O. A. Antonova

Enthalpies of 1,4-Dioxane, 1,2-Dimethoxyethane, and Ethylacetate Solvation in the Water–1-Propanol and Water–Glycerol Binary Mixtures

The enthalpies of 1,4-dioxane, 1,2-dimethoxyethane, and ethylacetate solution in binarymixtures of water with 1-propanol and glycerol were measured at 25°C using a precise isoperibol calorimeter. The enthalpies of the solute solvation were calculated and compared with the experimental data for other solutes. The results obtained were interpreted in terms of universal and specific solute solvation using parameters of a solvent polarity. It was found that the extreme shape of the curve ΔsolvH° vs. X for ethylacetate in the mixtures of water with 1-propanol results from peculiarities of carbotylate-group solvation and appears to be not connected with the influence of alcohol microaggregates in the mixed solvent.

Thermodynamics of aqueous L-proline solutions at 273–323 K

Enthalpies of dissolution of L-proline in water were measured calorimetrically at 283–313 K. The experimental temperature of dissolution of proline in water at the studied temperatures was shown to be almost independent of its concentration over the range 0.01–0.11 mol/kg. Standard enthalpies of dissolution and standard heat capacities of dissolution were calculated over this temperature range. The heat capacity of dissolution was ascertained to increase in the row glycine, proline, and alanine. The partial molar heat capacity of proline in water was determined and compared with the values obtained by extrapolation of the apparent heat capacities. The changes in entropy and reduced enthalpy and the Gibbs energy over the temperature range from 273 to 323 K were determined using familiar thermodynamic relations. The data for glycine and alanine were compared.

Solvation of Aniline in Mixtures of Water with N,N-Dimethylformamide and Acetonitrile

Thermal effects of aniline solution in water-N,N-dimethylformamide (DMF) and water-acetonitrile mixtures were measured at 25°C. In almost the whole range of compositions of the mixed solvents, the thermal effects are more positive in aqueous acetonitrile than in aqueous DMF. Particular attention was given to binary solvents with a very low content of the organic cosolvent. In the mixture with the mole fraction of DMF of 10-3, the enthalpy of aniline solution is higher than in water by 5%, and in the mixture with the mole fraction of acetonitrile of 4 × 10-4, even by 15%. Features of specific solvation of aniline and an aliphatic amine (n-BuNH2) in the water-DMF mixture were discussed taking into account the acid-base properties of the mixtures. The coefficients of pair interactions aniline-organic solvent in water and aniline-water in the organic solvent were calculated using the McMillan-Mayer theory. These coefficients correlate with the enthalpies of hydration of aprotic solvent molecules.

The Enthalpies and Heat Capacities of Solution of Tetraethyl- and Tetrabutylammonium Bromides in Methanol, Formamide, and Ethylene Glycol

The heat effects of solution of tetraethyl- and tetrabutylammonium bromides in methanol (MeOH), formamide (FA) and ethylene glycol (EG) were measured at 25 and 40°C at various concentrations. Various calculation methods were used to determine the standard enthalpies of solution. The results were compared with the available data on aqueous systems. The mean standard heat capacities of solution over the temperature range studied were calculated. The behaviors of tetraalkylammonium salts in water and FA were shown to be much less different than in water and alcohols, which was evidence of the possibility of the appearance of solvophobic solvation effects in the solution of nonpolar particles in FA.

Thermodynamic characteristics, structure, and interactions of L-proline in aqueous solutions of alcohols and urea

The enthalpies of dissolution of imino acid L-proline in aqueous solutions of methanol, 2-propanol, ethylene glycol, glycerin, and urea are measured by the calorimetric method at 313.15 K. Enthalpic parameters of the interaction of L-proline with nonaqueous components are calculated and compared with the data at 298.15 K. It is found that the sign of the heat capacity parameter of the pair and ternary interactions depends on whether the nonaqueous solvent component is a destroyer or stabilizer of the water structure. Partial molar heat capacities of proline in mixed solvents are obtained by the integral dissolution heat method. Temperature changes in the reduced enthalpy and entropy of the proline solution are determined at an increase in the temperature from 298 K to 313 K. It is shown that there is entropyenthalpy compensation at temperature changes in the characteristics during dissolution.

Dissolution enthalpies of L-proline and its interactions with methanol, 2-propanol, ethylene glycol, and glycerin in aqueous solution at 298.15 K

The dissolution enthalpies of L-proline in mixtures of water with methanol, 2-propanol, ethylene glycol, and glycerin were measured calorimetrically at 298.15 K. The enthalpy coefficients of the interaction of proline with alcohols in aqueous solutions were determined. The enthalpy coefficients of the pair interaction of proline and glycine with alcohols were shown to be directly proportional.

Heat properties of Bu4NBr solutions in binary mixtures based on formamide

Heat effects of tetrabutylammonium bromide dissolution in mixtures of formamide with methanol and ethylene glycol at 25°C were determined. Partial molar enthalpies of the components of formamide-ethylene glycol mixtures at 25°C were measured by the calorimetric method, and the mixing enthalpies of this system were determined. Within the limits of the second approximation of the Debye-Hueckel theory the standard enthalpies of dissolution ΔdisH0 were calculated, and the enthalpies of Bu4NBr transfer from formamide in its mixtures with water methanol and ethylene glycol were found on this basis. The enthalpy parameters of Bu4NBr pair interactions with the components of the formamide-water, formamide-methanol, and formamide-ethylene glycol mixtures were calculated. The results obtained were compared with the data for the systems containing N-methylformamide and N,N-dimethylformamide.

Thermochemistry of dissolution of aniline in mixtures of water with methanol andtert-butyl alcohol

The enthalpies of dissolution {ie2391-1} of aniline in mixtures of water with methanol andtert-butyl alcohol were determined in the whole concentration range of mixed solvents at 25 °C. Maxima of endothermicity were found in both systems at −0.3 and −0.06 molar fractions, respectively. The data obtained were compared with the thermochemical characteristics of the nonelectrolytes studied previously (dimethylsulfoxide, nitromethane, formamide,etc). The conclusion was drawn that the behavior of aniline in water-alcohol mixtures is mainly determined by its proton-donating ability and solvation of the benzene ring. A comparison of acoustic data and spectral and thermodynamic characteristics showed that thermochemical data are the most sensitive indicator for energy and structural changes occurring upon variation of the composition of a mixed solvent.

Enthalpies of dissolution of n-alkanes in a mixture of methanol-formamide

The enthalpies of dissolution of n-hexane, n-octane, and n-decane are determined thermochemically under standard conditions to describe nonspecific solvation in a mixed solvent of methanol-formamide. Experimental data are matched with the values obtained using model calculations. It is found that the differences between the experimental and calculated enthalpies of dissolution in the region with a high content of formamide could be due to the preferable solvation of n-alkanes by methanol.

Thermodynamics and structure of aqueous electrolyte solutions of glycine at different temperatures

The enthalpies of dissolution of glycine in aqueous electrolyte solutions are measured by calorimetry at temperatures of 288 K, 298 K, and 313 K in the molality range from 0.25 mol/kg to 6 mol/kg NaCl and to 4.5 mol/kg KCl. The enthalpy and heat capacity parameters are determined for the pair and triple interactions of glycine with electrolyte in water. Special (singular) points are discovered on the concentration dependences of the heats of dissolution of glycine in aqueous electrolyte solutions and in urea solutions at different temperatures. At these points, such a structurally sensitive property as the entropy of dissolution is temperature independent and the partial heat capacity of glycine is equal to that of the crystalline amino acid. The position of the singular point on the concentration axis is identical for NaCl and KCl solutions; in the case of urea solutions, the singular point is achieved at a much higher concentration of urea.