n-Hexane dehydrocyclization on modified L-zeolite

Platinum dispersity and catalytic activity of L-zeolite-metal catalysts at 773 K have been studied depending on the nature of a modifying agent. The mean size of Pt particles is shown to decrease by a factor of 1.5–2 upon adding Re or W. No relation between Pt dispersity and activity in n-hexane dehydrocyclization has been revealed.

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773 L . 1, 5–2 Re W. -.

     

Study of the evolution of a MoO3+Bi2MoO6 mixture in air and in the conditions of mild propene oxidation

MoO₃ can react with the gamma phase of bismuth molybdate (Bi₂MoO₆) in the conditions of propene oxidation to form the alpha phase (Bi₂Mo₃O₁₂) resulting in a more selective catalyst for propene oxidation to acrolein. Intimate contact between MoO₃ and the gamma phase is an important factor favoring the formation of the alpha phase.

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MoO₃ - (Bi₂MoO₆), - (Bi₂Mo₃O₁₂), .

     

Influence of oxygen compound structural elements of stretching vibration frequency of surface hydroxy groups

Stretching vibration frequencies of OH groups ( OH) in acidic oxygen compounds are determined by the electrostatic characteristics (E_p) of the polyhedron containing this group. Empirical dependence of OH various hydroxy groups on the number and nature of their binding cations is suggested.

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, OH- ( OH) (). .

     

Influence of the properties of an oxide film on the oxidation of aluminium powders

The structure of oxide films of aluminium powders has been established to depend on the size of its particles. The temperature dependence of the oxidation of the powder in air is ascribed to changes in both the structure of the oxide laver and the pressure of saturated aluminium vapor. The porous, permeable product consists of hollow microspheres of -Al₂O₃.

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. , . , –Al₂O₃.

     

Thermoanalytical investigations on the decomposition of double salts

The melting and decomposition behaviour of carnallite was investigated in the closed system under dynamic heating conditions and in the open system under dynamic and quasi-isothermal and quasi-isobaric conditions in the temperature range between 20 and 300°. DTA heating and cooling cycles in the closed system illustrate the incongruent melting of carnallite and the occurrence of different magnesium chloride hydrate phases. The thermal decomposition under quasi-isothermal and quasi-isobaric conditions begins at a pressure of at least 100 kPa from the melt and under reduced pressure from the solid. In any case KCl · MgCl₂ · 2 H₂O is formed which is decomposed to a basic product KMgCl_2.84–2.90(OH_0.10–0.16.

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Zusammenfassung Die Schmelz- und Zersetzungseigenschaften des Carnallits wurden im geschlossenen System unter dynamischen Heizbedingungen und im offenen System under dynamischen und quasi-isothermen und quasi-isobaren Bedingungen im Temperaturbereich von 20 bis 300°C untersucht. DTA Heiz- und Kühlzyklen im geschlossenen System verdeutlichen das inkongruente Schmelzen des Carnallits und das Auftreten verschiedener Magnesiumchlorid-Hydratphasen. Die thermische Zersetzung beginnt unter quasi-isothermen und quasi-isobaren Bedingungen bei einem Druck von mindestens 100 kPa aus der Schmelze und unter verminderten Druck aus der festen Phase. Die Zersetung verläuft stets über KCl · MgCl₂ · 2 H₂O zu einem basischen Produkt KMgCl_2.84–2.90(OH)_0.10–0.16.

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— -, - V 20–300°. . - - 100 , — . KCl · l₂ · 2 ₂, Kgl_2.84–2.90()_0.10–0.16.

     

Thermal decomposition of decavanadates of bivalent metals

The thermal decomposition of Cd₃V₁₀O₂₈ · 16H₂O and Mg₃V₁₀O₂₈ · 18H₂O has been investigated. It was found by means of IR spectroscopy and X-ray phase analysis that the final products of decomposition of the given compounds are V₂O₅, the corresponding metavanadates and the vanadium bronzes of cadmium and magnesium. Present and previous results allow conclusions on the thermal decomposition of decavanadates of bivalent metals.

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Zusammenfassung Die thermische Zersetzung von Cd₃V₁₀O₂₈ · 16 H₂O und Mg₃V₁₀O₂₈ · · 18 H₂O wurde untersucht. Durch IR-Spektroskopie und Röntgen-Phasenanalyse wurde festgestellt, daß die Endprodukte der Zersetzung der gegebenen Verbindungen V₂O₅ ist, entsprechend den Metavanadate und den Vanadiumbronze von Cadmium und Magnesium. Die gegenwärtigen und früheren Ergebnisse gestatten Folgerungen bezüglich der thermischen Zersetzung von Dekavanadaten zweiwertiger Metalle.

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Résumé On a étudié la décomposition thermique de Cd₃V₁₀O₂₈ · 16 H₂O et Mg₃V₁₀O₂₈ · · 18 H₂O. A l'aide des techniques de spectroscopie IR et de rayon X, on a établi que les produits finaux de la décomposition de ces composés sont V₂O₅, les métavanadates correspondants et les bronzes au vanadium, de cadmium et magnésium. Les résultats présents et antérieurs permettent de tirer des conclusions sur la décomposition thermique des décavanadates des métaux divalents.

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d₃V₁₀₂₈ · 16₂ Mg₃V₁₀O₂₈· 18H₂O. , , V₂O₅, . , , .

     

Synthesis of Two New Glycophanes Comprised of Thioglucose Molecules Linked by Hydrocarbons

Preparation of two new glycophanes is reported. These compounds arecomprised of two glucose molecules linked by hydrocarbon units at the 1,1 and 3, 3 or 3, 3 and 6, 6 positions. Thecrystal structure of one of the glycophanes is also described.     

Instability of potassium permanganate solubilized in organic solvents

The instability of the solutions of potassium permanganate solubilized in benzene, toluene and chloroform by the action of 15-crown-5, 18-crown-6, dibenzo-18-crown-6, tetra-butylammonium bromide and trilaurylmethyl ammonium bromide as phase-transfer catalysts, is reported. The kinetic parameters depend markedly on the catalyst used, the solvation of reactants is also important.

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, , 15- -5, 18- -6, -18- -6, , . .

     

Thin-layer chromatographic separation of some closely related olefinic benzo- and naphtofurans

Summary A method is reported for the separation of 16 closely related 2-(1, 2-diphenylvinyl)-3-phenylbenzofuran and 2-(1, 2-diphenylvinyl)-1-phenylnaphtho[2,1-b] furan derivatives on thin-layers of silica gel-G.     

Ammoxidation of 3- and 4-picolines over V2O5?SnO2/γ?Al2O3 catalyst

The ammoxidation of 3- and 4-picolines has been studied over V₂O₅–SnO₂/–Al₂O₃ catalysts prepared by surface impregnation technique. Best results were obtained for the generation of cyanopyridines in the temperature range 400–450°C and sub-stoichiometric value with respect to O₂. Catalysts that were calcined above 700°C showed no activity.

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3- 4- V₂O₅–SnO₂/–Al₂O₃, . 400–450°C O₂. , 700 K, .

     

Specific changes in the activity of titanium carbides with various Ti/C ratios in propylene hydrogenation

According to X ray emission spectra, the established regularity in the activity change for titanium carbides with various Ti/C ratios is attributed to the filling degree of the t_2g states of titanium atoms determining the metallicity of chemical bonds of the compounds.

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Ti/C t_2g , .

     

Vacuum ultraviolet spectroscopic analysis of nitrogen in iron and steel with low-voltage condensed-spark discharge

Summary The determination of nitrogen in steels was investigated by low voltage condensed spark discharge and far ultraviolet vacuum spectroscopy. The excitation conditions were 1,000V, 193, 63 F and 50H in helium atmosphere of 700 mm Hg. Nitrogen contents from 20 ppm to 100 ppm in steel could be determined with the line pair of N I 1,745 Å/Fe I 1,876 Å or N I 1,742 Å/Fe I 1,876 Å.

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Zusammenfassung Zur Bestimmung von Stickstoff (20–100 ppm) in Stählen wurde eine UV-vakuumspektrometrische Methode mit Niederspannungs-Funkenentladung benutzt. Die Entladungsbedingungen waren: 1000 V, 193 , 63 F und 50 H, unter Heliumatmosphäre von 700 mm Hg; verwendet wurden die Linienpaare N I 1,745 Å/Fe I 1,876 Å oder N I 1,742 Å/ Fe I 1,876 Å.

     

Artifacts caused by plastics in chemical experiments: Absorption, degradation, catalysis and irreproducible behavior

In the experimental praxis of our chemical laboratory we have been surprised and impressed by a few uncontrollable results caused by plastics. These materials are generally considered to be chemically more or less unreactive and inert. Absorption and chemical degradation—especially during long use—can activate the surface of silicon rubber, polyethylene or teflon, which are constituents of tubes, reaction vessels, stirring bars and other parts of instruments. In a few cases catalytic activation can be interpreted in terms of the interaction between the microporous surfaces of plastics and reactants. These observations require careful consideration and control of the properties and quality of plastics before using them even in the simplest chemical experiments.

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, . . — — , , , , , . , . .

     

Magnetic properties of new copper(II) and [copper(II)]3-manganese(II) complexes of [14]N4 macrocyclic oxamides

Four new complexes of [14]N4 macrocyclic oxamides, namely [CuL1], [CuL2], [(CuL1)3Mn](ClO4)3 and [(CuL2)3 Mn](ClO4)3 [L1 and L2 are the dianions of 2,3-dioxo-5,6: 3,14-dibenzo-7,12-bis(ethoxycarbonyl)-1,4,8,11-tetraazacyclotetradeca-7,11-diene (H2L1) and 2,3-dioxo-5,6:13,14-dibenzo-9-methyl-7,12-bis(ethoxycarbonyl)-1,4,8,11-tetraazacyclo-tetradeca-7,11-diene (H2L2), respectively], have been prepared and characterized. The observed magnetic susceptibilities of the [(CuL1)3Mn] (ClO4)3 complex over the ca. 2–300 K range have been fitted to theoretical equations based on the Heisenberg spin Hamiltonian =–2JMn(Cu1+ Cu2+Cu3) and molecular field approximation. The results indicated that both the intramolecular and intermolecular magnetic interactions are antiferromagnetic with JCuMn= –19.8cm–1 and zJ=–1.41cm–1.     

Molecular Interactions and Thermodynamic Aspects of the Complexation Reaction between Gentian Violet and Several Cyclodextrins

The complexation process between gentian violet (CV+) and four different cyclodextrins (-, -, -, and HP--CDs) has been investigated under different reaction conditions (pH, solvent, and temperature) by electronic absorption and 1H NMR (NOE and NOESY) spectroscopies. All the binding constants were determined by the direct spectroscopic method. The H and S complexation values have been evaluated and discussed according to the diverse factors that affect the chemical interactions in these systems. A simple association takes place between the secondary hydroxyl or the hydroxypropyl groups of and HP--cycloamyloses, respectively, with the amine group of the gentian violet, while the binding between CV+ and - or -CDs corresponds to a real inclusion. Also, a CV22+ dimmeric species within the -CD cavity was detected in aqueous solution, while two molecules of -CD react with one molecule of gentian violet in DMSO at 294 K. In all the reaction media the -CD forms 1 : 1 complexes, but in the buffered aqueous solution at pH 7.5 the inclusion is deeper than in the other solvents. It is important to point out that the solvophobic effect is the most important binding factor in the complexation of the CV+ with the - and HP--CDs, while the complexes with -, and -cyclodextrins are mainly stabilized by van der Waals interactions between the guest and the host cavity. In all cases, the inclusion orientation is probably determined by the ion-dipole interactions between gentian violet and the solvent.     

Structures of some lilioglycosides from the bulbs ofLilium regale

Six steroid glycosides, which gave been called lilioglycosides B, C, E, F, H, and I have been isolated from fresh bulbs ofLilium regale Wills. The structure of each compound has been determined by methods of physicochemical analysis. This is the first time that lilioglycosides B, C, H, and I, have been described; they are, respectively: (25S)-spirost-5-ene-3,27-diol3-O--D-glucopyranoside; (25R)-spirost-5-ene-3,27-diol3-O--D-glucopyranoside27-(3-hydroxy-3-methylglutarate); (25S)-spirost-5-ene-3,27-diol3-O-{[O--L-rhamnopyranosyl-(12)],[O--D-glucopyranosyl-(13)]--D-glucopyranoside}; and (25S)-spirost-5-ene-3,27-diol 3-O-{[O--L-rhamnopyranosyl-(12)],[O--D-glucopyranosyl-(13)]-O--D-glucopyranoside} 27-[(S)-3-hydroxy-3-methylglutarate].Institute of Genetics, Academy of Sciences of the Republic of Moldava, 2002, Kishinev, ul. Padurilor, 20. Translated from Khimiya Prirodnykh Soedinenii, No. 6, pp. 841–847, November–December, 1997.     

Condensation of aldehydes and ketones

The alkaline condensation of -aceto-and -propionaphthalenes with furfural has given, respectively, 2-(-furfuryl)-1, 3-di(-naphthoyl)-propane and 3-(-furyl)-2,4-di(-naphthoyl)pentane; both -diketones have also been obtained by the Michael condensation. Under more severe conditions, two molecules of furfural condense with three molecules of -acetonaphthalene to form 2, 4-di(-furyl)-1, 3, 5-tri(-naphthoyl)pentane. Under similar conditions, benzaldehyde exhibits only a feeble capacity for triketone condensation with -acetonaphthalene. The condensation of -propionaphthalene with furfural has given the new compound furylidenepropionaphthalene. It has been shown that both under the conditions of the improved Chichibabin pyridine synthesis and under the conditions of the Leuckhardt reaction, 3-(-furyl)-1, 3-di(-naphthoyl)propane gives 4-(-furyl)-2, 6-di(-naphthyl)pyridine.     

Oxidation of ethanol on platinum/alumina and copper oxide catalysts

The oxidation of ethanol on CuO, CuO/Al₂O₃ and Pt/Al₂O₃ catalysts has been studied at various concentrations of alcohol, oxygen and water vapor in the reaction mixture. The reaction order and activation energies have been determined for both complete and partial oxidation processes. A consecutive oxidation scheme is suggested.

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CuO, CuO/Al₂O₃ Pt/Al₂O₃ , . . .

     

Übergangsmetall-Chalkogensysteme, 3. Mitt.: Das System Nickel-Tellur

Zusammenfassung Auf Grund thermischer und röntgenographischer Unter-suchungen wurde das vollständige Phasendiagramm Ni–Te aufgestellt. Die Anlage für die thermische Analyse wurde teilweise automatisiert, so daß ausgewählte Temperaturintervalle mit einstellbaren Heiz- udn Kühlgeschwindigkeiten periodisch durchlaufen werden konnten. Zwischen Ni und der kub. f. z. Hochtemperaturphase ₁ (Ni_3±x Te₂) liegt ein Eutektikum bei 34 At% Te und 1004,5°C. ₁ schmilzt kongruent bei 38 At% Te und 1021,5°C und hat eine maximale Phasenbreite von 37 At% Te (1004,5°C) bis 43,5 At% Te (880°C). Nickelreiches ₁ wandelt sich zwischen 796 und 789°C in eine Ordnungsphase ₁ um, die bei 37,7 At% Te und 731°C eutektoidisch in Ni und ₂ zerfällt. ₁ und ₁ wandeln sich unterhalb bei 790°C in die tetragonale ₂-Phase um, deren maximaler Homogenitätsbereich von 38,8 At% Te (731°C) bis 41 At% Te (775°C) reicht. Bei 42,5 At% Te und 775°C zerfällt ₁ eutektoidisch in ₂ und ₂. Die ₂-Phase (NiTe_0,85) bildet sich peritektisch bei 880°C und zerfällt bei 690°C nach _{2 1} + . Orthorhombisches ₁ disproportioniert sich peritektoidisch bei 742,5°C in ₂ und ₂. ₂ bildet bei 873°C und 49,5 At% Te ein Eutektikum mit der -Phase vom NiAs-Typ. hat einen kongruenten Schmelzpunkt von 900,5°C bei 56 At% Te und eine maximale Phasenbreite von 52 At% Te (690°C) bis 66,6 At% Te (448,5°C). Mit Te bildet die -Phase ein entartetes Eutektikum bei 448,5°C. Die Phasen ₂, ₁ und wurden röntgenographisch verifiziert und die Abhängigkeit der Gitterparameter der -Phase von der Konzentration vermessen.

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Transition metal-chalcogene systems, III: The system Ni–Te

Based on thermal and X-ray measurements the complete Ni–Te phase diagram was constructed. The equipment for thermal analysis was partially automated so that selected temperature intervals could be periodically scanned by programmed heating and cooling rates. Between Ni and thefcc high temperature phase ₁ (Ni_3±x Te₂) a eutectic exists at 34 at% Te and 1004.5°C. ₁ melts congruently at 38 at% Te and 1004.5°C, and has a maximum phase width from 37 at% Te (1004.5°C) to 43.5 at% Te (880°C). Nickel-rich ₁ transforms between 796 and 789°C into an ordered phase ₁ which decomposes eutectoidally into Ni and ₂ at 37.7 at% Te and 731°C. ₁ and ₁ transform at temperatures below 790°C into the tetragonal ₂-phase which has a maximum range of homogeneity from 38.8 at% Te (731°C) to 41 at% Te (775°C). At 42.5 at% Te and 775°C ₁ decomposes eutectoidally into ₂ and ₂. The ₂-phase (NiTe_0.85) is formed by the peritectic reactionL + _{1 2} at 880°C and decomposes at 690°C according to _{2 1} + . Orthorhombic ₁ disproportionates peritectoidally at 742.5°C into ₂ and ₂. ₂ forms at 873°C and 49.5 at% Te a eutectic with the -phase of the NiAs-type. has a congruent melting point of 900.5°C at 56 at% Te and a maximum phase width from 52 at% Te (690°C) to 66.6 at% Te (448.5°C). Te and the -phase form a degenerate eutectic at 448.5°C. The phases ₂, ₁, and were verified by X-ray diffraction and the lattice parameters of the -phase were determined as a function of concentration.

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Mit 2 Abbildungen     

Electron microscopic studies of platinum catalysts prepared via decomposition of Al2O3-anchored metal complexes

Reduced alumoplatinum and alumoplatinum-tin catalysts prepared via interaction of an organometallic platinum complex and platinum-tin compounds of various composition with Al₂O₃ mainly contain platinum particles of 10 Å.

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, Al₂O₃, , , 10 Å.