Hydrophobic−Hydrophilic Solvation of Variously Substituted N-Alkylureas in Aqueous Solution: A Calorimetric Study at a Temperature of 298.15 K

Abstract

Enthalpies of solution, ΔsolHm, in water, of some di-, tri-, and tetra-substituted N-alkylureas were measured by isothermal calorimetry at T = (296.84, 306.89, and 316.95) K. The molar enthalpies of solution at infinite dilution (i.d.), ΔsolHm∞, and molar heat capacity changes for the solution process at i.d., ΔsolCp,m∞, were obtained at T = 298.15 K. Molar enthalpies of solvation, ΔsolvHm∞, and partial molar heat capacities, Cp,2∞, at i.d. were then calculated from the molar enthalpies of sublimation or vaporization and molar heat capacities, Cp,m, of pure compounds in solid or liquid states, respectively. The methylene group contributions to the enthalpy of solvation was −3.7 kJ·mol−1 for di- and tri-N-alkylureas and −3.2 kJ·mol−1 for tetra-N-alkyureas, whereas the contribution to partial molar heat capacity was 91 J·K−1·mol−1 and 93 J·K−1·mol−1, respectively, in very good agreement with our earlier data for monosubstituted N-alkylureas and the literature data for various homologous series of alkyl-substituted compounds. Contributions of the functional groups of N-alkylureas were derived and compared with our earlier data for mono-N-alkylureas.