Studies of decomposition kinetics for ozone complexes with cumene and chlorobenzene

Kinetic regularities in decomposition of complexes of aromatic compounds with O₃ have been studied for ozone complexes with cumene and chlorobenzene. Oxidation effect of these complexes on both aromatic compounds and olefins has been established.

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O₃. .

     

Study of CO oxidation on the (111) face of nickel during Ni?NiO phase transition

CO oxidation on the (111) face of Ni has been studied over a wide temperature range and reactant ratio in CO+O₂ reaction mixtures. A significant nonstationary increase in the reaction rate due to the formation of a two-dimensional surface oxide has been found. Subsequent formation of threedimensional NiO(111) phase sharply decreases the CO oxidation rate.

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CO (111) Ni (CO+O₂). , . , NiO(111) CO.

     

Differential scanning calorimetry applied to cross-linking of a filled epoxy resin: Accuracy of the Borchardt and Daniels equation for describing the curing process kinetics

From the point of view of the chemical reactions describing the curing process of a mixture epoxy resin-dicarboxylic acid anhydride-tertiary amine-polyol and silica filler, it is difficult to understand the network formation: several different reactions are involved, so that the interaction between the epoxy resin and the other components of the mixture is unquestionably complex. However, a linear plot is obtained when Kissinger's method is applied to dynamic DSC results (four different scanning rates), which confirms the calculation assumptions. In particular, the Borchardt and Daniels equation, where the specific rate constant is assumed to be of Arrhenius form appears to be a good mathematical model for describing the curing process under dynamic DSC conditions. The apparent activation energy determined by means of this analytical method is in good agreement with those obtained by other methods in the literature.

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Zusammenfassung Die bei der Härtung eines Epoxidharz, Dicarboxylsäure-Anhydrid, tertiäres Amin, Polyol und einen SiO₂-Füllstoff enthaltenden Gemisches vor sich gehende Vernetzung ist schwer zu überblicken; es verlaufen mehrere unterschiedliche Reaktionen, so daß die Wechselwirkung zwischen dem Epoxidharz und den anderen Komponenten außerordentlich komplex ist. Eine lineare Abhängigkeit wird jedoch erhalten, wenn dynamische DSC-Ergebnisse erhalten bei 4 verschiedenen Scanning-Geschwindigkeiten nach der Kissinger-Methode aufgearbeitet werden, was die Richtigkeit der für die Berechnung gemachten Annahmen bestätigt. Besonders die Gleichung von Borchardt und Daniel, bei deren Ableitung für die spezifische Geschwindigkeitskonstante eine Arrhenius-Form angenommen wird, scheint ein gutes mathematisches Modell zur Beschreibung des Härteprozesses unter DSC-Bedingungen zu sein. Die nach dieser Methode bestimmte scheinbare Aktivierungsenergie stimmt gut mit den nach anderen in der Literatur beschriebenen Methoden bestimmten Werten überein.

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, — — — ( ), . . ( ), , . , , , , . , , , .

     

Catalytic oxidation of water to dioxygen by Ru(bpy)3+ in the presence of mixed iron and cobalt hydroxides

The catalytic activity of Co(III) and Fe(III) hydroxides as well as of their mixtures produced by co-precipitation with hydroxides of some highly charged transition and non-transition metals has been studied over the pH range from 5 to 11. In some cases mixed hydroxides demonstrate an increase in efficiency of the catalytic action.

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pH 5–11 Co(III) Fe(III) , . .

     

Differential thermoanalytical investigation of Fe(II) salt solutions frozen at different pressures

Phase transitions of pure water and aqueous Fe(II) perchlorate solutions, frozen between 1 and 5 kbar were detected by the DTA method at atmospheric pressure. Only the crystal structure of the primarily formed ice varies with the pressure, while water molecules remaining in the near eutectic solution — which solidifies into a glassy state — show no sensitivity towards pressure.

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Zusammenfassung Phasenübergänge von reinem Wasser und zwischen 1 und 5 kbar gefrorenen wäßrigen Eisen(II)perchlorat Lösungen wurden durch DTA bei atmosphärischem Druck nachgewiesen. Nur die Kristallstruktur des primär segregierenden Eises wird durch den Druck beeinflußt. Die in der beinahe eutektischen Lösung zurückbleibenden Wassermoleküle, die in einem glasartigen Zustand erstarren, scheinen nicht druckempfindlich zu sein.

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Résumé Mise en évidence par ATD à la pression atmosphérique des transitions de phase de l'eau pure et de solutions aqueuses de perchlorate de fer(II) préalablement congelées sous une pression allant de 1 à 5 kbar. Seule la structure cristalline de la phase qui se dépose la première dépend de la pression. Par contre, les molécules qui restent dans la solution presque eutectique — qui se solidifie à l'état vitreux — ne sont pas sensibles à la pression.

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, 1 5 . , , , , .

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The authors are indebted to Dr. L. Keszthelyi for his extensive help and to Mr. I. Klim. Mr. B. Molnár and Mr. T. Grünstein for their assistance in the measurements.     

Basicity of alumina-magnesia catalysts

In the series of Al₂O₃, MgO and Al₂O₃–MgO catalysts, those containing about 75% Al₂O₃ and 25% MgO show the highest activity in the decomposition of diacetone alcohol in non-polar solvents. The fastest rates of reaction, which follows the zero-order kinetics over the whole range of conversion, coincide with the occurrence of strong basic sites on the catalyst surface.

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Al₂O₃, MgO Al₂O₃–MgO , 75% Al₂O₃ 25% MgO, . , .

     

Thermal and X-ray analysis of cerium oxy-carbonate

This work describes the thermal decomposition behaviour of cerium oxy-carbonate. DTA, TG, DTG and X-ray examinations were performed.The results indicate that the thermal decomposition of cerium oxy-carbonate in static air at a heating rate of 10 deg min^–1 involves three steps: dehydration at 58 °C, removal of crystal water at 200 °C and CO₂ release at 235 °C.The activation energies of removal of crystal water and carbon dioxide release were found to be 59.48 and 82.33 kJ mol^–1, respectively.

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Zusammenfassung Das Verhalten von Ceroxycarbonat bei der thermischen Zersetzung wird beschrieben. DTA, TG, DTG und Röntgendiffraktometrie wurden zur Untersuchung herangezogen. Die thermische Zersetzung erfolgt in statischer Luftatmosphäre bei einer Aufheizgeschwindigkeit von 10° min^–1 in drei Schritten. Der erste Schritt bei 58 °C ist der Dehydratisierung, der zweite bei 200 °C dem Austritt von Kristallwasser und der letzte bei 235 °C der Abspaltung von CO₂ zuzuschreiben. Für die Kristallwasserabgabe wurde eine Aktivierungsenergie von 59.48 kJ · mol^–1 und für die CO₂-Abspaltung von 82.33 kJ · mol^–1 berechnet.

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, , . , 10°/ . 58° , 200 °C- , 235 °C- . , , 59,48 82,33 ·^–1

     

Catalytic-fluorimetric determination of EDTA and iron(III) by flow injection analysis

Summary In this paper the authors report on several methods for the direct determination of EDTA and indirect determination of iron(III), based on the inhibition effect of EDTA on the catalytic action of copper (II) on the oxidation of 2,2-dipyridyl ketone hydrazone by hydrogen peroxide and on the decrease of this inhibition effect in the presence of Fe(III), respectively. These methods allow the determination of EDTA in the ranges of 0.4–2.0 g · ml^–1 and 0.2–1.0 g · ml^–1 for the normal and reversed FIA modes, respectively, and of 40–240 ng · ml^–1 for Fe(III) by reversed FIA.

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Katalytisch-fluorimetrische Bestimmung von EDTA und Eisen(III) durch FließinjektionsanalyseInhibitionsmethoden

Zusammenfassung Verfahren zur direkten Bestimmung von EDTA sowie zur indirekten Bestimmung von Eisen(III) werden beschrieben. Sie beruhen auf der Inhibitorwirkung von EDTA auf den katalytischen Effekt von Kupfer(II) bei der Oxidation von 2,2-Dipyridylketonhydrazon mit Wasserstoffperoxid bzw. auf der Schwächung dieser Inhibitorwirkung in Gegenwart von Eisen(III). Es ist mit diesen Methoden möglich, EDTA im Bereich von 0,4–2,0 g/ml (normale FIA) bzw. 0,2–1,0 g/ml (umgekehrte FIA) und Eisen im Bereich von 40–240 ng/ml (umgekehrte FIA) zu bestimmen.

     

Hydrogenation of theΒ and γ isomers of 1,4-bis(4′-hydroxy-1′,2′, 5′-trimethyl-4′-piperidyl)-1,3-butadiyne

The kinetics of the hydrogenation of the and isomers of 1,4-bis(4-hydroxy-1, 2, 5-trimethyl-4-piperidyl)-1, 3-butadiyne in methanol and ethanol on the catalysts Raney nickel, platinized carbon, and palladium on supports has been studied. It has been shown that the rates of hydrogenation of the and isomers differ on all the catalysts. In the presence of platinum and nickel, hydrogenation takes place as far as the saturated compound, and in the presence of palladium to the diene.     

Selective Spectrophotometric Determination of Aluminium in the Presence of Beryllium and Lanthanide Cations

A spectrophotometric method for the selective determination of Al(III) in the presence of Be and Ln (lanthanide) cations is proposed. It is based on the selective reaction of SXO (Semi-Xylenol Orange) with Al(III) at pH 2.6. The presence of 8%v/v of 1,2-ethanediol serves to stabilize the chelate formed by heating at 100°C for 5min. 0.5mg each of Be(II), Ce(III), La(III), 4mg of Mn(II), 1.2mg of Pb(II), 1mg of Tl(I), 40mg each of Ca(II) and Mg(II) and 1.9mg of sodium dihydrogen phosphate are tolerable. A ligand buffer of HEDTA-Pb is incorporated to further enhance the selectivity of the color reaction. Under the specified conditions SXO reacts with Al(III) to form a 1:1 chelate. Its molar absorptivity at 526nm was found to be 3.3×10⁴Lmol^–1cm^–1. The linear regression equation for 2–20µg of Al(III) is A=0.04458C+0.0112 (where C stands for the concentration of Al(III), µg per 25mL) and correlation coefficient =0.9988. The RSD at the level of 10µg (n=10) and LOQ were found to be 3.5% and 2µg, respectively.     

The multicomponent temperature-programmed desorption technique

After adsorption of 1-butene on NaHY zeolite, the desorbate consists of about twelve different components. The application of the temperature-programmed desorption technique to such a system is shown. As a result a modification of the TPD method, the so-called multicomponent TPD, is proposed.

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-1 NaHY , . - () . , .., .

     

In-Situ Separation and Determination of Palladium from Platinum Based on Different Vaporization Temperatures by Electrothermal Vaporization Inductively Coupled Plasma Optical Emission Spectrometry with YPA4 Resin Acting Both as Adsorption Material and Chemical Modifier

A new method has been developed for in-situ separation of Pd from a Pt matrix and determination of trace Pd based on different vaporization temperatures by electrothermal vaporization (ETV) inductively coupled plasma optical emission spectrometry (ICP-OES) with the use of polythioether backbone modified with a diaminoisopropylmercaptane chelating group (YPA₄), both as solid phase extractant and chemical modifier. In 0.5M HNO₃, Pd and Pt can be adsorbed by YPA₄. The resin loaded with Pd and Pt was then prepared to form a slurry that can be directly introduced into the graphite furnace without any pretreatment. The factors affecting in-situ separation of Pd from the Pt matrix were investigated in detail. It was found that, in the presence of YPA₄, Pd could be quantitatively vaporized at lower vaporization temperatures (1800°C–1900°C), while Pt could not be vaporized from the graphite furnace at the same temperature, its quantitative vaporization temperature being 2600°C. Based on the different vaporization temperatures, in-situ separation of Pd from the Pt matrix and determination of trace Pd by ETV-ICP-OES was achieved in the temperature range of 1800°C–1900°C. Under the optimized conditions, the detection limit (3) of Pd is 60pg, and the relative standard deviation (RSD) is 5.6% (n=9, C=0.2µgmL^–1). The method has been applied to the determination of trace Pd in anode slime and Auto Catalyst NIST SRM 2557 reference material, and the determined values coincide with the certified values.     

Determination of Arsenic in Food Samples by Hydride Generation – Atomic Absorption Spectrometry

A method for the determination of trace amounts of arsenic in food samples using flow injection analysis and atomic absorption spectrometry with hydride generation (FI-HG AAS) was developed. The parameters of the flow injection system and the hydride generation were optimized with respect to reagent concentrations, atomization temperature, injection volume, reaction coil length and carrier flow rate. The limits of detection and quantification were 0.34µgL^–1 and 1.2µgL^–:1, respectively, and the analytical curve is linear up to 30.0µgL^–1 arsenic. The relative standard deviation for 12 replicates varies between 5% for 4.0µgL^–1 As and 1.8% for 30.0µgL^–1 As, with an injection frequency of up to 135h^–1. Interferences from Ni(II), Cu(II), Fe(III), Cr(III), Mo(II), Bi(III), Se(IV), Se(VI), Sb(III) and Sb(V) could be masked with a mixture of ascorbic acid-KI in a 5.0molL^–1 HCl solution. The accuracy of the proposed method was evaluated by using certified reference materials of biological samples, and the method was used to determine the content of arsenic in fish and coffee beans.     

Differential determination of arsenic (III) and total arsenic with L-cysteine as prereductant using a flow injection non-dispersive atomic absorption device

Speciation of arsenic in environmental samples gains increasingly importance, as the toxic effects of arsenic are related to its oxidation state. A method was developed for the determination of trace amounts of arsenic(III) and total arsenic by flow injection hydride generation coupled with an in-house made non-dispersive AAS device. The total arsenic is determined after prereduction of arsenic(V) to arsenic(III) with L-cysteine in a low concentration of hydrochloric, acetic or nitric acid. The conditions for the prereduction, hydride generation and atomization were systematically investigated. A quartz tube temperature of 800°C was found to be optimum in view of peak shape and baseline stability. Pb(II), Ni(II), Fe(III), Cu(II), Ag(I), Al(III), Ga(II), Se(IV), Bi(III) were checked for interfering with the 2g/L As(V) signal. A serious signal depression was only observed for Se(IV) and Bi(III) at a 150-fold excess. With the above system, arsenic was determined at a sampling frequency of about 1/min with a detection limit (3) of 0.01g/L using a 0.5mL sample. The reagent blank was 0.001±0.0003 absorbance units and the standard deviation of 10 measurements of the 2 g/l As signal was found to be 1.2%. Results obtained for standard reference materials and water samples are in good agreement with the certified values and those obtained by ICP-MS     

Determination of Iron(III), Cobalt(II) and Chromium(III) in Various Water Samples by Flame Atomic Absorption Spectrometry After Preconcentration by Means of Saccharomyces Carlsbergensis Immobilized on Amberlite XAD-4

A method for the determination of Fe(III), Co(II) and Cr(III) by flame atomic absorption spectrophotometry (FAAS) after preconcentrating on a column containing S. carlsbergensis immobilized on Amberlite XAD-4 has been developed. The optimum values of pH, amount of adsorbent, elution solution and flow rate of the sample solution were determined for the quantitative recovery of the analytes. The effect of interfering ions on the recovery of the analytes was also investigated. Under the optimum conditions, recoveries of Fe(III), Co(II) and Cr(III) by S. carlsbergensis immobilized on Amberlite XAD-4 were 99±2, 100±2 and 98±2% at 95% confidence level, respectively. The limit of detections for Fe(III), Co(II) and Cr(III) were 2.8, 3.9 and 7.4ngmL^–1, respectively. The proposed method was applied to the determination of the analytes in various water samples. The validity of the method was checked with spiked water samples. Fe(III), Co(II) and Cr(III) was determined with a relative error of less than 5%.     

Solid-Phase Extraction with Slurry Injection of the Resin Into ETAAS for Trace Determination of Thallium in Natural Water

Thallium in natural water samples was determined by electrothermal atomic absorption spectrometry after 1000-fold enrichment by mini solid-phase extraction from a 100-mL sample solution. A Tl-pyrrolidine-1-carbodithioate complex formed in a sample solution of pH 1.6 was extracted on fine particles of a cellulose nitrate resin dispersed in the sample solution. The cellulose nitrate resin was then collected on a membrane filter (25mm^ø) by filtration under suction using a glass funnel with an effective filtration area of 0.64cm². As a result, a circular thin layer of the resin phase with a diameter of 9mm was obtained. Then the resin phase was carved out by an acrylate resin puncher with a 10-mm^ø hole to put it into a sample cup containing 100µL of 10mM HNO₃ containing 0.5mM NaCl. The resin phase was suspended in the solution by ultrasonication. 1000-fold enrichment was thus attained within 15min, and the suspension was delivered to electrothermal atomic absorption spectrometry. The linear calibration graph was obtained in the range of 0–4ng of Tl in 100mL of a sample solution. The detection limit obtained by 3 method was 0.19ng. The proposed method was applied to the determination of Tl in natural water samples. The results showed the concentration of Tl in seawater was 12.1±1.8pgmL^–1 for the calibration graph method and 12.6±1.4pgmL^–1 for the standard addition method. A snowmelt sample contained 20.7±1.0pgmL^–1 of Tl.     

Transformed steroids. 189. Synthesis and transformations of 21-hydroxy-5α-H-pregnane 2′,2′-dimethyl-[16α,17α-d]-thioxalanes

In a continuation of the research on use of 20-keto-16,17-epoxysteroid 20-hydrazones for synthesis of 17-thio analogs of 20-ketosteroid 16,17-acetonides [2, 3], we synthesized 5-H-pregnane-3,16,21-trihydroxy-17-thiol-20-one 16,17-acetonide and found methods for its microbiological dehydrogenation and hydroxylation into ⁴-3-keto-and 9-hydroxy-⁴-3-keto derivatives.See [1] for Communication 188.N. D. Zelinskii Institute of Organic Chemistry, Russian Academy of Sciences, 117913 Moscow. Translated from Izvestiya Akademii Nauk, Seriya Khimicheskaya, No. 5, pp. 1182–1186, May, 1992.     

Investigation of the electronic effect of the diphenylphosphino group

We have synthesized meta-substituted derivatives of benzoic acid, determined their ionization constants in water-alcohol solutions of concentration 11 and 14 by volume, and calculated the Hammett constant _m of the diphenylphosphino (0.12), diphenylamino (–0.04), diphenylphosphinyl (0.40) and diphenylthiophosphinyl (0.32) groups. Unlike the diphenylamine group, the diphenylphosphino group is metaorienting, which is probably to be explained by the absence or the weak nature of p- conjugation of incomplete electron pairs on the phosphorus and the presence of an electron-acceptor effect (d-p conjugation).     

Synthesis and characterization of carboxymethylcelluloses (CMC) from non-wood fibers I.Accessibility of cellulose fibers and CMC synthesis

This paper explores the production of carboxymethylcellulose (CMC) fromseveral bleached cellulose pulps obtained from non-wood species. The chemicalcomposition (-cellulose, hemicellulose and lignin content), the degreeofswelling, viscosity, solubility in concentrated NaOH and crystallinity ofsoda/AQ cellulose pulps from abaca, jute, sisal, linen and Miscanthussinensis were determined. The pulps were carboxymethylated by one andtwo successive reaction steps in aqueous medium under identical conditions. Thedegree of substitution (DS) of CMC was found to be dependent upon the source ofthe cellulose pulp, but generally it was close to 1 with one etherificationtreatment and around 2 after the second. The molar mass of CMC was found to bedependent on the initial intrinsic viscosity of the cellulose pulp. The weightaverage molar mass of our CMCs ranged from 1.5×10⁵ to2.8×10⁵. Increasing the DS up to 2 improved the CMC solubility, butviscosity slightly decreased due to a slight degradation of the polymer.