Thermodynamics Research Center / ThermoML | Journal of Chemical and Engineering Data

ABSTRACT

Densities of urea (U) and tetramethylurea (TMU) solutions in formamide (FA) and water with a solute molality being up to ~2 mol*kg-1 were measured at T = (288.15, 298.15, 308.15, 318.15, and 328.15) K and p = 99.6 kPa. All experiments were performed using a precision vibrating-Utube densimeter at measuring uncertainty did not exceeding 0.03 kgm-3. Standard partial and excess molar volumes as well as volume-related parameters of solute - solute interactions for U and TMU in both solvents under comparison were computed. The derived results were discussed on the assumption of that FA, like water or ethylene glycol (EG), is a solvent having a capability to form the spatial hydrogen-bonding network, inducing effects of solvophobic solvation. It was found that a structure-compression effect during the solvation of TMU in FA becomes somewhat enhanced with increasing temperature. In turn, the process of forming the "solvation complex" of U in FA is accompanied already by structure-loosening at temperatures higher than T = 288 K. The same goes both (EG + TMU) and (EG + U) systems, too, but the "loosening effect" in the last case is appeared at T greater than 308 K only. Similarly to aqueous solutions, the temperature has a differentiating effects on trends of changing in both the standard partial molar expansibility of U and TMU and volume coefficients of the U - U and TMU - TMU pair interactions in FA as well as EG. The data obtained here confirm the fact that the solvophobity of TMU in water is markedly stronger pronounced than it occurs in FA and EG media. Herewith the previous conclusion on that, in a thermochemical sense, the solvation behavior of compared ureas in FA is more "water-like" than in liquid EG, is in overall true for the solute TMU only.