Thermodynamics of amide + ketone mixtures. 2. Volumetric, speed of sound and refractive index data for N,N-dimethylacetamide + 2-alkanone systems at several temperatures. Application of Flory's model to tertiary amide + n-alkanone systems

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 BU034U1

Orientational effects in alkanone, alkanal or dialkyl carbonate + alkane mixtures and in alkanone + alkanone or + dialkyl carbonate systems

Interactions and structure of alkanone, or alkanal or dialkyl carbonate + alkane mixtures, or of 2-alkanone + 2-alkanone, or of ketone + dialkyl carbonate systems have been investigated by means of a set of thermodynamic properties and by the application of the Flory model. The properties considered are excess molar quantities: enthalpies, HmE, volumes, VmE, or isobaric heat capacities, CpmE, and liquid-liquid equilibria. Experimental data show that alkane mixtures are characterized by rather strong dipolar interactions. In the case of systems containing ketones with the same number of C atoms and a given alkane, dipolar interactions become weaker in the sequence: aromatic > cyclic > linear. In addition, the mentioned interactions become also weaker in the order: dialkyl carbonate > linear alkanone > linear alkanal. This is an important result, as carbonates show lower effective dipole moments than the other compounds, and it suggests that the group size may be relevant when evaluating thermodynamic properties of liquid mixtures. Results on HmE from the Flory model show that orientational effects (i.e., non-random mixing) are rather similar for systems with linear, cyclic or aromatic ketones or alkanals and alkanes. In contrast, orientational effects become weaker in dialkyl carbonate + alkane mixtures. The behavior of 2-alkanone + 2-alkanone systems and of mixtures of longer 2-alkanones or cyclohexanone with dialkyl carbonate is close to random mixing. Larger orientational effects are encountered in solutions of carbonates and shorter 2-alkanones.Consejería de Educación y Cultura of Junta de Castilla y León, under Project BU034U16

Thermodynamics of mixtures containing a very strongly polar compound. 12. Systems with nitrobenzene or 1-nitroalkane and hydrocarbons or 1-alkanols

Mixtures involving nitrobenzene and hydrocarbons, or 1-alkanols and 1-nitroalkane, or nitrobenzene have been investigated on the basis of a whole set of thermophysical properties available in the literature. The properties considered are: excess molar functions (enthalpies, entropies, isobaric heat capacities, and volumes), vapour-liquid and liquid-liquid equilibria, permittivities or dynamic viscosities. In addition, the mixtures have been studied by means of the application of the DISQUAC, ERAS, and UNIFAC models, and using the formalism of the concentration-concentration structure factor. The corresponding interaction parameters in the framework of the DISQUAC and ERAS models are reported. In alkane mixtures, dipolar interactions between 1-nitroalkane molecules are weakened when the size of the polar compound increases, accordingly with the relative variation of their effective dipolar moment. Dipolar interactions are stronger in nitrobenzene solutions than in those containing the smaller 1-nitropropane, although both nitroalkanes have very similar effective dipole moment (aromaticity effect). Systems with 1-alkanols are characterized by dipolar interactions between like molecules which sharply increases when the alkanol size increases. Simultaneously, interactions between unlike molecules become weaker, as the OH group is then more sterically hindered. Interactions between unlike molecules are stronger in systems with nitromethane than in nitrobenzene solutions. The replacement of nitromethane by nitroethane in systems with a given 1-alkanol leads to strengthen those effects related with the alcohol self-association. Permittivity data and results on Kirkwood's correlation factors show that the addition of 1-alkanol to a nitroalkane leads to cooperative effects, which increase the dipolar polarization of the solution, in such way that the destruction of the existing structure in pure liquids is partially counterbalanced. This effect is less important when longer 1-alkanols are involved.Consejería de Educacion y Cultura of Junta deCastilla y Leon, under Project BU034U1

Thermodynamics of mixtures containing aromatic nitriles

The coexistence curves of liquid-liquid equilibrium (LLE) for the mixtures: phenylacetonitrile + heptane, + octane, + nonane, + cyclooctane, or + 2,2,4-trimethylpentane and for 3-phenylpropionitrile + heptane, or + octane are reported. Aromatic nitrile + alkane, + aromatic hydrocarbon or + 1 alkanol systems are investigated using a set of thermophysical properties: phase equilibria (solid-liquid, SLE, vapour-liquid, VLE and LLE), excess molar functions, enthalpies (), isochoric internal energies (), isobaric heat capacities () and volumes (), and the Kirkwood’s correlation factor. Due to proximity effects between the phenyl and the CN groups, dipolar interactions between molecules of aromatic nitriles are stronger than those between molecules of isomeric linear nitriles. Dipolar interactions become weaker in the order: 3-phenylpropionitrile > phenylacetonitrile > benzonitrile. Benzonitrile + aromatic hydrocarbon mixtures are characterized by dispersive interactions and structural effects. The latter are more important in systems with phenylacetonitrile. Structural effects are also present in benzonitrile + n-alkane, or + 1-alkanol + mixtures. The systems mentioned above have been studied using DISQUAC. Interaction parameters for contacts where the CN group in aromatic nitriles participates are given. DISQUAC describes correctly any type of phase equilibria, of benzonitrile + hydrocarbon mixtures and of benzonitrile + cyclohexane, or 1-alkanol systems. Large differences encountered between theoretical values and experimental data for some solutions are discussed. 1-Alkanol + benzonitrile mixtures are also investigated by means of the ERAS model. ERAS represents well of these systems. The curves of solutions with longer 1-alkanols are more poorly described, which has been explained in terms of the existence of structural effects.Consejería de Educación y Cultura of Junta de Castilla y León, under Project BU034U1

Liquid−Liquid Equilibria for 2‑Phenylethan-1-ol + Alkane Systems

The liquid–liquid equilibrium (LLE) curves for 2-phenylethan-1-ol (2-phenylethanol, 2PhEtOH) + octane, + decane, + dodecane, + tetradecane or + 2,2,4-trimethylpentane have been determined by a method of turbidimetry using a laser scattering technique. Experimental results reveal that the systems are characterized by an upper critical solution temperature (UCST), which increases linearly with the number of C atoms of the n-alkane. In addition, the LLE curves have a rather horizontal top and become skewed to higher mole fractions of the n-alkane, when its size increases. For a given n-alkane, UCST decreases as follows: phenol > phenylmethanol > 2-PhEtOH, indicating that dipolar interactions decrease in the same sequence. This has been ascribed to a weakening in the same order of the proximity effects between the phenyl and OH groups of the aromatic alkanols. DISQUAC interaction parameters for OH/aliphatic and OH/aromatic contacts in the investigated systems are reported. Phenol, or phenylmethanol or 2-PhEtOH, + n-alkane mixtures only differ by the first dispersive Gibbs energy interaction parameter for the (OH/aliphatic) contactJunta de Castilla y León, under Project BU034U16 F

Liquid-liquid equilibria for the systems 2-ethoxy-benzenamine + CH3(CH2) CH3 (n = 6,8,10,12) and 4-ethoxy-benzenamine + CH3(CH2) CH3 (n = 5,6)

Liquid-liquid equilibria (LLE) phase diagrams have been determined for the systems: 2-ethoxy-benzenamine + octane, or +decane, or +dodecane, or +tetradecane and for 4-ethoxy-benzenamine + heptane, or +octane. The experimental method used is based on the observation, by mean of a laser scattering technique, of the turbidity produced on cooling when a second phase takes place. All the mixtures show an upper critical solution temperature, which increases with the alkane size. Dipolar interactions between like molecules become stronger in the sequence: 2-ethoxy-benzenamine < aniline < 4-ethoxy-benzenamine. Data available in the literature suggest that this relative variation is also valid for alkane mixtures containing other substituted anilines or phenols, characterized by having a second polar group. The dependence of the UCST values with the molecular structure of the polar aromatic compound involved is shortly discussed in terms of intramolecular and steric effects

Thermodynamics of Mixtures Containing Aromatic Alcohols. 1. Liquid–Liquid Equilibria for (Phenylmethanol + Alkane) Systems

The liquid−liquid equilibrium (LLE) curves for (phenylmethanol + CH3(CH2)nCH3) mixtures (n = 5, 6, 8, 10, 12) have been obtained by the critical opalescence method using a laser scattering technique. All of the systems show an upper critical solution temperature (UCST). In addition, the LLE curves have a rather horizontal top, and their symmetry depends on the alkane size. The UCST increases almost linearly with n. For systems including a given alkane and phenol or phenylmethanol, the UCST is much higher than that of the corresponding mixtures with hexan-1-ol or heptan-1-ol. This reveals that dipolar interactions are stronger in solutions with aromatic alcohols. Preliminary DISQUAC interaction parameters for OH/aliphatic contacts in the investigated systems were obtained. It is remarkable that the coordinates of the critical points of (phenol or phenylmethanol + alkane) mixtures can be described using the same quasichemical interaction parameters for the OH/aliphatic and OH/ aromatic contacts.Ministerio de Educación y Ciencia, under Project FIS2007-61833

Thermodynamics of Mixtures Containing a Very Strongly Polar Compound. 10. Liquid–Liquid Equilibria for N,N-Dimethylacetamide + Selected Alkanes

Liquid−liquid equilibrium (LLE) temperatures versus composition for N,Ndimethylacetamide (DMA) + decane, + dodecane, + tetradecane, + 2,2,4-trimethylpentane, + methylcyclohexane, or + cyclooctane mixtures have been measured by means of the critical opalescence method using a laser scattering technique. All the systems show an upper critical solution temperature (UCST). In the case of n-alkane mixtures, UCST increases almost linearly with the chain length of the n-alkane. Moreover, these solutions show higher UCST values than those with isomeric cyclic alkanes. Branching leads to a strong decrease of UCST. The symmetry of the LLE curves depends on the size and shape of the alkane. DISQUAC correctly represents the coordinates of the critical points using interaction parameters available in the literature.Ministerio de Ciencia e Innovación, under the Project FIS2010-1695

Determinación experimental del equilibrio líquido-liquido de mezclas binarias fenilacetona + alcano

La fenilacetona es un precursor de la anfetamina y metanfetamina, potentes estimulantes del sistema nervioso central y utilizadas como drogas de “diseño”. Además, la fenilacetona es el producto de la desaminación de la anfetamina en el cuerpo humano. Por otra parte, el estudio de mezclas que contienen un compuesto aromático con un grupo funcional polar permite investigar una serie de efectos tales como interacciones intramoleculares entre el anillo bencénico y un grupo funcional polar (interacciones n- π). En este trabajo se han determinado las curvas de los equilibrios líquido-líquido de mezclas binarias formadas por fenilacetona + CH3(CH2)uCH3 (u = 8,12,14) mediante el método de la opalescencia crítica utilizando un sistema de dispersión de luz láser durante la transición. Todos los sistemas muestran una temperatura de solución crítica superior (UCST), que aumenta casi linealmente con la longitud del n-alcano, u

Determinación experimental del equilibrio sólido líquido mediante DSC

Aunque las aplicaciones más importantes del estudio del equilibrio sólido-líquido están en el campo de la metalurgia y la mineralogía, la información que puede aportar este estudio resulta también de gran aplicabilidad en el área de la fabricación de alimentos y productos farmacéuticos, cosmética y el almacenamiento energético con los materiales de cambio de fase (PCM’s). Sin embargo, tal vez es de los procesos de cambio de fase, el que ha suscitado menos atención. Convencionalmente, los datos de equilibrio sólido-líquido se han determinado mediante técnicas de enfriamiento estático, procedimientos largos y muy laboriosos si se pretenden obtener diagramas precisos. Alternativas más actuales son las técnicas de análisis térmico diferencial (DTA) y la calorimetría diferencial de barrido (DSC), que reducen considerablemente el tiempo de experimentación y aumentan la precisión de las medidas[1]. En este trabajo se describe la puesta a punto de un sistema DSC para la determinación del equilibrio sólido-líquido de sistemas binarios. Para determinar la bondad del equipo se utiliza como sistema test el sistema ciclohexano-benceno[2], sistema del que, además del diagrama de fases, se determina la composición del eutéctico. Validada la técnica experimental, se procede al estudio del equilibrio sólido-líquido de sistemas binarios formados por ciclohexilamina + alcanos