Temperature dependence of adsorption parameters of n-butanol and n-valeric acid at their adsorption on mercury electrode from aqueous solutions

Adsorption parameters that enter into the Frumkin isotherm and the model of two parallel capacitors are calculated based on the data of the regression analysis of differential capacitance curves of a mercury electrode in solutions of n-butanol and n-valeric acid at 25, 50, and 75°C. The analysis of the temperature dependences of these parameters allowed free energies, entropies, and enthalpies of adsorption to be found. It is shown that the hydrophobic effect, which is associated with the increase in the enthalpy of liquid water when adsorbate molecules leave it, makes a substantial contribution into the adsorption free energy of studied compounds.     

Refining adsorption parameters of n-butyl alcohol at the interface of mercury electrode with aqueous NaF and Na2SO4 solutions by correcting the adsorbate concentration

As an adjunct to the regression analysis of differential capacitance curves, which allows refining the adsorption parameters, a program, which takes into account possible errors in volume concentrations of organic substances, is developed. Using this procedure, the earlier data on the differential capacitance of a mercury electrode in aqueous solutions of normal butanol (1-BuOH) containing either 0.1 M NaF or 0.05 and 0.5 M Na₂SO₄ as the supporting electrolyte are analyzed. This allows obtaining the most accurate values of adsorption parameters for the systems mentioned above within the framework of the model of two parallel capacitors and the Frumkin isotherm. It is shown that, when a linear dependence of the intermolecular interaction parameter on the electrode potential is taken into account, the standard deviation of experimental capacitance values from those calculated using the mentioned model is 6.8–8.8%, which points to very high accuracy of this phenomenological model.     

Determining Sodium Kryptate Adsorption Parameters on a Mercury Electrode in 1 M Na2SO4

The adsorption of a complex of sodium cations with a macrocyclic ligand (Kryptofix^R 222, composition C₁₈H₃₆N₂O₆) as a function of its concentration in 1 M Na₂SO₄ is studied by measuring the differential capacitance on a stationary Hg drop. Adsorption parameters of sodium kryptate are found using a regression analysis method and various versions of a model of two parallel capacitors complemented with the Frumkin adsorption isotherm. The differential capacitance curves, calculated on the basis of these, are compared with experimental data. The difference in model versions that most adequately describe the adsorption data, established for systems in 0.1 and 1 M Na₂SO₄, is explained by the influence of the supporting electrolyte on the adsorption layer structure. Conclusions are made on the absence in the system under study of the salting-out from the bulk solution and on a change in the properties of an adsorption layer of sodium kryptate in the region of potentials of the anodic adsorption–desorption peak following expansion of the adsorption region.     

Adsorption of the lanthanum and thorium cryptates at mercury electrode

The adsorption behavior of cryptates of La³⁺ and Th⁴⁺ cations at the Hg/aqueous solution interface is studied by using the electrochemical impedance spectroscopy method. It was shown that the studied complexes have high surface activity at the interface. The lanthanum cryptate adsorption parameters are found using the regression analysis based on the two parallel capacitor model supplemented by the Frumkin adsorption isotherm. The differential capacitance curves calculated by using these parameters agree satisfactorily with the experimental ones. The more complicated adsorption behavior of lanthanum cryptate, as compared with the complexes of lower valence cations, is interpreted with taking into consideration the strong interaction of the La³⁺ cation contained in the [2.2.2.] cryptand intramolecular cavity with the supporting electrolyte anions.     

Adsorption phenomena on a mercury electrode in aqueous cryptand[2.2.2] solutions by the background of tetraalkylammonium salts

The electrochemical behavior of cryptand[2.2.2] (Cry) is studied on a mercury electrode in aqueous solutions of tetraalkylammonium tetrafluoroborates (Me₄N⁺, Et₄N⁺, and Bu₄N⁺). Cryptand [2.2.2] is shown to exhibit high surface activity in Me₄ NBF₄ nd Et₄NBF₄ solutions. Based on the model of two parallel capacitors supplemented by the Frumkin adsorption isotherm, the adsorption parameters of Cry by the background of Me₄BNF₄ were calculated using the regression analysis methods. The calculated dependences of the differential capacitance on the potential adequately agree with experimental curves. The adsorption characteristics of Cry in the studied solutions are compared with those in MgSO₄ solutions. By the background of Bu₄NBF₄, Cry molecules and Bu₄N⁺ cations exhibit very close surface activity and form a mixed adsorption layer.     

Estimation of parameters characterizing the adsorption of sodium,potassium, and rubidium cryptates at the mercury electrode/solution interface

The adsorption of complexes formed by sodium, potassium, and rubidium cations with macrobicyclic ligand (kryptofix 222 with C₁₈H₃₆N₂O₆ composition) is studied as a function of the ligand concentration on a stationary mercury drop in 0.1 M solutions of corresponding sulfates and chlorides by using the differential capacitance technique. Based on the model of two parallel capacitors supplemented by the Frumkin isotherm, the adsorption parameters of studied cryptates are estimated by using the regression analysis technique. Differential capacitance curves calculated with the parameters found are compared with experimental data. The comparison of the found adsorption parameters makes it possible to reveal the effects of the nature of included cations and specifically adsorbed supporting-electrolyte anions on the adsorption behavior of cryptates under study.__________Translated from Elektrokhimiya, Vol. 41, No. 4, 2005, pp. 475–481.Original Russian Text Copyright © 2005 by Stenina, Sviridova.     

Modelling the thermal behaviour of carboxylic acid derivatives with cylcodextrins in the solid-state

The application of classical QSAR and molecular modelling to the inclusion complexation of natural and modified cyclodextrins (CDs) with carboxylic acid derivatives as guest molecules was examined. Information was available on the thermal behaviour, in the solid-state of benzoic acid (BA), salicylic acid (SA), and various substituted aminosalicylic acids (3-aminosalicylic acid, 3-ASA, 4-aminosalicylic acid, 4-ASA and 5-aminosalicylic acid, 5-ASA), as well as on the thermal behaviour of 1:1 molar ratio physical and kneaded mixtures of these acids with each of three different cyclodextrins, β-, (BCD) 2-hydroxypropyl-β-, (HPBCD) and γ-cyclodextrin (GCD). The thermal behaviour of the binary (1:1 stoichiometry) mixtures was modelled using stepwise multiple regression (SMR). Two models for the prediction of the percentage mass loss and enthalpy of dehydration of the physical mixtures were established with correlation coefficients (r) of 0.79 and 0.92, respectively. Decreased correlation in the thermal behaviour of kneaded mixtures indicated significant interaction and possible formation of inclusion complexes. This revised version was published online in July 2006 with corrections to the Cover Date.     

Radiolysis of acid water (0.4 M H2SO4) at elevated temperatures with fast neutrons and proton beam

To elucidate the G-values of water decomposition products at elevated temperatures up to 270°C, radiolysis of acid water, 0.4 M H₂SO₄, has been carried out with fast neutrons in a reactor by a combination of the Fricke, cerium and bichromate dosimeters. At room temperature, the radical yield is smaller and the molecular yield is larger than those established in γ-radiolysis and net water decomposition is smaller. With increasing temperature, the ratio of the radical to molecular yields becomes similar to that in γ-radiolysis at room temperature. In order to check the above evaluation, proton beam radiolysis was also conducted at elevated temperatures as a model experiment. Although the temperature range was limited between room temperature and 80°C, the proton beam experiment confirms the evaluation obtained in the fast neutron radiolysis.     

Activity coefficients for the system NaCl+Na2SO4+H2O at various temperatures. Application of Pitzer's equations

The mean activity coefficients of NaCl in the system NaCl+Na₂SO₄+H₂O at various compositions were determined in the temperature range 5–45°C from the emf of potentiometric cells. By processing the results using Pitzer's equations the mixing parameters describing the non-ideal behavior of electrolytes were calculated. The temperature coefficients of the mixing parameters were determined and found not to be significant. The mixing parameters and temperature coefficients calculated for the binary mixture can be used to describe the behavior of multicomponent systems containing NaCl and Na₂SO₄, and eventually sea water.     

Thermodynamic quantities for the interaction of SO 4 2− with H+ and Na+ in aqueous solution from 150 to 320°C

The aqueous reactions,

Theoretical study of the first acid dissociation of H2SO4 at a model aqueous surface

Electronic structure calculations on the H2SO4.(H2O)(4,6) model system embedded at the surface of an aqueous layer have been performed to examine the feasibility of the first acid dissociation of H2SO4 to an H2SO4-.H3O+ contact ion pair over a wide temperature range, with a special focus on the 190-250 K range relevant for atmospheric sulfate aerosols. The results indicate that the acid dissociation can be either thermodynamically favored or disfavored depending on the degree of solvation of the acid and the produced ions, as well as on the temperature.     

Thermodynamic Study of the NaCl + Na2SO4 + H2O System by Emf Measurements at Four Temperatures

Activity coefficients for sodium chloride in the NaCl + Na₂SO₄ + H₂O ternary system were determined from emf measurements of the cell

Synthesis, Characterization and Crystal Structure of [Na2(APZC)2(μ-H2O)2(μ3-H2O)]n

The synthesis and spectroscopic properties of a Na^＋ complex with ligand 3-aminopyrazine-2-carboxylic acid were described. The resulting complex was characterized by elemental analysis, IR, UV-Vis, NMR spectroscopy and single crystal X-ray diffraction method. The title compound crystallizes in the triclinic system with space group . The crystalline structure of this compound consists of supramolecular architectures involving strong intramolecular N—H…O in pyrazine molecules and intermolecular O—H…N, O—H…O, and N—H…N hydrogen bonds between substituted pyrazine and water molecules.     

The temperature dependence of hydrogen and anion adsorption at a Pt( 100) electrode in aqueous H2SO4 solution

Research on the underpotential deposition of H (upd H) and anion adsorption on Pt( 100) in 0.5 M aqueous H₂SO₄ solution by cyclic voltammetry (CV) indicates that the overall adsorption/desorption charge density is affected strongly by variation of the temperature T, and that it decreases by about 1/3 when T is raised from 293 to 328 K. The sharp peak at 0.375 V vs. RHE assigned to the anion adsorption decreases its potential, current density and charge density. The CV feature assigned to the upd H, a wide shoulder overlapping the sharp peak, also decreases with T augmentation, but the decline of its charge density is less pronounced. The results indicate that the H_upd and anion surface coverages, θ_HAN and θ_AN respectively are strongly temperature-dependent. This behavior may be assigned to lateral repulsive interactions.     

Measurement of ordered associate of protonated tetraphenylporphine formed at toluene/aqueous H2SO4 interface by attenuated total internal reflection spectroscopy with polarized light

Attenuated total internal reflection (ATR) spectroscopy with an s- or p-polarized visible light was examined for some species of protonated 5,10,15,20-tetraphenylporphine (tpp) at toluene/aqueous H₂SO₄ (3-6 mol dm⁻³) interface. Tpp initially dissolved in the toluene phase was diprotonated at the interface to form monomeric H₂tpp²⁺, the absorption peak of which was 438 nm. At the same time, a long H₂tpp²⁺ oligomer was formed, the absorption peak of which was 448 nm. The two interfacial species were transient. Just after their disappearance, a rod-shaped H₂tpp²⁺ associate was formed at the interface, the absorption peak of which was 417 and 478 nm. The former and latter wavelengths corresponded to H- and J-bands of the associate, respectively. Theoretical calculation of the strength of electric field of light at the interface allowed one to estimate the interfacial concentration of the three species with measured reflection absorbance (A_R). The monomeric H₂tpp²⁺ and its oligomer were at sub-monolayer levels, whereas the associate was at a multilayer level. Reflection absorption anisotropy (K_R), which was calculated from A_R with the s- and p-polarized lights, was adopted for the evaluation of out-of-plane orientation of the interfacial species for the first time. The K_R value suggested that the rod-shaped associate lay at the interface.     

Thermodynamic quantities for the interaction of H+ and Na+ with C2H3O 2 − and Cl− in aqueous solution from 275 to 320°C

The aqueous reactions, {ie865-1}were studied as a function of ionic strength at 275, 300, and 320°C using a flow calorimetric technique. Log K, H and S values were determined from the fits of the calculated and experimental heats while Cp values were calculated from the variation of H values with temperature. The log K and H values for the first two reactions agree well with literature values at these temperatures. No previous results have been reported for the third reaction. The use of equations containing identical numbers of positive and identical numbers of negative charges on both sides of the equal sign (isocoulombic reaction principle) was applied to the log K values determined in this study. The resulting plots of log K for the isocoulombic reactions vs. I/T were approximately linear, which demonstrates that the Cp values for these reactions are approximately zero.Deceased 5 September 1987     

An aqueous thermodynamic model for a high valence 4∶2 electrolyte Th4+−SO 4 2− in the system Na+−K+−Li+−NH 4 + −Th4+−SO 4 2− −HSO 4 − −H2O to high concentration

An aqueous thermodynamic model that is valid from zero to high concentration is proposed for the Na⁺–K⁺–Li⁺–NH ₄ ⁺ –Th⁴⁺–SO ₄ ^2– –HSO ₄ ^– –H₂O system. The model is based on the aqueous ion-interaction model of Pitzer and coworkers. The thorium sulfate complex species Th(SO₄)₂(aq) and Th(SO₄) ₃ ^2– are also included in the model. The final thermodynamic model presented here accurately predicts all reliable thermodynamic data, including solvent extraction and solubility data, for the Na⁺–K⁺–Li⁺–NH ₄ ⁺ –Th⁴⁺–SO ₄ ^2– –HSO ₄ ^– –H₂O system to high concentration. The aqueous thermodynamics of high-valence (3:2, 4:2), electrolytes are complicated by very strong specific ion interactions or ion pairing in dilute solution and by an effective redissociation of aqueous complex species at high concentration. Methods of treating these complications, in terms of valid aqueous thermodynamic models, are discussed in detail for the high-valence Th⁴⁺–SO ₄ ^2– –H₂O system.     

Equilibrium isotope effects in aqueous systems. IV. The vapor pressures of NaBr,Nal, KF,Na2SO4, and CaCl2 solutions in H2O and D2O (O to 90°C). Vapor pressures of Na2SO4·10H2O, ·10D2O and CaCl2·2H2O, ·2D2O

Solvent vapor pressure isotope effects have been measured in HOH/DOD between approximately 0 and 90°C on the following electrolyte solutions: NaBr (2, 5, 7, and 9m), NaI (4, 6, 8, and 10m), KF (3, 6, 9, and 12m), Na₂SO₄ (2m and saturated solutions, and hydrated cyrstal), and CaCl₂ (3, 5.5, 8, and 10m, and hydrated crystal). Values of the isotope effects on the various excess thermodynamic properties of solution, including the osmotic and activity coefficients and the excess free energies, enthalpies, and entropies, have been extracted from least-square expressions which fit the VPIE over the entire concentration and temperature range. The results are compared with those obtained for alkali metal chloride solutions (I, II) and literature data where possible. They are discussed briefly in terms of solution structure.     

Kinetics and mechanism of the reactions of C6H12, C5H10 and C6D12 cycloalkanes with peroxynitrous acid in aqueous solution and the gas phase

The c-C₆H₁₂/c-C₆D₁₂ kinetic isotope effect (KIE), the k₆/k₅ rate constant ratio (c-C₆H₁₂/c-C₅H₁₀), and the temperature dependence of these ratios in the gas-phase reactions of cycloalkanes with peroxynitrous acid and OH radicals are identical. The same result was obtained for the reactions in aqueous solution. These data are in accord with the conclusion that OH^· radicals formed in the homolysis of the HO-ONO bond are the active species in the reactions of HOONO with hydrocarbons in aqueous solution and in the gas phase. __________ Translated from Teoreticheskaya i éksperimental’naya Khimiya, Vol. 44, No. 2, pp. 105–110, March–April, 2008.     

Formic acid catalyzed gas-phase reaction of H2O with SO3 and the reverse reaction: a theoretical study

The formic acid catalyzed gas‐phase reaction between H₂O and SO₃ and its reverse reaction are respectively investigated by means of quantum chemical calculations at the CCSD(T)//B3LYP/cc‐pv(T+d)z and CCSD(T)//MP2/aug‐cc‐pv(T+d)z levels of theory. Remarkably, the activation energy relative to the reactants for the reaction of H₂O with SO₃ is lowered through formic acid catalysis from 15.97 kcal mol^?1 to ?15.12 and ?14.83 kcal mol^?1 for the formed H₂O ??? SO₃ complex plus HCOOH and the formed H₂O ??? HCOOH complex plus SO₃, respectively, at the CCSD(T)//MP2/aug‐cc‐pv(T+d)z level. For the reverse reaction, the energy barrier for decomposition of sulfuric acid is reduced to ?3.07 kcal mol^?1 from 35.82 kcal mol^?1 with the aid of formic acid. The results show that formic acid plays a strong catalytic role in facilitating the formation and decomposition of sulfuric acid. The rate constant of the SO₃+H₂O reaction with formic acid is 10⁵ times greater than that of the corresponding reaction with water dimer. The calculated rate constant for the HCOOH+H₂SO₄ reaction is about 10^?13 cm³ molecule^?1 s^?1 in the temperature range 200–280 K. The results of the present investigation show that formic acid plays a crucial role in the cycle between SO₃ and H₂SO₄ in atmospheric chemistry.