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

Abstract

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.

Solutions of Urea in tert-Butylamine: The Phenomenon of “Partial Molar Isobaric Compaction of the Solute” According to Density Measurements between 278.15 and 303.15 K at Ambient Pressure

“…In turn, taking into account the fact that the PMICS phenomenon was also found for water as a solute in tert -butylamine ( t -BuNH 2 ) and ethylenediamine (EDA), ,, we are entitled to expect the manifestation of a similar effect in the infinitely dilute solutions of U in these two alkylamines. This suggestion seems to be fairly reasonable keeping in mind the fact that water and U, interacting with each other in dilute aqueous solutions, form in overall topologically compatible structures. − …”

“…This table also provides data on the molar volume of U, V 2 ○ , and the excess standard (partial) molar volume, V̅ 2 E, ○ = V 2 ○ – V̅ 2 ○ . The latter quantity makes sense of “the volume change in the isobaric–isothermal process of transfer of one mole of the solute from its pure (crystalline) state to the infinitely dilute solution”. ,, Hence, V̅ 2 E, ○ has essentially a meaning of the volume effect of a solute dissolution (Δ sol V̅ 2 ○ ) …”

“…To estimate the V 2 ○ ( T ) values, we have used a simple equation proposed previously for describing the molar volume of crystalline U in the temperature range from T 0 = 273.15 K to T m. p. = 405.85 K, where T m. p. is the melting point , V 2 ○ ( cryst . ) = V 2 ○ ( θ ) + 1 . 5 × 10 − 8 ( T − θ ) + 1 . 8 × 10 − 10 false( T − θ false) 2 , r 2 = 0 . 996 …”

“…The prepared sample of crystalline U placed in the sealed flask was stored in a light-proof vacuum desiccator over P 2 O 5 . Immediately before use, U was dried to constant weight in a vacuum chamber at T = 310 K for 2 days. , Given the high hygroscopicity of alkylamines, special attention in the present work was paid to the preparation of t -BuNH 2 and its testing during the densimetric experiments. Therefore, the purified t -BuNH 2 specimen was poured into five separate hermetically sealed Pyrex-glass vessels of a 150 cm 3 each being placed in a dry transparent glovebox filled with nitrogen gas .…”

“…The solutions of U in t -BuNH 2 were prepared by weighting (with an error of 1 × 10 –8 kg) using the analytical balance of AND GH-202 type (Japan) under airtight conditions. , For this purpose, as we detailed in ref , the hermetically sealed glass flasks (of a 50 cm 3 volume) placed in a dry transparent glove-box were employed. To prepare solutions, we also used a number of the above 150 cm 3 vessels with t -BuNH 2 (see Section ).…”