Vladimír Dohnal

A new variant of the Rayleigh distillation method for the determination of limiting activity coefficients

Abstract Dohnal, V. and Horakova, I., 1991. A new variant of the Rayleigh distillation method for the determination of limiting activity coefficients. Fluid Phase Equilibria, 68: 173-185. A new variant of the Rayleigh distillation method for the measurement of limiting activity coefficients has been developed. The method is based on the determination of changes in the concentration and amount of the dilute solution caused by saturation with the solution vapor of an inert gas bubbled through the solution. Experimental conditions needed to obtain accurate values of limiting activity coefficients have been identified by means of an error analysis. In terms of limiting relative volatility, the applicability range of the proposed method appears to be 1

Activity coefficients at infinite dilution of organic solutes in the ionic liquid 1-ethyl-3-methyl-imidazolium nitrate.

Infinite dilution activity coefficients gamma(1)(infinity) and gas-liquid partition coefficients K(L) of 30 selected hydrocarbons, alcohols, ketones, ethers, esters, haloalkanes, nitrogen- and sulfur-containing compounds in the ionic liquid (IL) 1-ethyl-3-methylimidazolium nitrate [EMIM][NO(3)] were determined by gas-liquid chromatography at five temperatures in the range from 318.15 to 353.15 K. Relative contribution of adsorption at gas-liquid interphase to the overall solute retention, as examined by varying sample size and IL loading in the column, was found negligible. Partial molar excess enthalpies and entropies at infinite dilution were derived from the temperature dependence of the gamma(1)(infinity) values. The linear free energy relationship (LFER) solvation model was used to correlate successfully the KL values. The LFER correlation parameters and excess thermodynamic functions were analyzed to disclose molecular interactions operating between the IL and the individual solutes. In addition, the promising potential of [EMIM][NO(3)] for applications in solvent-aided separation processes was identified, the selectivities of [EMIM][NO(3)] for separation of aromatic hydrocarbons and thiophene from saturated hydrocarbons ranking among the highest ever observed with ILs or molecular solvents.

Limiting Partial Molar Excess Heat Capacities and Volumes of Selected Organic Compounds in Water at 25°C

Well-known Picker flow microcalorimeters for the differential measurements of volumetric heat capacities have been employed in conjunction with vibrating tube densimeters to determine the molar heat capacity, volume, and the apparent properties in dilute aqueous solutions for 17 organic solutes of moderate hydrophobicity. The dependence on concentration of the apparent properties allowed the limiting partial molar quantities at infinite dilution to be extrapolated and the limiting partial molar excess quantities to be evaluated. Comparison with available literature data shows good agreement. The application of group contribution rules to the limiting partial properties has been tested using the original method and parameters proposed by Cabani et al. The predicted values of the partial molar volumes are in fair agreement with the present data except for some less common solutes. With partial molar heat capacities, the agreement is less satisfactory. To improve the performance of the method, missing parameters for some types of monofunctional and bifunctional molecules have been evaluated.

Interaction of ionic liquids ions with natural cyclodextrins.

The interaction of natural α-, β-, and γ-cyclodextrins (CDs) with 14 hydrophobic ionic moieties of ionic liquids (ILs) was systematically examined in dilute aqueous solutions using isothermal titration microcalorimetry (ITC) and NMR spectroscopy. The studied cationic and anionic moieties involved some recently developed heavily fluorinated structures, as well as some others of common use. To isolate the effect of a given ion, the measurements were performed on salts containing the hydrophobic IL ion in question and a complexation-inactive counterion. Additional ITC experiments on ILs whose both cation and anion can interact appreciably with the CD cavity demonstrated that to resolve the effect of individual ions from such data is generally a tricky task and confirmed the superiority of the isolation strategy adopted for the purpose throughout this work. The binding constant, enthalpy and entropy determined at 298.15 K for the 1:1 (ion:CD) inclusion complex formation range in broad limits, being 0 < K < 2 × 10(5), 0 < -Δ(r)H°/(kJ·mol(-1)) < 44, and -28 < TΔ(r)S°/(kJ·mol(-1)) < 14, respectively. The stabilities of complexes of perfluorohexyl bearing ions with β-CD belong to the highest ever observed with natural CDs in water. The established binding affinity scales were discussed in both thermodynamic and molecular terms. The concepts of hydrophobic interaction and guest-host size matching supported by simple molecular modeling proved useful to rationalize the observed widely different binding affinities and suggest possible binding modes. Enthalpy and entropy contributions to the stability of the ion-CD complexes were found to compensate each other considerably obeying more or less the linear compensation relationship marked by existing literature data on binding other guests to natural CDs. As outliers to this pattern, the most stable complexes of -C(6)F(13) bearing ions with β-CD were found to receive an enhanced inherent entropy stabilization due to extraordinarily high extent of desolvation occurring in the course of binding.

Temperature Dependences of Limiting Activity Coefficients, Henry’s Law Constants, and Derivative Infinite Dilution Properties of Lower (C1–C5) 1-Alkanols in Water. Critical Compilation, Correlation, and Recommended Data

A comprehensive review is presented of experimental data on the limiting activity coefficients γ1∞, infinite dilution partial molar excess enthalpies H¯1E,∞ and heat capacities C¯p,1E,∞ of lower 1-alkanols (C1–C5) in water. For each alkanol, the compiled data are critically evaluated and correlated with a suitable model equation providing adequate simultaneous description of the equilibrium measurements and the calorimetric information. As a result, recommended thermodynamically consistent temperature dependences of γ1∞, H¯1E,∞, and C¯p,1E,∞ of superior accuracy are established in the range from the melting point to the normal boiling point of water. In addition, by employing literature data on the respective residual properties of the pure 1-alkanols, analogous recommendations are also derived for the temperature dependences of the Henry’s law constants, hydration enthalpies, and hydration heat capacities. Evolution of the various infinite dilution thermodynamic properties of aqueous 1-alkanols with temp...

Limiting activity coefficients in the 1-alkanol + n-alkane systems: survey, critical evaluation and recommended values, interpretation in terms of association models☆

Abstract The survey of critically evaluated experimental limiting activity coefficients for 1-alkanol (C1C10) + n-alkane (C5C16) systems prepared on the occasion of the 1991 IUPAC Workshop on Vapor-Liquid Equilibria in 1-alkanol + n-alkane mixtures has been updated by newly available data. Major update is due to a recent experimental effort of our research group which carried out extensive and accurate measurements using several experimental techniques. Thanks to our own measurements, forming now 27% of all available data, the accuracy of our knowledge of limiting activity coefficients in the given systems has clearly improved. The methodology employed for the critical assessment of data is described and illustrated by a number of examples. Recommended values and their uncertainties generated as a result of the process of critical evaluation are reported. For systems, where the underlying experimental information justify the determination of a temperature dependence, a smoothing equation is presented, otherwise a recommended value is given at a single temperature only. Reported and discussed are also some interesting statistical characteristics inferred from the comprehensive 1-alkanol + n-alkane data file. Several athermal and non-athermal association models have been fitted to the critically evaluated data. Performances of these models are compared mutually and to those of three leading group contribution prediction methods.

Infinite-dilution activity coefficients by comparative ebulliometry: the mixtures of freon 112 with oxygenated solvents and hydrocarbons

Abstract Using the comparative ebulliometric technique, infinite-dilution activity coefficients were measured for 1,1,2,2-tetrachlorodifluoroethane (Freon 112) in 15 oxygenated solvents and hydrocarbons at several temperatures. A rather high melting temperature of Freon 112 prevents the activity coefficients from being determined at the opposite concentration limit. As a substitute, the total pressure was measured at one finite concentration for some of these systems to provide a data base for the group-contribution analysis. The UNIFAC and the ASOG parameters were calculated for the interactions of Freon 112 with aliphatic and aromatic hydrocarbons, ketones, alcohols and esters. The evaluation of reliable interaction parameters for Freon 112 with ethers proved unsuccessful. As demonstrated by comparing the experimental and the predicted γ∞1s for the systems not included in the data base, the UNIFAC method performs slightly better than the ASOG.

1H NMR and thermodynamic study of self-association and complex formation equilibria by hydrogen bonding. Methanol with chloroform or halothane

Mixtures of methanol with two strong proton donors, chloroform and halothane (2-bromo-2-chloro-1,1,1-trifluoroethane), were studied. The behaviour of these systems is governed by aggregate formation through H-bonding, where methanol self-association and its complex formation with the proton donors compete. In order to obtain information about these aggregate formation equilibria, 1H NMR chemical shifts of the chloroform or halothane proton and of the hydroxy proton of methanol were measured as a function of concentration and temperature. The NMR data are expressed in the form of a new quantity, defined in this work, the relative change of the chemical shift. This quantity is convenient because it gives directly the extent of H-bonding without containing any NMR-specific parameter. The NMR data and the excess thermodynamic functions from the literature (GE or ln γi, HE and CPE) were analysed using simple models of athermal association, amended by physical or thermal terms estimated on the basis of coupled homomorph and solution-of-groups approaches. Three particular models were tested, two of continuous methanol association (from tetramers to infinite size species) and one model that considers only methanol tetramerization. For the three models, methanol self-association parameters were previously obtained from independent data. Using enthalpy of solvation values obtained from quantum mechanical calculations, the equilibrium constant for the formation of methanol–chloroform and methanol–halothane complexes was the only fitted parameter. The continuous association models failed to fit the present data even qualitatively, whereas the tetramerization model gave reasonable agreement with experiment both for NMR and the excess thermodynamic functions. In accordance with previously studied mixtures of chloroform and halothane with oxygenated compounds, the methanol–halothane complex is found to be stronger than the methanol–chloroform complex; this is due to a more acidic hydrogen atom in halothane than in chloroform.

Excess volumes of (cyclopentane + an isomeric hexane or heptane) at 298.15 K

Abstract Using a Sodev vibrating-tube densimeter the excess molar volumes were measured for cyclopentane + one of five hexanes or + one of eight heptanes) at 298.15 K. The V m E s show a consistent trend towards more negative values when the number of methyl groups increases correlating well with the cohesive energy density. The Flory theory was tested with respect to its ability to reflect such a behaviour.

Excess molar enthalpies of binary mixtures of 2-bromo-2-chloro-1,1,1-trifluoroethane (halothane) with oxygenated and hydrocarbon solvents

Abstract Excess molar enthalpies, H E , were determined at 298.15 K for the following eighteen mixtures: 2-bromo-2-chloro-1,1,1-trifluoroethane (halothane) + acetone, +dipropyl ether, + diisopropyl ether, + methyl tert -butyl ether, + ethylene glycol dimethyl ether or monoglyme, + diethylene glycol dimethyl ether or diglyme, + tetraethylene glycol dimethyl ether or tetraglyme, + methyl phenyl ether, + tetrahydrofuran, + 1,4-dioxane, + methyl acetate, + benzene, + cyclopentane, + cyclohexane, + n -hexane, + n -heptane, + 2,2-dimethylbutane and + 2,4-dimethylpentane. The value of H E for all oxygenated solvents is strongly negative whereas for the equal-structure hydrocarbon solvents (taken as homomorphs) it is positive. This is a clear indication of the formation of a halothaneoxygenated-compound complex. The complexation is through a H-bond between the oxygen atom in the solvent molecules and the hydrogen atom in halothane. As the number of oxygen atoms in the solvent increases, H E becomes more negative and asymmetrical, its minimum being displaced towards higher halothane concentrations. The H E values for halothane mixed with the glymes are amongst the largest ever found for mixtures of non-electrolytes. The increase in asymmetry in going from monoglyme to tetraglyme is indicative of the presence of multisolvated species in the solution. A clear correlation between the solvent Kamlet-Taft β parameter (H-bonding acceptor ability) and H E was found. A comparison between the H E vs. β correlation for the present data and that for chloroform showed that for a given oxygenated solvent H E with halothane is always more negative than with chloroform. This indicates that the acidity of the hydrogen atom in halothane is greater than that in chloroform.