Search

Excess molar volumes, VE, of binary mixtures of dibromomethane (DBM) with n-hexane, n-heptane, n-octane, cyclohexane, tetrachloromethane, dipropyl and dibutyl ether, tetrahydrofuran, and 3-pentanone are determined at 298.15 K in the whole composition range by means of a vibrating tube densimeter. For the same DBM mixtures plus with n-pentane and except with dipropyl ether and 3-pentanone, partial molar enthalpies, Hi, and excess molar enthalpies, HE, are obtained through a heat flow calorimeter and a titration method purposely devised. Both excess properties are positive for cyclohexane, tetrachloromethane, and n-alkanes, the latter exhibiting an increase with increasing number of carbon atoms. Dipropyl and dibutyl ether mixtures exhibit negative VE values, while n-hexane, tetrahydrofuran, and 3-pentanone mixtures show an S-shaped VE curve. Negative HEs are observed only for tetrahydrofuran, whereas dibutyl ether exhibits an S-shaped HE curve. HE results are compared with the predictions of the DISQUAC model. The partial molar volumes at infinite dilution, V°, as well as the enthalpies of solvation, ΔsolvH°, of the examined substances in DBM are evaluated and discussed also considering data on other compounds found in the literature. For V° and ΔsolvH°, a group additivity scheme is proposed to enable the estimation of these properties for other molecules and how much structural peculiarities such as chain length, polarity of groups, and cyclic structures influence their values.

Isothermal vapor–liquid equilibria at 298.15 K for dibromomethane + an organic compound (C5–C8 n-alkanes, cyclohexane, tetrachloromethane, diethyl ether, dipropyl ether, dibutyl ether, tetrahydrofuran, and 3-pentanone) were determined by head-space gas chromatographic analysis of the vapor phase. Excess molar Gibbs energies, GE, and activity coefficients for the investigated systems were obtained by a least-square treatment of equilibrium data. All systems except mixtures with tetrahydrofuran and 3-pentanone revealed positive deviations from ideality. The Gibbs energies of solvation, ΔsolvG°, for the examined substances in dibromomethane were evaluated and compared with those in dichlorometane. The effect of polar groups, chain lengthening, and cyclization upon ΔsolvG° was discussed.

The vapor pressures p of 28 organic compounds were accurately measured by a static method in the temperatures range (273 to 323) K. These include cyclic amines (CH2)nNH with n = 2–7, N-methylpyrrolidine, N-methylpiperidine, morpholine, N-methylmorpholine, piperazine, N-methylpiperazine, N,N′-dimethylpiperazine), cyclic ethers (tetrahydrofuran, 2-methyltetrahydrofuran, 2,5-dimethyltetrahydrofuran, tetrahydropyran, 1,3-dioxolan, 1,4-dioxan), cyclic and open-chain secondary alcohols (cyclopentanol, cyclohexanol, cycloheptanol, 2-butanol, 3-pentanol, 3-hexanol, 4-heptanol), as well as 2-methoxyethylamine and 3-methoxypropylamine. For six substances, no p data were already available in the literature at any temperature, and for another eight only one paper each was found. The parameters of the Antoine equation were determined to allow interpolation and extrapolation of the experimental results. The enthalpy of vaporization, ΔvapH, at 298.15 was obtained for each compound from the derivative dp/dT. For nine com...

Data on the solubility of neutral compounds in perfluoro-hexane, -heptane, and –octane have been obtained from the literature. It is shown that water-solvent and gas-solvent partition coefficients, P and K respectively, are effectively the same for all three perfluoroalkanes. Linear free energy relationships, LFERs, have been set up for these partition coefficients, as log P and log K. Comparison of the LFER coefficients in the log K equation for perfluoroheptane with those for a large number of other solvents shows that perfluoroheptane is an unusual solvent, in that small nonpolar solutes are more soluble than in other solvents. The comparative solubility of small nonpolar gaseous compounds in perfluoroheptane is due to a combination of cavity and interaction terms. Calculations using Pierotti's version of Scaled Particle Theory indicates that the solute-perfluoroheptane unfavourable cavity term is always smaller than that for solution in other solvents, which by itself would lead to enhanced solubilities in perfluoroheptane, as shown by small nonpolar solutes. As the solute becomes larger and more polar, the favourable interaction terms in other organic solvents become much larger than the corresponding interaction terms in perfluoroheptane. This results in the larger and/or more polar gaseous solutes being much more soluble in other organic solvents than in perfluoroheptane.

Vapor–liquid equilibria at 298.15 K have been determined for binary mixtures of tetrachloromethane or heptane plus a cyclic hydrocarbon (cyclopentane, cyclohexane, cycloheptane, cyclooctane, cyclodecane, cis-decalin, norbornane, octahydro-4,7-methano-1H-indene, adamantane), using a head-space gas chromatographic technique. Excess molar Gibbs energies and activity coefficients for the systems investigated have been obtained by a least-squares treatment of the equilibrium results. All mixtures exhibit positive deviations from ideality, increasing with the cycloalkane size. The Gibbs energies of solvation, Δsolv G°, for cyclic hydrocarbons in the two solvents have been evaluated and compared with those of linear and branched alkanes. The effect of cyclization upon Δsolv G° has been discussed.

Excess molar volumes V (E) for 40 mixtures of heptane with a liquid alkane and apparent molar volumes in heptane for eight solid alkanes have been obtained at 298.15 K. They include five linear, 30 branched-chain, and 13 cyclic alkanes. Almost all systems exhibit negative V (E) values. For mixtures with open chain alkanes, V (E) increases from C5 to C7 and then decreases. A similar trend is shown by mixtures with cycloalkanes. V (E) values are compared with known H (E) data for mixtures with heptane and tetrachloromethane. Signs and trends of V (E) and H (E) are correlated with the free volume and interactional terms of the Flory theory. The partial molar volumes at infinite dilution in heptane, VA degrees, have also been obtained and discussed together with literature data on other hydrocarbons and polar compounds. The calculated contributions to VA degrees by CH3, CH2, CH and C groups are compared with previously determined contributions of polar groups. The lower contributions of the latter groups are explained with the volume contraction caused by dipole-induced dipole interaction. The volume effects associated with branching and cyclization have been evaluated and compared with the corresponding effects on solvation enthalpy. The branching effect, in the order of magnitude of few cm(3)center dot mol(-1), and the larger negative values of cyclization volumes, down to -24 cm(3)center dot mol(-1), are discussed in terms of packing and solute-solvent interactions, in analogy to polar organic solutes either in heptane and tetrachloromethane. A negative cyclization effect is also exhibited by the solvation enthalpies.

Excess molar volumes VE and partial molar enthalpies and excess enthalpies HE of binary mixtures of heptane + linear (hexamethyldisiloxane, octamethyltrisiloxane, decamethyltetrasiloxane, dodecamet...

Excess molar volumes VE at 298.15 K were determined by means of a vibrating tube densimeter for binary mixtures of {heptane + open chain secondary (diethyl to dibutyl) and tertiary (triethyl to tripentyl) amines} as well as for cyclic imines (C2, C3, C4, C6, and C7) and primary cycloalkylamines (C5, C6, C7, and C12). The VE values were found positive for mixtures involving small size amines, with VE decreasing as the size increases. Negative VE’s were found for tributyl- and tripentylamine, heptamethylenimine, and cyclododecylamine. Mixtures of heptane with cycloheptylamine showed an s-shaped curve. Partial molar volumes V ∘ of amines at infinite dilution in heptane were obtained from VE and compared with V ∘ of hydrocarbons and other classes of organic compounds taken from literature. An additivity scheme, based on the intrinsic volume approach, was applied to estimate group (CH3, CH2, CH, C, NH2, NH, N, OH, O, CO, and COO) contributions to V ∘ . These contributions, the effect of cyclization on V ∘ , and the limiting slope of the apparent excess molar volumes were discussed in terms of solute–solvent and solute–solute interactions.

Partial molar enthalpies and excess enthalpies HE of binary mixtures of heptane + secondary and tertiary n-alkyl, primary cycloalkyl, and secondary (hetero)cyclic amines have been determined at 298.15 K by isothermal titration calorimetry in the whole composition range. All mixtures showed positive HE values which decrease with increasing amine size in each category, and decrease in the order cyclic primary > cyclic secondary > linear primary [1] > secondary > tertiary when comparing amines of similar size in different categories. From partial molar enthalpies at infinite dilution and known enthalpies of vaporization, the solvation enthalpies have been calculated either for heptane in amines and for amines in heptane. These quantities, together with their cavitational and interactional terms obtained applying the scaled particle theory, are discussed to get insight into the types and relative strength of solute–solvent interactions and into their effects on molecular structure features such as branching and cyclization.

Excess molar volumes VE at 298.15 K were determined by means of a vibrating tube densimeter for binary mixtures of heptane + primary n-alkyl (C3 to C10) and branched amines (iso-propyl-, iso-, sec-, and tert-butyl-, iso-, tert-pentyl-, and pentan-3-amine) in the whole composition range. The apparent molar volumes of solid dodecyl- and tetradecylamine in heptane dilute solution were also determined. The VE values were found positive for mixtures involving C3 to C8 linear amines, with VE decreasing with chain lengthening. Heptane + nonyl and decylamine showed s-shaped, markedly asymmetric, curves. Mixtures with branched C3 to C5 amines displayed positive VE’s larger than those observed in the mixtures of the corresponding linear isomers. Partial molar volumes V° at infinite dilution in heptane were evaluated for the examined amines and compared with those of alkanes and alkanols taken from the literature. An additivity scheme, based on the intrinsic volume approach, was applied to estimate group (CH3, CH2, CH, C, NH2, and OH) contributions to V°. The effect of branching on V° and the limiting slope of the apparent excess molar volumes were evaluated and discussed in terms of solute–solvent and solute–solute interactions.

There are little data in the literature on how to authenticate edible oils through calorimetry techniques. However, oil melting curves can be used to represent correlations between calorimetric results and oil quality. A calorimetric method has been developed for studying the solid–liquid phase transitions of olive oil and seed oils, in which melting peak behavior is correlated to the type, quality, and composition of the oil. Good reproducible thermograms were obtained by defining precise protocols for use in testing, which take into account the specific characteristics of a particular oil. This approach does not replace classical analytical methods; nevertheless, it is believed that calorimetric tests could be a useful preliminary stage for quality testing. The calorimetric technique allows the detection of the adulterant (seed oils or refined olive oil), oil origin, and possible photo-oxidation degradation processes, before more complex and expensive procedures and analyses are applied.

Vapour–liquid equilibria (VLE), liquid–liquid equilibria (LLE), and excess enthalpies (HE) of binary mixtures of perfluoro-n-hexane plus an ether (diethyl, dipropyl, dibutyl, butyl methyl, and butyl ethyl ether), have been determined using a head-space gas-chromatographic technique, a turbidimetric apparatus, and a heat-flow calorimeter, respectively. A recently designed titration technique and calculation procedure have been used to obtain HE from heats of solution. The observed liquid–liquid coexistence curves have been compared with those predicted by the activity coefficients γi and their temperature dependence. All mixtures are strongly endothermic (HE > 0) and show large positive deviations from ideality (GE > 0), which increase with the size of the ether. Molecular interactions have been examined by calculating and discussing solvation functions and Kirkwood–Buff (KB) integrals. Perfluorohexane proved to be an inert molecule that interacts with ethers more weakly than hexane.

The aim of this paper is to promote calorimetry for olive oil authentication. It is our belief that the melting and freezing curves by DSC of olive oil and other edible oils could be correlated with quality, origin and storage history of the oil in a simple way, suitable for oil industry and market. Nucleation, crystallization kinetics and transition enthalpies of oil are indeed strongly dependent on molecular interactions, that is any change of oil acidic composition and minor components can be detected, as we have recently demonstrated. In particular, addition of low-cost oils to extra virgin olive oil (EVOO) and thermal and/or mechanical treatments (refinement, deodorization, filtration, etc.) of EVOO can be assessed by a first-sight analysis of the thermograms. Protocols to obtain reproducible DSC thermograms and experiments to understand the origin of the often-observed non-reproducibility, which prevented until now the use of calorimetry for oil authentication, are here described. An explanation of the melting curves even limited to the main features is a hard task owing to the polymorphism of the numerous triacylglycerols (TAG), the main component of the oil, the complexity of their mutual interactions and the effects of the minority components. To outline the level of this challenge we report: (i) the evidence that thermodynamic and kinetic processes overlap during heating of solid EVOOs and (ii) the melting curve of one pure TAG with its polymorphic transitions.

Double filling (DF) with perfluorohexyloctane (F6H8) and silicone oil (SIL) has been recently proposed and tested clinically as a means to improve the tamponade properties of single components. This in vitro study investigated (1) the kinetics of the mixing process of F6H8 with SIL (1,000 mPa s) and (2) the contact and emulsification behaviour of DF as compared with pure liquids, with the aim of assessing the tamponade efficiency and its evolution with time.(1) The velocity of the mixing process for F6H8+SIL was estimated by monitoring the position of the interphase in a rectangular cell kept at constant temperature. (2) The surface contact and the tendency to emulsification of DF and of SIL and F6H8 were visually examined by using a Perspex eye model.(1) The mixing process for F6H8+SIL is slow. In the absence of stirring, equilibrium is reached no earlier than 1 month at 37 degrees C. (2) F6H8 was found to show close contact with the eye model and dispersion into droplets; SIL showed poor contact with the cell surface and no dispersion; DF exhibited poor contact with the superior cell surface and little evidence of dispersion.F6H8 dissolves slowly in SIL and equilibrium is only reached after 1 month. The final ratio of the DF phases differs from the initial ratio. An initial F6H8/SIL ratio of 70%:30% vol results in 25% vol of pure F6H8 (density, 1.33 g/cm(3)) and 75% vol of a solution containing F6H8, viz. 60% vol F6H8 in SIL (density 1.17 g/cm(3)). Because of its density and contact properties, the investigated DF has a tamponade effectiveness better than that of SIL on the inferior retina. Compared with using F6H8 alone, DF reduces emulsification.

The excess molar volumes V m E at T =298.15 have been determined in the whole composition domain for (2-methoxyethanol + tetrahydrofuran + cyclohexane) and for the parent binary mixtures. Data on V m E are also reported for (2-ethoxyethanol + cyclohexane). All binaries showed positive V m E values, small for (methoxyethanol + tetrahydrofuran) and large for the other ones. The ternary V m E surface is always positive and exhibits a smooth trend with a maximum corresponding to the binary (2-methoxyethanol + cyclohexane). The capabilities of various models of either predicting or reproducing the ternary data have been compared. The behaviour of V m E and of the excess apparent molar volume of the components is discussed in both binary and ternary mixtures. The results suggest that hydrogen bonding decreases with alcohol dilution and increases with the tetrahydrofuran content in the ternary solutions.

Excess molar volumes VE at 298.15 K have been determined by means of a vibrating-tube densimeter for binary mixtures of n-hexane with a perfluoroalkane, C5–C8, and of perfluorohexane with a n-alkane, C5–C8, or an ether (diethyl, dipropyl, dibutyl, butyl methyl, and butyl ethyl ether). The systems perfluoropentane+hexane, perfluorohexane+pentane or hexane or diethyl ether have been investigated in the entire mole fraction range, while the other mixtures only in the miscibility regions. The observed VE values are positive (up to 5.5 cm3 mol−1) and among the largest known for non-electrolyte systems. Limiting partial molar volumes, V ° , have been evaluated for each component of the examined mixtures. The behaviour of V ° has been discussed in terms of the scaled particle theory (SPT) and of a simple group additivity scheme based on surface interactions. An estimate has been made of the average separation distance of solvent from solute molecules.

Vapour–liquid equilibria (VLE) of binary mixtures of n -perfluorohexane plus a n -alkane (C 5 –C 8 ) and of n -hexane plus a n -perfluoroalkane (C 5 –C 8 ) were determined using a head-space gas-chromatographic technique. Excess molar Gibbs energies, G E , for the systems investigated have been obtained by a least-square treatment of equilibrium data. Liquid–liquid equilibria (LLE) were determined by turbidimetry for n -perfluorohexane+ n -C n H 2 n +2 ( n =6–8) mixtures and the observed T – x curves compared with those predicted by the temperature dependence of activity coefficients. All mixtures show strong positive deviations from ideality, which increase with the size of the second component. Solute–solvent and solute–solute interactions have been examined by calculating and discussing solvation Gibbs energies and Kirkwood–Buff integrals. Perfluoroalkanes proved to be inert molecules that interact weakly with themselves as well as with alkanes.

Excess molar volumes VmEof {di- n -butyl ether (DBE) + a monofunctional organic compound} have been determined atT = 298.15 K over the whole composition range by means of a vibrating-tube densimeter. TheVmE values were either positive (propylamine, or butylamine, or acetone, or tetrahydrofuran + DBE) or negative (methanol, or butanol, or diethyl ether, or cyclopentanone, or acetonitrile + DBE). Markedly asymmetric VmEcurves were displayed by (DBE + methanol) and (DBE + acetonitrile). Partial molar volumes __ Vmoat infinite dilution in DBE, both from this work and the literature, were analysed in terms of an additivity scheme, and the group contributions thus obtained were discussed and compared with analogous results in water. DBE revealed a greater capability of distinguishing between polar and non-polar solutes, as well as in discriminating differently shaped molecules (unbranched, branched, cyclic). The limiting slopes of apparent excess molar volumes are evaluated and briefly discussed in terms of solute–solute and solute–solvent interactions.

A calorimetric technique and a calculation procedure to obtain excess enthalpies HE of liquid mixtures is described and tested. It is based on a heat-flow calorimeter used as a titration calorimeter to measure the heat effects associated to small additions of one of the components, or a mixture of them, to the ampoule containing a known amount of the other component or of a mixture of them. The procedure takes into account the presence of a small vapour space and calculates the heat involved in the vapour–liquid equilibration after each addition. The experimental values are fitted with a parametric equation such as Redlich–Kister to determine the HE parameters by least-squares adjustment. The technique has been tested with respect to the systems ethanol+cyclohexane, dioxane+water and tetrachloromethane+benzene. The results show a good agreement with literature data for these mixtures, and confirm the capability of this technique to reliably replace the mix-flow technique when the components mix slowly, or show a mixture gap, or are available in small quantities. HE results are reported for the system perfluorohexane+hexane for which the mixing process is slow.

The Gibbs energies and enthalpies of solvation of some hydrocarbons (n-hexane, n-octane, cyclohexane), alcohols (methanol, propan-1-ol, butan-1-ol, butan-2-ol), ethers (diethyl ether, tetrahydrofuran), ketones (propanone, pentan-3-one, cyclopentanone), amines (n-propylamine, n-butylamine), and acetonitrile in di-n-butyl ether have been determined at 298.15 K from vapour–liquid equilibrium measurements and from limiting enthalpies of solution. The data obtained have been compared with the corresponding values of the solvation functions in octan-1-ol and hexadecane. The phenomenology has been discussed in terms of a simple group additivity scheme. The interaction effects of polar and non-polar groups with the solvents have been deduced from the above group contributions combined with the cavity terms estimated through the scaled particle theory. The linear solvation energy relationships (LSER) have also been used for correlating the thermodynamic solvation function to the structural features of the solutes. All the approaches consistently highlight that the hydrophobic groups exhibit interactions with the solvent of nearly the same strength in the three media, while clearly different interactions are shown by polar groups.

The partial molar enthalpy H at 323.15K of each component (solvaton) of the ternary systems ethanol + trichloromethane (TCM) + dioxane, methanol + TCM + acetone and ethanol + TCM + n-heptane is analyzed in order to estimate the relative weight of the contributions due to: i) the interactions between solvaton and pure solvents; ii) a local composition in the neighbourhood of the solvaton that is different from the bulk one; iii) specific solvaton-solvent and solvent-solvent interactions. These systems have been chosen because present a wide range of the strength of interactions that can take place between the same or different species: hydrogen bonds, dipole-dipole and dispersion. This analysis is carried out by using the Kirkwood-Buff theory to calculate the local composition and the results as regards this quantity are presented and discussed. The results of the whole treatment indicate that non-zero excess local composition is the main cause of the H trend when the solvaton is alcohol dissolved in the binary mixture of alcohol + TCM, alcohol + heptane and TCM + heptane. This contribution is also effective but to a smaller extent for dioxane in ethanol + TCM, for acetone in methanol + TCM, and for heptane in ethanol + heptane. For ethanol infinitely diluted in dioxane + TCM and for methanol also at infinite dilution in acetone + TCM, the particular trends of H are not due non-zero excess local composition in the neighbourhood of the solvatons, but to solvent-solvent association through hydrogen bonding which allows a favourable solvaton-solvent interaction. In the other cases, the H trend is mostly determined by the same interactions that take place in the solution of the solvatons with the neat substances. The present study indicates that for excess local composition to play a significant role in determining H , one of the solvent components needs to be able to self-associate through hydrogen bonding.

By means of a vibrating tube densimeter, the excess molar volumes V E at 298.15 K have been determined in the whole composition domain for the ternary system ethanol+tetrahydrofuran+cyclohexane and for the relevant binary mixtures. While ethanol+tetrahydrofuran shows slight V E values and a S-shaped V E curve, the other two binaries have similar largely positive V E s. The ternary V E surface is almost always positive with a small maximum. The binary V E data have been described with different correlation equations. The capabilities of different models of either predicting or reproducing the ternary data have been compared. The behaviour of V E and of the partial molar excess volumes of the components in the ternary system is discussed and it is found that hydrogen-bonding decreases with alcohol dilution and increases with the tetrahydrofuran solution content.

A systematic study of a series of room-temperature ionic liquids, belonging to the alkylammonium nitrate family (XAN), was carried out at 298.15 K and 0.1 MPa with the aim of investigating the effect of the cationic chain length on some thermo-physical properties and their behavior in the organic solvent N-methyl-2-pyrrolidone (NMP), over the whole concentration range. Experimental densities were used to calculate molar volumes, V-m, and excess molar volumes, V-E. Complementary information was obtained by isothermal titration calorimetry that provided the values of the heat of mixing, H-E, and the excess partial molar enthalpies of each component, (H) over bar (E)(1) and (H) over bar (E)(2). The density values of neat XAN samples decreased as the alkyl chain length of the cation increases, whereas, the addition of the methoxy group to the considered smaller alkyl chain resulted in an increase of density. Negative V-E and H-E values were found for each XAN + NMP system, indicating the presence of strong attracting interactions between the constituents. (C) 2014 Elsevier B.V. All rights reserved.

It is shown that a reference state is necessary for the correct interpretation of the Kirkwood−Buff integrals, Gij, of liquid mixtures in terms of interactions between the components and for their use in the calculation of the local composition. This state is identified with the symmetrical ideal system, and its Gij's are taken as zero-level. The equations for calculating the Gij of the reference mixtures are derived and discussed, and those for calculating local composition and preferential solvation are reformulated with respect to the reference system. The mixtures of compounds with large size mismatch and/or small deviations from Raoult's law are those for which the new equations should be applied in order to get correct indications on the interactions that take place and influence the preferential solvation. A comparison with Flory−Huggins athermal mixtures (GE = −TSE) as reference systems is also made, allowing one to estimate the relative weights of the contributions to Gij and preferential solvati...

Vapour-liquid equilibria for the ternary system ethanol + tetrahydrofuran + cyclohexane and for the relevant binary mixtures have been determined at 298.15 K by head-space gas-chromatographic analysis of the vapour phase directly withdrawn from an equilibration apparatus. Experimental data have been described with different equations (Redlich-Kister, Wilson, NRTL and UNIQUAC) and excess Gibbs energies GE as well as activity coefficients γi of components have been obtained. All systems exhibit positive deviations. The binaries containing cyclohexane form azeotropic mixtures at 298.15 K, while ethanol + tetrahydrofuran and the ternary systems do not. The excess entropy and the temperature dependence of GE and γi have been calculated in the whole ternary domain from the known excess enthalpy and heat capacity.

Densities and viscosities of binary mixtures (H2O or D2O) (1) + (DMSO or DMSO-D6)(2) have been measured over the entire mole fraction range; and the excess volumes, excess viscosities, and excess partial molar volumes Vf of the components have been obtained. All systems show negative excess volume Ve at all compositions, values for mixtures containing D2O being more negative than those with H2O byca. 0.03 cm3-mol-1 at x1, = 0.6, where a minimum is observed. The difference between DMSO and DMSO-D6 containing mixtures is negligible. The excess viscosity ηe is always positive and shows a maximum at x1 = 0.65; at this composition, the substitution of H2O with D2O causes an excess viscosity increment ofca. 0.35 mPa-s, while deuteration of DMSO brings about a smaller increase,ca. 0.1 mPa-s. The trend of V2E with concentration shows the characteristic features of moderately hydrophobic solutes in water (negative values and a minimum in the water-rich region), features that are slightly but significantly more marked in D2O than in H2O. The V2E values in the water-diluted region and at x1, =0 are more negative for D2O than for H2O.

The self-association of hydrophobic propan-1-ol has been studied in binary aqueous mixtures and in mixtures containing urea as a third component. We applied an NMR technique to obtain the so-called association parameter A22, which is based on the measurement of intermolecular 1H–1H dipole–dipole relaxation rates and on self-diffusion coefficients of the component of interest. The composition dependence of A22 reflects a weak tendency for the self-association of propan-1-ol in the binary mixture. Addition of urea leads to a strongly increased self-association of propan-1-ol. The same qualitative result has been obtained from recent studies of the Kirkwood–Buff integral G22 by one of the present authors. A22 is governed by short-range contributions but G22 by long-range contributions and the common study of the two quantities has delivered interesting complementary information about liquid mixtures. Propanol–propanol correlations in binary systems were never found to extend longer than one to two propanol diameters, however when urea is added the correlation length can extend up to four diameters. Measurements of BD parameters, showing the influence of urea on the translational motion of propan-1-ol, revealed only a weak effect. Thus no rigid self-associated species could be detected and the self-association found from A22 and G22 can be interpreted as ‘preferential self-solvation’ by relatively weak intermolecular interactions.

Excess enthalpies and excess heat capacities at 298.15 K for the ternary system ethanol + dimethylformamide + tetrahydrofuran were determined by means of a flow calorimetric apparatus built in our laboratory. Experimental data were described with a Redlich-Kister type equation and compared with those of other ternary systems previously studied (ethanol + tetrahydrofuran + cyclohexane, ethanol + dimethylformamide + cyclohexane, dimethylformamide + tetrahydrofuran + cyclohexane). A peculiar behaviour was observed for mixtures containing dimethylformamide, namely the negative values of both H E and C p E ternary contributions. A satisfactory prediction of experimental H E data is provided by the UNIQUAC model, while UNIFAC (Dortmund, Germany) clearly fails probably owing to an unsufficient definition of interaction parameters involving dimethylformamide.

Excess enthalpies and excess heat capacities at 298.15 K for the ternary system ethanol + dimethylformamide + cyclohexane, and for the related binary mixtures dimethylformamide + ethanol or cyclohexane were determined by means of a flow calorimetric apparatus built in our laboratory. Experimental data were described with a Redlich-Kister type equation. H E and C P E data are positive in the whole region of miscibility; however, their ternary contributions to the excess quantities, referred to the combination of the Redlich-Kister representation of the parent binary mixtures, present opposite features. UNIQUAC and UNIFAC models were used for the description or prediction of experimental results.

Equations for the calculation of the Kirkwood–Buff integrals (KBI) for the components of a ternary system from thermodynamic data are presented and applied to a number of mixtures of non-electrolytes. The mixtures comprise substances which may develope strong mutual interactions due to e.g. permanent dipoles and hydrogen bonds; they are: (I) water–propan-1-ol–N,N-dimethylformamide (DMF), (II) water–ethane-1,2-diol–acetonitrile, (III) water–ethane-1,2-diol–ethanol, (IV) ethanol–trichloromethane–1,4-dioxane; the system (V), water–propanol–urea, previously studied is also discussed. The observed KBIs have been correlated to interactions among functional groups and to the structure of the solvent components. Moreover, a preferential solvation coefficient of a given compound with respect to the other two is given a different definition to that of previous authors and calculated; its change with changing concentration of solvating components is examined. These quantities have proved to be useful indicators of the predominant types of interactions in various concentration regions.In systems I and V we compare the effect of the addition of either DMF or urea to the binary mixture, water–propanol, which is characterised by large positive values of the like (i–i) KBI. A markedly different behaviour is found: whereas urea causes a strong increase of the like KBIs, DMF has the opposite effect. Moreover, urea is mostly solvated by water over the whole water–propanol mole fraction range, whilst DMF presents a sharp change of preference at ca. xw= 0.8, being preferentially solvated by propanol in the water-rich region. The results from systems II and III, where the effect of the addition of either ethanol or acetonitrile to the mixture water–ethanediol is examined show, in particular, that the KBIs of ethanol and acetonitrile behave as if the mixture water–ethanediol were a single component. In system IV the observed KBI behaviour is related to the competition between hydrogen-bond and dipole–dipole type interactions.

By means of a vibrating-tube densimeter, the densities at 25°C have been determined for binary mixtures of tetrachloromethane with a liquid (cyclodecane, cis-decahydronaphthalene, trans-decahydronaphthalene, bicyclohexyl, pentane) or a solid hydrocarbon (cyclododecane, cyclopentadecane, norbornane, adamantane, octahydro-4,7-methano-1H-indene). Excess molar volumes have been obtained in the whole mole fraction range for mixtures containing a liquid hydrocarbon. For solid cycloalkanes, apparent molar volumes have been evaluated in the whole range of miscibility. The partial molar volumes at infinite dilution\(\bar V^\circ \) have been calculated for all examined cycloalkanes and compared with those of n-alkanes. The dependence of\(\bar V^\circ \) upon the size and shape of the ring or cage structure of the solute is discussed. The capability of the Flory theory to reproduce VE for these mixtures is also tested.

By means of a flow calorimeter, the specific heats of aqueous solutions containing AlCl3 with and without added HCl have been measured at 50, 100, and 150°C. The apparent molar heat capacity Cp,φ of the HCl-containing solutions have allowed the calculation of the standard molar heat capacity of AlCl3, C 0 p,AlCl 3 . These data satisfactorily link together with those of Hovey and Tremaine in the range 10–55°C ( Hovey and Tremaine , 1986), afterwards reassessed by Barta and Hepler 1986. The treatment of the Cp,φ data with the ionic interactions model of Pitzer has provided the values of β(0)J and β(1)J for the calculation of CAlCl3p,φ in the concentration range 0.03–0.75 mol kg−1 at the temperatures studied. Experimental values of the apparent molar heat capacities obtained for hydrolyzed solutions have been compared with the analogous quantities calculated accounting for the Cp,φ,i of all species present at equilibrium, as well as for the chemical relaxation term, Crelp,φ, which is due to the energy absorbed by the hydrolysis shift induced by the heating inherent in the specific heat measurement. The calculation has been carried out on the basis of some hydrolytic schemes proposed in the literature and has provided useful insights on the hydrolysis reaction at temperatures where the extent of reaction is quite marked.

The heat produced when NaOH is added to Al 3+ ( m 0 Al ⋍ 0.03 mol kg −1 ) in water has been measured in the range 25–150°C. These calorimetric data are consistent with the chemical model proposed by Mesmer and Baes which considers two polynuclear and one polymeric hydrolytic species of aluminium ion. Other models which consider, in addition, the presence of mononuclear species might be valid as well, while models involving these latter species alone should be ruled out, at least in the experimental conditions adopted in this work. A simple equation is proposed for calculating the enthalpy of formation of hydrolytic species of aluminium from the measured value of the average enthalpy for addition to aqueous Al 3+ of one mole of hydroxy groups.

Spanedda, A., Lepori, L. and Matteoli, E., 1991. Volumes of mixing of ethers with tetrachloromethane at 298.15 K. Fluid Phase Equilibria , 69: 209-222. The excess molar volumes V E , at 298.15 K, have been determined by means of a vibrating-tube densimeter in the whole mole fraction range for binary mixtures of tetra-chloromethane with an ether (diethyl ether, dimethoxymethane, diethoxymethane, 1,2-di-methoxyethane, 1,2-diethoxyethane, diethyleneglycol dimethyl ether, oxepane or 1,3-dioxolane). The V E values are negative for all systems and become less negative with increasing number of oxygen atoms in the ether molecule. The V E values of some of the present mixtures have been analyzed in terms of the Flory theory of non-polar solutions. Limiting partial molar volumes − V o have been evaluated for each component of the examined systems. The behaviour of − V o of ethers is discussed and a simple group additivity scheme is presented.

Vapor-liquid equilibria for dichloromethane or chlorobutane+a linear mono-, or diether (diethyl ether, dipropyl ether, methyl butyl ether, 1,2-dimethoxyethane,) or an acetal (diethoxymethane), were determined at 25°C by head-space gas chromatographic analysis of the vapor phase directly withdrawn from an equilibration apparatus. Excess Gibbs energies, G E , activity coefficients at infinite dilution, f i o as well as free energy of solvation, ΔG o , were evaluated for all the systems. A tentative approach is presented based either on an additivity scheme of surface interactions and scaled particle theory to calculate group contribution to the free energy of solvation.

A head-space gas chromatographic technique has been used to determine vapour—liquid equilibria for binary mixtures of: cyclohexane+an aldehyde (ethanal, butanal, pentanal); tetrachloromethane+ethanal, +pentanal and +cyclobutanone; and heptane+cyclobutanone or+a diketone (2,3-butanedione, 2,5-hexanedione). Excess molar Gibbs energies, GE, for the mixtures investigated were obtained by a least-squares treatment of the equilibrium results. All systems exhibit positive deviations. For mixtures involving aldehydes, the GE values are larger when the other component is cyclohexane than when it is tetrachloromethane and decrease with increasing aldehyde chain length. Activity coefficients at infinite dilution, f∞, as well as free energies of solvation, δG°, were evaluated for each component of the systems examined. A tentative approach, based on an additivity scheme of surface interactions combined with the Scaled Particle Theory, is presented to estimate and to analyse group contributions to δG°.

Marongiu, B., Pittau, B., Porcedda, S., and Tine, M.R., 1994. Thermodynamics of binary mixtures containing linear or cyclic alkenes + n -alkanes or cyclohexane. Fluid Phase Equilibria 93; 249-276. A head-space technique has been used to determine vapor-phase equilibria for binary mixtures of linear or cyclic mono- and polyalkenes + n-alkanes or + cyclohexane. Excess molar Gibbs energies GE for the mixtures investigated were obtained by a least-squares treatment of the equilibrium results. These data the previously measured excess enthalpies HE and the data available in the literature on GE HE activity coefficients at infinite dilution γi∞ and molar excess enthalpies at infinite dilution hiE,∞ are examined on the basis of the DISQUAC group contribution model. The model provides a fairly consistent description of the phase equilibria and the related excess functions using a unique set of structure-dependent dispersive parameters.

The activity coefficiens, γi, and the partial molal volumes, Vi, of the three components of the ternary system water(1)+1-propanol(2)+urea(3) have been measured at 298.15 K in the entire domain of full miscibility. These data have been used to calculate the six Kirkwood-Buff (K-B) integrals, Gij, of the ternary mixture. γ1 and γ2 are found very little dependent on urea mole fraction x3. indicating the scarce influence of urea on the interaction free energy between water and propanol. V1 and V2 too are little dependent on urea concentration; V2 shows a characteristic minimum in dilute alcohol solution even at high x3 values. The increase of V3 with x3, a characteristic of hydrophilic compounds in water, is found even at high x2. The observed increase of the three homologous Gii's and of G12 and the decrease of G23 and G12 with addition of urea indicate that this compound brings about an enhanced homocoordination of the three components, as well as an increase of the urea-water affinity, and suggest that the observed increase of G22 with urea addition may be due to the abduction of water molecules from the solvation sphere of propanol.

A newly designed calorimetric technique and calculation procedure have been used to obtain partial molar enthalpies, H ¯ i , and excess enthalpies, HE, for binary mixture of hexane + perfluoro-n-alkanes (C5–C8) and perfluorohexane + n-alkanes (C5–C8), + cyclohexane, and + 2-methylheptane. All mixtures are endothermic, and the heat effects increase with the size of the second component. The HE and H ¯ i values found are the largest ever observed for mixtures of non-polar compounds. An estimate of the excess heat capacity for (perfluorohexane + 2-methylheptane) has been obtained from H ¯ i at two different temperatures. From H ¯ i at infinite dilution and from the known enthalpies of vaporization, the enthalpies of solvation, ΔsolvH∘, have been evaluated either for alkanes and perfluoroalkanes in both hexane and perfluorohexane solvent. Solute–solvent interactions have been examined by describing the ΔsolvH∘ with an additive scheme of surface interactions and by applying the Scaled Particle Theory. The effects of chain lengthening, branching, and cyclization have been discussed. Perfluoroalkanes proved to be inert molecules that interact weakly with themselves as well as with alkanes.

Summary Equations (10.14) and (10.15), which are the basis of the present theory, are mathematically exact. The choice of the closure expression, Equation (10.21), relating the cross-direct-correlation integral to the other two integrals in a binary mixture allows us to solve these equations simply and analytically using only the pure-fluid thermodynamic data. It is demonstrated here that simple geometric- and arithmetic-mean closures are needed for simple model fluids. It is also demonstrated that a weighted-arithmetic-mean closure expression is sufficient to represent the relation between the cross-direct-correlation integral to the other two correlation integrals of binary mixtures. Success of this theory in its application to a variety of mixtures comprised of components with polar and associating intermolecular potential energies is indicative of its promise as a strong technique for prediction of properties of complex dissimilar mixtures of practical interest. The present theory has allowed us to perform calculations of properties and phase equilibria of mixtures. There are several points to be noted about the advantages of the present techniques compared with other existing thermodynamic calculation methods for mixtures: (i) The present theory allows us to perform thermodynamic calculations for the whole range of mixture compositions and not just at the infinite-dilution and high-concentration limits as has been the case for most of the fluctuation-theory techniques. (ii) The present theory is applicable for mixtures consisting of dissimilar species with large differences in molecular size, shape, and energetics. It is specifically useful for polar and associating molecular fluids for which, generally, no accurate intermolecular-potential-energy functions are available. (iii) With the application of the weighted-arithmetic-mean closure for the cross-direct-correlation-function integrals, Equation (10.21), it has become possible to derive analytic expressions for activity coefficients in complex mixtures consisting the dissimilar molecules. The resulting activity-coefficient expressions allow us to perform vapor-liquid and liquidliquid equilibria computations for such mixtures. The accuracy of these calculations are is good as the best available phase-equilibria computational techniques for mixtures. (iv) What makes the relations among the direct-correlation-function integrals (or fluctuation integrals) introduced here particularly interesting is the fact that only one closure relation is needed to determine all the binary-mixture properties. Detailed studies are under way in order to develop analytic expressions for total and partial molar properties of multicomponent systems using the present theory.

A head-space gas chromatographic technique has been used to determine vapour/liquid equilibria at 298.15 K of binary mixtures of di-n-butyl ether plus an organic compound (hexane, octane, diethyl ether, tetrahydrofuran, propylamine, butylamine, propanone, cyclopentanone, methanol, butan-1-ol, acetonitrile). Excess molar Gibbs energies, GE, for the systems investigated have been obtained by a least-squares treatment of equilibrium data. Mixtures with hexane, octane and diethyl ether revealed an almost ideal behaviour. Other systems showed positive deviations, which increase with the polarity of the second component. Dibutyl ether + butanol and + cyclopentanone revealed the formation of azeotropic compositions. The Kirkwood–Buff integrals over the entire composition range have been calculated from the composition dependence of GE, and briefly discussed.

Excess enthalpies and excess heat capacities at 25°C for the ternary system ethanol + tetrahydrofuran + cyclohexane, and for the related binary mixtures, were determined by means of a flow calorimetric apparatus built in our laboratory. Experimental data were described with a Redlich—Kister-type equation. Both H E and C E p ternary data show large positive contributions. Theoretical models were used for the description or prediction of experimental results. In the case of binary systems, the examined models are able to reproduce satisfactorily the experimental data for H E , though less satisfactorily for C E p . Ternary experimental data are predicted by the modified unifac method (Dortmund, Germany) but not by the Nitta—Chao model. Both these models are unsuccessful in predicting ternary C E p data.

Vapor-liquid equilibria for tetrachloromethane+a linear mono-, di-, or triether (diethyl ether, dipropyl ether, dibutyl ether, methyl butyl ether, ethyl butyl ether, 1,2-dimethoxyethane, 1,2-diethoxyethane, di(ethylene glycol) dimethyl ether) or an acetal (dimethoxymethane, diethoxymethane) were determined at 298.15 K by head-space gas chromatographic analysis of the vapor phase directly withdrawn from an equilibration apparatus. Excess molar Gibbs energies G E for the investigated mixtures were determined by a least-squares treatment of the equilibrium data