Deep eutectic solvents (DESs) are now widely acknowledged as
a new class of ionic liquid (IL) analogues because they share
many characteristics and properties with ILs. The terms DES and
IL have been used interchangeably in the literature though it is
necessary to point out that these are actually two different types
of solvent. DESs are systems formed from a eutectic mixture of
Lewis or Brønsted acids and bases which can contain a variety of
anionic and/or cationic species; in contrast, ILs are formed from
systems composed primarily of one type of discrete anion and
cation. It is illustrated here that although the physical properties
of DESs are similar to other ILs, their chemical properties suggest
application areas which are significantly different.