DESs contain large, nonsymmetric ions that have low lattice energy and hence low melting points. They are usually obtained by the complexation of a quaternary ammonium salt with a metal salt or hydrogen bond donor (HBD). The charge delocalization occurring through hydrogen bonding between for example a halide ion and the hydrogen-donor moiety is responsible for the decrease in the melting point of the mixture relative to the melting points of the individual components.In a 2001 study by Abbott et al. a range of quaternary ammonium salts were heated with ZnCl2 and the freezing points of the resulting liquids measured. It was found that the lowest melting point, 23−25 °C, was obtained when choline chloride was used as the ammonium salt.This initial study has been extended, and a range of liquids formed from eutectic mixtures of salts and hydrogen bond donors have now been developed.2 These liquids were termed deep eutectic solvents to differentiate them from ionic liquids which contain only discrete anions. The term DES refers to lliquids close to the eutectic composition of the mixtures, the molar ratio of the components which gives the lowest melting point