Effect of adding H2SO4 and NaCl TO palladium-containing catalysts on the results of methane oxidation at 220°C

A study has been made of the interaction of methane at 220°C with silica gel-supported complexes of palladium(II), Na_n H_9-n[PMo₆V₆O₄₀], H₉[PMo₆V₆O₄₀], H₃[PMo₁₂O₄₀], NaCl, and with added sulfuric acid. Competition between electrophilic and chloride pathways is examined. Additions of Na⁺ and Cl^– direct the reaction along the chloride pathway, leading to the formation of CH₃Cl. Without NaCl, the electrophilic mechanism is realized, the main product of which is CO₂.L. M. Litvinenko Institute of Physical-Organic Chemistry and Coal Tar Chemistry, National Academy of Sciences of the Ukraine, 70 R. Luxembourg Street, Donetsk 340114, Ukraine. Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 32, No. 2, pp. 92–96, March–April, 1996. Original article submitted June 30, 1995.     

Catalysis by titanium (IV) ions of reactions forming chlorohydrins from olefins

A study was made of reactions forming chlorohydrins from cyclohexane and other olefins acted upon by H₂O₂ and HCl or H₂O₂ and TiCl₄ in alcoholic solutions. The catalyzing action of titanium (1V) was established, and possible reaction mechanisms are discussed.L. V. Pisarzhevskii Institute of Physical Chemistry, National Academy of Sciences of Ukraine, 31 Prosp. Nauki, 252039, Kiev, Ukraine. Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 32, No. 5, pp. 295—299, September–October, 1996. Original article submitted February 9, 1996.     

Structures of Concentrated Sulfuric Acid Determined from Density, Conductivity, Viscosity, and Raman Spectroscopic Data

Addition of water to stoichiometric 100% sulfuric acid increases the density untila maximum results near 87 mole% H₂SO₄. The density and conductivity maximaand viscosity minimum, the latter two near 75 mole%, are direct macroscopicresponses to microscopic quantum mechanical properties of H₃O⁺ and of nearlysymmetric H-bond double-well potentials, as follows: (1) lack of H bonding tothe O atom of H₃O⁺; (2) short, 2.4–2.6 A, O—O distances of nearly symmetricH bonds; and, (3) increased mobility of protons in such short H bonds, give riseto the density maximum via (1) and (2); (1) produces the viscosity minimum;and the conductivity maximum results from (2) and (3). A pronounced minimumnear 1030 cm^–1 in the symmetric SO₃ stretching Raman frequency of HSO₄ ^–,observed near 45 mole% also results from double-well effects involving the shortH bonds of direct hydronium ion—bisulfate ion pair interactions. Estimates of theconcentrations of the (H₃O⁺)(HSO₄ ^–) and (H₂SO₄)(HSO₄ ^–) pair interactions weredetermined from Raman intensity data and are given for compositions between42–100 mole%     

Kinetics and Substrate Selectivity of the Oxidation of Saturated Hydrocarbons by Adamantyl Cations in Sulfuric Acid

It was shown that at 70 °C sulfuric acid ([H₂SO₄] > 85 wt.%) solutions of 1-hydroxyadamantane and the solutions obtained in the reaction of adamantane with concentrated sulfuric acid oxidize saturated hydrocarbons (RH). Data on the kinetics, selectivity, kinetic isotope effect, and the effect of the acidity of the medium on the oxidation rate of RH indicate cleavage of the C—H bond in the substrate at the rate-determining stage and the direct participation of adamantyl carbocations.     

Reduction of NO by C1-C4 hydrocarbons on cation-exchanged zeolites

New data are presented for the reduction of nitric oxide by C₁-C₄ hydrocarbons (alkanes and olefins) on active copper, cerium, and cobalt zeolite catalysts both with and without oxygen in the reaction mixture. The following hydrocarbon reactivity series were obtained. Olefins: C₄H₈ > C₃H₆ > C₂H₄. Alkanes: C₄H₁₀ > C₃H₈ > CH₄.L. V. Pisarzhevskii Institute of Physical Chemistry, National Academy of Sciences of Ukraine, 31 Prospekt Nauki, 252039 Kiev, Ukraine. Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 32, No. 4, pp. 238–242, July–August, 1996. Original article submitted September 14, 1995.     

Thermodynamics of the system H2O−NaCl−Na2SO4−MgSO4 to the saturation limit of NaCl at 25°C

Isopiestic results are reported for the quaternary system H₂O–NaCl–Na₂SO₄–MgSO₄. The excess free energies for mixing the double salt Na₂ Mg(SO₄)₂ with NaCl are fairly large and negative, as also are the free energies for mixing the three salts to form the quaternary aqueous system.     

Osmium(VIII) mediated oxidation of mercury(I) by cerium(IV) in aqueous sulphuric acid – a kinetic and mechanistic study

The oxidation of Hg^I by Ce^IV has been studied in aqueous H₂SO₄. A minute amount (10^–6 mol dm^–3) of Os^VIII is sufficient to catalyse the reaction. The active catalyst, substrate and oxidant species are H₂OsO₅, [Hg₂(SO₄)HSO₄]^– and H₃Ce(SO₄)^– ₄, respectively. Possible mechanisms are proposed and the reaction constants involved have been determined.     

Kinetics and mechanism of the oxidation of arenes in the presence of heteropoly acids and palladium(II) complexes supported on silica gel

Pd(II) complexes and twelfth-series heteropoly acids (HPA) H₉[PMo₆V₆O₄₀] and H₃[PMo₁₂O₄₀] supported on silica gel oxidize benzene and toluene at 95°C. The formation of methyldiphenylmethane in the oxidation of toluene on HPA/SiO₂ and (PdCl₂−HPA)/SiO₂ catalysts, KIE>1 for the toluene/toluene-d₈ pair, and greater rate for toluene than for benzene are in accord with a one-electron transfer mechanism. 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. 4, pp. 249–252, July–August, 1999.     

Kinetics and mechanism of the photochemical hydrolysis of phosphoenolpyruvic acid

It was established that phosphoenolpyruvic acid, photoexcited by UV light at 20°C, loses its phosphoryl group under the action of acids and bases. Raising the temperature to 50°C induces dissociation of the photoexcited molecule into enolpyruvate and metaphosphate, which in turn phosphorylates HPO₄ ^2– and H₂P₂O₇ ^2– ions and AMP.Institute of Bioorganic Chemistry and Petrochemistry, National Academy of Sciences of Ukraine, 1 Murmanskaya St., 253094 Kiev-94, Ukraine. Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 32, No. 5, pp. 287–290, September–October, 1996. Original article submitted December 1, 1995.     

Reduction of NO by C1-C4 hydrocarbons at cobalt-containing zeolites

Data are given on the activity of high-silicon zeolites in the reduction of nitrogen oxides by methane and C₂-C₄ hydrocarbons (paraffins and olefins). It was shown that the highest degree of conversion of NO during selective catalytic reduction is obtained at the mixed forms of Co-containing zeolites at temperatures 100°C lower than at the usual Co-containing zeolites of the ZSM-5 type.L. V. Pisarzhevskii Institute of Physical Chemistry, National Academy of Sciences of Ukraine, Kiev. Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 32, No. 1, pp. 47–50, January–February, 1996. Original article submitted April 3, 1995.     

Thermodynamics of aqueous mixtures of sodium chloride,potassium chloride,sodium sulfate,and potassium sulfate at 25°C

Aqueous solutions of sodium chloride, potassium chloride, sodium sulfate, and potassium sulfate can be mixed in six ways to give ternary mixtures. Two of these have already been studied and results are now presented for the remaining four systems: H₂O–NaCl–K₂SO₄, H₂O–Na₂SO₄–K₂SO₄, H₂O–KCl–Na₂SO₄, and H₂O–KCl–K₂SO₄.     

Acidity function scale for H2SO4 solutions in phenol-acetone solvents with low water content at 25°C

The indicator method was employed to measure the acidity function H ₀ ^S of H₂SO₄ solutions in solvents consisting of an equimolar mixture of phenol and acetone with 0.8% water (from 3.6·10^–4 to 2.6·10^–2 M H₂SO₄) and 2.5% water (from 4.3·10^–4 to 0.32 M H₂SO₄) and of phenol and acetone in a molar ratio of 1:1.5 with 0.67% water (from 1.63·10^–4 to 7.77·10^–2 M H₂SO₄) and 2.09% water (from 4.49·10^–4 to 0.35 M H₂SO₄) at 25°C. The indicators employed were 4- and 2-nitroaniline.Deceased.N. N. Semenov Institute of Chemical Physics, Russian Academy of Sciences, 117977 Moscow. Lenneftekhim Scientific-Commercial Association, St. Petersburg. Translated from Izvestiya Akademii Nauk, Seriya Khimicheskaya, No. 1, pp. 72–78, January, 1992.     

Optimization of the method of isolating (25R)-spirost-5-ene-3β,17α-diol (pennogenin) from plant material

The method for the acid hydrolysis of pennogenin glycosides with the aim of isolating the native aglycon has been optimized. The highest yield of pennogenin (49.5% of its amount in the plant material) is given by hydrolysis with 1 N H₂SO₄ in 96% ethanol at 100°C for 3 h.Pacific Institute of Bioorganic Chemistry, Far Eastern Scientific Center, Academy of Sciences of the USSR, Vladivostok. Translated from Khimiya Prirodnykh Soedinenii, No. 1, pp. 115–119, January–February, 1987.     

Potentiometric determination of free acidity and uranium in uranyl nitrate solutions using sulfate as complexing agent

In this paper free acid and uranium present together in the range of 0.05–3.0 meq and 20–250 mg, respectively, have been determined by potentiometric titration, using Na₂SO₄ and (NH₄)₂SO₄ complexants and NaOH and Na₂CO₃ as titrants. The results are presented as percentage recovery of free acidity and uranium over the range studied. It has been shown that percentage recovery of free acidity suggests a bias which varied from –5% to +74% at different free acidity and uranium concentrations for the Na₂SO₄–NaOH, Na₂SO₄–Na₂CO₃ and (NH₄)₂SO₄–NaOH complexant — titrant combinations. The percentage recovery of uranium always showed a positive bias which could be up to +8% for extreme free acidity — uranium ratios in the case of Na₂SO₄–Na₂CO₃ complexant — titrant combination. For the other Na₂SO₄–NaOH and (NH₄)₂SO₄–NaOH complexant — titrant combinations a positive bias of up to only +4% has been noticed.     

Partial oxidation and oxidative condensation of methane with the participation of N2O on a V2O5/SiO2 catalyst

The catalytic reaction of CH₄, with N₂O at 773–823 K on a V₂O₅/SiO₂ catalyst affords products of the partial oxidation (HCHO and CH₃OH), exhaustive oxidation (CO), and oxidative condensation (C₂H₅OH and CH₃CHO) of methane. A mechanism is proposed for the complex reaction, including the intermediate compounds V⁵⁺O and V⁴⁺CH₃OH as common intermediates for all the routes.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 23, No. 5, pp. 641–646, September–October, 1987.     

Electrochemical Amination of Benzene in Aqueous Solutions of Sulfuric Acid and an Organic Solvent

Electrolysis of the Ti(IV)–NH₂OH–C₆H₆ system in 11 M H₂SO₄ reveals that out of four organic solvents—methanol, formic acid, acetonitrile, and acetic acid—only the last two meet conditions imposed on solvents to be used in indirect cathodic amination of aromatic compounds. They improve the aromatic substrate solubility in the catholyte and affect the process mechanism, determining, together with other factors, the substitution's rate and selectivity.     

Kinetics, substrate selectivity and mechanisms of the first step in the oxidation of alkylbenzenes in the HVO3−H2SO4 system

The kinetics, kinetic isotope effects, and substrate selectivity were studied for the oxidation of alkylbenzenes in the HVO₃−H₂SO₄ system at 30°C. The reaction proceeds by an electrophilic substitution mechanism through a slow step involving formation of a charge transfer complex between the arene and VO ₂ ⁺ cation and is similar to nitration by the NO ₂ ⁺ cation. 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. 6, pp. 349–353, November–December, 1999.     

DTA studies on the corrosion behavior of titanium powder in NaCl and Na2SO4

The corrosion/oxidation behavior of titanium powder in air and in the presence of corrodents NaCl and Na₂SO₄ was investigated by employing the DTA technique.The DTA results for pure and fine titanium powder in air indicate two high-temperature exotherms, one at 700° and the other at around 750°. The first exotherm is due to the formation of anatase (TiO₂) and the second to rutile (TiO₂), as evidenced by the XRD data. However, the presence of NaCl and Na₂SO₄ promote the direct oxidation of titanium to rutile, which is indicated by a large exotherm ranging between 600 and 850°. The endotherm at 690° for mixtures containing 25 to 30% NaCl to Na₂SO₄ corresponds to formation of the eutectic mixture. The DTA data clearly indicate that the presence of the corrodents not only lowers the temperature of oxidation, but also induce the catastrophic oxidation of titanium powder.

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Zusammenfassung Mittels DTA-Techniken wurde das Korrosions-/Oxydationsverhalten von Titanpulver an Luft und in Gegenwart von NaCl und Na₂SO₄ untersucht.Die DTA-Ergebnisse für reines, feines Titanpulver zeigen bei 700° und bei etwa 750° zwei Hochtemperaturexothermen. Wie durch Röntgendiffraktionsangaben bestätigt, gehört die erste Exotherme zur Bildung von Anatas (TiO₂), die zweite zur Bildung von Rutil (TiO₂). In jedem Falle begünstigt die Gegenwart von NaCl und Na₂SO₄ die direkte Oxydation von Titanpulver zu Rutil, was durch eine breite Exotherme im Bereich von 600–850° angezeigt wird. Der Endothermen bei 690° bei Gemischen mit einem Gehalt an 25–30% NaCl oder Na₂SO₄ liegt die Bildung von eutektischen Gemischen zugrunde. Die DTA-Daten zeigen eindeutig, daß die Wirkung der korrodenten Zusätze nicht nur in einer Herabsetzung der Oxydationstemperetur, sondern auch in einem eindeutigen Vorantrieb der Oxydation besteht.

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The author thanks Dr. P. Rama Rao, Director, DMRL, for his encouragement and permission to publish these research findings; he also expresses thanks to the XRD, AES, and chemical analysis group for their help, and to Mr. M. Hema Reddy for supplying the DTA specimen holders.     

Hydrate numbers of scandium sulfate as deduced from solubility data

A simple method for determination of the hydrate numbers of saturating multi-hydrate salts in developed. The method demonstrated for scandium sulfate is based upon estimation of the enthalpy of solution of the hydrates from the solubility smoothing equations. It is shown that in the Sc₂(SO₄)₃–H₂O system, contrary to common opinion, the equilibrium solid phases are: Sc₂(SO₄)₃.6H₂O at 273–295 K, Sc₂(SO₄)₃.5H₂O at 295–333 K and Sc₂(SO₄)₃.4H₂O at 333–373 K. The solubility smoothing equations for the hexa-, penta- and tetrahydrate of scandium sulfate are given.     

The oxidative stream reforming of methane to syngas in a thin tubular mixed-conducting membrane reactor

The oxidative stream reforming of methane (OSRM) to syngas, involving coupling of exothermic partial oxidation of methane (POM) and endothermic steam reforming of methane (SRM) processes, was studied in a thin tubular Al₂O₃-doped SrCo_0.8Fe_0.2O_3−δ membrane reactor packed with a Ni/γ-Al₂O₃ catalyst. The influences of the temperature and feed concentration on the membrane reaction performances were investigated in detail. The methane and steam conversions increased with increasing the temperature and high conversions were obtained in 850–900 °C. Different from the POM reaction, in the OSRM reaction the temperature and H₂O/CH₄ profoundly influenced the CO selectivity, H₂/CO and heat of the reaction. The CO selectivity increased with increasing the temperature or decreasing the H₂O/CH₄ ratio in the feed owing to the water gas shift reaction (H₂O + CO → CO₂ + H₂). And the H₂ selectivity based on methane conversion was always 100% because the net steam conversion was greater than zero. The H₂/CO in product could be tuned from 1.9 to 2.8 by adjusting the reaction temperature or H₂O/CH₄. Depending on the temperature or H₂O/CH₄, furthermore, the OSRM process could be performed auto-thermally with idealized reaction condition.