Type III eutectics, formed from choline chloride and hydrogen
bond donors, have been of interest due to their ability to solvate a
wide range of transition metal species, including chlorides15 and
oxides.15,16 A range of hydrogen bond donors have been studied
to date, with deep eutectic solvents formed using amides,
carboxylic acids, and alcohols (see Figure 1). These liquids are
simple to prepare, and relatively unreactive with water; many are
biodegradable and are relatively low cost. The wide range of
hydrogen bond donors available means that this class of deep
eutectic solvents is particularly adaptable. The physical properties of the liquid are dependent upon the hydrogen bond donor
and can be easily tailored for specific applications. Although the
electrochemical windows are significantly smaller than those for
some of the imidazolium salt−discrete anion ionic liquids, they
are sufficiently wide to allow the deposition of metals such as Zn
with high current efficiencies. This class of deep eutectic solvents
have been shown to be particularly versatile, with a wide range of
possible applications investigated including the removal of
glycerol from biodiesel,17 processing of metal oxides,16 and the
synthesis of cellulose derivatives