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

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 = 28...