Stable supercooling formation of guanidine monohydrochloride-based deep eutectic solvent induced by monosubstitution of urea as hydrogen bond donor

Two- and three-component mixtures were prepared using the monosubstituted urea of 1-methylurea (Um) and 1-hydroxyurea (Uh) as hydrogen bond donors, and guanidine monohydrochloride (GuHCl) as a hydrogen bond acceptor. Differential scanning calorimetry (DSC) thermograms and the solution-state nuclear magnetic resonance (NMR) spectra of the mixtures were compared with those of a deep eutectic solvent (DES) composed of urea (U) and GuHCl. At room temperature, 2Um-GuHCl was a DES in the supercooled state unlike solid state 2 U-GuHCl. Conversely, 2Uh-GuHCl did not form a DES. The methylation of urea resulted in the weakening of the hydrogen bonding of Cl− with others.