Evgeniy V. Ivanov

Volumetric properties of mixtures of water and methanol H/D-isotopomers between 5 and 45°C

Densities of H/D-isotopomers mixtures of water (H2O, D2O) and methanol (CH3OH, CD3OH, CH3OD, and CD3OD) over the full range of compositions were measured at 5, 15, 25, 35, and 45°C. Results have been used to calculate molar volumes, excess molar volumes, apparent molar volumes, and isotope effects of the mixtures. The volumetric properties are discussed in terms of the structural changes in water-methanol solutions under the influence of isotope substitution.

Volumetric properties of H2O, D2O, and methanol in acetonitrile at 278.15—318.15 K

The densities of H2O, D2O, and MeOH solutions in acetonitrile with the solute concentrations up to 0.07 molar fractions at 278.15, 288.15, 298.15, 308.15, and 318.15 K were measured using vibrating-tube densimetry with an error ≤8·10–6 g cm–3. The limiting partial molar volumes for the H/D isotopomers of water and IaII in acetonitrile (V–2∞) and the isotope effects in V–2∞ and in excess molar volumes of acetonitrile—water mixtures were calculated. Molecules of H2O, D2O, and IaII form associates with acetonitrile molecules via hydrogen bonds. The associates have the packing volumes close to those in the individual solute. The water and methanol molecules were assumed to be incorporated into the acetonitrile structure without substantial changes in the latter. However, this process results in some compression of the system with a simultaneous increase in its expansibility.

Influence of Water Microimpurities on Acetone Structure: Volume Effects of H 2 O and D 2 O Solvation

Here, we report the limiting partial molar volumes of ordinary water (H 2 O) and heavy water (D 2 O) in acetone and the excess molar volumes of these mixtures derived from precision density measurements at T = 288.15‐318.15 K and p ≈ 0.1 MPa. We have found the following. In the presence of water microimpurities (with water mole fractions up to 0.03), the molecular packing of acetone acquires a greater expansibility due to the appearance of new structural fragments (solvate complexes) in which bonding is stronger than in the bulk of the solvent. This weakens acetone‐acetone interactions and loosens the initial solvent structure as a whole; the effect is especially noticeable for the limiting dilution of acetone solutions of heavy water. We discovered the nontrivial fact that the negative (in sign) isotope effect on the limiting partial molar volume of water dissolved in acetone increases considerably with rising temperature. Acetone of high purity grade (from Khimmed; no more than 0.008 wt % water according to Fisher’s test) was used in experiments. Bidistilled water of the natural isotope abundance (electrical conductivity σ ≈ 1.3 × 10 –5 S/m) and heavy water D 2 O (from Izotop; 99.92 ± 0.02 wt % D) (based on density [3]) were used to prepare solutions. The solutions were prepared by a gravimetric method by diluting the degassed host solvent accurate to 2 × 10 ‐5 c sm,2 units, where c sm,2 is the solvomolality of the water isotopologue. Solvomolality c sm,2 is a dimensionless parameter of the solution compositions expressed through

Influence of N-metylation effect on the dissolution enthalpy of glycoluryl in water

Earlier [3, 4] we have shown that 2,4,6,8-tetramethyl-bis-carbamide (TMbCA), or mebicar, on dissolving in water shows small endothermic effect ( solH 2 3.67 kJ mol ) despite the presence in its molecule of the same number of CH3 groups as in hydrophobically hydrating tetramethylcarbamide (TMCA: solH 2 24.53 kJ mol 1 [5]). Accounting for this observation we suggest that the problem how the process of N-methylation affects enthalpy characteristics of dissolving in water protonated (that is, unsubstituted) glycoluril of bis-carbamide series (see the scheme) is also significant. The glycoluril bis-carbamide (bCA) is much more hydrophilic than TMbCA but is scarcely dissolving in water (5 10 3 mol per 1000 g of H2O at 298.15 K, or less).

Enthalpies of transfer of mebicarum from water to aqueous solutions of carbamide and its methyl-substituted derivatives at 298.15 K

The standard molar enthalpies of solution of Mebicarum (MbCA) in aqueous solutions of carbamide (CA), 1,3-dimethylcarbamide (1,3-DMCA), and 1,1,3,3-tetramethylcarbamide (TMCA) of various molalities, as well as the enthalpies of dilution of solutions of these compounds, were measured at 298.15 K. The enthalpy of transfer of MbCA from water to aqueous solutions of 1,3-DMCA exhibits an unusual dependence on the concentration of 1,3-DMCA. An analysis of the McMillan-Mayer enthalpy parameters of pair interactions revealed that the hydration of MbCA should be regarded as a superposition of the hydrophobic and hydrophilic mechanisms, with the latter one being predominant.

H/D Isotope Substitution Effect on the Structural and Thermodynamic Parameters of Intermolecular Interaction in Methanol at 278-318 K

The effect of H/D isotope substitution in methanol molecules on the geometrical parameters of the latter and the energetics of particle interactions is discussed in terms of scale particle theory and a model using internal pressure as a measure of nonspecific interactions in liquids. Deuteration leads to reduced space occupied by a molecule in the structural matrix of methanol. It is established that isotopic substitution differentiates the distribution of specific and van der Waals interactions. The former are strengthened and the latter weakened when protium is substituted by deuterium in a group forming hydrogen bonds, and the case is opposite when deuterium is replaced in the methyl radical of methanol.

Limiting Partial Molar Volumes of Solutions of Oleic, Linoleic, and Linolenic Acids in Cyclohexane and Benzene

AbstractHigh-precision vibration densimetry was used to measure (with an error of less than 5 × 10−6 g/cm3) the density of dilute solutions (0≤ x2 ≤ 0.01 mole fractions) of oleic, linoleic, and linolenic acids in cyclohexane and benzene at 298.15 K. The limiting

Solubility and thermodynamics of solvation of krypton in aqueous-methanol solutions of urea at 101 325 Pa and 278–318 K: I. Effect of H/D isotope substitution

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