The ability of different models to predict speeds of sound, u, of binary mixtures formed by alkoxyethanol and octane, oxaalkane or propylamine has been examined. The models applied are: the free length theory (LFT), the collision factor theory (CFT), and equations such as those proposed by Nomoto, Junjie or Van Dael. Collision factor theory, Nomoto's and Junjie's equations provide similar deviations between experimental and calculated u, which is represented quite accurately by these three models. Poorer predictions are obtained when applying the Junjie's equation to propylamine systems, probably due to the existence of strong interactions between unlike molecules in such mixtures. In contrast, slightly better u predictions from CFT are obtained for the systems 2-methoxyethanol + polyether, or hydroxyether + propylamine. The good u predictions obtained using Nomoto's equation remark the validity of Rao's assumption on additivity of molar sound velocity contributions from atoms, atom groups and chemical bonds of the constituent molecules. Discrepancies between experimental and calculated u are larger when using FLT than those obtained from CFT, Nomoto's or Junjie's equations. This has been ascribed to association and size or shape effects. The linear dependence on the molar fractions of the component liquids of the Rao's and Wada's constants suggests that there is no complex formation in the investigated mixtures, and that the interactions present in such systems are of dipolar type.

The binodal curves of the liquid–liquid equilibria (LLE) for systems of o-toluidine with heptane, octane, nonane, decane or dodecane have been determined visually. All the curves show an upper critical solution temperature (UCST), which increases with the chain length of the alkane. The bimodal curves have a rather flat horizontal top and their symmetry depends on the chain length of the alkane. For the studied systems, interaction parameters in the framework of the DISQUAC model are reported. DISQUAC represents the coordinates of the critical points in the correct range of temperature and composition.

The physical meaning of the energetic parameter, chi(12), that is characteristic of Flory theory is explored in connection to the random mixing hypothesis. It is known that, if such a hypothesis is valid, chi(12) is independent of the concentration (x(1)). Here, deviations from the random mixing hypothesis are attributed to an excess of interactions between like molecules (if chi(12)(x(1)) > chi(12)(x(1) = 0.5)) or of interactions between unlike molecules (if chi(12)(x(1)) < chi(12)(x(1) = 0.5)). Binary mixtures of the type hydroxyether + dibutyl ether, or + 1-alkanol, or + 2-methoxyethanol have been investigated studying the chi(12) variation with x(1). Toward this end, we provide a new expression for chi(12) which makes possible the exact determination of this magnitude at any composition if the corresponding molar excess enthalpy, H-mE, is known. Orientational effects are present in the studied solutions, although the model can represent the H-m(E) for hydroxyether + 1-alkanol or + 2-methoxyethanol, where the mentioned effects are weaker. The excess molar volumes, V-m(E), are only described for the systems with two cellosolves, due to the existence in the remainder mixtures of structural effects. Results from the Kirkwood-Buff formalism, applied to 2-ethoxyethanol + dibutyl ether, or + 1-butanol, systems are in agreement with those obtained using Flory theory.

The coexistence curves of the liquid-liquid equilibria (LLE) for systems of dimethylformamide (DMF) with hexane, heptane. octane, or nonane and of dimethylacetamide (DMA) with heptane have been determined visually. All the curves show an upper critical solution temperature (UCST) and have a rather horizontal top. The measured LLE curves for DMF mixtures show that their symmetry depends on the size of the alkane. For a given alkane, the UCST is higher for systems with DMF. This reveals that dipole-dipole interactions between amide molecules are stronger in such solutions. The DISQUAC model represents fairly well the LLE curves.

Alkoxyethanol+linear monoether, or +1-alkanol mixtures have been investigated in terms of the DISQUAC and ERAS models and using the so-called concentration–concentration structure factor, SCC(0). DISQUAC and ERAS interaction parameters are reported. DISQUAC describes consistently a whole set of thermodynamic properties: vapor–liquid equilibria, VLE, molar excess functions as Gibbs energy, GE, enthalpy, HE, or heat capacity at constant pressure, CPE and SCC(0). In the framework of DISQUAC, the intramolecular H-bonds between the O and OH of the cellosolve are independent, except for short chain ethers, of the molecular environment (linear ether, or 1-alcohol). ERAS describes systems with dibutylether by means of a large physical contribution to the excess thermodynamic properties. The model overestimates the self-association of the lower 1-alkanols in their mixtures with 2-alkoxyethanols, which leads to a poor representation of the properties of such systems. Mixtures with dibutylether are characterized by homocoordination with interactions which can be assumed to be of dipolar type. In systems with 1-alkanols, interactions between like and unlike molecules and structural effects are compensated, and SCC(0) is nearly ideal.

Mixtures formed by linear alkanoates and CHCl3 or 1,1,2,2-tetrachloroethane, which show strongly negative deviations from the Raoult's law, have been studied in the framework of the dispersive-quasichemical (DISQUAC) model. Systems involving CH2Cl2; CCl4, Cl3C-CH3 or ClCH=CH2Cl have also been briefly considered in order to carry out a more complete study. The corresponding interaction parameters are reported. As in other previous applications, the first (Gibbs energy) and third (heat capacity) quasichemical interaction parameters do not depend on the mixture components. DISQUAC represents fairly well vapor-liquid equilibria, VLE, and molar excess enthalpies, H-E, of the systems considered. VLE of the methyl ethanoate+CHCl3+benzene mixture is also well described by the model neglecting ternary interactions. UNIFAC (universal functional activity coefficient) fails when representing HE of systems containing very long alkanoates. The mixture structure is investigated using the concentration-concentration structure factor, S-CC(0). Heterocoordination is prevalent even at very high temperatures.

Binary mixtures of aniline with benzene, toluene, alkane, alkanol, or N,N-dialkylamide have been investigated in the framework of the DISQUAC model. The reported interaction parameters change regularly with the molecular structure of the mixture components. The model consistently describes a set of thermodynamic properties including liquid-liquid equilibria, vapor-liquid equilibria, and molar excess enthalpies. The two latter properties for ternary systems are well-represented by DISQUAC using binary parameters only (i.e., neglecting ternary interactions). A comparison of DISQUAC results and those obtained from the UNIFAC (Dortmund version) and ERAS models is also shown. The experimental molar excess enthalpies for binary and ternary mixtures are better described by DISQUAC than by UNIFAC. ERAS fails when representing molar excess enthalpies of those binary systems including methanol or ethanol. This may be due to the existence of strong dipolar interactions among aniline molecules as well as to effects related to the equation of state term, evaluated comparing molar excess enthalpies, and molar excess internal energies at constant volume. The study of the aniline systems in terms of the concentration-concentration structure factor also underlines the importance of dipolar interactions in solutions with alkanes or alcohols, which may be due to the high polarizability of the aniline molecule.

Liquid-liquid equilibria temperatures for systems of 2,5,8,11-tetraoxadodecane with decane and tetradecane and of 2,5,8,11,14-pentaoxapentadecane with heptane, octane, and tetradecane have been measured between 264.85 K and the upper critical solution temperature (UCST). The coexistence curves were determined visually. They have a rather horizontal top, and their symmetry depends on the size of the alkane. For a given alkane, the UCST is higher for mixtures containing the pentaether. This reveals that dipole-dipole interactions between oxaalkane molecules are stronger in such solutions.

DISQUAC predictions on molar excess enthalpies, H-E, are shown for a set of 67 ternary mixtures formed by one alcohol, one active compound (not self-associated), and one hydrocarbon; two alkanols and one hydrocarbon; two alkanols and one polar compound; or three alkanols. DISQUAC provides reliable predictions on HI (approximate to8%) for the ternary mixtures considered using binary interaction parameters only, i.e., neglecting ternary interactions. Differences between experimental results and theoretical calculations are of the same order for the ternary mixtures and for the constituent binaries. On the other hand, predictions are practically independent of the mixture compounds or of the number of contacts present in the solution. The poorer results are obtained for systems with a binary that shows strongly negative deviations from Raoult's law. A systematic comparison between DISQUAC results and those from the Dortmund UNIFAC model is presented. DISQUAC improves UNIFAC predictions, as well as those from ERAS for 1-alkanol + oxaalkane + alkane mixtures. More complex association models yield results that are similar to those from DISQUAC. Therefore, DISQUAC should. be applied when the interaction parameters used are available. The interaction parameters used are valid for the description of the thermodynamic properties of binary mixtures (vapor-liquid, solid-liquid, and liquid-liquid equilibria, H-E, and the molar excess heat capacity at constant pressure, C-p(E)) as well as for predictions on vapor-liquid equilibria, H-E, and C-p(E) for ternary mixtures.