D2O–H2O solvent isotope effects on the enthalpy of 1,3-dimethylpropyleneurea hydration at temperatures from (278.15 to 313.15) K and atmospheric pressure

The enthalpies of solution of 1,3-dimethylpropyleneurea in ordinary (H2O) and heavy (D2O) water were measured at (278.15, 283.15, 288.15, 298.15, and 313.15) K and atmospheric pressure. Standard enthalpies and heat capacities of solution (hydration), along with D2O–H2O solvent isotope effects on the quantities studied, were computed. The enthalpies of solution as well as corresponding solvent isotope effects were found to be negative and decreasing in magnitude with increasing temperature. It was established that the hydration (mainly of a hydrophobic type) is enhanced in D2O and on going from 1,3-dimethylethyleneurea (1,1,3,3-tetramethylurea) to 1,3-dimethylpropyleneurea, whereas the enthalpy-isotope effects become less appreciable in the latter case.