Phase Equilibria in the System NH4Al(SO4)2–H2SO4–H2O

Equilibrium solubility curves of the ammonium aluminium sulphate in aqueous solutions of sulphuric acid have been calculated using checked literature data and our own measurements. The concentration of sulphuric acid ranged from 0 to 23 mass%, temperature range between 20 and 60°C has been extrapolated up to 75°C by means of a thermodynamically based correlation method. The solubility correlation as well as the hydration analysis implied a possible destructuralization of solutions at higher acid concentrations. This revised version was published online in August 2006 with corrections to the Cover Date.     

A theoretical study of the H2SO4+H2O → HSO4 −+H3O+ reaction at the surface of aqueous aerosols

The surface region of sulfate aerosols (supercooled aqueous concentrated sulfuric acid solutions) is the likely site of a number of important heterogeneous reactions in various locations in the atmosphere, but the surface region ionic composition is not known. As a first step in exploring this issue, the first acid ionization reaction for sulfuric acid, H₂SO₄ + H₂O HSO₄^– + H₃O⁺, is studied via electronic structure calculations at the Hartree–Fock level on an H₂SO₄ molecule embedded in the surface region of a cluster containing 33 water molecules. An initial H₂SO₄ configuration is selected which could produce H₃O⁺ readily available for heterogeneous reactions, but which involves reduced solvation and is consistent with no dangling OH bonds for H₂SO₄. It is found that at 0 K and with zero-point energy included, the proton transfer is endothermic by 3.4 kcal/mol. This result is discussed in the context of reactions on sulfate aerosol surfaces and, further, more complex calculations.Contribution to the Jacopo Tomasi Honorary Issue     

Determination of the dielectric tensor function of triclinic CuSO4·5H2O

We present the first successful dispersion analysis of a triclinic crystal in the infrared spectral region. The corresponding scheme involves the parallel evaluation of 12 polarized reflection spectra recorded from three mutual perpendicular faces of a cube-shaped crystal. The dispersion analysis was carried out on a CuSO₄·5H₂O single crystal. The determined oscillator parameters and the corresponding dielectric function tensor were used to model the spectra of polycrystalline CuSO₄·5H₂O. The good correspondence between modeled and experimental spectra of the polycrystalline species proves the correctness of the approach.     

Oxidation of Deactivated Cage Substrates in the System H2SO4–HNO3

Russian Journal of Organic Chemistry - The kinetics of oxidation of 16 carboxylic acid esters of the adamantane series in the system H2SO4–HNO3 have been studied, and the effective rate...     

New approach to simplify the equation for the excess Gibbs free energy of aqueous solutions of electrolytes applied to the modelling of the NH3–CO2–H2O vapour–liquid equilibria

A new, simple, empirical equation for G^E (excess Gibbs free energy) of electrolyte solutions is proposed in which, contrary to the commonly used Pitzer equation, binary and ternary interaction parameters relate to the interactions of electrolytes in a solution rather than to the interactions of real species in a solution (i.e., anions, cations and nondissociated molecules). Such an approach radically reduces the number of parameters in the new equation for G^E as compared with the Pitzer equation and consequently significantly simplifies their calculation. The efficiency of the new approach is demonstrated on the example of modelling the vapour–liquid equilibria of the industrially important and widely investigated NH₃–CO₂–H₂O system.     

Estimation of activity coefficients of ionic species of aqueous strong electrolytes within the extended Debye–Hückel concentration range

The concentration curve of mean activity coefficient to the required power was fitted by a product function. The product function can be factorized in factor functions which represent the concentration dependence of the single-ion species (J Solid State Electrochem, in press, 1). With a simplified procedure of this method, it is possible to split the mean activity coefficients into the individual parts for the ionic species within the extended Debye–Hückel concentration range. This method is applicable to all strong electrolytes because it is not necessary to have further data or additional assumptions.     

Temperature dependence of the substrate selectivity in the hydroxylation of alkylbenzenes in the H2O2−H2SO4 system

The substrate selectivity in the hydroxylation of methylbenzenes in the H₂O₂−H₂SO₄ (70 wt.%) system was studied at 15–55 °C. The activation entropy correlates with the basicity of the arenes, while the substrate selectivity and activation enthalpy correspond both with the basicity and ionization potentials of ArH. We concluded that the structure of the reaction transition state is intermediate between a charge transfer complex and σ-complex. L. M. Litvinenko Institute of Physical Organic and Coal Chemistry, National Academy of Sciences of Ukraine, 70 R. Lyuksemburg ul., Donetsk 340114, Ukraine. Translated from Teoreticheskaya i éksperimental’naya Khimiya, Vol. 35, No. 1, pp. 39–43, January–February, 1999.     

Interaction parameters and (solid + liquid) equilibria calculation for KCl–H2O–HCl–C2H5OH,K2SO4–H2O–H2SO4 and K2SO4–H2O–C2H5OH mixed solvent-electrolyte systems

This work deals with the prediction and experimental measurements of the (solid + liquid) equilibrium (SLE) in acid medium for industrial purposes. Specific systems including KCl–ethanol–water–HCl and K₂SO₄–water–H₂SO₄ were analyzed. At first, a critical discussion of SLE calculations was given, based on the well-known UNIQUAC extended and LIQUAC models. Two new proposals were derived, considering the explicit necessity of a new reference state for SLE calculations for the studied (solvents + acid) mixtures. The solubility of KCl in water–ethanol–HCl mixed solvents was measured in the temperature range of 300.15 to 315.15 K using an analytical gravimetric method. These results combined with some other experimental data reported in the open literature let us to propose a set of parameters for the new models. They included the interaction parameters between ethanol and the H⁺ ion. The prediction capability of the new models, for calculations in acid medium, was illustrated. Experimentally, it was observed that the (K₂SO₄ + water + H₂SO₄) system presented the unusual behavior of increasing K₂SO₄ solubility with an increase in the sulfuric acid concentration. This was accurately predicted by the newly proposed models.     

Secondary environment effects on the first step of the protonation of SO 4 2− in saline aqueous solutions

The solubility of strontium sulfate in the mixtures of isomolar LiClO₄(NaClO₄) and HClO₄ aqueous solutions was determined at 25°C and ionic strengths of I = 0.5, 1.0, 2.0, 3.0, and 4.0. At I>-2, the solubility of SrSO₄ as a function of the hydrogen ion (HClO₄) concentration passes through a maximum, clearly showing a substantial contribution from environment effects (H⁺ substitution for Li⁺ or Na⁺), which counteract complexation (i.e., HSO ₄ ^? formation). A correct method for separating these two effects was proposed, and the parameters of the environment effect and the standard values of pSP° and logβ° were evaluated.     

Electrochemical amination of anisole in 4–6 M solutions of H2SO4 and acetonitrile

Indirect cathode amination of anisole with Ti(IV)/Ti(III) and NH₂OH in media containing 4 or 6 M H₂SO₄, CH₃CN, and H₂O (in small amounts) was studied. Para- and ortho-anisidines were the major products of radical cation substitution at 15–45°C. The total yield of monoamino compounds based on the source of amino radicals (with its full conversion) may be up to 84% in these conditions.     

An investigation of the polythermal diagram of the H2ONa2HPO4Na2SO4 system

The polythermal diagram of the ternary system H₂ONa₂HPO₄Na₂SO₄ has been established, setting up nine isotherms obtained between 0 and 25°C by conductimetric analysis. The solubility domains of the various solid phases have been determined. One eutectic, three stable and one metastable transitional transformations have been observed. Temperature and composition of the eutectic point have been obtained by thermal analysis at constant flow.     

A Facile H2SO4-SiO2–Catalyzed Ferrier Rearrangement of 3,4,6-Tri-O-benzyl-d-glucal

Sulfuric acid immobilized on silica gel (H₂SO₄-SiO₂) was used as an efficient and convenient promoter for Ferrier-type rearrangement of 3,4,6-tri-O-benzyl-d-glucal in CH₂Cl₂, which is a difficult donor for this type of reaction. The acceptors include primary alcohols, secondary alcohols, pentanol, halogenated alcohol, sterols, thiol, and 2-naphthol. Thus, 2,3-unsaturated glycosides were obtained rapidly (<2 h) and efficiently (>62%) in good α-selectivity (α/β>4.2:1) under mild conditions.     

Modeling of esterification of acetic acid with n-butanol in the presence of Zr(SO4)2·4H2O coupled pervaporation

Modeling of esterification of acetic acid with n-butanol in the presence of Zr(SO₄)₂·4H₂O coupled pervaporation was studied in this paper. The influence of several process variables, such as process temperature, initial mole ratio of acetic acid over n-butanol, the ratio of the effective membrane area over the volume of reacting mixture and catalyst content, on the esterification was discussed. The calculated results for the conversion of n-butanol to water and permeation flux were consistence with the experimental data. The permselectivity and water content can be roughly estimated by the model equations.     

Solubility and stability of (NH4)2SO4 · H2O2 in aqueous solutions and change in some crystallographic parameters of (NH4)2SO4 precipitates

Stability of (NH₄)₂SO₄ · H₂O₂ aqueous solutions and some structural changes in ammonium sulfate in the course of its solvation and subsequent desolvation were studied.     

Sodium ion-conducting solid electrolytes in the system Na3PO4Na2SO4

In the system Na₃PO₄Na₂SO₄, the high-temperature, cubic γ form of Na₃PO₄ forms an extensive range of solid solutions: Na_3−x(P_1−xS_x)O₄, 0 < x < (0.57 to 0.70, depending on temperature). For compositions in the range x = ca. 0.33 to 0.57, these γ solid solutions are thermodynamically stable at all temperatures. The conductivity of the γ solid solutions increases with increasing x and reaches a maximum at x = 0.5 to 0.6, with values of 2 × 10⁻⁵ ohm⁻¹ cm⁻¹ at 100°C, rising to 1.3 × 10⁻² ohm⁻¹ cm⁻¹ by 300°C; this conductivity increase with x is attributed to an increase in the sodium ion vacancy concentration, associated with the solid solution mechanism Na + PS. The phase diagram for the system Na₃PO₄Na₂SO₄ is given together with lattice parameters of the γ solid solutions.     

Measurements of the Solid–Liquid Equilibria in the Quaternary System NaCl–NaBr–Na2SO4–H2O at 323 K

Phase equilibria of the quaternary NaCl–NaBr–Na₂SO₄–H₂O system at 323 K were studied by the isothermal dissolution equilibrium method. The solubilities of salts and densities of saturated solutions were determined. Solid solutions [Na(Cl, Br)] were found in the experiments. The phase diagram of the quaternary system has no invariant point, but has one univariant curve at the boundary of Na(Cl, Br) and Na₂SO₄ crystallization fields. The experimental results show that an increase of the NaBr concentration is accompanied by an obvious increase of the solution density and the decrease of the solubilities of NaCl and Na₂SO₄.     

Transport properties of electrodialysis membranes in the presence of Zn2+ complexes with Cl−

The aim of this paper is to investigate the properties of anion exchange electrodialysis membranes in contact with aqueous solutions containing zinc chloride complexes. Measurements of electric resistance, water content, quantity of sorbed electrolytes, self-diffusion and electrotransport ionic fluxes were performed as a function of the composition of the external solutions. The results were analysed in relation to the complex formation inside the solutions.     

On the Reaction Mechanism of Br2 with OCS

The reaction mechanism of photochemical reaction between Br2 (^1∑) and OCS (^1∑) is predicted by means of theoretical methods. The calculated results indicate that the direct addition of Br2 to the CS bond of OCS molecule is more favorable in energy than the direct addition of Br2 to the CO bond. Furthermore, the intermediate isomer syn-BrC(O)SBr is more stablethe rmodynamically and kinetically than anti-BrC(O)SBr. The original resultant anti-BrC(O)SBr formed in the most favorable reaction channel can easily isomerize into the final product syn-BrC(O)SBr with only 31.72 kJ/mol reaction barrier height. The suggested mechanism is in good agreement with previous experimental study.