Isabel M. S. Lampreia

Partial molar volumes of secondary amines in methanol. Specific interactions

Abstract Lampreia I.M.S. and Barbosa E.F.G., 1992. Partial molar volumes of secondary amines in methanol. Specific interactions. Fluid Phase Equilibria, 71: 125-142. Limiting partial molar volumes, − V ∞ B , at 25° C, for diethyl-, di- n -propyl-, di- n -butyl- and di- n -hexylamines in methanol were determined from density measurements using a vibrating tube densimeter. Contributions to − V ∞ B of the secondary amine group and of the interaction of the secondary amine group with methanol, calculated with linear hydrocarbons as reference compounds, have been derived and discussed by using an additive scheme and a hard sphere model respectively. Transference partial molar volumes from benzene to methanol have been calculated and split into various contributions including solvent effects such as the differences in size and in packing density as well as interaction terms. Complementary information about intermolecular interactions in these systems, and in the range of the dilute region studied were obtained by means of excess volumes calculated in terms of Henrys model.

Volumetric properties of 2-ethylaminoethanol in water from 283.15 to 303.15 K

Accurate density values, at ambient pressure, were obtained in aqueous binary mixtures of 2-ethylaminoethanol (EEA) over the whole composition range at intervals of 5 K in the temperature range between 283.15 and 303.15 K. To gain some insight into the several aggregation patterns present in these mixtures, calculation of excess molar volumes of the mixture, apparent molar and excess partial molar volumes of both components were made over the entire composition and temperature ranges. Thermal expansibility effects on this amphiphile/water mixture are analysed in terms of excess molar isobaric expansions EEP,m for the mixture and of excess apparent molar isobaric expansions EEP,φ,i for both chemical substances in the mixture. Limiting excess partial molar isobaric expansions have been calculated as well, from the temperature dependence of limiting excess partial molar volumes. An analytical method based on Redlich–Kister fitting equations for VEm as a function of the mole fraction, has been used to obtain VE,∞i. The excess properties are referred to a thermodynamically defined ideal liquid mixture. Interesting insights into the mixing process are gained from the visual impact of plots showing the composition and temperature dependence of different excess molar thermodynamic properties.

Conformational studies by Raman spectroscopy and statistical analysis of gauche interactions in n-butylamine

Abstract Raman spectra of n -butylamine recorded at different temperatures show pairs of bands whose temperature-dependent intensities clearly suggest their assignment to different conformers in simultaneous equilibria. Normal coordinate analysis and i.r. spectra of n -butylamine are also used to assign the spectra. These vibrational data are interpreted and correlated with structural information obtained from a statistical analysis of gauche skeletal arrangements in n -butylamine at different temperatures.

Isobaric expansions and isentropic compressions of aqueous binary mixtures of 2-diethylaminoethanol from 283 to 303 K

Densities and ultrasound speeds were determined in aqueous binary mixtures of 2-diethylaminoethanol over the whole composition range at intervals of 5 K in the temperature range between 283 and 303 K. Thermal expansibility effects on this amphiphile/water mixture are analysed in terms of excess molar isobaric expansions EEP,m for the mixture and of excess apparent molar isobaric expansions EEP,ϕ,i for both chemical substances in the mixture. Different strategies are used and discussed for obtaining limiting (infinite dilution) excess partial molar isobaric expansions. Compressibility effects are described in terms of excess molar isentropic compressions KES,m and excess partial molar isentropic compressions KES,i. The latter properties are analytically calculated from the fit of experimental KES,m data to a Redlich–Kister equation. A method based on this equation yields limiting excess partial molar isentropic compressions. Additionally, excess ultrasound speeds uE are also examined. All these excess properties are referred to a thermodynamically defined ideal liquid mixture. Interesting insights into the mixing process are gained from the visual impact of plots showing the composition and temperature dependence of different excess molar thermodynamic properties. Comparison of expansibility- and compressibility-related quantities shows that these two types of thermodynamic properties probe different aspects of intermolecular and packing effects on the process of mixing amphiphiles and water.

Volumetric properties of aqueous binary mixtures of 2-diethylaminoethanol from 283.15 to 303.15 K

We report volumetric properties of the binary mixture of 2-diethylaminoethanol (DEEA) with water. Density values were determined as a function of composition in the temperature range 283.15 to 303.15 K. For the DEEA at 298.15 K (molar volume, 133.2 cm3 mol−1) the measurements have given a limiting partial molar volume of 123.3 cm3 mol−1. To gain some insight into the several aggregation patterns present in the mixtures studied, calculation of excess molar volumes of the mixture, apparent molar volumes of DEEA, as well as excess partial molar volumes of both components were made over the entire composition and temperature ranges. As expected the whole set of results reveals strong deviations from ideality. The excess molar volumes exhibit negative deviations while apparent molar volumes of DEEA and excess partial molar volumes show a complex dependence on composition and temperature.

Chemical Thermodynamics of Ultrasound Speed in Solutions and Liquid Mixtures

A comprehensive formalism is developed to treat thermodynamically speed of ultrasound data for solutions and liquid mixtures. For solutions, the apparent speed of ultrasound of a solute is introduced and proposed to take the place of empirically defined quantities. The partial speed of ultrasound of a solute is defined and related to the partial molar volume and partial molar isentropic compression. For liquid mixtures, the concept of speed of sound before mixing pure liquids is presented and used to define the change in speed of ultrasound upon ideal mixing, which is predicted to be generally a negative quantity. A new thermodynamic equation is derived linking the values for excess speed of ultrasound, excess molar volume and excess molar isentropic compression of a mixture, and its applications are discussed. Ideal and excess apparent speeds of ultrasound, as well as ideal and excess partial speeds of ultrasound, are defined for substances making up a liquid mixture. Accurate speeds of ultrasound in 31 mixtures of water with the amphiphile 2-(ethylamino)ethanol at 293.15 K are reported. These data are used to demonstrate the ability of the apparent speed of ultrasound to describe the impact of solutes on sonic properties of solutions and the advantages of analysing thermodynamic properties of binary liquid mixtures in terms of the dependence on composition of Balankinas ratios between excess and ideal values. It is concluded that the new thermodynamic functions defined for speeds of ultrasound in solutions and liquid mixtures give, at the least, equivalent information on molecular aspects to the usual functions related to the isentropic compressibility, without needing density data for this purpose.

Ultrasonic velocities and isentropic compressions of triethylamine in water and in aqueous tetraethylammonium chloride solutions from 15 to 35°C

Abstract Ultrasonic velocities in ternary systems of triethylamine in water and in aqueous tetraethylammonium chloride solutions were measured from 15 to 35°C, for molalities in tetraethylammonium chloride from 0 up to 0.9 mol kg−1. The concentration of triethylamine was varied from 0 to ca. 0.35 mol kg−1 in pure water and in three concentration-fixed Et4NClaq solutions used as solvents. Isentropic compressibilities, κS, were calculated from ultrasonic velocity and density data and fitted to linear functions of molality. Excess molar isentropic compressions, KES,m, were estimated and their variations with the amine mole fraction were fitted to the Redlich-Kister equation. Negative values of KES,m were obtained for all the systems in the concentration and temperature ranges studied. Evaluation of triethylamine limiting partial molar isentropic compressions, K∞S,Et3N, were thus made for each system, using d K E S,m d x Et 3 N derivatives. Negative values of K∞S,Et3N were obtained on decreasing the absolute value either with temperature for the same salt concentration or with salt concentration for the same temperature. Apparent molar isentropic compressions of Et3N, KS,o,Et3N were also calculated and plotted against amine concentration. The interpretation of the results based on the changes in packing efficiency and on water structure, complies with and complements the conclusions deduced from limiting partial molar volumes and expansions concerning their variations with temperature and salt concentration.

Partial molar volumes of linear hydrocarbons in methanol in the very dilute region. Intermolecular interactions. H-bond effects

Limiting partial molar volumes VB∞ for the linear hydrocarbons, C5, C6 , C7, C8 and C10 in methanol were determined with a vibrating tube densimeter at 24.994°C (ITS-90). VB∞ and bV were discussed in terms of solute–solvent and solute–solute molecular interactions, focusing on H-bond cleavage, hydrocarbon short-range correlations of molecular orbitals and conformational effects. VB∞ (HS)/VB (HS) values calculated according to Lees hard-sphere mixtures model are compared with experimental values. A discussion is presented and deviations are interpreted in terms of size, shape, packing densities and H-bond effects.

Limiting partial molar volumes and expansions for triethylamine in water and in aqueous tetraethylammonium chloride solutions from 15 to 35 °C

The densities of ternary systems of triethylamine in aqueous tetraethylammonium chloride solutions have been measured, at 5 °C intervals from 15 to 35 °C, with a vibrating tube densimeter. The molalities in tetraethylammonium chloride studied were 0, 0.05, 0.4 and 0.9 mol kg −1 . The concentration of triethylamine was varied from 0 to ca. 0.35 mol kg −1 in each solvent. Negative excess molar volumes, V m E , were obtained for all the systems and their variations with the amine mole fraction were fitted to the Redlich–Kister equation. Limiting partial molar volumes and expansions of triethylamine, V Et3 N ∞ and E P,Et3 N ∞ , were evaluated using the derivatives dV m E /dx Et3 N and dV Et3 N ∞ /dT, respectively. Values of V Et3 N ∞ increase with temperature for all the solvents. Limiting excess partial molar volumes of triethylamine, V Et3 N E,∞ , are considerably negative and decrease with the salt concentration. This means a shift from ideality in the direction of a better packing efficiency of Et 3 N in the cage structure of the water and this effect increases as the concentration of the salt is increased. Values of E P,Et3 N ∞ are all positive and increase with the salt concentration. This may signify that the accommodation of Et 3 N in the water structure decreases with temperature. Molar expansions were also derived and plotted vs. the amine concentration.

Dipole moments of isomeric alkoxyalcohols in cyclohexane. Comparison of Hedestrand and Fröhlich procedures with a new formula

Limiting dipole moments of four isomeric alkoxyalcohols dissolved in cyclohexane at 298.15 K were determined from measurements of the relative permittivity of at least 17 dilute solutions up to solute mole fraction of 0.03. In addition, 5 to 7 data points were obtained up to a mole fraction of 0.1. A stepwise dilution device ensured dielectric measurements to be performed in highly dilute solutions with accurately determined concentrations. Densities of these solutions and refractive indices of the pure liquids were independently measured. Limiting dipole moments were calculated using Hedestrands equation and an improved method of implementing Fröhlichs equation, which circumvents extrapolation difficulties referred to in the literature. A new formula, based on the one-liquid approach for extending the Onsager-Kirkwood-Fröhlich equation to liquid mixtures, is introduced and shown to yield a reliable and robust procedure for estimating dipole moments of polar molecules dissolved in non-polar solvents. Limiting dipole moment values for 2-tert-butoxyethanol (2.31 D), 1-propoxypropan-2-ol (2.14 D), 2-butoxyethanol (2.14 D) and 2-isobutoxyethanol (2.08 D) are recommended. The relative order of these values appears to determine the order of hydrophilicity of these four alkoxyalcohols as suggested by their recently reported limiting partial molar volumes and isentropic compressions in aqueous solutions.