Deep-eutectic solvents (DESs) have recently been described as a new class of ILs. DESs are obtained by complexion of quaternary ammonium salts with hydrogenbond donors. The charge delocalization occurring through hydrogen bonding between the halide anion with the hydrogen-donor moiety is responsible for the decrease in the freezing point of the mixture relative to the melting points of the individual components.
DESs share many characteristics of conventional ILs (e.g. they are nonreactive with water, nonvolatile, and biodegradable), but their low cost makes them particularly desirable (more so than conventional ILs) for large-scale synthetic applications.