Apparent molal heat capacities and volumes of pyridine and methyl-substituted pyridines in aqueous solution at 25°C

We have made calorimetric measurements leading to apparent molal heat capacities of pyridine and four methyl-substituted pyridines in aqueous solution at 25.0°C. Measurements of densities of the same solutions have led to apparent molal volumes. The results are as follows: pyridine, _C ^° = 305.7 J–°K^–1-mole^–1 and _V ^° = 77.5 cm³-mole^–1; 2-methylpyridine, _C ^° = 370.0 J–°K^–1-mole^–1 and _V ^° = 94.3 cm³-mole^–1; 3-methylpyridine, _C ^° = 380.2 J–°K^–1-mole^–1 and _V ^° = 93.7 cm³-mole^–1; 4-methylpyridine, _C ^° = 378.9 J–°K^–1-mole^–1 and _V ^° = 94.3 cm³-mole^–1; 2,6-dimethylpyridine, _C ^° = 441.8 J–°K^–1-mole^–1 and _V ^° = 109.9 cm³-mole^–1. These _C ^° and _V ^° values are discussed in terms of effects of substitution of CH₃-for H– in the various solute molecules.The research reported here was carried out in the Department of Chemistry, University of Lethbridge, Lethbridge, Alberta, Canada T1K 3M4.     

Thermodynamic Characteristics of Phenacetin in Solid State and Saturated Solutions in Several Neat and Binary Solvents

The thermodynamic properties of phenacetin in solid state and in saturated conditions in neat and binary solvents were characterized based on differential scanning calorimetry and spectroscopic solubility measurements. The temperature-related heat capacity values measured for both the solid and melt states were provided and used for precise determination of the values for ideal solubility, fusion thermodynamic functions, and activity coefficients in the studied solutions. Factors affecting the accuracy of these values were discussed in terms of various models of specific heat capacity difference for phenacetin in crystal and super-cooled liquid states. It was concluded that different properties have varying sensitivity in relation to the accuracy of heat capacity values. The values of temperature-related excess solubility in aqueous binary mixtures were interpreted using the Jouyban–Acree solubility equation for aqueous binary mixtures of methanol, DMSO, DMF, 1,4-dioxane, and acetonitrile. All binary solvent systems studied exhibited strong positive non-ideal deviations from an algebraic rule of mixing. Additionally, an interesting co-solvency phenomenon was observed with phenacetin solubility in aqueous mixtures with acetonitrile or 1,4-dioxane. The remaining three solvents acted as strong co-solvents.     

Effect of pressure on solute capacity factor in HPLC using a non-porous stationary phase

Summary The pressure applied in liquid chromatography (LC) can influence the capacity factor of analytes. Using commercial equipment, column (33×4.6 mm) and 1.5 μm non-porous, tetradecyl (C₁₄) coated silica particles, a moderate but significant change in the capacity factor was observed with increasing pressure. Depending on the experimental conditions the relationship was found to be either linear or non-linear. In the latter case the retention increased at first, but later tended to decrease at still higher pressure. The results direct attention to the role of the pressure (and hence of flow rate and heat of friction) in determining capacity factors. Presented at Balaton Symposium on High Performance Separation Methods, Siófok, Hungary, September 1–3, 1999     

The enthalpies of solution and crystallization of sodium nitrate in water at 25°C

The differential enthalpies of solution of sodium nitrate in water have been measured calorimetrically at 25°C, from 0.5 to 10.4 mol (kg H₂O)^–1. The concentration dependence is described by the equation H=20.4537+1.0562m^1/2-7.0568m+2.8659m^3/2-0.3382m² From the calorimetric measurements, the enthalpy of crystallization of sodium nitrate was calculated as H_c=9.98±0.16 kL-mol^-1. The literature data on the solubility, activity and osmotic coefficients of NaNO₃ at 25°C yielded a value of –9.98±0.38 kJ-mol^–1. The good agreement between the experimental and calculated H_c values indicate the reliability of the input data.     

Determination of the solubilising character of 2-methoxyethyl-(dimethyl)ethylammonium tris(pentafluoroethyl)trifluorophosphate based on the Abraham solvation parameter model

Gas–liquid chromatographic retention factors have been measured for 42 different organic probes on a 2-methoxyethyl(dimethyl)ethylammonium tris(pentafluoroethyl)trifluorophosphate, ([MeoeM₂EAm]⁺[FAP]^–), stationary phase capillary column at 323 and 353 K. The measured retention factors were combined with published gas-to-liquid partition coefficient data for solutes dissolved in ([MeoeM₂EAm]⁺[FAP]^–) and with published gas-to-water partition coefficient data to yield 107 gas-to-anhydrous ionic liquid and 105 water-to-anhydrous ionic liquid partition coefficients. Abraham model correlations for describing solute transfer into ([MeoeM₂EAm]⁺[FAP]^–) were derived from the three sets of experimental partition coefficient data. The derived correlations back-calculated the experimental gas-to-([MeoeM₂EAm]⁺[FAP]^–) and water-to-([MeoeM₂EAm]⁺[FAP]^–) partition coefficient data to within 0.13 and 0.15 log units, respectively.     

Solute retention in the stationary phase of a liquid-solid chromatographic system

Summary Utilizing the UNIFAC group model of activity coefficients the retention behaviour of a solute in the stationary phase of a liquid-solid chromatographic system is studied. By comparison of experimentally observed capacity ratios and calculated activity coefficients of solutes in the mobile phase, varying the concentration of a polar moderator, it is shown that the calculated activity coefficients in the stationary phase fit very well the equation formally identical with the Langmuir function. Comparison of activity coefficients in the mobile and the stationary phase proves equivalence between the solvent interaction and the competition theory.     

Heat Capacities of Three Isomeric Chlorobenzenes and of Three Isomeric Chlorophenols

Isobaric heat capacities C _p in the liquid and in the solid phase of 1,2-dichlorobenzene, 1,3-dichlorobenzene, 1,2,4-trichlorobenzene, 3-chlorophenol and 4-chlorophenol and in the liquid phase of 2-chlorophenol were measured by commercial Setaram heat conduction and power compensated calorimeters. Results obtained cover the following temperature range (depending on the compound and state of aggregation): 1,2-dichlorobenzene 208 to 323 K,1,3-dichlorobenzene 183 to 323 K, 1,2,4-trichlorobenzene 133 to 323 K, 2-chlorophenol from293 to 353 K, 3-chlorophenol and 4-chlorophenol from 133 to 353 K. The heat capacity data obtained in this work were merged with available experimental data from literature, critically assessed and sets of recommended data were developed by correlating selected data as a function of temperature. Temperature and enthalpy of fusion of two isomeric chlorophenols and of 1,2,4-trichlorobenzene were also determined. This revised version was published online in August 2006 with corrections to the Cover Date.     

Relationship between the gas chromatographic behaviour and the molecular structure of hydrocarbon samples and various stationary phases Part I. Correlation of retention data and thermodynamic functions with chemical structure

Summary Retention parameters of different hydrocarbon classes were determined at 90–120°C on non-polar and medium-polar stationary phases. The specific retention volumes, and the thermodynamic functions of solution were calculated and the relationship between these data, the physicochemical properties and the chemical structure of the solutes (samples) and solvents (liquid phases) investigated.     

Towards a modellisation of the solvation energy in multi-component solvents. The interesting case of a charged solute imbedded in a polymer-containing electrolyte solution

In this paper we propose a mean-field theory to calculate the solvation free energy of a charged solute imbedded in a complex multi-component solvent. We considered a solvent made up of a mixture of small (electrolyte solution) and large (polymer) components. The presence of macromolecules ensures reduced mixing entropy among the different solvent components, an effect due to polymer connectivity. The reduced entropy favours strong preferential distribution of a particular solvent even in the presence of weak preferential solute–solvent interactions. In addition, two energy terms must be considered: (a) the interaction between the solute electrostatic potential and the electrolyte solution and (b) the formation of a polymer–solute interface. Because of the different dielectric permittivity of the solvent components, the electrolyte and polymer distribution functions are strongly coupled: ions, indeed, are more solvated in regions of higher local dielectric permittivity arising from the inhomogeneous mixing of solvent and polymer. We combined together the different energy terms in the framework of the de Gennes free energy functional for polymer solutions along with a generalised Poisson–Boltzmann equation developed for inhomogeneous dielectric media. Moreover, the preferential electrolyte solvation in regions of greater polarity was considered by an extension of the Born equation. Setting the polymer dielectric permittivity smaller than the solvent one and making null the specific polymer–solute interactions, we calculated enhanced electrolyte concentration and reduced polymer concentration near the solute surface on raising the solute surface charge density. The theory shows also the breakdown of the widely used separation between electrostatic and surface tension-dependent contributions to solvation energy when non-ideal mixed solvents are considered. In fact, according to the model, the surface tension of such mixed solvents strongly depends on the solute surface charge density: at high potentials the interfacial tension may increase rather than decrease on raising the polymer volume fraction. The theoretical results have been compared with experimental data on polymer+electrolyte solution surface tension and with solubility data of colloidal particles. The comparison evidences the complex behaviour of multi-component solvents going well beyond the trivial weighted average of the dielectric permittivity and surface tension of the isolated chemical components. Deviations from the simple behaviour predicted by an average picture of multi-component solvents could be understood by developing more sophisticated, but still simple, approaches like that proposed in this paper.Contribution to the Jacopo Tomasi Honorary Issue. This paper is dedicated to Jacopo Tomasi. I learned much of the difficult art of transforming complex problems into simple models after reading his early works on solvation energy.     

Activity of acetamide in acetamide-calcium nitrate melt solutions

Activity coefficients of acetamide in acetamide-calcium nitrate melt solutions were determined from cryoscopic data in the concentration range O to 0.151 mole fraction of calcium nitrate. Enthalpies of melting and melting point depressions were obtained from DSC measurements. Melt solutions were obtained from two crystalline forms of acetamide. Eutectic formation was observed in both crystalline forms. Heat capacity of pure acetamide in the two forms was measured in the temperature range 20 to 100°C. Activity coefficients obtained for molten acetamide from two sets of cryoscopic data were in good agreement. Change of activity coefficients with calcium nitrate concentration indicate strong association between solvent and solute and water-like acting of molten acetamide.     

Thermodynamics of BaNd2Fe2O7(s) and BaNdFeO4(s) in the system BaNdFeO

Two compounds, BaNd₂Fe₂O₇(s) and BaNdFeO₄(s) in the quaternary system BaNdFeO were prepared by citrate-nitrate gel combustion route and characterized by X-ray diffraction analysis. Heat capacities of these two oxides were measured in two different temperature ranges: (i) 130-325 K and (ii) 310-845 K, using a heat flux type differential scanning calorimeter. Two different types of solid-state electrochemical cells with CaF₂(s) as the solid electrolyte were employed to measure the e.m.f. as a function of temperature. The standard molar Gibbs energies of formation of these quaternary oxides were calculated as a function of temperature from the e.m.f. data. The standard molar enthalpies of formation from elements at 298.15 K, ΔfHm° (298.15 K) and the standard entropies, Sm° (298.15 K) of these oxides were calculated by the second law method. The values of ΔfHm° (298.15 K) and Sm° (298.15 K) obtained for BaNd₂Fe₂O₇(s) are: −2756.9 kJ mol⁻¹ and 234.0 J K⁻¹ mol⁻¹ whereas those for BaNdFeO₄(s) are: −2061.5 kJ mol⁻¹ and 91.6 J K⁻¹ mol⁻¹, respectively.     

Importance of heat capacity effects in the association of hydrocarbon moieties in aqueous solution

Values are reported for changes in heat capacity that accompany the formation of hydrocarbon-hydrocarbon dimers and hydrocarbon-polar hydrocarbon derivative dimers in dilute aqueous solution. Highly negative C _p ^o are obtained; the enthalpy changes, endothermic at room temperature, tend to decrease to zero in the range 50 to 80°C. A discussion is given of the importance of heat capacity effects in relation to the stability of hydrophobic association complexes.     

一个描述液相色谱体系中溶质进样量与保留值关系的方程

通过考虑溶质和溶剂在液相色谱体系中的相互作用,从理论上给出了一个描述溶质在液相色谱体系中进样量与保留值之间关系的方程。由方程可以证明,当进样量趋于零时,溶质的保留值为一定值,当进样量无限大时,溶质的保留值趋于零,且随着进样量的增加,溶质的保留值必然减小。通过方程的线性形式,可以获得两个描述色谱体系特征的重要参数：一个是溶质与固定相相互作用的平衡常数Ｋ,另一个是假想的分布在固定相表面上的活性点总数。