Abstract
A variable-temperature isothermic-shell calorimeter was used to measure the heat effects of dissolution of N,N-dimethylpropyleneurea (DMPU) in the water-N,N-dimethylpropyleneurea system at 298 and 313 K over the interval of compositions x2 = 0−0.1 mole fractions. The partial molar enthalpies of mixture components and the enthalpies and heat capacities of mixing were calculated. The results were compared with the data on water-amide systems. The exothermic effect of mixing of nonelectrolytes with water was found to increase in the series dimethylformamide < dimethylacetamide ∼ DMPU < hexamethylphosphorotriamide (HMPT). The McMillan-Mayer formalism was used to determine the enthalpy and heat capacity parameters of pair and three-particle interactions between DMPU molecules in water. The behavior of DMPU in water was to a substantial extent determined by hydrophobic interactions between nonpolar molecule moieties. This interaction was, however, noticeably weaker than in solutions of HMPT.
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