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. The first generation eutectic solvents were based on mixtures of quaternary ammonium salts with hydrogen donors such as amines and carboxylic acids. The deep eutectic phenomenon was first described in 2003 for a mixture of choline chloride (2-hydroxyethyl-trimethylammonium chloride) and urea in a 1:2 mole ratio, respectively. Choline chloride has a melting point of 302 °C and that of urea is 133 °C. The eutectic mixture melts as low as 12 °C.

This DES is 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. 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 ionic liquids which share many charactistics but are ionic compounds and not ionic mixtures, deep eutectic solvents are cheaper to make, much less toxic and sometimes biodegradable.

[edit] References

1. Andrew P. Abbott, Glen Capper, David L. Davies, Raymond K. Rasheed, Vasuki Tambyrajah (2003). "Novel solvent properties of choline chloride/urea mixtures". Chemical Communications (1): 70–71. doi:10.1039/b210714g. 
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. 

[edit] External links

• Deep eutectics at www.rsc.org Website