Quantum chemical calculations on the catalytic dehydration of 2-propanol

The charge on atoms and the bond strengths in CH₃CHOHCH₃, CH₃ CH₃, CH₃CHOHCH ₂ ^– , CH₃ CH ₂ ^– and CH₃ CH₃...O(H)CH(CH₃)₂ have been calculated by the CNDO/2 method. The results are in agreement with published experimental observations on catalytic dehydration. A modified mechanism of anti-elimination on solid catalysts is proposed.

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CH₃CHOHCH₃, CH₃ CH₃, CH₃CHOHCH ₂ ^– , CH₃ CH ₂ ^– CH₃ CH₃...O(H)CH(CH₃)₂, CNDO/2. . .

     

Ru(III) catalysis in the oxidation of arenes by periodate. A kinetic study

The title reactions are zero order in periodate and first order in Ru(III). All substrates show a first order dependence except for p-xylene and fluorene which follow a Michaelis-Menten behavior. The Hammett plot gives a values of-2.0. A mechanism involving metal arene -interaction is discussed.

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Ru(III). , - , -. =–2,0. . , -- .

     

Binding energy of oxygen to the surface of promoted V?Mo?O catalysts for acrolein oxidation to acrylic acid

It has been established that P, Cs and Cu additives to V–Mo–O catalysts affect essentially both binding energy of surface oxygen and mobility of bulk oxygen.

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P, Cs Cu V–Mo–O .

     

Synthesis and properties of hydrodesulfurization catalysts, III. Support effect on the catalytic activity of Co?Mo?Al2O3 catalysts

By means of DTA, reflectanc spectra and measurement of catalytic activity in thiophene hydrogenolysis, the effect of support (aluminium hydroxide and oxide) as well as of the order of introduction of molybdenum and cobalt compounds on the structure and catalytic surface of Co–Mo–Al₂O₃ catalysts is shown.

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, ( ) , Co–Mo–Al₂O₃.

     

The question of thermal decomposition of pyrite

The thermal decomposition of monomineral pyrite was studied in an inert atmostphere. From an analysis of the values of the thermal effects, an interpretation of the hree physicochemical processes recorded in the thermoanalytical curves is proposed.

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Zusammenfassung Die thermische Zersetzung von monomineralem Pyrit wurde in inerter Atmosphäre untersucht. An Hand der Analyse der Werte der thermischen Effekte wird eine Beschreibung dreier, in den thermoanalytischen Kurven festgehaltener physikalischchemischer Vorgänge vorgeschlagen.

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Résumé On a étudié la décomposition thermique de la pyrite, en atmosphère inerte. On propose une interprétation des trois processus physicochimiques enregistrés sur les courbes thermoanalytiques, qui repose sur l'analyse des effects thermiques.

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- , .

     

Electrocatalytic effect of metal ions on lead and lead dioxide electrode reactions

The electrochemical reactions which take place on lead and lead dioxide electrodes of a lead-acid battery are highly influenced by the presence in the electrolytic solution of ions Cd(II), Ni(II), Zn(II) and Co(II). Current density-potential curves were obtained in this work by using a Pb/Ca alloy. It was observed that Co(II) and Ni(II) ions catalyzed both hydrogen and oxygen evolution reactions. On the other hand, Cd(II) and Zn(II) ions decreased the hydrogen evolution rate.

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, - , Cd(II), Ni(II), Zn(II) Co(II). - , Pb/Ca. , Co(II) Ni(II) , . , Cd(II) Zn(II) .

     

Chiral recognition of enantiomeric peptides in water at 25° by calorimetry

The heats of dilution in water of binary and ternary solutions of the two enantiomeric forms ofN-acetylalanineamide have been measured at 25°. The excess enthalpies, expressed as virial expansion series, permit evaluation of the pairwise self and cross enthalpic coefficients. As for the chiral forms of some monosaccharides, the cross coefficient for the interaction between theD andL forms ofN-acetylalanineamide is slightly but significantly different from the corresponding self coefficient. A weak, water-mediated chiral recognition can be assumed to exist between pairs of amide molecules.

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Zusammenfassung Die Verdünnungswärmen von binären und ternären wässrigen Lösungen der zwei enantiomeren Formen von N-Acetylalaninamid wurden bei 25 °C gemessen. Die in einer Virialexpansionsreihe entwickelten Überschußenthalpien ermöglichen die Berechnung der self und cross Enthalpiekoeffizientenpaare. Was die optisch aktiven Formen einiger Monosaccharide anbetrifft, so ist der cross Koeffizient für die Wechselwirkung zwischen der D- und L-Form von N-Acetylalaninamid etwas, aber signifikant verschieden von dem entsprechenden self Koeffizienten. Es kann angenommen werden, daß Paare von Amidmolekülen eine schwache, durch Wasser vermittelte Unterscheidungsfähigkeit hinsichtlich der optischen Aktivität zeigen.

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25° - N-. . L- N- , , , . .

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This work was carried out with the financial support from the italian C. N. R. (Rome) and from the Ministry of Public Education.     

Isomerization of olefins on Ta2O5 catalysts

The double bond and skeletal isomerization of olefins was investigated on Ta₂O₅ catalysts calcined at different temperatures. A remarkable minimum of catalytic activity and surface acidity (as characterized by pyridine adsorption) was found at 600°C calcination temperature. A further peculiarity of Ta₂O₅ catalyts was found in the exceptionally low surface OH coverage (0.01–0.3 OH nm^–2). Pyridine is a total poison, water is a partial poison, whereas CO₂ has no effect on the catalytic activity.

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Ta₂O₅, . ( ) 600°C. Ta₂O₅ OH (0,01–0,3 OH nm^–2). , CO₂ - .

     

Effect of free phosphine on the reactivity of phosphine-containing rhodium(I) complexes

The photolysis products of SO₂-pentane-NO mixtures are N₂O, H₂O and a compound designated as RNO. Kinetic data obtained by OC method confirm the previously proposed scheme of photolysis. Also studied was the photolysis of SO₂, NO and cyclohexane mixtures. From comparison of spectral characteristics of RNO and its analog 2-methyl-2-nitrosopropane, the probable structure of RNO is suggested.

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SO₂--NO N₂O, H₂O , RNO. , , . SO₂ NO . RNO 2--2- RNO.

     

A thermal decomposition study of some nickel(II)thioureachloride complexes

TG/DTA and Thermal Degradation Mass spectrometry (TDMS) data are presented for a series of nickel(II)thiourea chloride complexes: NiL₄Cl₂:L=thiourea or methyl-, dimethyl-, tetramethyl-, di-n-butyl, naphthyl-, ethylene- or allylthiourea. Two different thermal decomposition mechanisms are proposed for these complexes, and it is apparent that the thermal decomposition mechanism adopted by a particular complex depends on the structure of the relevant thiourea ligand and not on the nature of the halide ligand or on the existence of geometrical isomerism for these complexes.

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Zusammenfassung Durch TG, DTA und thermodegradative Massenspektrometrie (TDMS) von Nickel(II)-thioharnstoff-chlorid-Komplexen, NiL₄Cl₂ (L=Thioharnstoff oder Methyl-, Dimethyl-, Tetramethyl-, Di-n-butyl-, Naphthyl-, Vinyl- oder Allylharnstoff), erhaltene Daten werden angegeben. Zwei verschiedene Mechanismen werden für die thermische Zersetzung vorgeschlagen. Es ist offensichtlich, daß der Mechanismus, nach der die thermische Zersetzung eines gegebenen Komplexes verläuft, von der Struktur des relevanten Thioharnstoffliganden und nicht von der Natur des Halidliganden oder vom Vorliegen einer geometrischen Isomerie abhängt.

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/ - NiL₄Cl₂, L= , -, -, -, ---, -, - . . , .

     

Effect of the medium in hexacyanoferrate (III)-iodide and peroxodisulfate-iodide reaction

The kinetics of the two reactions hexacyanoferrate (III)-iodide and peroxodisulfate-iodide in several isodielectric water-cosolvent mixtures have been studied. The results can be rationalized as a consequence of the cosolventwater interaction.

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(III) -. -.

     

Some peculiarities in ESR spectra of titanium complexes in catalysts for isoprene polymerization in excess A1R3

It has been established that at low temperatures of TiCl₄+AOC catalyst preparation in solution (with Ti/Al1/15), ESR spectra exhibit rhombic anisotropy of the g-factor. Experiments with the sample having 61 % concentration of⁴⁷Ti isotopes suggest the formation of associates of Ti³⁺ with magnetic ordering, apparently due to the Jahn-Teller cooperative effect.

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TiCl₄+ AOC ( Ti/Al1/15) g-. ⁴⁷Ti (61%) Ti³⁺ , , -.

     

A metal reactor for the diaphragm method with chambers providing complete mixing

A new metal reactor with two chambers in which complete mixing of gases is achieved has been developed for use in the diaphragm method. This apparatus is suitable for the determination of the effective diffusion coefficient and its temperature dependence. It can also be used to determine the type of transport, the gas permeability coefficient and to investigate the macrokinetics of catalytic processes.

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. : ; ; .

     

Kinetics and mechanism of hydrazine oxidation by oxygenated Co2(L-his)4O2 complex

The kinetics of Co₂ (L-his)₄O₂ reduction by hydrazine in aqueous solution has been studied and the rate constants, the energy and entropy of activation have been determined.

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, , Co₂ (L-)₄O₂ .

     

Effect of bromination on the thermal properties of poly(2,6-dimethyl-1,4-phenylene oxide)

The thermal behavior of poly(2,6-dimethyl-1,4-phenyiene oxide) (PPO R resin), poly(3-bromo-2,6-dimethyl-1,4-phenylene oxide), and a series of their statistical copolymers with identical average molecular lengths has been characterized by thermogravimetry and computer-interfaced differential scanning calorimetry. The heat capacities are found to be additive with respect to the concentrations of the two components. The change in heat capacity at the glass transition ( C _p) is independent of composition for bromination of up to 75% of the repeat units. At higher bromine levels C _p decreases abruptly. This behavior is attributed to the temperature dependence of C _p for the two components. The glass transition temperature (T _g) of the copolymers varies nearly linearly with composition. A comparison of the experimental values ofT _g is made with various equations derived for statistical copolymers and homogeneous polymer blends. A modification of the Couchman equation is presented taking into account the temperature dependence ofC _p.

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Zusammenfassung Das thermische Verhalten von Poly(2.6-dimethyl-1.4-phenylenoxyd) (PPO R-Harz), Poly(3-brom-2.6-dimethyl-1.4-phenylenoxyd) und einer Reihe von statistischen Copolymeren dieser Verbindungen mit gleicher durchschnittlicher Moleküllänge wurde durch Thermogravimetrie und Differential-Scanning-Kalorimetrie mit Computerinterface charakterisiert. Die Wärmekapazitäten sind hinsichtlich der Konzentrationen der beiden Komponenten additiv. Die Veränderung in der Wärmekapazität beim Übergang zum Glas (C_p) ist unabhängig von der Zusammensetzung bei Bromierung bis zu 75% der wiederho-lungseinheiten. Bei höheren Bromierungsgraden nimmtC _p abrupt ab. Dieses Verhalten wird der Temperaturabhängigkeit vonC _p der beiden Komponenten zugeschrieben. Die Glasübergangstemperatur (T_g) der Copolymeren verändert sich nahezu linear mit der Zusammensetzung. Ein Vergleich der experimentellen Werte von T_g wird mit verschiedenen für statistische Copolymere und Mischungen homogener Polymere abgeleiteten Gleichungen ausgeführt. Eine die Temperaturabhängigkeit vonC _p berücksichtigende Modifikation der Gleichung von Couchman wird angegeben.

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, , (2,6- -1,4), (3--2,6--1,4- ) . , ë . ë (C ) 75%. C . C . T . . T . , . , C .

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This work was supported by the National Science Foundation, Polymers Program (DMR 78-15279) and the General Electric Corporate Research and Development Center. The authors are indebted to the following individuals at General Electric CRD for their experimental assistance: S. R. Weissman and P. E. Gundlach (molecular weight characterizations); D. W. Marsh (X-ray analysis); V. H. Watkins and E. L. Hall (electron microscopy); and N. A. Marotta (thermogravimetry). P. E. Donahue and E. A. Williams are gratefully acknowledged for carrying out and interpreting the NMR experiments.

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One of the authors (R. C. Bopp) would like to thank A. R. Shultz, J. T. Bendler, and D. M. White at General Electric CRD for their helpful discussions of this work and express his sincere appreciation to Professor P. R. Couchman (Rutgers University) for his illuminating discussions of the thermodynamic basis of his equation.     

Catalytic properties of phosphorus-containing rhenium complexes in the hydrogenation of hexene-1

Rhenium (V, VI) complexes with organophosphorus ligands proved to be catalytically active in hexene-1 hydrogenation. The kinetics of this process catalyzed by ReOCl₃(PPh₃)₂ has been examined. The organic ligand in the coordination sphere of rhenium complexes was found to affect selectivity to olefin bonds or nitro groups in the hydrogenation of hydrocarbons.

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(V, VI) -1. , ReOCl₃ (PPh₃)₂. , .

     

Conversion of cyclohexene on a gold-plated palladium-nickel membrane catalyst

Under flow conditions, on the gold-covered external surface of a tube made of Pd containing 5.9% Ni cyclohexene is dehydrogenated into benzene and the hydrogen formed does not desorb but is consumed in cyclohexene hydrogenation to cyclohexane and diffuses through the membrane catalyst. In the presence of added hydrogen, cyclohexene hydrogenation takes place below 200°C. Upon the introduction of hydrogen through the membrane catalyst the hydrogenation rate strongly increases relative to the case when hydrogen is fed in mixture with cyclohexene vapors.

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- , Pd–Ni (5,9%), , . 200 °C, , .

     

Study of hydroisomerization of n-hexane on natural mordenite catalyst

A mordenite-containing rock sample from the Tokaj Mountains (Hungary) and its various forms modified by chemical treatment have been tested for catalytic properties during isomerization of n-hexane. Addition of Pt to the catalyst leads to a sharp decrease in the rate of cracking and in the rate of deactivation and this results in a catalyst of high selectivity for hexane isomers.

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(), , , , -. Pt , .

     

A model of reaction front propagation in crystals

A spatio-temporal model of anisotropic propagation of the dehydration front in Na₃P₃O₉ · 6H₂O single-crystals is discussed. It is based on the assumption that dehydration proceeds as a periodic displacement of the reaction front from one reacting elementary block to another, and that experimentally fixed dehydration patterns are composed of a multitude of elementary patterns having the same shape. The model can be applied to other crystals.

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Zusammenfassung Ein Zeit- und Raummodell der anisotropischen Fortschreitung der Dehydratationsgrenzfläche in Na₃P₃O₉ · 6H₂O Einkristallen wird diskutiert. Das Modell ist auf einer Annahme begründet, dass die Wasserabspaltung als eine periodische Propagation der Reaktionsgrenzfläche von einem reagierendem Elementarblock zu anderem verläuft und dass die experimentell fixierte Entwässerungsfiguren aus einer Menge von Elementarfiguren von identischer Form zusammengestellt sind. Das Modell kann auf andere Kristallen verbreitet werden.

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- Na₃P₃O₉· 6₂. , , . .

     

Investigation of thermooxidative stability of oils by thermal analysis methods

Two base oils, obtained on a laboratory scale, were investigated with a derivatograph and by means of DSC. The sensitivities of the oils to some antioxidants were also examined. The high thermooxidative stability of the oil obtained from a preoxidized atmospheric crude residue was confirmed.

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Zusammenfassung Zwei im Labormaßstab hergestellte Rohöle wurden mit einem Derivatographen und mittels DSC untersucht. Die Empfindlichkeit der Öle gegenüber Antioxidanten wurde ebenfalls geprüft. Es wurde eine hohe thermooxidative Stabilität des aus einem präoxidierten atmosphärischen Rohstoffrestes erhaltenen Öls nachgewiesen.

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, . . , .

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The authors are grateful to the Institute of Petroleum Technology for the DSC measurements.