Table 1.

Classification and examples of deep eutectic solvents.

Type	Composition
Type I	Organic salt + metal chloride (e.g., choline chloride–${\mathrm{ZnCl}}_2$)
Type II	Organic salt + metal chloride hydrate (e.g., choline chloride–${\mathrm{CoCl}}_2·6{\mathrm{H}}_2\mathrm{O}$)
Type III	Organic salt + hydrogen bond donor (e.g., choline chloride–urea)
Type IV	Hydrogen bond donor + metal chloride hydrate (e.g., urea–${\mathrm{ZnCl}}_2$)