Deep eutectic solvent

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A deep eutectic solvent or DES is a type of ionic solvent with special properties composed of a mixture which forms a eutectic with a melting point much lower than either of the individual components.[1] One of the most significant deep eutectic phenomenon was observed for a mixture of choline chloride and urea in a 1:2 mole ratio, respectively. The resulting mixture has a melting point of 12 °C (far less than the melting point of choline, 302 °C and urea, 133 °C).[2] Which makes it liquid at room temperature.


The first generation eutectic solvents were based on mixtures of quaternary ammonium salts with hydrogen bond donors such as amines and carboxylic acids. There are four types of eutectic solvents:[3]

Type I Quaternary ammonium salt + metal chloride
Type II Quaternary ammonium salt + metal chloride hydrate
Type III Quaternary ammonium salt + hydrogen bond donor
Type IV Metal chloride hydrate + hydrogen bond donor

Type I Eutectics therefore also include the wide range of chlorometallate ionic liquids widely studied in the 1980's, such as the ever-popular imidazolium chloroaluminates which are based on mixtures of AlCl3 + 1-Ethyl-3-methylimidazolium chloride.[4] In addition to ionic liquids with discrete anions, the electrode-position of a range of metals has been previously carried out in deep eutectic solvents (DESs). These comprise of quaternary ammonium salts (e.g. choline chloride, ChCl), metal salts or metal salt hydrates and hydrogen bond donors (e.g. urea) and are commonly divided into four groups (Table 1),[5] and have been particularly successful on a large scale for metal polishing and immersion silver deposition. While most ionic liquids and DESs include a quaternary ammonium ion as the cationic component, it has recently been shown that eutectics can also be formed between a metal salt (hydrate) and a simple amide or alcohol to form a metalcontaining solution composed of cations and anions via disproportionation processes e.g.

2AlCl3 + urea ↔ [AlCl2•urea]+ + [AlCl4]-
These so called Type 4 eutectics are useful as they produce cationic metal complexes, ensuring that the double layer close to the electrode surface has a high metal ion concentration.[6]

Application[edit]

DESs have been studied for their applicability in industry at lab level, such as for production and purification of biodiesel,[7][8] and the DES described above was found to be able to dissolve many metal salts like lithium chloride (solubility 2.5 mol/L) and copper(II) oxide (solubility 0.12 mol/L). In this capacity these solvents are used for metal cleaning prior to electroplating. Because the solvent is conductive it also has a potential application in electropolishing. Organic compounds such as benzoic acid (solubility 0.82 mol/L) also have great solubility and this even includes cellulose.[9] Compared to ordinary solvents, eutectic solvents also have a very low VOC and are non-flammable. Other deep eutectic solvents of choline chloride are formed with malonic acid at 0 °C, phenol at -40 °C and glycerol at -35 °C. Compared to modern ionic liquids based on discrete anions, such as bistriflimide, which share many characteristics but are ionic compounds and not ionic mixtures, deep eutectic solvents are cheaper to make, much less toxic and sometimes biodegradable.Deep eutectic solvent can be used as a safe, efficient, simple, and low–cost solvent for complete dissolution of biological samples and quantitative extraction of metals for analysis.[10], Incorporating microwave heating with deep eutectic solvent can efficiently increase the solubility power of DES and reduce the time required for complete dissolution of biological samples at atmospheric pressure [11].

References[edit]

  1. ^ "Deep Eutectic Solvents". kuleuven.be. University of Leicester. Retrieved 17 June 2014. 
  2. ^ Andrew P. Abbott, Glen Capper, David L. Davies, Raymond K. Rasheed and Vasuki Tambyrajah (2003). "Novel solvent properties of choline chloride/urea mixtures". Chem. Commun: 70–71. doi:10.1039/B210714G. 
  3. ^ Andrew Abbott; John Barron, Karl Ryder and David Wilson (2007). "Eutectic-Based Ionic Liquids with Metal-Containing Anions and Cations". Chem. Eur. J. 13: 6495– 6501. doi:10.1002/chem.200601738. 
  4. ^ J. S. Wilkes; J. A. Levisky, R. A. Wilson and C. L. Hussey (1982). "Dialkylimidazolium chloroaluminate melts: a new class of room-temperature ionic liquids for electrochemistry, spectroscopy and synthesis". Inorg. Chem. 21: 1263–1264. doi:10.1021/ic00133a078. 
  5. ^ Andrew Abbott; Azeez Al-Barzinjy,Paul Abbott,Gero Frisch,Robert Harris,Jennifer Hartley and Karl Ryder (2014). "Speciation, physical and electrolytic properties of eutectic mixtures based on CrCl3.6H2O and urea". Phys.Chem.Chem.Phys 16: 9047– 9055. doi:10.1039/c4cp00057a. 
  6. ^ Andrew Abbott; Azeez Al-Barzinjy,Paul Abbott,Gero Frisch,Robert Harris,Jennifer Hartley and Karl Ryder (2014). "Speciation, physical and electrolytic properties of eutectic mixtures based on CrCl3.6H2O and urea". Phys.Chem.Chem.Phys 16: 9047– 9055. doi:10.1039/c4cp00057a. 
  7. ^ Maan Hayyan; Farouq S. Mjalli; Mohd Ali Hashim; Inas M. AlNashef (2010). "A Novel Technique For Separating Glycerine From Palm Oil-Based Biodiesel Using Ionic Liquids". Fuel Processing Technology 91: 116–120. doi:10.1016/j.fuproc.2009.09.002. 
  8. ^ Adeeb Hayyan; Mohd Ali Hashim; Maan Hayyan; Farouq S. Mjalli; Inas M. AlNashef (2013). "A Novel Ammonium Based Eutectic Solvent for Pre-treatment of Low Grade Crude Palm Oil and Synthesis High Quality Biodiesel Fuel". Industrial Crops and Products 46: 392–398. doi:10.1016/j.indcrop.2013.01.033. 
  9. ^ Richard F. Miller. 2010. Deep eutectic solvents and applications. Patent number: 8022014. Filing date: Mar 25, 2009. Issue date: Sep 20, 2011. Application number: 12/410,662. (http://www.google.com/patents/US8022014)
  1. Andrew P. Abbott,Azeez A. Al-Barzinjy,Paul Abbott,Gero Frisch,Robert Harris,Jennifer Hartley and Karl Ryder (2014). "Speciation, physical and electrolytic properties of eutectic mixtures based on CrCl3.6H2O and urea". Phys.Chem.Chem.Phys ]] 16: 9047– 9055. doi:10.1039/c4cp00057a. 
  2. Abbott, A. P.; Boothby, D.; Capper, G.; Davies, D. L.; Rasheed, R. K. (2004). "Deep Eutectic Solvents Formed between Choline Chloride and Carboxylic Acids: Versatile Alternatives to Ionic Liquids". J. Am. Chem. Soc. 126 (29): 9142–9147. doi:10.1021/ja048266j. PMID 15264850. 
  3. Mukhtar A. Kareem; Farouq S. Mjalli; Mohd Ali Hashim; Inas M. AlNashef (2010). "Phosphonium-Based Ionic Liquids Analogues and Their Physical Properties". J. Chem. & Eng. Data 55 (11): 4632–4637. doi:10.1021/je100104v. 

4. Maan Hayyan, Farouq S. Mjalli, Mohd Ali Hashim, Inas M. AlNashef. A Novel Technique For Separating Glycerine From Palm Oil-Based Biodiesel Using Ionic Liquids, Fuel Processing Technology, 91 (1), 116–120, 2010. doi:10.1016/j.fuproc.2009.09.002