A Study of Kinetic Characteristics of Dodecylpyridinium Cation in Aqueous Solutions of Its Chloride

The conductivity of aqueous solutions of dodecylpyridinium chloride was studied in wide temperature and concentration ranges. At the temperature below 35°C, the change in activation energy of translational motion of water molecules was shown to decrease with addition of the surfactant studied and to increase above this temperature.     

Investigation of the automated determination of As,Sb and Bi by flow-injection hydride generation using in-situ trapping on stable coatings in graphite furnace atomic absorption spectrometry

Flow-injection hydride generation and in situ concentration of As, Sb and Bi hydrides in graphite furnace atomic absorption spectrometry can be automated by means of a long-term stable trapping reagent replacing the Pd modifier. In a systematic study, carbide-forming elements (Zr, Nb, Ta, W) and noble metals (Ir, Ir/Mg, Pd/Ir) were investigated as stable adsorbers which require only a single application. Trapping temperature curves indicate high signals for trapping of As at 750–800°C, Sb at 450–8000°C and Bi at 100–500°C on Zr-coated tubes. Ir- and Ir/Mg-coated tubes showed a high response for Sb and Bi at lower temperatures, but based on signal stability and reproducibility (over 400 trapping and atomization cycles tested) the better performance was found with the Zr-coated tubes. The radiotracers Sb-125 and Bi-207 were used to measure the hydride generation (>95% for both elements) and trapping efficiency (91% for Sb and 56% for Bi) on the Zr-coated tube. An adsorptive carry-over effect was observed with Sb and Bi but not with As, and trapping temperatures above 450°C with Sb and 350°C with Bi (the critical temperatures) can lead to errors in absorbance values. On a Zr-coated tube the characteristic mass was about 16 pg for As, 15 pg for Sb and 9 pg for Bi (peak height) and the detection limits (3 sigma) were about 0.015, 0.010 and 0.027 ng, respectively, with a 1 ml sample loop. The method was tested by the determination of the elements in NIST low-alloy steel certified reference materials.     

Electron-impact-induced anisotropic etching of silicon by hydrogen

The etch rate of silicon in a hydrogen low-pressure discharge plasma can be strongly enhanced by electron bombardment, reaching presently up to 1000 Å/min. The etch rate increases linearly with increasing electron current density and hydrogen pressure (range 0.05–0.7 mbar) and decreases with increasing temperature, yielding an activation energy of –4.2 kcal/mole in a temperature range of 80 to 300°C. The etching remains anisotropic within the whole pressure range studied.     

Thermodynamics of protonation of amino acid carboxylate groups from 50 to 125°C

Flow calorimetry has been used to study the interaction of glycine, DL--alanine, DL-2-aminobutyric acid, -alanine, 4-aminobutyric acid, and 6-aminocaproic acid with protons in aqueous solutions from 323.15 K to 398.15 K and at 1.52 MPa. LogK, H°, S°, and C _p ^° for the protonation of the carboxylate groups of these amino acids have been obtained at each temperature studied. Equations are given expressing these values as functions of temperature. The protonation reactions are exothermic at lower temperatures and become endothermic as temperature increases. The logK, H°, and S° values are close together over the temperature range studied for the protonation of -amino acids, i.e., glycine, DL--alanine, and 2-aminobutyric acid. At each temperature, the magnitudes of these thermodynamic quantities increase as the number of methylene groups between the amino group and the carboxylate group increases. The C _p ^° value for the protonation of the carboxyl group is found to lie between those of an isocoulombic reaction and a charge reduction reaction. At 323.15 K, the protonation reactions of the carboxylate groups have larger C _p ^° values which approach those associated with charge reduction reactions. As the temperature increases, C _p ^° decreases and approaches those found for isocoulombic reactions. This result is explained by considering long-range and short-range solvent effects. The trend in H° and S° with temperature and with charge separation in the zwitterions is interpreted in terms of solvent-solute interactions and the electrostatic interaction of the two oppositely charged groups within the molecule.     

Role of Water on Fast Proton Conduction in Sol-Gel Glasses

Fast proton-conducting P2O5-ZrO2-SiO2 glasses were prepared by sol-gel processing of metal alkoxides. Glasses heated to 150 to 400°C exhibited room temperature conductivities of 10–4 S/cm, larger by 2 order of magnitude than that of as-prepared gel, 3 × 10–7 S/cm at 30°C. The conductivity increased quadratically with the increasing product of proton and molecular water concentration. These high conductivities were regarded as fast proton transfer accelerated by molecular water bonded with the hydroxyl groups.     

Thermische Zersetzung des Lithiumhexacyanoferrats(III)

Zusammenfassung Die thermische Zersetzung von Lithiumhexacyanoferrat (III) in Luft führt in drei Temperaturbereichen, d.h. zwischen 250 und 400°, 500 und 650° und 925 und 1000° zur Bildung ferromagnetischer Produkte. Durch Röntgendiffraktionsuntersuchung und magnetische Messungen wurde bewiesen, daß im ersten Temperaturbereich-Fe₂O₃ die für die ferromagnetischen Eigenschaften der Zersetzungsprodukte verantwortliche Phase ist, während in den anderen Bereichen diese Eigenschaften durch Lithiumferrit der Formel Li_0.5Fe_2.5O₄ verursacht werden.

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The thermal decomposition of lithium hexacyanoferrate (III) in air leads to the formation of ferromagnetic products in three temperature ranges, namely 250–400°, 500–650° and 925–1000°. By X-ray diffraction studies and magnetic measurements it has been proved that in the first temperature region-Fe₂O₃ is the phase responsible for the ferromagnetic properties of the decomposition products, whereas in the other regions these properties are due to the presence of the lithium ferrite Li_0.5Fe_2.5O₄.

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Résumé La décomposition thermique du ferricyanure de lithium dans l'air conduit à des produits ferromagnétiques dans trois intervalles de température: 250–400°, 500–650° et 925–1000°. Par diffraction des rayons X et mesures magnétiques, on montre que lors de la première étape de décomposition c'est l'oxyde-Fe₂O₃ qui est responsable des propriétés ferromagnétiques des produits de décomposition, tandis que pour les deux autres étapes, le ferromagnétisme est dû à la présence de ferrite de lithium de formule Li_0.5Fe_2.5O₄.

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-()- : 250–400°, 500–650° 925–1000°. - , , , , -Fe₂O₃. Li_0.5Fe_2.5O₄.

     

Décomposition thermique du sulfite de fer(II) anhydre

Résumé Sous azote ou sous vide, le sulfite ferreux anhydre se décompose vers 210° en magnétite, pyrite et dioxyde de soufre. Concurremment une réaction de dismutation intervient avec formation de FeSO₄, Fe₃O₄ et FeS₂. Lorsque la température atteint 320°, la pyrite et le sulfate réagissent ensemble pour donner Fe_1–xS, Fe₃O₄ et SO₂. Au-delà de 370° le sulfure ferreux non-stchiométrique commence à réagir à son tour avec le sulfate restant pour former de la magnetite et du dioxyde de soufre.

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In nitrogen or under vacuum, anhydrous iron(II) sulfite decomposes near 210° to magnetite, pyrite and sulfur dioxide. A parallel disproportionation reaction occurs with formation of FeSO₄, Fe₃O₄ and FeS₂. When the temperature reaches 320°, pyrite and sulfate react together to give Fe_1–xS, Fe₃O₄ and SO₂. Above 370° the non-stoichiometric ferrous sulfide begins to react with the remaining sulfate to give magnetite and sulfur dioxide.

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Zusammenfassung Unter Stickstoff oder im Vakuum zersetzt sich das wasserfreie Eisen(II)-sulfit in der Nähe von 210 °C zu Magnetit, Pyrit und Schwefeldioxid. Parallel hierzu findet eine Disproportionierung unter Bildung von FeSO₄, Fe₃O₄ und FeS₂ statt. Wenn die Temperatur 320 °C erreicht, reagieren Pyrit und Sulfat unter Bildung von Fe_1–xS, Fe₃O₄ und SO₂ Oberhalb von 370 °C beginnt das nichtstöchiometrische Eisensulfit seinerseits mit dem restlichen Sulfat zu reagieren um Magnetit und Schwefeldioxid zu ergeben.

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(II) 210° , . FeSO₄, Fe₃O₄ FeS₂. 320°, , Fe_1–xS, Fe₃O₄ SO₂. 370° .

     

Phase equilibria in the V2O5-Cr2O3 system

The phase equilibria in the total range of component concentrations in the V₂O₅-Cr₂O₃ system up to 1000 °C were studied by means of phase powder diffraction and DTA. Two compounds exist in the system: CrVO₄, melting incongruently at 860±5 °C, and Cr₂V₄O₁₃, which decomposes in the solid state at 640±5 °C to CrVO_4(s) and V₂O_5(s). At 645±5 °C, CrVO₄ and V₂O₅ form a eutectic mixture with the CrVO₄ content not exceeding 2% mol.

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Zusammenfassung Mittels DTA und Pulverdiffraktionsaufnahmen wurde das Phasengleichgewicht des Systems V₂O₅-Cr₂O₃ bis 1000 °C im gesamten Konzentrationsbereich untersucht. Innerhalb des Systemes existieren zwei Verbindungen: CrVO₄ mit einem inkongruentem Schmelzpunkt bei 860±5 °C und Cr₂V₄O₁₃, das sich in festem Zustand bei 640±5 °C in CrVO_4(s) und V₂O_5(s) zersetzt. Bei 645±5 °C bilden CrVO₄ und V₂O₅ ein eutektisches Gemisch mit einem maximalen CrVO₄-Gehalt von 2 mol%.

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DTA V₂₅-Cr₂₃ 1000° . : CrVO₄, 860±5° Cr₂V₄O₁₃, 640±5° CrVO₄ V₂O₅, 645±5° CrVO₄, 2 %.

     

Synthetic investigations in the field of the curare alkaloids

It has been shown that the compounds obtained previously corresponding in comparison to the -[4-(5-carboxymethyl-2-hydroxyphenoxy)3-methoxyphenyl]ethylamide of 4-benzyloxyphenylacetic acid have practically the same spectra and on further condensation with 3-bromo-4-hydroxy-5-methoxyphenylethylamine give an equilibrium mixture of diamide compounds. The difference in the physicochemical properties of the diphenyl esters and the diamides can be explained by steric differences. On cyclization, the diamides are converted into bis-dihydroisoquinoline compounds of the same elementary composition. The hydrochloride of 7-[2-acetoxy-5-(7-acetoxy-8-bromo-6methoxy-3, 4dihydroisoquinol-1-ylmethyl)phenoxyl)-1-(4-benzyloxybenzyl)-6-methoxy-3,4-dihydroisoquinoline, with mp 180–181° C, after saponification, intramolecular Ullman condensation, reduction, and stepwise methylation, was converted into isomeric tubocurarin iodides with mp 189–190.5° C, 164–166.5° C, 257–260.5° C, and 210–212° C, which were separated on the basis of their different solubilities in organic solvents and water.For part XII, see [1].     

Equilibrium between α- and β-isomers of dihydroartemisinine and its multiple-peaks in high-performance liquid chromatography

Summary The interconversion between the - and -isomers and the multiple-peaks of dihydroartemisinine (dihydroqinghaosu) were investigated in reversed-phase, highperformance liquid chromatography. A convenient method using the Gaussian distribution function instead of the Schmidt graphical method for the theoretical calculation of the diffuse probability curves versus the fraction of the dead time on column as form was introduced. Based on the theoretical probability curves and the experimental multiple-peak chomatograms, the effects of temperature and flow velocity on the accuracy and precision of analysis of dihydroartemisinine are indicated and the activation energy of the interconversion between - and -isomers of dihydroartemisinine is estimated.     

Improvement of Solubility and Dissolution of 19-Norprogesterone via Inclusion Complexation

In an effort to modify the solubility and dissolution rate of the contraceptive steroid, 19-norprogesterone in order to improve its bioavailability, the cyclodextrin complexation approach was chosen. In solution, the complex formation with -cyclodextrin (-CD), hydroxyethyl -cyclodextrin (HE--CD) and hydroxypropyl -cyclodextrin (HP--CD) was confirmed by using solubility, UV, IR and ¹H-NMR spectrophotometric techniques. The phase solubility diagrams were categorized as A_L-type. The complexing affinity of the CDs investigated were ranked as follows: -CD > HP--CD > HE--CD. The complexation thermodynamic parameters were obtained from the temperature dependence of the dissociation constants. In the solid state, differential scanning calorimetery (DSC) and optical microscopy methods were utilized to characterize the complexes. Dissolution studies showed that such molecularly encapsulated forms offered a marked improvement in the dissolution rate compared to the parent drug.     

Order and disorder in mixed metal linear chains: The homo and heterobimetallic EDTA (M(H2O)4OIOII)[M′(EDTA)] · 6H2O complexes (M = Mg,Mn, Co,Zn and Ni; M′ = Co,Ni, Cu and Zn)

Summary Polymetallic solid solutions of the ethylenediaminetetracetic acid (EDTA) and six divalent metal ions exist in the range: MgMnCoZnNiCu(EDTA) · 6H₂O where + + + + + =2, 01, 0,,2, 0, 1.This type of structure is characterized by the presence of two different octahedral carboxylate-bridged coordination sites forming infinite zig-zag chains. Visible and i.r. spectra and t.g.a. analysis show that there is occupational preference for the two coordination sites in the crystalline structure.Due to this preference, and also to the structural features, the heterobimetallic MM(EDTA) · 6H₂O compounds constitute a structurally new class of materials which can be described as ordered alternating-heterobimetallic polymeric coordination complexes.     

First and second thermodynamic mixing properties of ethylbenzene +n-alkanes: Experimental and theory

Isobaric expansibilities _P and isothermal compressibilities _T have been determined at 25 and 45°C for binary mixtures of ethylbenzene + n-tetradecane and + n-hexadecane and the corresponding excess functions (V ^E /T)_P and (V ^E /P)_T have also been obtained. With these data and supplementary literature values, the following second order mixing properties are also reported at 25°C: _S ^E , (V ^E /P)_T, C_V and (VT). All mixing quantities have been compared with the results obtained at 25°C by using the Prigogine-Flory-Patterson theory of liquid mixtures. The predicted values suggest that the ability of ethylbenzene as a breaker of the pure n-C_n orientations is similar to what we found for toluene and higher than for p-xylene.     

Interaction of V2O5 with oxygen in the gas phase

Sorption/evolution of oxygen from V₂O₅ in the temperature range of 480–520°C is due to a shift in the defect equilibrium 1/2 O₂ (gas)+V_oO_o. A first-order kinetic equation can be derived under the assumption that the activation energy depends on the concentration of defects.

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/ V₂O₅ 480–520°C 1/2 O₂ ()+V_oO_o. , , .

     

Atom States and Interatomic Interactions in Complex Perovskite-Like Oxides: XV.1 Magnetic Susceptibility of La0.67Ca0.33MnO3-LaAlO3 Solid Solutions

Magnetic susceptibility of diluted solid solutions of manganites with perovskite structure having a colossal magnetoresistivity was studied. It was found that the systems are characterized by ferromagnetic type strong exchange interactions, which are characterized by an exchange parameter varying with temperature.     

Catalytic activity of honeycomb catalysts, I. The benzene-cyclohexane (de)hydrogenation reaction

Monolithic supported platinum catalysts were investigated with respect to their hydrogenation and dehydrogenation activity towards benzene and cyclohexane, respectively, between 250° and 350°C. Conversion of benzene to cyclohexane is optimal for the volume ratio H₂/Bz=5 at lower temperatures. In the cyclohexane dehydrogenation reaction, high temperatures, associated with lower N₂/Cy ratios, are beneficial. No byproducts were observed in the two reactions.

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, , 250 °C 350 °C. H₂/=5. N₂/ . .

     

Crystal Structures of the Inclusion Complexes of β-Cyclodextrin with Aliphatic Monoacids Tridecanoic Acid and (Z)-Tetradec-7-enoic Acid. Formation of [3]Pseudorotaxanes

The structures of the inclusion complexes of beta cyclodextrin with the aliphatic mono-acids tridecanoic acid (1) and (Z)-tetradec-7-enoic acid (2) have been determined at room temperature. Both compounds crystallise in P1, a = 15.654(6) Å, b = 15.650(6) Å, c = 15.937(6) Å, = 101.58(1)°, = 101.59(1)°, = 103.58(1)°, Z = 1, for 1 and a = 15.6259(9) Å, b = 15.623(1) Å, c = 15.935(1) Å, = 101.547(2)°, = 101.555(2)°, = 103.642(2)°, Z = 1, for 2. One molecule of the monoacids threads through two cyclodextrin macrocycles arranged in dimers thus forming [3]pseudorotaxanes. The host dimers are aligned along a channel in order to create a hydrophobic environment for the terminal methyl group of the guest and isolate it from the aqueous environment that surrounds the cyclodextrin dimeric units. The guests exhibit disorder over two orientations resulting in hydrogen bonding between the carboxyl groups of adjacent guest molecules along the channel and formation of carboxylic dimers. This crystal packing differs from that of -CD complexes of homologous dicarboxylic acids.     

Kinetics of thermal decomposition of pyrite in an inert atmosphere

The thermal decomposition of pyrite in an inert atmosphere was studied in order to obtain a detailed knowledge of the kinetics and mechanism of the reaction 2 FeS₂=2FeS+S₂, which is one of the methods of producing elementary sulphur. The process was studied under isothermal conditions at temperatures of 600, 660, 700, 750, 800 and 850 °C in a nitrogen atmosphere, by means of a thermobalance. The rate-controlling processes were determined and their kinetic parameters were calculated. The optimum temperature for the process was found to be 800 °C.

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Zusammenfassung Es wurde die thermische Zersetzung von Pyrit in inerter Atmosphäre bestimmt, um detaillierte Informationen über Kinetik und Mechanismus der Reaktion 2 FeS₂=2FeS+S₂, einer der Darstellungsreaktionen von elementarem Schwefel zu erlangen. Der Vorgang wurde mittels einer Thermowaage unter isothermen Bedingungen bei Temperaturen von 600, 660, 700, 750, 800 und 850 °C untersucht. Es wurden die geschwindigkeitsbestimmenden Schritte bestimmt und deren kinetische Parameter errechnet. Als Optimumtemperatur für diesen Prozeß erwies sich 800 °C.

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- 2FeS₂=2FeS + S₂, . 600, 660, 700, 750, 800 850 ° . , 800°.

     

Exchange of propene-d6 with hydrogen of HY zeolites

The exchange of C₃D₆ with hydroxylated and partially dehydroxylated HY zeolites was studied by the analysis of the gas (MS) and the solid (IR) phase at 300°C and at the temperature of the IR beam.

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C₃D₆ HY () () 300°C .

     

Structure and Magnetic Properties of Solid Solutions of Molecular Magnetics Based on Ni(II) and Co(II) Complexes with Nitroxyl Radicals

Ni(II) and Co(II) complexes with deprotonated paramagnetic enaminoketones 4(3,3,3trifluorine2oxopropylidene) 2,2,5,5tetramethyl3imidazolidine1oxyl (L) and 4(3,3,3trifluorine1chlorine2oxopropylidene)2,2,5,5tetramethyl3imidazolidine1oxyl (L¹) and alcohols are shown to form continuous solid solutions Ni_xCo_1-xL₂(C₂H₅OH)₂ and Ni_xCo_1-xL₂ ¹(CH₃OH)₂. Single crystal Xray diffraction analysis showed that concentration variation practically does not affect the structural characteristics of the solid solutions. Distinguishing features if the magnetic behavior of Ni_xCo_1-xL₂ · (C₂H₅OH)₂ and Ni_xCo_1-xL₂ ¹(CH₃OH)₂ are the antiferromagnetic interaction of the moments of the nickel and cobalt sublattices inside the polymeric layers and the antiferromagnetic nature of interlayer interaction of the magnetic moments.