Search

The liquid-liquid equilibrium (LLE) curves have been determined for the 2-hydroxyl-benzaldehyde (salicylaldehyde, SAC) + CH3(CH2)nCH3 mixtures (n = 5,6,7,8,9). The equilibrium temperatures were determined observing, by means of a laser scattering technique, the turbidity produced on cooling when a second phase takes place. All the systems show an upper critical solution temperature, which linearly increases with n. Intermolecular effects have been investigated in alkanol + benzaldehyde systems using data from the literature. Interactions in 1-alkanol mixtures are mainly of dipolar type. The corresponding excess molar enthalpies, H m E , are large and positive, which reveals that interactions between like molecules are dominant. Interactions between unlike molecules are stronger for the methanol-containing system. For the other mixtures, the enthalpy of the 1-alkanol-benzaldehyde interactions remains more or less constant. At 298.15 K and equimolar composition, the replacement of a linear polar solvent by the isomeric aromatic one leads to increased H m E values in systems with a given 1-alkanol. The phenol + benzaldehyde system shows strongly negative deviations from the Raoult’s law. Proximity effects have been examined in SAC + hydrocarbon mixtures. Alkane-containing systems are essentially characterized by dipolar interactions, while dispersive interactions are prevalent in the solution with benzene. All the mixtures have been treated in terms of DISQUAC. The interaction parameters for the OH/CHO contacts and for the SAC/aromatic and SAC/alkane contacts have been reported. DISQUAC provides a correct description of the thermodynamic properties considered. In the case of SAC systems, this is done by defining a new specific group HO–C–C–CHO for salicylaldehyde.

Mixtures formed by 1-alkanol and one strongly polar compound, nitromethane (NM), ethanenitrile (EtN), dimethyl sulfoxide (DMSO, sulfolane (SULF), nitrobenzene (NTBz) or benzonitrile (BzCN), have been investigated on the basis of a set of thermophysical data, which includes: excess molar functions, enthalpies, H m E , Gibbs energies, G m E , entropies, T S m E , isobaric heat capacities, C p m E , volumes, V m E ; liquid-liquid equilibria (LLE), excess permittivies and deviations from the linearity of dynamic viscosities. In addition, calculations have been conducted to determine the Kirkwood-Buff integrals and the Kirkwood correlations factors, g K , of the investigated mixtures. In the former case, DISQUAC has been employed for modeling the needed vapour-liquid equilibria data. Many systems under consideration are characterized by dipolar interactions between like molecules and have positive values of H m E , C p m E and T S m E . On the other hand, alkanol-solvent interactions, for mixtures with a fixed 1-alkanol, become weakened in the sequence: DMSO ≈ SULF > EtN > NM > BzCN > NTBz. In systems with a given solvent, such interactions become also weaker when the chain length of the 1-alkanol is increased. Interestingly, the considered mixtures also show strong structural effects. Results on Kirkwood-Buff integrals reveal that nitriles are more preferred than nitroalkanes around a central alcohol molecule. Calculations on g K show that, in terms of the mixture polarization, the systems are rather unstructured, and that this trend becomes more important when the 1-alkanol size increases in solutions with a given solvent.

Relative permittivities at 1 MHz, er, and refractive indices at the sodium D-line, nD, are reported at 0.1 MPa and at (293.15–303.15) K for the binary systems 1-alkanol + di-n-propylamine (DPA). Their corresponding excess functions are calculated and correlated. For the methanol mixture, positive values of the excess permittivities, erE, are found. Except at high concentrations of the alcohol in the 1-propanol mixture, the remaining systems show negative values of this property. This fact reveals that the creation of (1-alkanol)-DPA interactions contributes positively to erE, being this contribution dominant in the methanol mixture. The negative contributions arising from the disruption of interactions between like molecules are prevalent in the other mixtures. At ϕ1 (volume fraction) = 0.5, erE changes in the sequence: methanol > 1-propanol > 1-butanol > 1-pentanol

Data on density, ρ, speed of sound, c, and refractive index, nD, have been reported at (293–303.15) K for the N,N-dimethylacetamide (DMA) + CH3CO(CH2)u − 1CH3 (u = 1, 2, 3) systems, and at 298.15 K for the mixture with u = 5. These data have been used to compute excess molar volumes, VmE, excess adiabatic compressibilities, κSE, and excess speeds of sound cE. Negative VmE values indicate the existence of structural effects and interactions between unlike molecules. From molar excess enthalpies, HmE, available in the literature for N,N-dimethylformamide (DMF), or N-methylpyrrolidone (NMP) + n-alkanone systems, it is shown: (i) amide-ketone interactions are stronger in DMF systems than in those with NMP; (ii) they become weaker when u increases in mixtures with a given amide. Structural effects largely contribute toHmE and are more relevant in mixtures containing NMP. The application of the Flory's model reveals that the random mixing hypothesis is valid in large extent for DMF solutions, while NMP systems are characterized by rather strong orientational effects. From values of molar refraction and of the product PintVm (where Pint is the internal pressure and Vm the molar volume), it is concluded that dispersive interactions increase with u, or when DMF is replaced by DMA in mixtures with a fixed ketone., Junta de Castilla y León, under Project BU034U16

Interactions and structure of organic carbonate + alkane, and 1-alkanol + organic carbonate mixtures have been investigated by means of a set of molar excess functions, enthalpies ( H m E ), volumes ( V m E ), isobaric heat capacities, ( C p m E ) or entropies; and considering internal pressure ( P int ); liquid-liquid equilibria or permittivity data. In addition, the mentioned systems have been studied using the Flory model and the concentration-concentration structure factor S CC ( 0 ) , formalism. The mixtures under consideration are characterized by dipolar interactions and by homocoordination (that is, by interactions between like molecules). In systems with a given solvent, dipolar interactions are weakened in the order: propylene carbonate (PC) > dimethyl carbonate (DMC) > diethyl carbonate (DEC). Comparison of mixtures containing DMC or DEC with those involving 2-propanone or 3-pentanone shows that dipolar interactions are not determined merely by values of the dipole moment, but they also depend on the size group. The enthalpies of the alkanol-carbonate interactions have been evaluated from calorimetric data. They are stronger in DMC solutions, and become weaker when the alcohol size increases in mixtures with a given carbonate. Application of the Flory model to 43 systems of the type 1-alkanol + carbonate provides a mean relative standard deviation for H m E equal to 0.107. Results reveal that orientational effects decrease in the order DEC > PC > DMC. Orientational effects are particularly relevant in methanol or ethanol + DEC mixtures. Interestingly, the mentioned effects are weaker in 1-alkanol + DMC mixtures than in DMC + alkane systems. A similar trend is observed in DEC solutions when the considered alcohol is longer than ethanol.

Relative permittivities at 1 MHz, er, and at (293.15–303.15) K, are reported for the binary systems N,N-dimethylformamide (DMF) + N-propylpropan-1-amine (DPA), + N-butylbutan-1-amine (DBA), + butan-1-amine (BA) or + hexan-1-amine (HxA). The values of the excess relative permittivities, erE, have also been determined for these solutions. The measurements were realized by means of a precision impedance analyser 4294A, to which a 16452A cell connected using a 16048G test lead, all of them from Agilent. The erE values are large and negative, and diminish when the size of the amine increases along a homologous series, which has been ascribed mainly to the rupture of interactions between like molecules along mixing. Calculations on excess molar orientational polarizabilities support this conclusion, indicating a dominant contribution to erE from the orientational polarizability of the molecules in the mixture. The analysis of excess relative Kirkwood correlation factors shows that the correlation between dipoles is effectively decreased along the mixing process.

Fluorobenzene, or 1,4-difluorobenzene or hexafluorobenzene + alkane mixtures and hexafluorobenzene + benzene, or + toluene, or + 1,4-dimethylbenzene systems have been investigated using thermodynamic properties from the literature and through the application of the DISQUAC and UNIFAC (Dortmund) models and the concentration-concentration structure factor ( S CC ( 0 ) ) formalism. DISQUAC interaction parameters for the contacts F/alkane and F/aromatic have been determined. UNIFAC interaction parameters available in the literature for these contacts have been used along calculations. Both models predict double azeotropy for the C6F6 + C6H6 system, although in different temperature ranges. The H m E values of the fluorobenzene, or 1,4-difluorobenzene + n-alkane systems are positive and are accurately described by the models using interaction parameters independent of the n-alkane. This means that no Patterson’s effect exists in such mixtures. DISQUAC calculations allow state that such conclusion is still valid for C6F6 + n-alkane mixtures. DISQUAC provides better results than UNIFAC on C pm E of solutions involving n-alkanes, or on H m E of C6F6 + aromatic hydrocarbon systems. Mixtures with alkanes are characterized by interactions between like molecules, which are mainly of dispersive type, which is supported, e.g, by the negative C pm E values of these systems. It is shown that structural effects can contribute largely to H m E . This is investigated in terms of the excess molar internal energy at constant volume, U V m E , whose values are determined for the investigated solutions. For mixtures with a given n-alkane, the relative variation of H m E and U V m E with the fluorohydrocarbons is different. H m E values change in the sequence C6F6 > 1,4-C6H4F2 > C6H6 > C6H5F, while U V m E changes in the order: 1,4-C6H4F2 > C6H6 ≈ C6H5F > C6F6 . C6F6 + aromatic hydrocarbon mixtures are characterized by interactions between unlike molecules as it is demonstrated by their negative H m E values. The application of the S CC ( 0 ) formalism reveals that homocoordination is more important in C6F6 + n-alkane mixtures than in the corresponding systems with C6H5F, and that heterocoordination is dominant in the solutions of C6F6 with an aromatic hydrocarbon.

Excess molar enthalpies, H m E , have been measured using a Tian-Calvet microcalorimeter for the systems CH3(CH2)u-1OH (u = 1,2,3,4,7,10) + cyclohexylamine at 298.15 K and 0.1 MPa. The H m E values are large and negative, indicating the existence of strong interactions between unlike molecules, which is consistent with the also large and negative excess molar volumes, V m E of these solutions, previously measured by us. The contribution from the equation of state term to H m E has been evaluated for the 1-alkanol + cyclohexylamine, or + 1-hexylamine, or + aniline mixtures, and the corresponding excess molar internal energies at constant volumes, U m, V E , determined. It is shown that such contribution is particularly important for the methanol + aniline system, in such way that the excess functions H m E and U m, V E have different sign at x1 = 0.5. The DISQUAC and ERAS models have been applied to the cyclohexylamine systems, and the interaction parameters reported. DISQUAC improves ERAS results on H m E . The latter model describes correctly the V m E curves. The variation of H m E of CH3(CH2)u-1OH + cyclohexylamine, or + 1-hexylamine, or + aniline mixtures with u along a homologous series with a given amine, or with the amine in mixtures with a given 1-alkanol is discussed in terms of the different interactional contributions to H m E .

Densities, ρ, speeds of sound, c, and refractive indices, nD, have been measured for the systems N,N-dimethylformamide (DMF) + propanone, +2-butanone, or +2-pentanone in the temperature range from (293.15 to 303.15) K and at T = 298.15 K for the DMF + 2-heptanone mixture. Due to the high volatility of acetone, the corresponding nD measurements were developed at T = (293.15 and 298.15) K. The direct experimental data were used to determine the excess molar volumes, V m E , and the excess refractive indices, n D E , at the working temperatures. Values of the excess functions at T = 298.15 K, for the speed of sound, cE, the isentropic compressibility, κ S E and for the excess thermal expansion coefficient, α p E , were also calculated. The investigated systems are characterised by strong (amide + ketone) interactions, which become weaker when the alkanone size is increased. This is supported by negative V m E values; by the dependence on temperature and pressure of V m E , and by positive P int E (excess internal pressure) values. Analysis of the systems in terms of the Rao’s constant indicates that there is no complex formation. In addition, negative V m E values also reveal the existence of structural effects, which largely contribute to the excess molar enthalpy, H m E . V m E and H m E values increase with the chain length of the 2-alkanone. It allows conclude that the relative V m E variation with the ketone size is closely related to that of the interactional contribution to this excess function. Molar refraction values, Rm, show that dispersive interactions become more relevant for the systems including longer 2-alkanones.

1-Alkanol + alkanonitrile systems have been studied by means of the DISQUAC, ERAS and UNIFAC (Dortmund) models. DISQUAC and ERAS parameters for the alkanol/nitrile interactions are reported. DISQUAC describes a whole set of thermodynamic properties: phase equilibria, vapor–liquid (VLE), liquid–liquid (LLE) and solid–liquid (SLE) equilibria, molar excess functions: Gibbs energies, G m E , enthalpies, H m E , and partial excess molar enthalpies at infinite dilution, H m i E , ∞ using the same set of interaction parameters for each solution. The dependence on the molecular structure of the interaction parameters is similar to that observed in other previous applications to mixtures formed by 1-alkanols and a strongly polar compound, in such way that the quasichemical interchange coefficients can be kept constant from 1-propanol. However, methanol and ethanol solutions behave differently. From the analysis of experimental data for H m E , T S m E ( = H m E − G m E ) , and molar excess volumes, V m E , it is concluded that the studied systems are characterized by dipolar interactions and strong structural effects. The former are more relevant in acetonitrile solutions. Association effects are more important in butanenitrile mixtures. DISQUAC gives better results than the ERAS model. ERAS results on H m E for systems containing acetonitrile are also improved by UNIFAC. This remarks the importance of dipolar interactions in the investigated mixtures. ERAS describes the variation of V m E (x1 = 0.5) with the 1-alkanol size for mixtures with a given nitrile, but the concentration dependence of this excess function is poorly represented.