Densities, heat capacities, viscosities, 1H- and 13C-NMR spectra, and solvatochromic parameters of binary mixtures of 1,3-dimethyl-1,3-diazinan-2-one (DMPU) and water

The compound 1,3-dimethyl-1,3-diazinan-2-one (N,N'-dimethylpropyleneurea, DMPU) is a dipolar aprotic solvent with very strong electron-donating abilities but which is much less toxic and less carcinogenic than similar solvents such as the widely used HMPA (hexamethylphosphorictriamide). This paper reports densities and viscosities of the binary mixtures of (DMPU + water) in the temperature range (293.15 to 353.15) K at 5 K intervals, over the whole composition range. Isobaric heat capacities of these mixtures were measured by flow calorimetry at 298.15 K. The H-1- and C-13-NMR spectra as well as the solvatochromic parameters (polarizability, pi* , hydrogen-bond acceptor basicity, beta, and hydrogen-bond donor acidity, alpha) of the mixtures were also determined. The densities and viscosities were sensitive to traces of water in the organic-rich region while the heat capacities were not. Excess molar volumes were strongly negative, showing an extremum at mole fraction chi(DMPU) approximate to 0.40. The variation of viscosity with mixture composition was similar to the density with a sharp maximum at chi(DMPU) approximate to 0.35. Apparent molar volumes, V-phi, of the mixtures show that the water-DMPU interactions have a larger effect on V-phi of water than on DMPU. While the standard isobaric molar heat capacity of DMPU in water is much higher than that of DMPU itself, the corresponding value for water in DMPU was not much influenced by the presence of DMPU. The H-1-NMR spectra show that the chemical shift of the water protons is more influenced by mixture composition than those of the DMPU protons. A de-shielding of the DMPU carbonyl carbon resonance was observed in the C-13-NMR spectra at low chi(DMPU), indicative of H-bonding between the water protons and the non-bonding electrons of the carbonyl oxygen. (C) 2021 Elsevier Ltd.

Automated summary

This study reports the changes in density, viscosity, and isobaric heat capacities of binary mixtures of DMPU and water at different temperatures. Results show that the density and viscosity of the mixtures are sensitive to trace amounts of water in the organic-rich region, while the isobaric heat capacities are not, with excess molar volumes being negative.