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

Enthalpies of solution, Delta H-sol(m), 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.), Delta H-sol(m)infinity, and molar heat capacity changes for the solution process at i.d., Delta solC(p,m)(infinity), were obtained at T = 298.15 K. Molar enthalpies of solvation, Delta H-solv(m)infinity, and partial molar heat capacities, C-p.2(infinity), at i.d. were then calculated from the molar enthalpies of sublimation or vaporization and molar heat capacities, C-p,C-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 nionosubstituted 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.