which we attribute to the methylene and hydroxyl protons. The hydroxyl peak was far downfield. 

The eutectic solvent HCIO4-H2O is especially suitable for Salzkryoskopie of cations which are stable only in acid solutions and of acids. With the latter the depression of freezing point is not affected by the degree of acid dissociation. On the other hand, polymerization of the acid molecule (or its dissociated anion) will lead to a decreased freezing-point depression. Solutions of nitric acid in this medium have been reported to produce anomalously low depressions, indicative of dimer formation. The available data are not adequate to distinguish between such species as HaNgOg, HNaO", NaOg", or... 

Abbott, A. R, Capper, G., McKenzie, K. J., and Ryder, K. S. (2007]. Electrodeposition of zinc-tin alloys from deep eutectic solvents based on choline chloride./ Electroanal. Chem., 599, pp. 288-294. 

Another reported class of bio-ILs is the group of cholinium-based ILs (choline, an essential nutrient) with amino acids as the anion [16, 17], Reported applications of such ILs have focused on their activities for the pretreatment of lignocellulosic biomass and as catalysts [18, 19]. Recently gel-based electrolytes, choline chloride-based eutectic solvents, were also used as electrolyte for the fabrication of environmentally friendly supercapacitors on paper [20]. 

DES = Biodegradable deep eutectic solvent generated from choline chloride and urea. 

Nanoporous Carbons Derived from Deep Eutectic Solvents... 

Gutierrez MC, Carriazo D, Ania CO, Parra JB, Ferrer ML, del Monte F (2011) Deep eutectic solvents as both precursors and structure directing agents in the synthesis of nitrogen doped hierarchical carbons highly suitable for CO2 capture. Energy Environ Sci 4 3535-3544... 

Gutierrez MC, Rubio F, del Monte F (2010) Resorcinol-formaldehyde polycondensadon in deep eutectic solvents for the preparation of carbons and carbon—carbon nanotube composites. Chem Mater 22 2711-2719... 

Carriazo D, Gutierrez MC, Ferrer ML, del Monte F (2010) Resorcinol-based deep eutectic solvents as both carbonaceous precursors and templating agents in the synthesis of hierarchical porous carbon monolith. Schem Mater 22 6146-6152... 

Synthesis of aminooxazole derivatives via thermal and ultrasonic methods using deep eutectic solvent as the medium was recently reported by Singh et al. (2013). It was observed that the ultrasound-assisted method gave 90% yield in just 8 min as against 3.5 h required to achieve 69% yield by the thermal method. 2-Amino-4-aryloxazoles (80) were obtained via the reaction of phenacyl bromide derivatives (78) and amide derivatives (79) in a deep eutectic solvent (Scheme 8.25). The deep eutectic solvent used in this protocol was easily prepared from choline chloride (1 eq) and urea (2 eq) at 80°C by a previously reported method (Toukoniitty et al. 2006) with 100% atom economy. 

Singh, B. S., Lobo, H. R., Pinjari, D. V., Jarag, K. J., Pandit, A. B. and Shankarhng, G. S. 2013. Ultrasound and deep eutectic solvent (DES) A novel blend of techniques for rapid and energy efficient synthesis of oxazoles. Ultrason. Sonochem. 20 287-293. 

The aim of this book is to present the insights of experts on emerging experimental techniques and theoretical concepts that are or will be in the vanguard of the field of electrochemistry in ionic liquids. The two volumes of this book provides the reader with a broad and self-contained account of electrochemical techniques available to work in ionic liquids. It also gathers and critically discusses the important properties of protic ionic liquids, deep-eutectic solvents, task-specific ionic liquids, polymeric ion gels, and lithium-ion solvation, relevant to electrochemistry. 

Fashu S, Gu CD, Zhang JL et al (2014) Electrodeposition, morphology, composition, and corrosion performance of Zn-Mn coatings from a deep eutectic solvent. J Mater Eng Perform 24 434 4. doi 10.1007/sl 1665-014-1248-5... 

Chakrabarti MH, Mjalli FS, AlNashef IM et al (2014) Prospects of applying ionic liquids and deep eutectic solvents for renewable energy storage by means of redox flow batteries. Renew Sustain Energy Rev 30 254-270. doi 10.1016/j.rser.2013.10.004... 

Durand E, Lecomte J, Barea B, Piombo G, Dubreucq E, Viheneuve P. Evaluation of deep eutectic solvents as a new media for Candida Antarctica B lipase catalyzed reactions. Process Biochem 2012 47 2081-9. 

Keywords Configurational stability Deep eutectic solvents Direct metalation group Epoxides Natural products Organolithiums Oxetanes Oxygen heterocycles Stereoselective synthesis Tetrahydrofurans... 

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