In the past decade, a new generation of solvents with great potential for many industrial applications emerged. They were named deep eutectic solvents by Abbott et al. in 2003 from the Greek term ‘eutektos’ meaning ‘well melting’.
A combination of compounds, these solvents have much lower melting points than those of their individual components separately. The first reported deep eutectic solvent was a mixture of choline chloride (organic salt) and urea (hydrogen bond donor) melting as low as 12°C, which is considerably lower than that of either of its constituents (the melting point of choline chloride is 302°C, while urea is 133°C). This allows the mixture to be used as an ambient temperature solvent.