Thermodynamic characteristics of self-associated aminoalcohols

Thermodynamic characteristics of aminoalcohols self-associated by hydrogen bonds have been calculated. Specific and nonspecific components of the total energy of intermolecular interactions have been determined within the model approach. Main goal of this work is the search of thermodynamic characteristics of the liquid-phase systems effectively reflecting both features of intermolecular interactions, and structural changes of individual aminoalcohols. It is established that the most part of the studied aminoalcohols belongs to solvents with H-bonds networks in which there is an intensifying of nonspecific interactions with the temperature rise, and to solvents with chained self-association where the contribution of these interactions practically do not depend on temperature. The aminoalcohols obtained by the substitution of nitrogen atom protons of monoethanolamine by alkyl radicals belong to group of solvents similar aprotic ones at which nonspecific interactions are weakened with the temperature rise. The reasons of it have been discussed by comparison of the data with results for diols, oxyethylated glycols, monoalcohols, and aprotic amides obtained by us earlier.     

Thermodynamic characteristics of 2,2′-Dipyridyl solvation in binary methanol-acetonitrile solvents

The heat effects of 2,2′-dipyridyl (2,2′-Dipy) dissolution were measured by the calorimetric method at 298.15 K over the whole range of the mixed methanol-acetonitrile (MeOH-AN) solvent compositions. Transfer enthalpies of 2,2′-Dipy from MeOH into its mixtures with AN were calculated according to the obtained data. It was found that passing from MeOH to AN leads to a slight decrease in exothermicity of 2,2′-Dipy solvation in the solvents of compositions X _AN = 0.6–1.0, which probably indicates the prevailing contribution of desolvation of the nitrogen atoms over the one of the solvation of the aromatic rings of 2,2′-Dipy molecule with decreasing the basicity of the solvent.     

Thermodynamic characteristics of alanine-18-crown-6 ether complexes in binary water-acetone solvents

The formation of 18-crown-6 ether (18C6) complexes with D,L-alanine (Ala) in mixed wateracetone solvents with 0.0, 0.08, 0.17, 0.22, and 0.30 mole fractions of acetone (T = 298.15 K) was investigated by means of calorimetry. Thermodynamic characteristics of the reaction of the molecular [Ala18C6] complex formation (Δ_r G°, Δ_r H°, and TΔ_r S°) were calculated on the basis of calorimetric data. Analysis of solvation contributions of reagents into the enthalpy of the [Ala18C6] formation reaction showed that the changes in the reaction energy when the solvent composition is varied are determined by the changes in the solvate state of 18C6.     

Thermodynamic modeling of CTAB aggregation in water-ethanol mixed solvents

Accurate estimation of the CMC and aggregation numbers of individual surfactants is necessary to predict aggregation properties of surfactant mixtures, as well as to produce materials with controlled structures in the template synthesis. Thermodynamic equations are established to predict the aggregation behavior of cetyltrimethylammonium bromide (CTAB) in water-ethanol mixed solvent based on Nagarajan’s thermodynamic models. The calculated CMC and the aggregate size distribution are consistent with the experimental data and indicate that ethanol increases the CMC value and broadens the aggregate size distribution of CTAB. The calculated free energy reveals that ethanol greatly affects the transfer free energy of surfactant tails, the aggregate core-solvent interface free energy, and the ionic component of the free energy of head group interaction. The small angle XRD analysis of the pore structure of template-synthesized silica demonstrates that the suggested model can provide reasonable estimation of the CMC and the aggregation number of CTAB in water-ethanol mixed solvent, as well as indicates that the ethanol content in a solvent is one of the important factors affecting the periodic mesostructure of silica. The text was submitted by the authors in English.     

Thermodynamic characteristics of polyheteroarylene blends

The influence of the polybenzimidazole-to-polybismaleimide ratios and the chemical nature of sorbates on the thermodynamic characteristics of thermally structured blends of the polymers is studied. The optimum component ratio for the production of blends with good mechanical properties is found. The proton conductivity of the blends doped with phosphoric acid and acid zirconium phosphate is investigated.     

Thermodynamic functions of the mixing of methacrylic acid in organic solvents

The saturated vapor pressure over solutions of methacrylic acid is measured tensimetrically in acetonitrile, benzene, hexane, 1,2-dichloroethane, and acetic acid is measured tensimetrically at 290–350 K. The composition of equilibrium phases, the activity coefficients of the components, and the thermodynamic functions of the mixing (H ^E , G ^E , S ^E ) of the investigated solutions are calculated from the temperature dependence data.     

Thermodynamic characteristics of triphenylantimony diacrylate

The heat capacity of triphenylantimony diacrylate Ph₃Sb(O₂CCH=CH₂)₂ was studied in an adiabatic vacuum calorimeter at 6?C350 K and differential scanning calorimeter at 330?C450 K. Melting was revealed at these temperatures; the melting point was estimated at 428.4 ± 0.5 K. It was accompanied by the partial decomposition of the substance. The low-temperature (20 K ?? T ?? 50 K) heat capacity was treated using the Debye theory of the heat capacity of solids and its multifractal model. The type of the structure topology was determined. The standard thermodynamic functions C _p ^o (T), H ^o(T) ? H ^o(0), S ^o(T), and G ^o(T) ? H ^o(0) of the compound in the crystal state were calculated from the obtained experimental data in the range from T ?? 0 to 428 K. The standard entropy of the formation of the crystalline compound Ph₃Sb(O₂CCH=CH₂)₂ at T = 298.15 K was determined.     

Thermodynamic studies of some binary mixtures containing a self-associated component. II. Excess volumes of some mixtures of tetrahydrofuran with alcohols

Excess volumes of mixing, V^E, for binary mixtures of tetrahydrofuran (THF) with methanol, ethanol, n-butanol, tert-butanol, 2-bromoethanol and ethylene glycol have been determined from the experimental density measurements at 298.15 K over the entire composition range. The V^E data follow the order: ethylene glycol < 2-bromoethanol < methanol < ethanol < n-butanol < tert-butanol. The results have been explained in terms of self-association and the hydrogen bond-donating abilities of alcohols.     

Thermodynamic characteristics of small water clusters

Physicotechnical Institute of Low Temperatures, Academy of Sciences of the Ukrainian SSR. Translated from Zhurnal Strukturnoi Khimii, Vol. 29, No. 5, pp. 89–94, September–October, 1988.     

Structural and thermodynamic characteristics of amide solvents

The structural and thermodynamic characteristics of amide solvents are calculated with different types of molecular self-assembly through hydrogen bonding. Under a model-based approach, the specific and nonspecific components of the total energy of intermolecular interactions are identified for primary, secondary, and tertiary amides of carboxylic acids. It is found that similarly to water, primary amides have a network of hydrogen bonds and belong to the class of liquids characterized by an increase in nonspecific interactions with temperature. In secondary amides with the chain self-assembly, the contribution of these interactions is practically independent of temperature, and in tertiary amides it decreases with an increase in temperature. The molar values of the specific and nonspecific components are used to analyze the intermolecular interactions and the structural properties of amides with different degrees of N-substitution.     

Thermodynamic functions of solvation of 1,4-dioxane in various solvents at 298.15 K

The standard changes in enthalpy during the solvation of 1,4-dioxane in methanol, ethyl acetate, DMF, and acetonitrile were determined from calorimetric data and compared with the literature data for a series of solvents with different polarities. The standard changes in the Gibbs energy during the solvation of 1,4-dioxane in a wide series of solvents were calculated from the activity coefficients reported in the literature. The variation of the solvation functions of low-polar 1,4-dioxane in the series of solvents was found to be consistent with the enthalpy-entropy compensation rule. The results for 1,4-dioxane were compared with those for its open-chain analog and related large cyclic molecules. The electrostatic interactions of the solute with the solvents did not markedly affect the thermodynamic characteristics of ether in media with different polarities, but affected the interaction of the solute with the solvent more significantly. The solvation of the small ring of 1,4-dioxane in aprotic solvents was accompanied by a more significant exothermal effect than in the case of its open-chain analog. The conclusion was drawn that the enthalpies of the formation of hydrogen bonds between 1,4-dioxane and the associated water and chloroform molecules in solution were smaller in magnitude than the bonds of the similar open-chain polyether.     

Thermodynamic work of separation of a multicomponent mixture in systems with two solvents

An interpretation of the thermodynamic work performed in fractionation distribution systems upon the separation of a multicomponent mixture is offered.     

Thermodynamic characteristics of gelation for methyl-cellulose hydrogels

Methylcellulose (MC) is a thermo-reversible physical hydrogel. This study investigates the thermodynamic characteristics of gelation mechanism for MC. The relative and absolute specific heat capacity values of the hydrogel system were modeled using an empirical formulation to facilitate calculation of thermodynamic parameters. Experiments verifying the assumptions for the model formulation were conducted and are discussed. Parameters such as enthalpy, entropy, and changes in their magnitude as a function of temperature were calculated and their trends were studied. The implications of these observations on the various stages of the gel formation process and the associated mechanisms are evaluated. The studies revealed that the gelation of MC is a temperature- driven process rather than only driven by the heat input, and it attains a state of equilibrium under isothermal conditions. During gelation, the entropy of the overall (MC+water) system increases due to an increase in the disorderliness of the MC system.     

Thermodynamic characteristics of sodium ditungstate single crystal

The single crystal of Na₂W₂O₇ has been grown by the low-temperature-gradient Czochralski technique. The thermo- dynamic properties (standard enthalpy of formation, lattice enthalpy and stabilization energy), the knowledge of which is necessary to improve the growth technology, have been measured using reaction calorimetry. It has been shown that in the Na₂W₂O₇– Na₂Mo₂O₇ series, the luminescence wavelength increases from 540 to 650 nm, respectively, along with a change in the lattice enthalpy from −49030 to −54730 kJ mol⁻¹.     

Thermodynamic parameters of intermolecular interaction in strongly associated solvents and their mixtures with dimethylformamide

The specific and nonspecific constituents of the total energy of intermolecular interasction in ethylene glycol, diethylene glycol, and formamide were determined for the range 288.15–323.15 K using a simulation approach. Diethylene glycol, like formamide and ethylene glycol, forms networks of hydrogen bonds. In ethylene glycol and formamide, the hydrogen bonds make a predominant contribution to the total interaction energy. The specific and nonspecific contributions in mixtures of the above solvents with dimethyl-formamide were calculated, and the results were discussed in combination with the data for aqueous dimethyl-formamide solutions.Translated from Zhurnal Obshchei Khimii, Vol. 74, No. 11, 2004, pp. 1789–1796.Original Russian Text Copyright © 2004 by Zaichikov, KrestyaninovThis revised version was published online in April 2005 with a corrected cover date.     

Thermodynamic characteristics of thermal dissociation of platinum dichloride

The dissociation pressure for the process PtCl₂(s) → Pt(s) + Cl₂(g) was measured by the static method with diaphragm zero-pressure gauges. The approximating equation for the temperature dependence on the dissociation pressure for the above reaction was found. The enthalpy (137.7±0.3 kJ mol⁻¹) and entropy (163.6±0.4 J mol⁻¹ K⁻¹) of PtCl₂(s) dissociation and enthalpies of formation and absolute entropies of platinum di- and trichlorides at 298.15 K were calculated. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1345–1348, June, 2005.     

Thermodynamic characteristics of thermal dissociation of platinum trichloride

Single crystals of platinum trichloride were grown for the first time. The IR spectrum of single-crystal PtCl₃ was recorded. The pressure of thermal dissociation of PtCl₃ was measured by the static method with a quartz membrane-gauge zero-pressure manometer. An approximating equation for the dissociation pressure vs. temperature (540 K ≤ T ≤ 775 K) for the reaction 2 PtCl₃(s) → 2 PtCl₂(s) + Cl₂(g) was found. The enthalpy (123.1±1.7 kJ mol⁻¹) and entropy (183.6±2.8 J mol⁻¹ K⁻¹) for the dissociation of PtCl₃(s) were calculated at 298.15 K.__________Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 2032–2034, October, 2004.     

Thermodynamic characteristics of thermal dissociation of platinum tetrachloride

The pressure of thermal dissociation of platinum tetrachloride by the first step PtCl₄(s) = PtCl₃(s) + 0.5 Cl₂(g) was measured by the static method with a quartz membrane-gauge zero-pressure manometer. An approximating equation for the dissociation pressure vs. temperature was found. The enthalpy (52160±880 J mol⁻¹) and entropy (72.1±1.6 J mol⁻¹ K⁻¹) of dissociation were calculated. The heat of formation found for platinum tetrachloride (−246.3±1.3 kJ mol⁻¹) at 298.15 K agrees well with the value obtained by the calorimetric method (−245.6±1.9 kJ mol⁻¹).__________Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 2028–2031, October, 2004.