Kinetic regularities for the interaction of anion-radicals O2? with benzene and toluene on Mo?Mg oxide systems

Interaction of anion-radicals O ₂ ^– with adsorbed forms of benzene and toluene at 293–473 K is shown to be described by an equation corresponding to exponential activation energy distribution of O ₂ ^– . It has been established that under the same conditions the decay rate of O ₂ ^– is higher in the presence of toluene than with benzene.

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, - O ₂ ^– 293–473 , O ₂ ^– . , O ₂ ^– , .

     

On the modulation of electron energy distribution function in radiofrequency SiH4, SiH4−H2 bulk plasmas

Electron energy distribution functions (EDF) in SiH₄, SiH₄–H₂ radiofrequency discharges have been calculated by solving the time-dependent Boltzmann equation in the presence of a sinusoidal field. Particular emphasis is given to the modulation of EDF as a function of the applied frequency (·10⁶/p ₀ ·10⁸ sec^–1 torr^–1) and of gas composition. The results show that at /p ₀ = ·10⁶ sec^–1 torr^–1 EDF follows in a quasistationary mode the variation of the field with the exception of a small range of electric field near to the zero crossing. Still, at the higher considered frequency (/p ₀ =·10⁸ sec^–1 torr^–1), we observe some modulation of EDF. The necessity of using a time-dependent approach is tested by comparing the present results with the corresponding ones obtained by using the effective field approximation (i.e., the approximation which solves instead of the time-dependent Boltzmann equation the corresponding stationary one at the effective values of the rf field). The two sets of results can differ by orders of magnitude in the tail of EDF, the differences decreasing with increasing molar fraction of H₂ and increasing field frequency. The role of excited states (second-kind collisions) is studied by inserting in the Boltzmann equation given concentrations of vibrational and electronic states. The results show that second-kind collisions strongly affect EDF especially in pure silane. Finally a satisfactory agreement has been found between theoretical and experimental results concerning the modulation of electrons of given energy in pure silane discharges.     

Hydrocarbon conversion over Pt?Re/Al2O3-ZSM-5 bifunctional catalysts. I. Influence of the addition of ZSM-5

The influence of ZSM-5 on the behavior of a Pt–Re/Al₂O₃ catalyst was studied in normal heptane reforming in order to compare activity, selectivity and life of Pt–Re/Al₂O₃ and a mixture of Pt–Re/Al₂O₃ and ZSM-5 catalysts. It is suggested that the presence of ZSM-5 results in less pronounced catalyst deactivation but not in a sufficient increase in aromatic selectivity.

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ZSM-5 Pt–Re/Al₂O₃ - , Pt–Re/Al₂O₃ ZSM-5. , ZSM-5 , , .

     

Investigation of electronic structure of allenyl ethers by means of photoelectron and UV spectroscopy

A study of the photoelectron spectra of alkyl allenyl ethers has demonstrated their similarity to spectra of alkyl vinyl ethers, with the exception of a band in the 10.0–10.3 eV interval due to ionization of the -orbital of the allenyl fragment C=C. According to data obtained by photoelectron spectroscopy and MNDO quantum-chemical calculations, alkyl allenyl ethers with straightchain substituents exist primarily in the s-cis conformation. The stable conformation of allenyl tert-butyl ether is the s-trans form. The long-wave absorption bands in the UV spectra of alkyl allenyl ethers at 255–275 and 208–213 nm are assigned to electronic transitions of the ^* and ^{* *} types; these are quite insensitive to s-cis/s-trans isomerism.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 1, pp. 81–88, January, 1990.The authors are extremely grateful to V. K. Turchaninov for assistance in interpreting the spectra.     

Non-isothermal thermogravimetry of polymer

A Model of polymer decomposition is proposed which formally involves the termination of active centres. It yields reasonable activation energies for the decompositions of polypropylene, polyethylene, polystyrene and polymethyl methacrylate investigated by non-isothermal thermogravimetry. In the value of a formal reaction orders the model reflects the reaction conditions, such as initial sample weight, atmosphere, ventilation conditions, sample holder nature and shape, etc.

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Zusammenfassung Ein Modell für Zersetzungsreaktionen von Polymeren wurde entworfen, das auf dem Abbau von aktiven Zentren basiert. Es liefert richtige Aktivierungsenergien für die Zersetzung von Polypropylen, Polyäthylen, Polystyren und Polymethylmethakrylat (bestimmt durch nichtisotherme Thermogravimetrie) und macht es ausserdem möglich, die äusseren Reaktionsbedingungen, wie Einwaage, Atmosphäre, Ventillationsbedingungen, Art und Form des Probenhalters usw. zu berücksichtigen.

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, . , , , . «» , , , , . .

     

Mechanism of RuIV-catalyzed oxidation of alkanes in aqueous solutions

The Ru^IV-catalyzed oxidation of alkanes in aqueous solutions includes activation of the oxidant Ox (Cr^VI, HNO₃, HClO₄, etc.) via Ox–Ru^IV complex formation and is accompanied by H atom abstraction from the alkane by the activated oxidant.

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Ru^IV - Ox (Cr^IV, HNO₃, HClO₄ .) Ox–Ru^IV - .

     

Molecular structure of mono- and dicarbonyls of rhodium and palladium

Summary Density Functional Theory has been applied to the study of the molecular structure of neutral and positively charged mono- and dicarbonyls of rhodium and palladium. The calculated optimized geometries, dissociation energies and normal frequencies are reported for the MCO, MCO⁺, M(CO)₂ and M(CO) ₂ ⁺ systems (where M=Rh and Pd), and the trends are discussed in detail. For neutral carbonyls, we interpret the M–C bond strength in terms of repulsion, which must be avoided, and attraction. These are related to the metal atom properties, such as the atomic splittings and the atomic ionization energies. In ionic carbonyls, the bonding is characterized by electrostatic attraction and repulsion. The rhodium carbonyls are generally found to be more stable than the corresponding palladium carbonyls. The palladium dicarbonyls are found to be linear, while both linear and bent structures are stable for rhodium dicarbonyls. An interpretation of these trends is made.     

On chemical bonding between molecular fragments. Closed-shell fragments

The chemical bonding between two closed-shell molecular fragments has been analyzed in terms of comparison of the antisymmetrized product of wave functions of the fragments with the wave function of a molecule composed of these fragments ^M . As a measure of the fragments' electronic structure variation upon molecule formation we took the cosine of the angles between ^M and in Hilbert space, as well as between the corresponding first-order density matrices ^M and . As an example, compounds of the type BH₃L (L=CO, NH₃, PH₃, H₂O, PF₃) have been considered. It is stressed that a necessary condition of chemical bonding between closed-shell fragments is the contribution of vacant orbitals of fragments into the bond.Institute of Inorganic Chemistry, Siberian Branch, Russian Academy of Sciences. Translated fromZhurnal Struktumoi Khimii, Vol. 34, No. 3, pp. 3–8, May–June, 1993.Translated by L. Smolina     

Kinetics of EDTA-catalyzed oxidation of Indigo Carmine by vanadium(V)

The reaction is first order both in vanadium(V) and substrate and is markedly inhibited by H⁺ ions. Kinetic evidence for the formation of a 11 complex of vanadium(V) and EDTA is obtained. The stability constant of this complex and its thermodynamic parameters were evaluated. A suitable mechanism is proposed.

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(V), H⁺. 11 (V) . . .

     

Routes of catalytic oxidation of o-xylene to phthalic anhydride

Relative reactivity of o-xylene, o-tolualdehyde, phthalide, and phthalane and the rate of phthalic anhydride formation from them have been determined. The main route of o-xylene oxidation to phthalic anhydride is due to the o-arrangement of methyl groups, proceeding through bicyclic products, such as dihydrobenzofuran (phthalane) and 3,4-benzofuran.

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-, - , , . - - : () 3,4-.

     

Pyrolysis of n-pentane on ZSM-5 zeolite

Pyrolysis of n-pentane has been studied at the temperature range 653–753 K on ZSM-5 zeolite. High catalytic activity and selectivity of H-ZSM-5 zeolite was found. The yield of propane was about 80 wt. %. A mechanism of the process is proposed.

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H-ZSM-5 n- 653–153 . . 80%. n-.

     

Preparation and Characterization of Thin Optically Transparent Alumina and Ce-doped Alumina

Transparent and porous boehmite, -Al₂O₃ (500°C) and -Al₂O₃ (900° and 1000°C) thin sheets (50–100 m) have been prepared from boehmite sols. -Al₂O₃ shows about 48% porosity and 292 m²/g surface area. On transformation from -Al₂O₃ (500°C) to -Al₂O₃ (900°C), the porosity still remains high, i.e. 45%; however, the surface area becomes 138 m²/g. The porosity and surface area of -Al₂O₃ become about 41% and 97 m²/g respectively on further heating to 1000°C. A gradual increase of average pore radius during this thermal treatment suggests that coarsening of the pore occurred during the densification process. Both -Al₂O₃ and -Al₂O₃ show high degree of transmission from UV to NIR wavelength region. Cerium exists in +4 oxidation state in the boehmite as well as in the - and -Al₂O₃. The ultraviolet absorption edge of the alumina was tailored by varying the concentration of cerium.     

Neue Siderophore des Pyoverdin-Typs ausPseudomonas fluorescens

Summary The structure of four new pyoverdins (Pf12-IA, -IIA, -IB und IIB) isolated from the culture medium ofPseudomonas fluorescens 12 was elucidated by combination of spectroscopic methods and degradation reactions. The pyoverdins comprise (1S)-5-amino-2,3-dihydro-8,9-dihydroxy-1H-pyrimido[1,2-a]quinoline-1-carboxylic acid whose amino group carries a 3-carboxypropanoyl-(IA), succinamoyl- (IIA), 4-carboxy-4-oxobutanoyl- (IB) or L-4-amino-4-carboxybutanoylresidue (II B) and whose carboxyl group is bound amidically to the N-terminus of D-Ser-L-Lys-Gly-. According to the short-hand-nomenclature suggested in [2, 3] the pyoverdins may be described as pyoverdin-Q-sKGOsSGK*oES*-SUC(IA), pyoverdin-Q-sKGOsSGK*o-ES*-SUCA (IIA), pyoverdin-Q-sKGOsSGK*oES*-KGL (IB) and pyoverdin-Q-sKGOsSGK*oES*-GLU (IIB). The pyoverdins described here possess the most complex structure encountered so far as their peptide part comprises eleven amino acids and the cyclo-tetrapeptide substructure. In addition, they are of special interest as for the first time glutamic acid could be identified as a chromophore side chain which is the key compound for the citric acid cycle to which belong all dicarboxylic acids found so far in pyoverdins.

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Verwendete Abkürzungen ASK Acylseitenkette - Chr Chromophor1 a - (HO)Chr Chromophor1 b - Dns Dansyl-Rest - DP Dansylpeptid - EDTA Ethylendiamintetraessigsäure - FAB Fast Atom Bombardment (PI=positive Ionen) - (HO)Orn N⁵-Hydroxyornithin - (CHO, HO)Orn N⁵-Formyl-N⁵-hydroxyornithin - PITC Phenylisothiocyanat - RP-HPLC Reversed-Phase High Performance Liquid Chromatography - Kgl -Ketoglutarsäure bzw. 4-Carboxy-4-oxobutanoyl-Rest - R _t Retentionszeit - Suc Bernsteinsäure bzw. 3-Carboxypropanoyl-Rest - Suca Succinamoyl-Rest - Suci Succinimido-Rest - TAB Trifluoracetyl-n-butylester - TEA Triethylamin     

Carbonylation of lower olefins in the presence of complexes of BF3 with propionic,acetic, or monochloroacetic acids

Conclusions The 3BF₃·2CH₂C1COOH+BF₃-2CH₃COOH system effectively catalyzes the selective carbonylation of propylene and n-butylenes. At 95–105°C and a CO pressure of 200 atm, with an equimolar ratio catalystolefin water, propylene or mixed n-butylenes give isobutyric or-methylbutyric acid in near-quantitative yield.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 1, pp. 110–112, January, 1978.     

Migration of the η1:η6-C6H5Cr(CO)3 ligand into the cyclopentadienyl ring during metallation of the η5-C5H5(CO)2Fe η1:η6-C6H5Cr(CO)3 binuclear complex

It was found that the ¹⁶-C₆H₅Cr(CO)₃ ligand migrates into the cyclopentadienyl ring when the ⁵-C₅H₅(CO)₂Fe ¹⁶-C₆H₅Cr(CO)₃ binuclear complex is metallated with BuⁿLi. Under the same conditions, no migration of the phenyl ligand in the ⁵-C₅H₅(CO)₂Fe ¹-C₆H₅ complex was observed.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 325–326, February, 1994.     

Kinetics of formation of sulfur dimers in pure SF6 and SF6-O2 discharges

The emission band spectra of S, molecule (B³ _u ^– X³ _g ^– transition) and of SO molecule (A³ X^3–) were detected in SF₆ and SF₆-O₂ rf discharges. It has been observed that the presence of a material which can be etched by SF₆ products considerably enhances the density of S₂ in the reactor. By means of mass spectrometry it has been shown that the m/e =83 mu signal assigned to S₂F⁴ ions evolves exactly in the same manner as the S₂ band intensity during the etching of Si or W in SF₆-O₂ discharge. A reaction scheme involving S₂F radicals is proposed to explain these experimental results.     

Oxidizing supported reagents, III. Oxidation of alcohols by new supported K2Cr2O7 reagents

Several new supported K₂Cr₂O₇ reagents are used in the oxidation of secondary alcohols. The influence of the number of active sites and the nature of solid support on the yield is discussed. The influence of the structure of alcohol on the yield of ketone is analyzed.

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K₂Cr₂O₇ . . .

     

Monolayer vanadia on titania systems from alkoxide precursors. Part III. Activity in secondary alcohol oxidation

The activity of V⁵⁺ ion monolayer supported on anatase, rutile, and anatase-rutile mixed carrier and of bulk V₂O₅ was examined in isopropyl alcohol and cyclohexanol oxidation. Catalysts exhibited remarkable activity in ketone formation. At higher temperatures benzene was the predominant product of cyclohexanol reaction.

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V⁵⁺, , - V₂O₅, . . .

     

The relation between the nonlinear dielectric effect and solvent polarity

The relation between solvent polarity expressed through the Dimroth-Reichardt spectroscopic parameter E _T (30) and the nonlinear dielectric effect (NDE) expressed through the parameter /E² is demonstrated where is a change in the electric permittivity of a solvent in an external strong electric field E. Both E _T (20) and /E², determined in quite different ways, are extremely sensitive to the dielectric properties of a solvent which depend on molecular interactions. Linear correlations between /E² and E _T (30) have been found for n-alkanols representing hydrogenbond donor solvents, and for halogenobenzenes which are dipolar, aprotic, weakly-associated solvents.Part of this work was presented at The 22^nd International Conference on Solution Chemistry in Linz, Austria, July 1991.     

Reaktion der Azlactone mit Aminoverbindungen, 3. Mitt.: Über die Herstellung der Phenylhydrazide und 4-Nitrophenylhydrazide einiger α,β-disubstituierter Acrylsäuren

Zusammenfassung Ungesättigte Azlactone spalten sich mit Phenylhydrazin bzw. 4-Nitro-phenylhydrazin auf unter Bildung der Phenylhydrazide (1a–1o) bzw. 4-Nitro-phenylhydrazide (2a, 2b) der entsprechenden ,-disubstituierten Acrylsäuren. Zum Unterschied von den durch die Hydrazinolyse entstandenen Hydraziden der ,-disubstituierten Acrylsäuren, die sich leicht zu 3,5-disubstituierten 6-Hydroxy-1,2,4-triazinen^{1, 2} bzw. zu Pyrazolderivaten^{3, 4, 5} cyclisieren lassen, ist es nicht gelungen, unter gleichen Bedingungen die Phenylhydrazide bzw. 4-Nitro-phenylhydrazide zu cyclisieren. Zum Strukturbeweis dienten NMR-Spektren.

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Reaction of azlactones with amino compounds, III: Preparation of the phenylhydrazides and 4-nitrophenylhydrazides of several ,-disubstituted acrylic acids

The reaction of phenylhydrazine and 4-nitrophenylhydrazine with several unsaturated azlactones has resulted in their cleavage to the phenylhydrazides (1a–1o) and 4-nitrophenylhydrazides (2a, 2b), respectively, of the corresponding ,-unsaturated acrylic acids. In contradistinction to the hydrazides of ,-unsaturated acrylic acids, which had previoulsy been obtained by hydrazinolysis of unsaturated azlactones and had easily undergone cyclisation to 3,5-disubstituted 6-hydroxy-1,2,4-triazines^{1, 2} or pyrazole derivatives^3–5, the phenylhydrazides and 4-nitrophenylhydrazides could not be cyclised under comparable conditions. NMR spectroscopy was used to ascertain the structures of the reaction products.