Thermodynamics of mixtures containing linear monocarboxylic acids II. Binary systems showing cross-association between components: DISQUAC characterization of linear monocarboxylic acid + 1-alkanol,or + linear monocarboxylic acid mixtures

Binary mixtures containing compounds which show cross-association between them are investigated in terms of DISQUAC: namely, systems with two linear monocarboxylic acids, or with one acid and one 1-alkanol. In the former, the interactions between the COOH groups of the acids are represented by dispersive parameters only. Binary systems involving two 1-alkanols behave similarly. In the linear monocarboxylic acids + 1-alkanol mixtures, the COOH/OH interactions are represented by structure-dependent dispersive and quasichemical parameters. It is shown that those solutions with methanol and ethanol do not fit into the general scheme followed by the higher members of each homologous series considered here. A similar behaviour is found when mixtures containing methanol and benzene or CCl₄ are compared with those involving higher alkanols in the frameworks of DISQUAC or of the Barker's theory.Vapor-liquid equilibria, VLE, and excess enthalpy, H^E, data are consistently described by DISQUAC. Discrepancies are analysed.The UNIQUAC association model or an equation of state (Carnahan-Starling) with the association built in have been applied in the literature as pure correlations of the experimental data for acids + 1-alkanols systems. Their results are compared with those reported in this work by DISQUAC.     

Volumetric Properties of Ternary-Pseudobinary Mixtures Containing Benzene and Cyclohexane

Densities have been measured as a function of composition for ternary-pseudobinary mixtures of [(benzene + toluene or methylcyclohexane) + (cyclohexane + toluene or methylcyclohexane)] by means of a vibrating-tube densimeter at atmospheric pressure and the temperature 298.15 K. The excess molar volumes, V_m^E, were calculated from the densities and correlated using the Redlich–Kister equation to estimate the coefficients and standard errors. The experimental and calculated quantities are used to discuss the mixing behavior of the components. The results show the third component, toluene and methylcyclohexane, influences the interaction between benzene and cyclohexane.     

Excess enthalpies and molecular interactions in solutions of 1-fluoroalkanes in alkanes,benzene or tetrachloromethane. A group contribution (DISQUAC) study

Molar excess enthalpies H ^E at 298.15 K and atmospheric pressure were determined for 12 binary liquid mixtures, 1-fluoropentane, 1-fluorohexane, or 1-fluorononane + a non-polar solvent (hexane, cyclohexane, benzene, or tetrachloromethane) and were interpreted by the DISQUAC group contribution model. 1-Fluoroalkane + n-alkane mixtures are characterized by two types of groups or contact surfaces, fluorine (F) and alkane (CH₃, CH₂), the remaining mixtures by the additional contact surfaces of the solvents (C₆H₁₂ C₆H₆, or CCl₄). The interchange energies, entirely dispersive, of the alkane-solvent contacts were determined independently from the study of solvent-alkane mixtures. The dispersive F-alkane parameters were assumed to equal the parameters of perfluoroalkanes + n-alkanes. The shape of the H ^E curves of 1-fluorolkane + polarizable solvent (C₆H₆, CCl₄) mixtures are best reproduced by the model when the quasi-chemical F-solvent parameters are assumed to equal zero. The quasi-chemical F-alkane (the same for n-alkanes and cyclohexane) and the dispersive F-solvent parameters were estimated in this work. The 1-fluoroalkane solutions in C₆H₆ or CCl₄ exhibit the characteristic features of polar solute + polarizable solvent mixtures, viz., the deviations from the ideality are less positive than in alkanes and the experimental H ^E curves are strongly asymmetrical.     

Excess Volumes of Ternary Mixtures Containing N-Methylcyclohexylamine,Benzene with 1-Alkanols at 303.15 K

Abstract

New excess volume data have been measured for three ternary mixtures at 303.15 K. The mixtures included N-methylcyclohexylamine and benzene as common components. 1-propanol, 1-butanol and 1-pentanol were chosen as non-common components. The data were compared with those predicted by empirical relations. The experimental results have been analysed in terms of intermolecular interactions between unlike molecules.     

Thermodynamics of 1-alkanol+linear alkanoate mixtures

1-Alkanol?+?linear alkanoate mixtures have been investigated in the framework of the DISQUAC model. The interaction parameters for the OH/COO contacts are reported. The quasichemical parameters are independent of the mixture compounds. The dispersive parameters change with the molecular structure of the components. The same behaviour is observed for the OH/CO (carbonyl) and OH/OCOO (carbonate) contacts. DISQUAC represents well the molar excess Gibbs energies, coordinates of azeotropes and molar excess enthalpies. Using binary parameters only, DISQUAC improves meaningfully predictions on this property from the UNIFAC model for 1-alkanol?+?linear alkanoate?+?hydrocarbon systems. In contrast, the Nitta–Chao and the DISQUAC models yield similar results for the thermodynamic properties of the binary and ternary mixtures considered. 1-Alkanol?+?linear alkanoate mixtures are characterized by strong dipolar interactions between like molecules. In 1-alkanol?+?CH₃COO(CH₂) _{u ?1}CH₃ systems, dipole–dipole interactions between ester molecules are more important for u?≤?7. For u?≥?8, the more important contribution to the excess molar enthalpy comes from the disruption of the alkanol–alkanol interactions. For systems containing a polar compound such as alkanone, alkanoate or linear organic carbonate, dipolar interactions increase in the order: alkanone?<?alkanoate?<?carbonate.     

Excess volume of mixing and equation of state theories

Equation-of state theories of Flory and of Sanchez and Lacombe describe both enthalpy and volume of mixing of binary systems using single component properties and only one binary parameter X₁₂. We have evaluated this parameter from literature enthalpy data for numerous mixtures of two aromatic hydrocarbons, of alkanes with aromatic compounds, and of alkanes with carbonyl compounds. We have used this X₁₂ for calculation of excess volumes and compared the results with our previously measured experimental data. The agreement was fair for mixtures of two nonpolar components. Nevertheless, mixtures containing either cyclohexane or benzene displayed anomalies that could be traced to special packing of molecules in these compounds when pure. For mixtures of carbonyl compounds with alkanes, the theories predicted the qualitative trends correctly, but the quantitative agreement was rather poor. These results tend to support a model in which the enthalpy(cohesive energy) is inversely proportional to volume (as in the theories considered) only for dispersive interaction. When polar-polar interactions are involved, the dependence of excess volume on the excess enthalpy is much weaker.     

Excess Molar Volumes,Viscosity Deviations and Isentropic Compressibility of Binary Mixtures Containing 1,3-Dioxolane and Monoalcohols at 303.15 K

The excess molar volume (V ^E), viscosity deviations (Δη) and Gibbs excess energy of activation for viscous flow (G^∗E) have been investigated from density (ρ) and viscosity (η) measurements of eight binary mixtures of 1,3-dioxolane with methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, t-butanol, and i-amyl alcohol over the entire range of mole fractions at 303.15 K. The viscosity data have been correlated with the Grunberg and Nissan equation. Furthermore, excess isentropic compressibilities (K_S^E) have been calculated from ultrasonic speed measurements of these binary mixtures at 303.15 K. The deviations have been fitted by a Redlich–Kister equation and the results are discussed in terms of molecular interactions and structural effects. The excess properties are found to be either negative or positive depending on the molecular interactions and the nature of the liquid mixtures. The systems studied exhibit very strong cross association through hydrogen bonding.     

Surface Tension of Ternary Liquid Mixtures

Abstract

Surface tension has been measured by the differential capillary rise method for three ternary mixtures containing alkanes (hexane + cyclohexane+benzene, pentane + hexane + benzene and cyclohexane + heptane + toluene at 298.15\pm 0.1°K). The sign and magnitude of the excess surface tension and excess volume depend ultimately upon the chain length of the component of the mixtures. The results of the surface tension were compared with theoretical values obtained from Flory theory, Sanchez method, Brock-Bird relation and volume fraction statistics. There is reasonable agreement between theory and experiment.     

Excess Molar Volumes and Partial Molar Volumes of Binary Mixtures Containing Diethylcarbonate with Benzene and Substituted Benzenes at 293.15 K

Densities of the binary mixtures of diethylcarbonate with benzene and substituted benzenes, namely toluene, bromobenzene, chlorobenzene and nitrobenzene have been measured as a function of the composition, at 293.15 K and atmospheric pressure using a bicapillary pycnometer with an accuracy of 4 parts in 10⁴.The calculated excess molar volumes, V ^E were correlated with Redlich-Kister equation. The excess molar volumes are negative over the entire range of composition for the systems diethylcarbonate with benzene, toluene, bromobenzene and nitrobenzene. An inversion of the sign of V ^E is observed over some concentration for mixtures of diethylcarbonate with chlorobenzene. Partial molar volumes, V_i are also evaluated and their values have been extrapolated to zero concentration to obtain the limiting value at infinite dilution, V^o _i . The numerical values of the excess molar volumes for binary mixtures decrease in the order: chlorobenzene > benzene > bromobenzene ≈ toluene > nitrobenzene. The results are explained in terms of dissociation of the self-associated solute molecules and the formation of aggregates between unlike molecules.     

Solvent effect on the equilibrium constant of the chain reversible reaction of <Emphasis Type="Italic">N,N</Emphasis>′-diphenyl-1,4-benzoquinonediimine with 2,5-dichlorohydroquinone

The temperature dependences of the equilibrium constant K of the reversible chain reaction of N,N′-diphenyl-1,4-benzoquinonediimine with 2,5-dichlorohydroquinone in benzene, chlorobenzene, anisole, benzonitrile, and CCl₄ were studied. The enthalpies and entropies of the reaction in these solvents were determined, and a linear dependence between them in aromatic solvents was found. The equilibrium constant depends on the solvent nature: the replacement of CCl₄ by benzene at T = 298 K increases K from 13.6 to 140. The solvation effects are caused by several types of intermolecular interactions of participants of equilibrium with the medium. The decrease in K in the benzene-anisole-benzonitrile series is related, to a great extent, to complex formation with hydrogen bonding between 2,5-dichlorohydroquinone and the solvents. In anisole a charge-transfer complex is formed between the solvent and reaction product (2,5-dichloroquinone). The constant and enthalpy of the complexation were estimated. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 12, pp. 2296–2302, December, 2007.     

NMR chemical shifts of xenon in mixed aprotic solvents: A probe of liquid structure

The chemical shift of elemental xenon is extremely sensitive to the environment. In aprotic solvents, the presence of xenon has little effect on the solvent structure, and preferential solvation is not observed in any mixed solvent system. Consequently, xenon shifts can reveal the presence of short range order in certain liquids. Chemical shift data are presented for several model systems, including mixtures of different alkanes, alkanes with benzene, alkanes with acetone, and carbon tetrachloride with dimethylformamide (DMF). In certain cases, the xenon shift is strongly non-linear with composition. This effect arises from a specific interaction between the two solvents in the CCl₄-DMF system, while it reflects short range liquid order in the acetone-alkane systems. This effect is also apparent in the deviation of the densities of the acetone-alkane mixtures from ideality.     

CCl<Subscript>4</Subscript> Decomposition in RF Thermal Plasma in Inert and Oxidative Environments

The decomposition of carbon tetrachloride was investigated in an RF inductively coupled thermal plasma reactor in inert CCl₄–Ar and in oxidative CCl₄–O₂–Ar systems, respectively. The exhaust gases were analyzed by gas chromatography-mass spectrometry. The kinetics of CCl₄ decomposition at the experimental conditions was modeled in the temperature range of 300–7,000 K. The simulations predicted 67.0 and 97.9% net conversions of CCl₄ for CCl₄–Ar and for CCl₄–O₂–Ar, respectively. These values are close to the experimentally determined values of 60.6 and 92.5%. We concluded that in RF thermal plasma much less CCl₄ reconstructed in oxidative environment than in an oxygen-free mixture.     

Liquid Solution Densities of Ternary-Pseudobinary Mixtures of (Benzene + Cyclohexane) in the Presence of Tetrachloromethane or <Emphasis Type="Italic">n</Emphasis>-Hexane

Densities have been obtained as a function of composition for ternary-pseudobinary mixtures of [(benzene + tetrachloromethane or n-hexane) + (cyclohexane + tetrachloromethane or n-hexane)] at atmospheric pressure and the temperature 298.15 K, by means of a vibrating-tube densimeter. Excess molar volumes, V_m^E, partial molar volumes and excess partial molar volumes were calculated from the density data. The values of V_m^E have been correlated using the Redlich–Kister equation and the coefficients and standard errors were estimated. The experimental and calculated quantities are used to discuss the mixing behavior of the components. The results show that the third component, CCl₄ or n-C₆H₁₄, have quite different influences on the volumetric properties of binary liquid mixtures of benzene with cyclohexane.     

Molar Excess Volumes and Excess Isentropic Compressibilities of Ternary Mixtures Containing <Emphasis Type="Italic">o</Emphasis>-Toluidine

Molar excess volumes, V _ijk ^E, and speeds of sound, U _ijk , of o-toluidine (i) + benzene (j) + cyclohexane or n-hexane or n-heptane (k) ternary mixtures have been measured as a function of composition at 308.15 K. The observed speed of sound data have been utilized to determine the excess isentropic compressibilities, (K _S ^E) _ijk , of the ternary (i+j+k) mixtures. The Moelywn-Huggins concept (Huggins in Polymer 12: 389–399, 1971) of connectivity between the surfaces of the binary mixture constituents has been extended to ternary mixtures (using the concept of a connectivity parameter of third degree of molecules, ³ ξ, which in turn depends on its topology) to obtain an expression that describes well the measured V _ijk ^E and (K _S ^E) _ijk data. The observed data have also been analyzed in terms of Flory’s theory.     

Excess Molar Volumes for (Binary Mixtures of 1-Alkanol and 1-Alkene). I. The System 1-Alkanol + 1-Octene at 25°C

Excess volumes measured at 25°C are reported for binary mixtures of the C₃, C₄, C₆, C₈, and C₁₀ 1-alkanols with 1-octene. In this series of mixtures, the excess-volume curves change from positive values over the whole concentration range for short-chain alkanols C₃ and C₄, to sigmoid for longer-chain alkanols (with positive values in the alkanol-rich region). The positive region decreases with increasing chain length of the 1-alkanol. Excess partial molar volumes of the components are calculated. The results are compared with those for mixtures of 1-alkanols with n-octane. The model of associated mixtures proposed by Treszczanowicz and Benson³ describes very well the size and shape of the excess volume for the class of systems considered.     

Characterization of Heterogeneous Interaction Behavior in Ternary Mixtures by a Dielectric Analysis: Equi-Molar H–bonded Binary Polar Mixtures in Aqueous Solutions

The heterogeneous associating behavior of the aqueous binary mixtures of ethyl alcohol, ethylene glycol, glycerol and mono alkyl ethers of ethylene glycol, and aqueous ternary mixtures of equi-molar binary systems (i.e., mono alkyl ethers of ethylene glycol with ethyl alcohol, ethylene glycol and glycerol) have been investigated over the entire concentration range using accurately measured dielectric constants at 25 ^∘C. The concentration dependent values of the excess dielectric parameter ε^E and effective Kirkwood correlation factor g ^eff were determined using the measured values of the static dielectric constant, ε_o, at 1 MHz and the high frequency limiting dielectric constant ε_∞ = n _D ². The observed ε^E values in aqueous binary and ternary mixtures are negative over the entire concentration range, which implies the formation of heterogeneous complexes between these molecules that reduces the effective number of dipoles. The stoichiometric ratio corresponding to the maximum interaction in alcohol + water mixtures increases with an increase in the number of hydroxyl groups of the alcohol molecules, but for mono alkyl ethers of ethylene glycol + water mixtures it decreases with the increase in the molecular size of the mono alkyl ethers. In aqueous ternary mixtures the stoichiometric ratio for the maximum extent of heterogeneous interaction is governed by the molecular size of the mono alkyl ethers. It was also found that the strength of the heterogeneous H–bond connectivities in the water + alcohol systems decrease with an increase in the number of hydroxyl groups of the alcohol molecules. However in the case of water + mono alkyl ether binary mixtures and in ternary mixtures, the strength of H–bond connectivities increases with the increase in the molecular size of the mono alkyl ether. An analysis of the g ^eff values confirms that the heterogeneous interaction involves the orientation of molecular dipoles in the studied systems.     

Phase Transitions and Critical Behaviour of Binary Liquid Mixtures

Summary.  Compared to the simple one-component case, the phase behaviour of binary liquid mixtures shows an incredibly rich variety of phenomena. In this contribution we restrict ourselves to so-called binary symmetric mixtures, i.e. where like-particle interactions are equal (Φ₁₁(r) = Φ₂₂(r)), whereas the interactions between unlike fluid particles differ from those of likes ones (Φ₁₁(r) ≠ Φ₁₂(r)). Using both the simple mean spherical approximation and the more sophisticated self-consistent Ornstein-Zernike approximation, we have calculated the structural and thermodynamic properties of such a system and determine phase diagrams, paying particular attention to the critical behaviour (critical and tricritical points, critical end points). We then study the thermodynamic properties of the same binary mixture when it is in thermal equilibrium with a disordered porous matrix which we have realized by a frozen configuration of equally sized particles. We observe – in qualitative agreement with experiment – that already a minute matrix density is able to lead to drastic changes in the phase behaviour of the fluid. We systematically investigate the influence of the external system parameters (due to the matrix properties and the fluid–matrix interactions) and of the internal system parameters (due to the fluid properties) on the phase diagram. Received June 27, 2001. Accepted July 2, 2001     

Phase Transitions and Critical Behaviour of Binary Liquid Mixtures

 Compared to the simple one-component case, the phase behaviour of binary liquid mixtures shows an incredibly rich variety of phenomena. In this contribution we restrict ourselves to so-called binary symmetric mixtures, i.e. where like-particle interactions are equal (Φ₁₁(r) = Φ₂₂(r)), whereas the interactions between unlike fluid particles differ from those of likes ones (Φ₁₁(r) ≠ Φ₁₂(r)). Using both the simple mean spherical approximation and the more sophisticated self-consistent Ornstein-Zernike approximation, we have calculated the structural and thermodynamic properties of such a system and determine phase diagrams, paying particular attention to the critical behaviour (critical and tricritical points, critical end points). We then study the thermodynamic properties of the same binary mixture when it is in thermal equilibrium with a disordered porous matrix which we have realized by a frozen configuration of equally sized particles. We observe – in qualitative agreement with experiment – that already a minute matrix density is able to lead to drastic changes in the phase behaviour of the fluid. We systematically investigate the influence of the external system parameters (due to the matrix properties and the fluid–matrix interactions) and of the internal system parameters (due to the fluid properties) on the phase diagram.     

The Role of Binary and Many-centre Molecular Interactions in Spin Crossover in the Solid State. Part II. Non-ideality Parameters Defined via Binary Molecular Potentials

Summary. Parameters of the formalism [1–6] describing spin crossover in the solid state have been defined via molecular potentials in model systems of neutral and ionic complexes. In the first instance Lennard-Jones and electric dipole–dipole potentials have been used whereas in ionic systems Lennard-Jones and electric point-charge potentials have been used. Electric dipole–dipole interaction of neutral complexes brings about a positive excess energy controlled by the difference of electric dipole moments of HS and LS molecules. Differences of the order of Δμ = 1–2 D cause an abrupt spin crossover in systems with T_1/2 = 100–150 K. Magnetic coupling contributes both to the excess energy and excess entropy, however the overall effect is equivalent to a modest positive excess energy. Ionic systems in the absence of specific interactions are characterised by very small excess energies corresponding to practically linear van’t Hoff plots. Detectable positive and negative excess energies in these systems may arise from interactions of ligands belonging to neighbouring complexes. The HOMO–LUMO overlap in HS–LS pairs can bring about a nontrivial variation of the shape of transition curves. Examples of regression analysis of experimental transition curves in terms of molecular potentials are given.     

A dielectric study of the structure of propylene glycol

The dielectric spectra of propylene glycol over the frequency and temperature ranges 10 mHz–75 GHz and 175–423 K, respectively, were analyzed using the Dissado-Hill cluster model. A correlation between relaxation processes of breaking and formation of intermolecular H-bonds in clusters was obtained. A correlation of fluctuation processes of synchronous exchange of molecules between neighboring clusters corresponded to the redistribution of H-bonds between them. The Dissado-Hill theory was used to determine the integral relaxation times, n _DH and m _DH parameters and calculate the mean dipole moments of propylene glycol clusters and the energy characteristics of processes of their rearrangement. The mean dipole moments of clusters (23617–18.65 D) were compared with those of molecules in the liquid phase (3.67–3.03 D). The apparent activation enthalpy of processes of cluster rearrangements decreased from 141.8 to 25.2 kJ/mol, the activation energy decreased from 46.03 to 18.47 kJ/mol, and the energy of orientation dipole-dipole interactions, from 3.78 to 3.45 kJ/mol as the temperature increased.