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

Thermodynamics of mixtures with strongly negative deviations from Raoult's law. XV. Permittivities and refractive indices for 1-alkanol + n -hexylamine systems at (293.15–303.15) K. Application of the Kirkwood-Fröhlich model

Relative permittivities at 1 MHz, ε_r, and refractive indices at the sodium D-line, n_D, are reported at 0.1 MPa and at (293.15-303.15) K for the binary systems 1-alkanol + n-hexylamine (HxA). Also, their corresponding excess functions are calculated and correlated. Positive values of the excess permittivities, ε_r^E, are encountered for the methanol system, whereas the remaining mixtures show negative values. This reveals that interactions between unlike molecules contribute positively to ε_r^E. This contribution is dominant for the methanol mixture, while those arising from the breaking of interactions between like molecules are prevalent for the remaining mixtures. At ϕ_1(volume fraction) = 0.5, ε_r^E changes in the order: methanol > 1-propanol > 1-butanol > 1-pentanol < 1-heptanol. Similar variation with the chain length of the 1-alkanol is observed for mixtures such as 1-alkanol + heptane, or + cyclohexylamine, and can be explained in terms of the lower and weaker self-association of longer 1-alkanols. The effect of the replacement of HxA by cyclohexylamine, or by aniline, is also shown. Calculations on molar refractions indicate that dispersive interactions in the systems under study increase with the length of the 1-alkanol. The mixtures are studied by means of the application of the Kirkwood-Fröhlich model, and the Kirkwood correlation factors, including the corresponding excess values, are reported.Junta de Castilla y León Regional Grant BU034U16Ministerio de Educación, Cultura y Deporte (MECD): Grant FPU14/04104Ministerio de Educación, Cultura y Deporte (MECD): Grant FPU15/0545

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, rho, speed of sound, c, and refractive index, nD, have been reported at (293–303.15) K for the N,Ndimethylacetamide (DMA) + CH3CO(CH2)_(u – 1)CH3 (u = 1, 2, 3) systems, and at 298.15 K for the mixture with u=5. These data have been used to compute excessmolar volumes, VmE, excess adiabatic compressibilities, kSE, 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 to HmE 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 Regional Grant BU034U16Ministerio de Educación, Cultura y Deporte (MECD): Grant FPU14/04104Ministerio de Educación, Cultura y Deporte (MECD): Grant FPU15/0545

Thermodynamics of amide+ketone mixtures. 1. Volumetric, speed of sound and refractive index data for N,N-dimethylformamide+2-alkanone systems at several temperatures

Densities,ρ, speeds of sound, c, and refractive indices, n_D, 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 298.15 K for the DMF + 2-heptanone mixture. Due to the high volatility of acetone, the corresponding n_D measurements were developed at 293.15 K 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 298.15 K, for the speed of sound,c^E, the isentropic compressibility, κ_S^Eand for the excess thermal expansion coefficient, α_p^E, were also calculated. The investigated systems are characterized 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 positiveP_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, R_m, show that dispersive interactions become more relevant for the systems including longer 2-alkanones

Thermodynamics of mixtures containing a very strongly polar compound. 11. 1-Alkanol+alkanenitrile systems

1-Alkanol + alkanenitrile 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, vapour-liquid (VLE), liquid-liquid (LLE) and solid-liquid (SLE) equilibria, molar excess functions, Gibbs energies,G_m^E, and enthalpies, H_m^E, and partial excess molar enthalpies at infinite dilution, H_mi^(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, TS_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 improvesH_m^Eresults from the ERAS model. ERAS results onH_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(x_1=0.5) with the 1-alkanol size for mixtures with a given nitrile, but the concentration dependence of this excess function is poorly represented

Orientational effects in mixtures of organic carbonates with alkanes or 1-alkanols

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_pm^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.Junta de Castilla y León Regional Grant BU034U16Ministerio de Educación, Cultura y Deporte (MECD): Grant FPU14/0410

Liquid–Liquid Equilibria for Systems Containing 4-Phenylbutan-2-one or Benzyl Ethanoate and Selected Alkanes

The method of the critical opalescence with a laser scattering technique has been employed for the determination of the liquid-liquid equilibrium (LLE) curves for the systems 4-phenylbutan-2-one + CH3(CH2)nCH3 (n = 10,12,14) and for benzyl ethanoate + CH3(CH2)nCH3 (n = 12,14). The mixtures are characterized by having an upper critical solution temperature (UCST), which increases with n. The corresponding LLE curves have a rather horizontal top and become shifted to higher concentration of the polar compound when n is increased. Calorimetric data and LLE measurements show that the aromaticity effect leads to stronger interactions between molecules of the polar compound considered with respect to those between homomorphic linear molecules with the same functional group. This has been ascribed to proximity effects arising from the presence of the polar group and the aromatic ring within the same molecule. Proximity effects become weaker in the sequence: 1-phenylpropan-2-one > 4-phenylbutan-2-one > 1-phenylethanone, and are more relevant in benzyl ethanoate than in ethyl benzoate molecules. The DISQUAC group contribution model represents correctly the coordinates of the critical points of the investigated systems and the symmetry of the LLE curves.Ministerio de Educación, Cultura y Deporte (MECD): Grant FPU14/0410

Orientational Effects and Random Mixing in 1-Alkanol + Alkanone Mixtures

1-Alkanol + alkanone systems have been investigated through the data analysis of molar excess functions, enthalpies, isobaric heat capacities, volumes and entropies, and using the Flory model and the formalism of the concentrationconcentration structure factor (SCC(0)). The enthalpy of the hydroxyl-carbonyl interactions has been evaluated. These interactions are stronger in mixtures with shorter alcohols (methanol-1-butanol) and 2-propanone or 2-butanone. However, effects related to the self-association of alcohols and to solvation between unlike molecules are of minor importance when compared with those which arise from dipolar interactions. Physical interactions are more relevant in mixtures with longer 1-alkanols. The studied systems are characterized by large structural effects. The variation of the molar excess enthalpy with the alcohol size along systems with a given ketone or with the alkanone size in solutions with a given alcohol are discussed in terms of the different contributions to this excess function. Mixtures with methanol show rather large orientational effects. The random mixing hypothesis is attained to a large extent for mixtures with 1-alkanols ≠ methanol and 2-alkanones. Steric effects and cyclization lead to stronger orientational effects in mixtures with 3-pentanone, 4-heptanone, or cyclohexanone. The increase of temperature weakens orientational effects. Results from SCC(0) calculations show that homocoordination is predominant and support conclusions obtained from the Flory model.Ministerio de Ciencia e Innovación, under Project FIS2010-1695