Solutions of Urea and Tetramethylurea in Formamide and Water: A Comparative Analysis of Volume Characteristics and Solute–Solute Interaction Parameters at Temperatures from 288.15 to 328.15 K and Ambient Pressure

• Published in: Journal of chemical and engineering data Vol. 64; no. 12; pp. 5886 - 5899
• Main Authors: Ivanov, Evgeniy V, Kustov, Andrey V, Lebedeva, Elena Yu
• Format: Journal Article
• Language: English
• Published: American Chemical Society 12-12-2019
• ISSN: 0021-9568; 1520-5134
• DOI: 10.1021/acs.jced.9b00794

Densities of urea (U) and tetramethylurea (TMU) solutions in formamide (FA) and water with a solute molality of 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 U-tube densimeter at measuring uncertainty not exceeding 0.03 kg m–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 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 for both (EG + TMU) and (EG + U) systems, too, but the “loosening effect” in the last case appeared at T > 308 K only. Similarly to aqueous solutions, the temperature has a differentiating effect 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 that, in a thermochemical sense, the solvation behavior of compared ureas in FA is more “waterlike” than in liquid EG is overall true for the solute TMU only.