Kinetics of oxidative deamination of some amino acids by diperiodatoargentate(III) in alkaline medium

Kinetics of oxidation of some amino acids, viz. glycine, alanine, valine, leucine, phenylglycine and phenylalanine by diperiodatoargentate(III) have been investigated in alkaline medium. The order of the reaction is found to be one with respect to each reactant. The reaction rates are inversely dependent on both [OH^–] and [periodate]. The oxidation products are found to be ammonia and the corresponding keto acids. The presence of electron-withdrawing groups at the -carbon increases the rate of oxidation while the rate decreases with increasing alkyl chain length. A two-electron-transfer mechanism is proposed to explain the results.

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, , , , , , (III) . . OH^– . . - - ; . .

     

Hydrolysis of ethyl acetate on cation-form sulfonic resins

Catalytic properties of metal cations on sulfonic resin have been studied in ester hydrolysis. The catalytic activities were related to the electronegativity of the metal cation, while the activation energies were close to that for H-form resin and not affected by the cation concentration, suggesting the variation of entropy factors in catalysis.

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. . - . , .

     

Development and application of a simple routine method for the determination of selenium in serum by octopole reaction system ICPMS

The aim of the study was to develop an inductively coupled plasma mass spectrometry (ICPMS) method for robust and simple routine determination of selenium in serum. Polyatomic interferences on ⁷⁶Se, ⁷⁷Se, and ⁷⁸Se were removed by applying an octopole reaction system ICPMS with the reaction cell pressurized with H₂ gas. We developed a novel simple optimization routine for the H₂ gas flow based on a signal-to-noise ratio (SNR) calculation of the selenium signal measured in a single selenium standard. The optimum H₂ flow was 2.9 mL min^–1. The selenium content in serum was determined after a 50-fold dilution with 0.16 M HNO₃ and quantified by using addition calibration and gallium as an internal standard. The method detection limit was 0.10 g L^–1 for ⁷⁶Se and ⁷⁸Se and 0.13 g L^–1 for ⁷⁷Se. Human serum samples from a case-control study investigating if selenium was associated with risk of colorectal adenoma were analyzed. The average selenium concentration for the control group (n=768) was 137.1 g L^–1 and the range was 73.4–305.5 g L^–1. The within-batch repeatability (a batch is ten samples) estimated from 182 replicate analyses was 6.3% coefficient of variation (CV), whereas the between-batch repeatability was 7.4% CV estimated from 361 replicates between batches. The method accuracy was evaluated by analysis of a human serum certified reference material (Seronorm Serum level II, Sero A/S, Norway). There was a fairly good agreement between the measured average of 145±3 g L^–1 (n=36) and the certified value of 136±9 g L^–1. In addition the method was successfully applied for analysis of zinc serum concentrations without further optimization. For the Seronorm certified reference material a value of 911±75 g L^–1 (n=31) for zinc was obtained, which corresponds well to the certified zinc value of 920±60 g L^–1.     

Thermal Investigation of 1,2-propanediamine complexes of nickel(II) in the solid phase

Thermal studies have been carried out on [NiL₃]X₂·n H₂O, whereL=1,2-propanediamine;X=Cl^–, Br^–, SCN^–, 1/2SO ₄ ^2– and 1/2 SeO ₄ ^2– ; andn= 2, 1.5 and 0. [Ni₂L₅(NCS)₂](SCN)₂ and [NiL₂SO₄] have been synthesized pyrolytically in the solid-state from their mother diamine complexes. The deaquation behaviour of [NiL₃]SO₄·2 H₂O appears interesting, and its monohydrate undergoes a solid-state reaction (88–102°) without mass loss, showing an exothermic peak at 95 °C (H=– 5.1 kJ mole^–1).

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Zusammenfassung Thermische Untersuchungen wurden an [NiL₃]X₂,n H₂O ausgeführt, wobeiL-1,2-Propandiamin;X=Cl^–, Br^–, SCN^–, 1/2 SO ₄ ^2– und 1/2 SeO ₄ ^2– ;n=2, 1.5 und 0. [Ni₂Ls(NCS)₂](SCN)₂ und [NiL₂SO₄] wurden ausgehend von den entsprechenden Diaminkomplexen pyrolytisch im festen Zustand synthetisiert. Das Dehydratisierungsverhalten von [NiL₃]SO₄·2 H₂O scheint interessant zu sein, und beim entsprechenden Monohydrat wird eine ohne Massenverlust verlaufende Festkörperreaktion (88–102°) beobachtet, die sich durch einen exothermen Peak bei 95 °C (H=– 5.1 kJ mol^–1) zu erkennen gibt.

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[N³L₃]₂· n₂O, L=1,2-,=l^–, Br^–, SCN^–, 1/2 SO ₄ ^2- , 1/2SeO ₄ ^2- , an=2, 1.5 0. [Ni₂L₅(NCS)₂](SCN)₂ [NiL₂SO₄] . [N³L₃]S₄·2 ₂ , 88–102° , 95 ° =– 5.1 ·^–1.

     

State of copper in massive Cu?V?Mo oxide systems

ESR data for X(CuO) V₂O₅·8.3 MoO₃ system heated at 400–550 °C indicate the occurrence of a copper state with d_Z ²-ground state. Copper ions are orbitally ordered apparently in –Cu²⁺–O–Cu¹⁺–O–Cu²⁺-chains.

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B X(CuO) V₂O₅·8,3 MoO₃ , 400–550°C d_Z ²- . , , –Cu²⁺–O–Cu¹⁺–O–Cu²⁺-.

     

Development of an FI-ICP Method for On-Line Preconcentration and Determination of Platinum

This paper presents a new simple and rapid procedure for the preconcentration and determination of platinum. It is based on the adsorption of the metal ion and preconcentration on a micro-column (3cm×3mm) placed in the injection valve of a flow injection (FI) manifold and packed with 1,5-bis[(2-pyridyl)-3-sulphophenyl-methylene]thiocarbonohydrazide (PSTH) immobilised on an anion-exchange resin (Dowex 1X8-200). The metal was eluted from the column using a solution of 2M HNO₃. Various parameters and chemical variables affecting the preconcentration and determination of this metal by ICP-AES were evaluated. Five variables (sample flow rate, eluent flow rate, nebulizer flow rate, buffer concentration and mixing coil length) were considered as factors in the optimisation process. Interactions between analytical factors, and their optimal levels were investigated using two level factorial and central matrix designs. The optimum conditions established were applied to the determination of platinum by flow injection inductively coupled plasma atomic emission spectrometry (FI-ICP-AES). The method has a linear calibration range of 25 to at least 200ngmL^–1 with a detection limit of 7.4ngmL^–1 (S/N=3) and a throughput of 10 samples h^–1 using 5min. preconcentration time. The precision of the method (RSD) was 3.06% ngmL^–1 at the 50ngmL^–1 level of Pt(IV) and 2.93% at the 150ngmL^–1 level. The accuracy of the method was examined by determining the analyte content in spiked waters and by analysing an automobile catalyst standard reference material. The results show good agreement with the certified value and sufficiently high recoveries.     

Deactivation of reforming catalysts. Coke formation on metallic and acidic centers

To check coke formation on metallic (Pt^o) and acidic (Al₃₊) centers of Pt/Al₂O₃ and Pt–Sn/Al₂O₃ catalysts, the application of IR spectroscopy of adsorbed CO for detecting Pt^o–CO (2070 cm^–1) and Al³⁺–CO (2190 cm^–1) bonds has been substantiated. Decrease in the number of active Pt^o and Al³⁺ centers is shown to correlate with that in the dehydrogenation rate of cyclohexane and in the isomerization rate of heptane, respectively.

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(Pt^o) (Al³⁺) Pt/Al₂O₃ Pt–Sn/Al₂O₃ - CO Pt^o–CO (2070 ^–1) Al³⁺–CO (2190 ^–1). , Pt^o , Al³⁺- .

     

Determination of the surface hydroxy groups on alumina and silica-alumina catalysts by dimethylzinc

The earlier proposed pulse flow method for the determination of surface OH groups based on the reaction of gaseous dimethylzinc tetrahydrofuranate with active hydrogen was applied to alumina and silica-alumina catalysts. The concentrations of OH groups found by this method are in a good agreement with the published data, obtained by deuterium exchange and gravimetry.

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, , OH, , - . OH, , , .

     

Catalytic oxidation of cycloalkane heteroanalogs as a way to polyfunctional compounds

Liquid phase oxidation of cycloalkane diheteroanalogs catalyzed by compounds of Cu²⁺, Ni²⁺, Co²⁺, Cr³⁺, Fe³⁺ has been studied. It has been established that these catalysts can be applied to intensify, oxidize and increase the selectivity of this process.

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: Cu², Ni²⁺, Co²⁺, Cr³⁺, Fe³⁺. .

     

New possibilities for preparation of highly dispersed PtFe/SiO2 catalysts

Pt(CH₃)₃Cl complex has been applied for preparation of highly dispersed Pt/SiO₂ catalyst. Iron in different forms was used as second component for PtFe/SiO₂ catalyst. Dispersity of Pt is comparable to that obtained via Pt(NH₃) ₄ ²⁺ exchange. Catalytic activity and isomerization are explained in terms of Fe blocking of the surface.

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Pt(CH₃)₃Cl Pt/SiO₂. PtFe/SiO₂. Pt(NH₃) ₄ ⁺² . .

     

Mechanism of o-xylene conversion on magnesium modifications of Y zeolite

o-Xylene conversions has been investigated in the presence of MgNaY zeolites with different Si/Al ratios and degrees of exchange. Disproportionation proceeds to a higher degree than does isomerization. The distribution of reaction products is attributed to geometric factors. The results are in agreement with a monomolecular mechanism of isomerization.

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- MgNaY Si/Al . , , . . .

     

Dehydrocyclization of 1-heptene-1-14C over chromia on non-acidic alumina

The dehydrocyclization of 1-heptene-1-¹⁴C has been investigated over a chromia on nonacidic alumina catalyst with the aim of determining the¹⁴C distribution in the ring of the toluene product. As high as 80% of the¹⁴C was consistently found in the methyl position as predicted for direct six-carbon ring formation.

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1--1-C¹⁴ , , C¹⁴ . 80%- C¹⁴ , .

     

Comparative thermal analysis of commercial and low-grade bauxites

This paper presents qualitative and quantitative comparative results on the simultaneous TG-DTG DTA of five commercial and low-grade bauxites. The methodology of qualitative determination of the basic mineral forms contained in bauxites is currently being established. The weight losses relating to the steps in the TG curve allow determination of the contents of the basic minerals in bauxite. These are recalculated as percentages of Al₂O₃, SiO₂, CaO moisture and total volatiles. The final results are in accordance with the results of classical chemical analyses, and this jusitifies the use of this technique as a quick method for qualitative and quantitative determinations of both commercial and low-grade bauxites.

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Zusammenfassung Qualitative und quantitative Ergebnisse vergleichender simultaner TG-DTG-DTA-Untersuchungen an 5 kommerziellen und geringwertigen Bauxiten werden vorgestellt. Die Methodologie der qualitativen Bestimmung der wichtigsten im Bauxit enthaltenen Minerale wird ausgearbeitet. Die Gewichtsverluste bei den entsprechenden TG-Stufen erlauben die Berechnung der Gehalte an den wichtigsten Mineralen. Diese werden umgerechnet in die Anteile an Al₂O₃, SiO⁰², CaO, Feuchtigkeit und Glühverlust. Letztere Resultate stimmen mit denen klassisch-chemischer Analyse überein. Das erlaubt die Anwendung thermoanalytischer Methoden als Schnellverfahren für qualitative und quantitative Bestimmungen in kommerziellen und geringwertigen Bauxiten.

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, . , . , , , . , , .

     

Thermal stability and phase transformations in a commercial vanadia-molybdena alkali-promoted catalyst

Temperature-programmed decomposition, thermal analysis, thermogravimetry and high-temperature X-ray analysis have been used to investigate a commercial catalyst for the selective oxidation of benzene into maleic anhydride. It was shown that phase transformations took place in the vanadia-molybdena alkali-promoted catalyst. The transformations were caused either by high-temperature treatment or by catalytic work in an industrial plant. As a result, the-bronze phase was formed. In the high-temperature region a reversible transformation of the bronze phase was observed. This was interpreted as the phase transformation.

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Zusammenfassung Temperaturprogrammierte Zersetzung, Thermoanalyse, Thermogravimetrie und Hochtemperatur-Röntgenanalyse wurden zur Untersuchung eines kommerziellen Katalysators für die selektive Oxydation von Benzol zu Maleinsäure herangezogen. Es wird gezeigt, daß in dem einen Alkalipromotor enthaltenden Vanadinoxid-Molybdänoxid-Katalysator Phasenübergänge vor sich gehen. Die Phasenübergänge, als deren Ergebnis eine-Bronzephase gebildet wird, wurden entweder durch Hochtemperaturbehandlung oder durch sich in einer industriellen Anlage während des Betriebes abspielenden Vorgänge verursacht. Im Bereich hoher Temperaturen wurde eine reversible Umwandlung der Bronzephase beobachtet, die als Phasenübergang interpretiert wurde.

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- , , . , - , , . , , -. .

     

Pyrolysis of propane in the presence of acetylene

Pyrolysis of propane in the presence of acetylene and acetylene labeled with C-14 has been studied in the temperature range of 833–1019 K. The inhibition effect of acetylene on the thermal decomposition of propane is turning into an accelerating effect at higher temperature.

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C¹⁴ 833–1019 . .

     

Studies on the Fe2(MoO4)3-V2O5 system

The phase equilibria established in solid state in the whole range of component concentrations in the Fe₂(MoO₄)₃-V₂O₅ system were studied by DTA and X-ray powder diffraction. This system is not a real two-component system.

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Zusammenfassung Im gesamten Konzentrationsbereich der Komponenten des Systems Fe₂(MoO₄)₃-V₂O₅ wurde das im festen Aggregatzustand festgestellte Phasengleichgewicht mittels DTA und Pulverröntgendiffraktionsverfahren untersucht. Dieses System ist kein wirkliches Zweikomponentensystem.

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F₂(₄)₃-V₂O₅ . , .

     

Kinetics of the homogeneous oxidation of hydrogen by platinum(II) and platinum(IV) chloro complexes in aqueous solution

The kinetics of the homogeneous oxidation of hydrogen in the Pt(II)–Pt(IV)–Cl^––H₂O system has been studied for the first time in conditions permitting to avoid the formation of Pt-black. It is shown that platinum (II) [Pt(II)Cl_i(H₂O)_4-i, where i=1, 2, 2], is active in the reaction, whereas the PtCl ₄ ^2– complex and platinum(IV) do not react with hydrogen.

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, Pt-, H₂ Pt^II–Pt^IV–Cl^––H₂O. (II) (Pt^IICl_i(H₂O)_4-i, i=1, 2, 3); PtCl ₄ ^2– (IV) .

     

First Example of Construction of a Pyrrole Ring Bonded to a Steroid System by the Trofimov Reaction

The oxime of ⁵-pregnen-3-ol-20-one reacts with acetylene in the KOH-DMSO system to form a mixture of products containing 3-vinyloxy-17-(1-vinyl-2-pyrrolyl)-⁵-androstene as the major product (63% yield) and also the O-vinyloxime of 3-vinyloxy-⁵-pregnen-20-one (10%), 3-vinyloxy-17- and 3-vinyloxy-17-⁵-pregnen-20-one (25%, 1:4 ratio).     

Oxidation of propene over various doped tungsten oxides

The oxidation of propene was studied on several tungsten oxides which contained small amounts of Ti, Ta, Nb and Sn. Only the Sn-containing specimen was found to be selective in the conversion of propene to acrolein. The catalytic results are correlated with crystal structures determined by electron microscopy.

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, Ti, Ta, Nb Sn. , , Sn, . , .