Ionic association in acetonitrile and in formamide

In a recent derivation of relaxation effects in the Debye-Hückel-Onsager theory of electrolyte conductance, with a length parameter a, terms are included which have been omitted in earlier treatments (see Appendix). The new expression was applied earlier in a reanalysis of conductance data for aqueous solutions and is applied here to solutions in acetonitrile and in formamide, representing respectively dielectric constants considerably lower and higher than water. As in aqueous solutions, a minimum standard deviation is found over a wide range of (K _A,a) pairs without much effect on A ₀ , so that only approximate determinations ofK _A are possible. On the whole, the most appropriate length parametera is the physical contact distance between counterions, not a fixed radius, independent of ionic size, such as the Bjerrum value, nor a much larger radiusR serving as a boudary between free and associated ions in the ionic atmosphere about a central ion. Relaxation effects calculated by the new analysis are smaller than those from previous expressions for equal values ofa, and this leads to considerably larger values ofK _A than in the original papers. As a consequence, specific short-range ion-ion and ion-solvent forces in most solutions predominate over electrostatic attraction between counterions in their contribution toK _A. A table of limiting equivalent conductance based on the A ₀ values obtained is presented; this differs little from previous tables since A ₀ values obtained by the new analysis are similar to those obtained originally.     

Application of the Bjerrum Association Model to Electrolyte Solutions. III. Temperature and Pressure Dependencies of Association Constants

The Bjerrum association model, developed in 1926, is now incorporated in many conductance theories of electrolyte systems to extract ₀ and K _A from experimental data. The Bjerrum concept is simply a convenient way of taking into account short-range electrostatic interactions between ions. The equations of the Bjerrum model can be applied to the prediction of the temperature and pressure dependencies of K _A from the value of K _A at a reference T and P and from the dielectric properties of the solvent. This feature will be essential when the relaxation effect is taken into account when applying the model to heat capacities and compressibilities. These equations were tested against literature K _A values (obtained from treatment of conductance data by equations that incorporate the Bjerrum concept) in aqueous electrolyte solutions at high temperatures and pressures and in some electrolyte systems in acetonitrile, 2-butanone, propylene carbonate, -butyrolactone, and propanol. In the absence of specific interactions in solution, the agreement between experimental and predicted K _A are generally quite good. Notable exceptions are acids and bases in water, lithium perchlorate in most solvents, and the majority of electrolytes in propylene carbonate, suggesting that specific interactions in these systems may cause the model to fail.     

Determination of the dissociation constant and limiting equivalent conductance of a weak electrolyte from conductance measurements on the weak electrolyte

A method is described for computing the dissociation constant and equivalent conductance at infinite dilution, A_o , for a weak electrolyte from as few as two conductance measurements at different concentrations. The iterative procedure applied to acetic acid data yielded a dissociation constant of 1.80 X 10-⁵ and an average value (n = 4) of A_o of 389.5 compared with an expected value of 390.7.     

From restricted towards realistic models of salt solutions: Corrected Debye–Hückel theory and Monte Carlo simulations

The properties of bulk salt solutions over wide concentration ranges are explored by a combination of simple physical theory and Monte Carlo (MC) simulations. The corrected Debye–Hückel (CDH) theory which incorporates ion size effects in a linear response approximation is extended to yield free energy and other thermodynamic properties by integration of the chemical potential over concentration. Charging integration which is usually used to obtain an electrostatic contribution of total free energy of electrolytes is avoided in this new direct approach. MC simulations are performed with a modified Widom particle insertion method, which also provides directly the ionic activity coefficients. The validity of the CDH theory is tested by comparison with the MC simulation data for 1:1, 2:1, 2:2 and 3:1 restricted primitive model (RPM) electrolytes over a wide concentration range and at various ion sizes. Mean ionic activity and osmotic coefficients calculated by the CDH theory in RPM approximation of electrolyte are fitted to experimental data by adjusting only a mean ionic diameter. Good fits up to 1 molal (m) concentration are obtained for a large number of salt solutions. MC simulations data for unrestricted primitive model (UPM) of 1:1 and 2:1 electrolytes are also fitted to the experimental data by varying the cation radius while keeping the anion radius fixed at a crystallographic value. The success of this approach is found to be salt specific. For example good fits up to 2 and 3.5 m concentrations were obtained for LiCl and LiBr, respectively. However in the case of less dissociated salts such as NaCl and KI the experimental data could only be fitted up to one molal concentration. Possibility of extending the applicability range of the CDH theory to concentrations >2 m is explored by including a concentration dependent dielectric constant as measured in experiments. Mean ionic activity coefficients for a number of salts could successfully be fitted up to 3 m concentration by adjusting only a mean ionic diameter. Difficulties encountered in simultaneously fitting the mean ionic activity and osmotic coefficients at salt concentrations >2 m are discussed.     

Application of the Bjerrum Association Model to Electrolyte Solutions. IV. Apparent Molar Heat Capacities and Compressibilities in Water and Aprotic Solvents

The Bjerrum association model, which has already been applied successfully to volumes and enthalpies of dilution of electrolyte solutions, has now been extended to apparent molar heat capacities and compressibilities of these systems. The proposed method of calculation, which takes into account the relaxation effect observed in second derivatives of the excess Gibbs free energy, can be used to extrapolate to infinite dilution the experimental data for systems showing a wide range of association constants in acetonitrile, propylene carbonate, and water. The concentration dependence of the thermodynamic properties can be reproduced quantitatively by the addition of one or two virial coefficients. Literature data for C _P,2, and K _S,2, of electrolytes in aprotic solvents were refitted with this equation. For dissociated or slightly associated systems (K _A < 10), the standarY ₂ ^o d infinite dilution quantities () are in excellent agreement with literature values. For systems with high K _A, Y ₂ ^o obtained by the model are systematically lower than those reported in the literature. This is not surprising, since the traditional method of extrapolation using the Debye–Hückel limiting law or the Pitzer equation does not take association into account. A computer software that performs the calculations for the application of the Bjerrum model to thermodynamic properties has been designed and is presented in the appendix.     

Conductance of KCI-Glycerol Solutions: Test of the Fuoss Paired Ion Model

Abstract

The electrical conductance of KC1 in glycerol solutions has been measured at concentrations between 1.5 mol m^?3 and 353 mol m^?3 at 22°C. The results are compared with the Fuoss paired ion model and fits to the data are obtained assuming a Gurney co-sphere having a radius in the approximate range 6 ± 10^?10 m to 9 ± 10^?10 m. The model leads to an estimate of ionic association which is less than that given by the theory of Bjerrum.     

Remarks on the correlation function implied by the Bjerrum theory of ion pairing

The Friedman theory of correlation functions implied by the Bjerrum theory is generalized by taking into account additional terms and by improving the basic expression for the free energy. By combining the mean spherical approximation (MSA) and the mass action law (MAL) good agreement with HNC and MC data is reached.     

Electrolyte-UNIQUAC-NRF Model Based on Ion Specific Parameters for the Correlation of Mean Activity Coefficients of Electrolyte Solutions

The Electrolyte-UNIQUAC-NRF excess Gibbs function was applied to estimate ion specific adjustable parameters of various salts by global optimization of the experimental activity coefficients of 54 electrolyte solutions. Twenty-three ion specific parameters were obtained for water and several cations and anions. The estimated individual ion parameters have been used to predict osmotic coefficient of electrolyte solutions. By using only the specific values for ions, the anion–cation and ion–water interaction parameters of different salts can be precisely estimated. Consequently, the interaction parameters of sparingly insoluble salts without experimental activity data can be easily calculated. For a case study, the solubility of CaSO₄ was predicted in relatively good agreement with experimental values over a wide range of temperatures up to 473.18 K.     

Conductimetric study of cesium chloride in isodielectric aqueous tetrahydrofuran, 1,2-dimethoxyethane and dioxane mixtures from 0 to 35°C

CsCl in nearly isodielectric aqueous mixtures with tetrahydrofuran, 1,2-dimethoxyethane and dioxane has been studied at temperatures between 0° and 35°C. The conductance data are analyzed for the limiting conductance ₀ and the association constant K _A by means of the Justice-Ebeling conductance equation. By application of the Bjerrum equation an apparent distance of closest approach á is evaluated. This parameter is generally close to the crystallographic radius, 35Å. The deviations are attributed to solvation effects and are interpreted in terms of the Friedman-Rasaiah-Gurney cosphere overlap model. The variations of the effect with temperature permits an evaluation of enthalpy and entropy solvation parameters.     

Conductance of Lithium and Sodium Perchlorates and Tetraphenylborates in 2-Butanone from −35 to 25°C

Conductances of dilute solutions of LiClO₄, NaClO₄, LiBPh₄ and NaBPh₄ in 2-butanone were measured at seven temperatures from ?35 to 25°C. The limiting molar conductivities and association constants were evaluated using the conductance equation of Fuoss and Justice (including the Chen effect). The distance parameter was fixed at the Bjerrum distance. The limiting ionic conductivities, determined by assuming equal ionic conductivities of the i-Am₃ BuN⁺ and BPh ₄ ^? ions at all temperatures, were related to the crystallographic ionic radii using the Hubbard–Onsager model of dielectric friction corrected for the inhomogeneity of the electric field. The activation enthalpy of ionic transport in 2-butanone is almost independent of the nature of the electrolyte. The Walden products do not vary with the temperature. The correction to the conductance parameters for dielectric saturation computed for M⁺ClO ₄ ^? associates was found to be small. Thermodynamic functions characterizing the association process were evaluated from K _A data and their dependences on the temperature. The short-range, noncoulombic contributions to the Gibbs energy were estimated using Bjerrum's theory.     

计算离子液体溶液汽液相平衡的分子热力学模型

用平均球近似理论、微扰理论和UNIFAC基团贡献方法分别考虑离子之间的长程静电作用、离子与溶剂之间的中程静电作用以及所有粒子之间的短程作用,本文提出了一种新的分子热力学模型,可用于离子液体溶液中溶剂活度系数的计算.通过对含烷基咪唑磷酸酯类离子液体与水、甲醇或乙醇组成的9个二元体系的饱和蒸汽压数据进行关联,获得了相关的模型参数,即溶剂的分子直径和基团之间的交互作用能参数.溶剂活度系数及饱和蒸汽压的计算结果与实验值的平均偏差为1.40%,符合良好,因此本模型可望用于含离子液体体系汽液相平衡的预测.     

Electrolyte exclusion from charged adsorbent: replica Ornstein-Zernike theory and simulations

Structural and thermodynamic properties of the restrictive primitive model +1:-1 electrolyte solution adsorbed in a disordered charged media were studied by means of the Grand Canonical Monte Carlo simulation and the replica Ornstein-Zernike theory. Disordered media (adsorbent, matrix) was represented by a distribution of negatively charged hard spheres frozen in a particular equilibrium distribution. The annealed counterions and co-ions were assumed to be distributed within the nanoporous adsorbent in thermodynamic equilibrium with an external reservoir of the same electrolyte. In accordance with the primitive model of electrolyte solutions, the solvent was treated as a dielectric continuum. The simulations were performed for a set of model parameters, varying the net charge of the matrix (i.e., concentrations of matrix ions) and of annealed electrolyte, in addition to the dielectric constant of the invading solution. The concentration of adsorbed electrolyte was found to be lower than the corresponding concentration of the equilibrium bulk solution. This electrolyte "exclusion" depends strongly on the dielectric constant of the invading solution, as also on concentrations of all components. The most important parameter is the net charge of the matrix. Interestingly, the electrolyte rejection decreases with increasing Bjerrum length for the range of parameters studied here. The latter finding can be ascribed to strong inter-ionic correlation in cases where the Bjerumm length is high enough. To a minor extent, the adsorption also depends on the spacial distribution of fixed charges in adsorbent material. The replica Ornstein-Zernike theory was modified to cater for this model and tested against the computer simulations. For the range of parameters explored in this work, the agreement between the two methods is very good. These calculations were also compared with the results of the classical Donnan theory for electrolyte exclusion.     

A conductance investigation of HCl in aqueous solutions of tetrahydrofuran,dimethoxyethane and dioxane

Conductance of dilute solutions of HCl in water-tetrahydrofuran (THF), water-dioxane and water-dimethoxyethane (DME) were measured and the data processed using the Justice-Ebeling equation to evaluate the limiting conductance _O, the association constant K_A and the apparent distance of closest approach a'. The Friedman-Rasaiah Gurney cosphere overlap term d_+–/kT was calculated from a' values and illustrates the different solvation pattern of dioxane compared to that found for THF and DME. It would appear that dioxane can solvate cations more strongly due to its ability to form a boat configuration around a cation. The association constants are reasonably reproduced by the Bjerrum equation using realistic molecular dimensions of the ions involved for the distance of closest approach. The limiting conductance in the mixtures illustrates clearly the different mechanism for proton conductance compared to that for the cesium ion. The dielectric constants, viscosities and densities of the solvent mixtures were measured and are reported. The lowest dielectric constant for each type of solvent mixture was about 10.     

Kinetics and mechanism of oxidation of chloramphenicol by 1-chlorobenzotriazole in acidic medium

Chloramphenicol (CAP) is an antibiotic drug having a wide spectrum of activity. The kinetics of oxidation of chloramphenicol by 1-chlorobenzotriazole (CBT) in HClO₄ medium over the temperature range 293–323 K has been investigated. The reaction exhibits first-order kinetics with respect to [CBT]_o and zero-order with respect to [CAP]_o. The fractional-order dependence of rate on [H⁺] suggests complex formation between CBT and H⁺. It fails to induce polymerization of acrylonitrile under the experimental conditions employed. Activation parameters are evaluated. The observed solvent isotope effect indicates the absence of hydride transfer during oxidation. Effects of dielectric constant and ionic strength of the medium on the reaction rate have been studied. Oxidation products are identified. A suitable reaction scheme is proposed and an appropriate rate law is deduced to account for the observed kinetic data.     

A comparison of the conductimetric behavior of cesium chloride in water-tetrahydrofuran,water-dioxane,and water-1,2-dimethoxyethane mixtures

The association constants of CsCl in water-THF, water-dioxane, and water-1,2-DME mixtures have been evaluated from conductance data using the Pitts, the Fuoss-Hsia, and a new conductance equation which includes the Chen electrophoretic effect. It is shown that the three sets of results confirm the Bjerrum concept of association. The differences observed for the ion association in the three types of mixtures are interpreted in terms of differences in the dipolar nature of the three organic molecules and that of H₂O.     

Series approach to modeling ion size effects for symmetric electrolytes in the diffuse double layer

An analytical model is developed for the potential drop and differential capacity across the diffuse layer which considers the effects of ion size on these properties. For symmetric electrolytes, this potential drop is expressed in terms of a cubic polynomial in the corresponding estimate in the Gouy-Chapman theory. Optimal polynomial coefficients and model validation for 1:1 and 2:2 electrolytes are provided by fits of Monte Carlo data obtained for a restricted electrolyte in a primitive solvent. Simple relationships between these coefficients and parameters commonly associated with the mean spherical approximation are obtained. It is shown that the series approach accurately describes potential drops and differential capacities of the diffuse layer for 1:1 and 2:2 electrolytes for the chosen assumptions.     

Conductance of salts at moderate and high concentrations in propylene carbonate-dimethoxyethane mixtures at temperatures from −45°C to 25°C

The specific conductances of LiClO₄, KSCN, KPF₆, and Et₄NPF₆ in propylene carbonate-dimethoxyethane mixtures are reported for moderate to high concentrations at temperatures between –45°C to 25°C. The data analysis was established on the base of an empirical conductance equation permitting equally well adapted fits for all electrolyte solutions irrespective of temperature, electrolyte compound and solvent composition. The effects on the conductance resulting from ion-ion, ion-solvent interactions and solvent viscosity are rationalized in terms of the thermodynamic and hydrodynamic parameters characterizing the behaviour of electrolytes in dilute solutions. Some basic aspects are discussed for optimizing the conductance of battery electrolytes, especially those of high energy density batteries.     

Application of Restrictive Primitive SAFT Coupled with Different Hard-Sphere Equations to Model Mean Ionic Activity Coefficients of Electrolyte Solutions

In this work, the primitive SAFT equation of state along with three different hard-sphere equations was used to correlate and predict mean ionic activity coefficients of aqueous electrolyte solutions. The mean ionic activity coefficient of aqueous electrolyte solutions was considered as the contribution of hard-sphere and dispersion effects. The Mansoori (M), Wang-Khoshkbarchi-Vera (WKV) and Ghotbi-Vera (GV) hard-sphere equations were applied in correlating the mean ionic activity coefficient of electrolyte solutions. The comparison among above indicated equations was shown. First, vapor pressure and densities of water in the temperature range of 373.15 to 423.15 K was regressed by SAFT equation of state. In the restrictive primitive mean spherical model, ions were hard spheres without any chain structure. Neither association effects were considered in this study. Clearly, in common used five SAFT parameters were decreased to three, which were calculated by using the experimental mean ionic activity coefficients of electrolyte solutions. The comparison among three hard-sphere equations of state approved that Ghotbi-Vera hard-sphere model (GV) correlated the experimental data accurately than the others; two hard-sphere models. The mean ionic activity coefficients of some electrolyte solutions were being predicted by taking the advantage of the regressed values surely, in a wide range of molality.     

Measurements of vapour-liquid equilibria,densities, viscosities and dielectric properties of cyclohexanone + triethylamine mixtures with respect to keto-enol tautomerism

Densities, ?, kinematic viscosities ν, refractive indices n_D referred to the sodium D-line, static relative permittivities ε, specific conductances κ and vapour-liquid equilibrium data for cyclohexanone + triethylamine mixtures have been determined at two temperatures. Excess properties of mixing calculated from these data indicate that in such mixtures considerable amounts of enol-amine associates are formed. The permittivity data indicate that the formation of associates is an exothermic process, which also has a marked influence on the thermodynamic excess properties of the mixtures. The enol-amine associates may undergo electrolytic dissociation. A common evaluation of static relative permittivities and specific conductances shows that for the mixture the conductance data are affected considerably by the formation of undissociated ion pairs in the sense of Bjerrum theory, especially at concentrations of the mixture where it is less polar. The conductance data are also influenced considerably by the fact that the ion pairs are solvated if the molar ratio of triethylamine exceeds 0.5.