Effect of methanol concentration on substrate conversion in alkylation of toluene on zeolite catalysts

Influence of the concentration of toluene and methanol on the substrate conversion in toluene methylation reaction was studied by a pulse method. Increased methanol partial pressure gave better conversion to xylenes whereas toluene partial pressure did not affect the reaction. This behavior has been interpreted by supposing that the first step in toluene methylation is chemisorption of methanol on zeolite.

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. , . , .

     

The height of DSC phase transition peaks application to liquid crystals

A new method for differentiating first- and second-order transition in liquid crystalline systems is proposed. It is based on the use of the ratioN=h/h ₀, whereh ₀ is the height of the transition peak recorded by DSC at a heating rateT _p with a massm, andh is the height of the corresponding peak when the heating rate or the mass is doubled. The application of this new concept to phase transitions in octylcyanobiphenyl (8CB) is mentioned.

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Zusammenfassung Eine neue Methode zur Unterscheidung von Umwandlungen erster und zweiter Art in flüssigen Kristallen wird vorgeschlagen, die auf Anwendung des VerhältnissesN=h/h₀ basiert, wobeih ₀ die Höhe des durch DSC bei einer AufheizgeschwindigkeitT _p und für die Massem registrierten Umwandlungspeaks undh die Höhe des entsprechenden Peaks bei Verdoppelung der Aufheizgeschwindigkeit oder der Masse bedeuten. Auf die Anwendung dieses neuen Konzepts auf Phasenübergänge in Octylcyanobiphenyl (8CB) wird eingegangen.

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. N=h/h ₀, h ₀- , T _p m, h- . -.

     

Acetonation of L-sorbose catalyzed by heteropoly acids

Acetonation of L-sorbose—a step of ascorbic acid synthesis—takes place in acetone to yield 85% of diacetone-L-sorbose in the presence of heteropoly acids H₃PW₁₂O₄₀ and H₄SiW₁₂O₄₀ (0.1–0.35%) as catalysts.

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L-— L- — -L- 85% 0.1–0.35% H₃PW₁₂O₄₀ H₄SiW₁₂O₄₀ .

     

Studies of the reactions of Br(2P3/2) and Br(2P1/2) with SiH4

Photobromination of SiH₄ under uv-irradiation at various wavelengths has been studied. Rate constants for the elementary reactions Br(²P_3/2)+SiH₄HBr+SiH₃ (k=3.2×10^–11 exp(–21.8±2.5)/RT, cm³/s) and Br^* (²P_1/2)+SiH₄HBr+SiH₃ (k^*=(3±1)×10^–13 cm³/s) have been determined in the temperature range from 300 to 415 K.

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- . Br(²P_3/2)+SiH₄HBr+SiH₃, k=3,2×10^–11 exp (–21,8±2,5)/RT ³/ Br^*(²P_1/2)+SiH₄HBr+SiH₃, k^*=(3±1)×10^{–13 3}/ 300–415 K.

     

Kristalldaten und thermische Zersetzung der Modifikationen des Kaliumhydrogenjodats,KH(IO3)2

Zusammenfassung Die Kristalldaten der- und der-Modifikation des KH(JO₃)₂ wurden bestimmt; die von früheren Autoren angegebene rhombische-Modifikation konnte nicht aufgefunden werden. Bei der thermischen Zersetzung ergeben beide Kristallarten zunächst Wasser, dann I₂O₅ und O₂; es bleibt KI zurück. Als Zwischenstufe entsteht K₂I₄O₁₁. Die Temperaturen der DTA- und DTG-Spitzen zeigen bei der- und der-Modifikation sicher nachweisbare Unterschiede.

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The crystal data of the- and-modifications of KH(IO₃)₂ were determined. The rhombic-modification which has been described by earlier authors could not be obtained. In the course of thermal decomposition both crystal types release water, then I₂O₅ and O₂, leaving a residue of KI. As an intermediate, K₂I₄O₁₁ is formed. The temperatures of the DTA and DTG peaks of the- and-modifications, were found to be different.

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Résumé On a déterminé les données cristallographiques des modifications et de KH(IO₃)₂. On n'a pas pu retrouver la modification mentionnée par d'autres auteurs dans des travaux plus anciens. Lors de la décomposition thermique, les deux modifications cristallographiques perdent d'abord de l'eau, puis I₂O₅ et O₂; le résidu est constitué par KI. On décèle K₂I₄O₁₁ comme intermédiaire. Les températures des pics ATD et TGD des deux modifications montrent des différences marquées.

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- (IO₃)₂.- , . , I_{25 2}, KI. ₂I₄₁₁. - , , .

     

Preparation and characterization of Ru?Pb supported catalysts

Decomposition of Mn₃Mo₂TeO₁₂ during oxidation of toluene to benzaldehyde was observed. Depending on the surface composition of the initial catalyst, the decomposition leads to less active but highly selective MnMoTeO₆ or to MnMoO₄ which is not selective in toluene oxidation.

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Mn₃Mo₂TeO₁₂ . , MnMoTeO₆, MnMoO₆.

     

Effect of the central metal ion on the inhibiting properties of metal dithiocarbamates in oxidation processes

The dependence of inhibiting properties of M(dtc) on M for the complexes of M(II) and n M(III) has been studied. Inhibition is due to the interaction of M(dtc)_n with RO₂.

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M(dtc)_n M M(II) M(III). M(dtc)_n RO₂.

     

Possibilities of applying the Piloyan method of determination of decomposition activation energies in the differential thermal analysis of polynitroaromatic compounds and their derivatives

The Piloyan activation energiesE, as well as the initial exotherm temperaturesT _D, are determined for sixN-monoalkyl- and fiveN,N-dialkyl-2,4,6-trinitroanilines. By comparison withR _f-factors, orR _M-functions of paper chromatography, the molecular-structural dependences ofE andT _D are studied for these compounds. Relationships are also found between the termE · T _D ^–1 and theR _M-functions. The effects are discussed of the introduction of the 6-nitro group into the TV-substituted 2,4-dinitroanilines, and of the introduction of the 4-nitro group into the 2,6-dinitro analogues, upon the thermal stabilities of the resulting 2,4,6-trinitroanilines.

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Zusammenfassung Die AktivierungsenergienE nach Piloyan und die Anfangswerte der ExothermenT _D der sechsN-monoalkyl- und fünfN,N-Dialkyl-2,4,6-trinitroaniline wurden bestimmt. Unter Berücksichtigung des Vergleichs mitR _f-Faktoren oderR _M-Funktionen der Papierchromatographie wurden die molekularstrukturellen AbhÄngigkeiten der WerteE undT _D dieser Verbindungen untersucht. ZusammenhÄnge wurden auch zwischen dem AusdruckE · Tw _D ^–1 und denR _M-Funktionen gefunden. Der Einfluss der Einführung der 6-Nitrogruppe in dieN-substituierten 2,4-Dinitroaniline, sowie der Einfluss der Einführung der 4-Nitrogruppe in 2,6-Nitroanaloge auf die ThermostabilitÄt der resultierenden 2,4,6-Trinitroaniline werden erörtert.

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Résumé On a déterminé les énergies d'activation par la méthode de Piloyan ainsi que les températures initialesT _D de l'effet exothermique de sixN-monoalcoyl- et cinqN,N-dialcoyl-2,4,6-trinitroanilines. En se référant aux facteursR _F ou aux valeurs des fonctionsR _M en Chromatographie sur papier, on a étudié la dépendance entre les valeurs deE et deT _D sur les caractéristiques moléculaires-structurales de ces composés.On a également trouvé des rapports entre le termeE · T _D ^–1 et les fonctionsR _M. On discute l'influence de l'introduction du groupe 6-nitro dans les 2,4-dinitroanilinesN-substituées ainsi que l'influence de l'introduction du groupe 4-nitro dans les 2,6-dinitro analogues sur la stabilité thermique des 2,4,6-trinitroanilines qui en résultent.

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N-- N,N--2,4,6- E , T _D. R _f,- R _M — , - E T _D. E.T _D ^–1 R _M-. 6N- 2,4- 4 2,6- 2,4,6- .

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The authors would like to thank Mrs. Anna Colláková for careful DTA measurements, and Dr. Ladislav Smolka for help in the treatment of the measured results with the Wang 600 computer.     

Chemical reaction and phase transformations of the components of low temperature shift catalyst in various atmospheres

The systems CuO–Al₂O₃ and ZnO–Al₂O₃, as model systems of low temperature shift catalysts, have been studied in the temperature interval 100–700°C. The changes of their phase composition and surface area, influenced by gas atmosphere have been studied by X-ray, IR analysis and low temperature nitrogen adsorption.

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CuO–Al₂O₃ ZnO–Al₂O₃ CO 100–700°C. , - .

     

Thermal analysis of ferrous sulphate heptahydrate in air

The thermal decomposition of ferrous sulphate heptahydrate was carried out in air under dynamic and isothermal conditions. The intermediate phases were identified by chemical analysis and an X-ray technique. Ferrous sulphate heptahydrate is converted to tetrahydrate and monohydrate, but this conversion is accompanied by oxidation. Fe(OH)SO₄ and Fe₂O(SO₄)₂ are formed as oxidation products, and the latter decomposes to ferric oxide directly and/or through Fe₂(SO₄)₃.

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Zusammenfassung Die thermische Zersetzung von Eisen(II)sulfat Heptahydrat wurde in Luft unter dynamischen und isothermen Bedingungen durchgeführt. Die Intermediärphasen wurden durch chemische Analyse und Röntgentechnik identifiziert. Eisen(II)sulfat Heptahydrat wird in Tetrahydrat und Monohydrat überführt, doch wird diese Umwandlung durch eine Oxidation begleitet. Fe(OH)SO₄ und Fe₂O(SO₄)₂ werden als Oxidationsprodukte gebildet und letzteres wird unmittelbar und/oder über Fe₂(SO₄)₃ zu Eisen(III)oxid zersetzt.

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Résumé La décomposition thermique dans l'air du sulfate de fer(II) heptahydraté a été étudiée en conditions dynamiques et isothermes. Les phases intermédiaires ont été identifiées par analyse chimique et par rayons X. Le sulfate de fer(II) heptahydraté se transforme en tétrahydrate et en monohydrate mais cette conversion s'accompagne d'une oxydation. Il se forme Fe(OH)SO₄ et Fe₂O(SO₄)₂ comme produits d'oxydation et ce dernier se décompose en oxyde de fer(III) directement ou quelquefois avec formation intermédiaire de Fe₂(SO₄)₃.

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(II) . . (II) . Fe(OH)SO₄ Fe₂O(SO₄)₂. (III) Fe₂(SO₄)₃.

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The authors express their grateful thanks to Prof. P. K. Jena, Director, for his keen interest and permission to publish the paper, and to Dr. A. Lakshminarayana for the X-ray measurements. One of us (MSRS) also thanks the Regional Research Laboratory (CSIR) for a fellowship.     

Reduction of carbon dioxide with methane over Ni-catalyst

The reaction CO₂+CH₄=2CO+2H₂+60 kcal/mol was carried out over some transition metal catalysts (Ni, Fe and Co) and Ni/Al₂O₃ catalyst was then found to be the best for the reaction. The reaction rate expression and the apparent activation energy were also obtained over the Ni catalyst.

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CO₂+CH₄=2CO+2H₂+60 / (Ni, Fe Co). Ni/Al₂O₃ . Ni-.

     

Stochastic simulation of chemical reaction by digital computer, I. The model

A stochastic model of complex chemical reactions is outlined. A discrete Markov process corresponds to the complex chemical reaction in the model i.e. the concentrations of the components are discrete quantities. The differences between the stochastic and deterministic models are discussed.

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. , .. . .

     

Synthesis of β‐Chlorinated Macrocyclic [Au(C14H20N4Cl2)]X (X = AuCl2, ClO4, AuCl4) Gold(III) Complexes. Crystal and Molecular Structures of [Au(C14H20N4Cl2)]ClO4

A squareplanar [AuL₂]⁺ gold(III) complex [L₂ = 6.13dichloro5,7,12,14tetramethyl1,4,8,11tetraaza4,6,11,13tetraenato(2-)] containing two chlorine atoms in the position of the ligand hexacyclic ring was first synthesized by the reaction of the [AuL₁]⁺ tetraiminate complex [L₁ = 5,7,12,14tetramethyl1,4,8,11tetraaza4,6,11,13tetraenato(2-)] with HAuCl₄ in an acetone – DMFA solution. The complex was isolated in the form of dichloroaurite (I), perchlorate (II), and tetrachloroaurate (III). Compounds I–III were studied by elemental and Xray diffraction analyses and IR and NMR spectroscopies. Single crystals of [AuL₂]ClO₄ were obtained, and the crystal structure of this compound was determined from Xray diffraction patterns. The crystals are monoclinic: a = 10.147(2), b = 7.260(1), c = 12.519(2), = 96.70(1)°, V = 915.9(3)³, Z = 2, space group P2/c, d_calc = 2.218, d_meas = 2.209 g/cm³ The crystal structure is built of nearly planar [Au(C₁₄H₂₀N₄Cl₂)]⁺ cations and [ClO₄]^- anions. Introduction of chlorine atoms into the positions of the hexacyclic rings of the tetraazamacrocycle hardly changes the lengths of the delocalized C N and C C bonds.     

Effect of ligands on the hydrogenation selectivity in the presence of rhenium catalysts

It has been established that the catalytic activity of rhenium oxohalide complexes with phosphorus- or sulfur-containing ligands in hydroganation of C₆–C₁₀ olefins, nitrobenzene and p-nitrotoluene is primarily determined by the original ligand to rhenium ion bond. Chain length of olefins does not affect their hydrogenation rate.

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- C₆–C₁₀, - - . .

     

FTIR investigation of the structure of vanadium oxides on ZrO2 and oxidation of toluene on it

The oxidation of toluene has been studied on V₂O₅/ZrO₂ by both FTIR spectroscopy and pulse method. The results suggest that Lewis-acidic sites play a significant role in the formation of benzaldehyde from toluene.

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V₂O₅/ZrO₂ - , . .

     

Kinetics of the oxidation of rescinnamine by peroxodisulfate

The kinetics of the reaction between rescinnamine and potassium peroxodisulfate in acid media has been studied. The behavior of the system in the presence of a large excess of peroxodisulfate is mathematically equivalent to consecutive first-order reactions with pseudofirst order rate constants, k_1obs and k_2obs.

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. , , - k_1obs k_2obs.

     

Thermal behaviour of some new hydrazinium fluorometallates

Three new hydrazinium(1+) fluoro complexes, N₂H₅AsF₆, (N₂H₅)₂ZrF₆ and (N₂H₅)₂HfF₆, were prepared and characterized by means of chemical analysis, IR and Raman spectroscopy and X-ray powder diffraction. Study of their thermal behaviour via TG, DTG and DTA measurements showed that they decompose in stages; the decomposition of N₂H₅AsF₆ proceeded in two steps, through the intermediate NH₄AsF₆; (N₂H₅)₂ZrF₆. Decomposed in three steps, through (NH₄)₂ZrF₆ and NH₄ZrF₅. The thermal decomposition of (N₂H₅)₂HfF₆ is more complex; in the first step (NH₄)₂HfF₆ with some N₂H₅HfF₅ was obtained, and in the second NH₄HfF₅. The intermediates were identified by means of chemical analysis and vibrational spectroscopy.

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Zusammenfassung Die Hydrazinium(1+)-fluorokomplexe N₂H₅AsF₆, (N₂H₅)₂ZrF₆ und (N₂H₅)₂HfF₆ wurden dargestellt und durch chemische Analyse, IR- und Ramanspektren sowie Röntgenbeugungsdiagramme charakterisiert. Die Untersuchung ihres thermischen Verhaltens durch simultane TG-DTG-DTA-Messungen zeigte, dass sie sich schrittweise zersetzen: N₂H₅AsF₆ zersetzt sich in 2 Stufen mit NH₄AsF₆ als Zwischenprodukt; (N₂H₅)₂ZrF₆ zersetzt sich in 3 Stufen über (NH₄)₂ZrF₆ und NH₄ZrF₅. Die thermische Zersetzung von (N₂H₅)₂HfF₆ ist komplizierter, der erste Schritt liefert (NH₄)₂HfF₆ mit wenig N₂H₅HfF₅, der zweite NH₄HfF₅. Die Zwischenprodukte wurden durch chemische Analyse und Schwingungsspektroskopie identifiziert.

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N₂H₅AsF₆, (N₂H₅)₂ZrF₆ (N₂H₅)₂HfF₆, - , ., , . , N₂H₅AsF₆ NH₄AsF₆, (N₂H₅)₂ZrF₆ — (NH₄)₂ZrF₆ NH₄ZrF₅. (N₂H₅)₂HfF₆ : (NH₄)₂HfF₆ N₂H₅HfF₅, NH₄HfF₅. .

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We thank Miss B. Sedej for chemical analysis. The work was financed through the Research Community of Slovenia.     

Chemical algebra. II: Discriminating pairing products

The algebra of stereogenic pairing equlibria is presented in a very general context. Starting from the notions of fuzzy subgroup and conjugacy link, chemical pairing constants between molecular speciesu andv having a skeletal symmetry groupG are formulated as pairing products on aG-Hilbert space. Discriminating pairing productsK are defined by the conditions: K 1 and K = 1 the representative vectors of the paired species areG-equivalent. WhenG has only two elements, the pairing product is always discriminating. For several skeletal symmetries, if the vectors are enantiomorphic (v = u, ² =e, G), thenK is greater than 1 and reaches 1 only ifu is achiral: chirality indexes and general permutational indexes are then defined fromK(u u). The general model is illustrated by some examples.     

Thermodynamic aspects of conformational transitions in synthetic polypeptides

The helix-coil transition of organic solvent soluble homopolypeptides has been discussed from a largely thermodynamic view-point. The present state and the future prospects are considered.

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Zusammenfassung Der Helix-Ungeordnete Übergang von in organischen Lösungsmitteln löslichen Homopolypeptiden wurde aus einem breiten Gesichtspunkt diskutiert, gegenwärtige Lage und zukünftige Entwicklungsaussichten erörtert.

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R'esumé On a discuté d'une pointe de vue thermodynamique large la transition helix—non helix des homopolypeptides solubles dans des solvants organiques et considéré la situation actuelle ainsi que les perspectives futures.

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, , . .

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The present paper was supported by NSF Grant GB 33484.