Determination de C,N, O,F et de quelques autres elements par activation au moyen des photons gamma

The (γ, n) activation curves for 17 elements were determined as a function of energy between 25 and 42 MeV. From these are deduced the detection sensitivities intrinsically possible for an average beam intensity of 100 μA. Our experimental results are compared with values calculated byG. J. Lutz. The activation curves relative to certain competitive nuclear reactions on N, O and Na, liable to interfere in the measurements of C, N and F, were also determined. It is shown that the relative importance of these competitive nuclear reactions decreases rapidly for energies below 30 MeV and becomes practically negligible at 25 MeV.      

Die Konstitution von Roridin D. Verrucarine und Roridine, 12. Mitteilung

The antibiotic roridin D (C₂₉H₃₈O₉), a companion of roridin A, yields on base catalysed hydrolysis verrucarol ( 3 ) and the hitherto unknown 2, 3-epoxy-2-anhydrororidinic acid ( 4 ) (C₁₄H₁₈O₇). Roridin D is a macrocyclic diester to which structure 1 is assigned. In roridin D an epoxy group replaces the hydroxyl group of roridin A.     

Stereochemistry of Macrocyclization of cis-4-Cyclohexene-1,2-dicarboxylic Acid with Dihalogen Derivatives

Stereochemistry of [2+2]- and [1+1]-macrocylization of cis-4-cyclohexene-1,2-dicarboxylic acid with 1,2-dibromoethane, 1,3-dichloro-2-propanol, and 1,5-dichloro-3-oxapentane was studied. The reaction of cis-4-cyclohexene-1,2-dicarboxylic acid with 1,2-dibromoethane according to the [2+2]-cyclization scheme gave a mixture of stereoisomeric macroheterocycles with cis,syn,cis- and cis,anti,cis-junction of the polyether and cyclohexene rings. In the reaction of cis-4-cyclohexene-1,2-dicarboxylic acid with 1,5-dichloro-3-oxapentane, a mixture of crown compounds with cis,anti,cis- and cis-junction of the polyether and cyclohexene rings was obtained. The structure of the products was established on the basis of their chemical transformations and spectral data.     

Methylbis (dithiocarbamato)stibane Synthese und Kristallstruktur

Methylbis(dithicarbamato) stibanes. Synthesis and Crystal Structure . The title compounds are obtained by reaction of methyldibromostibane with the sodium dithiocarbamates in methanol at low temperature (?78°C). The crystal structure of CH₃Sb(S₂CNEt₂)₂ as elucidated by X-ray diffraction shows no special intermolecular interactions. It can be compared to that of the corresponding bismutane CH₃Bi(S₂CNEt₂)₂ and the arsane C₆H₅As(S₂CNEt₂)₂.     

Extraction of Aromatic Hydrocarbons from Hydrofined Diesel Fraction with 2-Methoxyethanol in the Presence of Pentane

Five-step countercurrent extraction of aromatic hydrocarbons from hydrofined diesel fraction with the 2-methoxyethanol-water-pentane extraction system was studied. The process was performed on a rotary-disk extractor.     

Electron bombardment fragmentation of size selected molecular clusters

(CO₂) _n , (NO) _n and (NH₃) _n clusters are generated in a supersonic molecular beam and size selected by scattering from an He beam. By measurements of angular dependent mass spectra, TOF distributions and the angular dependence of the scattered signal quantitative information on the fragmentation probability by electron impact is derived. The van der Waals systems (CO₂) _n and (NO) _n appear only at masses which are simply multiples of the monomer mass. The preferred cluster ion is the monomer ion for all investigated cluster sizes withn=2 to 4. The fragment pattern for the quasi-hydrogen bonded (NH₃) _n -cluster shows, beside a large number of fragment masses, a preference for protonated ions. The results are explained in terms of simple models based on the structural change from the neutral to the ionized configuration and the fragmentation pattern of the monomer followed by ionmolecule reactions.     

Novel Catalytic Dielectric Barrier Discharge Reactor for Gas-Phase Abatement of Isopropanol

Catalytic gas-phase abatement of air containing 250 ppm of isopropanol (IPA) was carried out with a novel dielectric barrier discharge (DBD) reactor with the inner catalytic electrode made of sintered metal fibers (SMF). The optimization of the reactor performance was carried out by varying the voltage from 12.5 to 22.5 kV and the frequency in the range 200–275 Hz. The performance was significantly improved by modifying SMF with Mn and Co oxide. Under the experimental conditions used, the MnO _x /SMF showed a higher activity towards total oxidation of IPA as compared to CoO _x /SMF and SMF electrodes. The complete destruction of 250 ppm of IPA was attained with a specific input energy of ∼235 J/L using the MnO _x /SMF catalytic electrode, whereas, the total oxidation was achieved at 760 J/L. The better performance of the MnO _x /SMF compared to other catalytic electrodes suggests the formation of short-lived active species on its surface by the in-situ decomposition of ozone.     

Numeric simulation of epoxy cure in molds

Thermodynamic and kinetic parameters have been determined suitable for the numerical simulation of the curing reaction of the epoxy/anhydride based casting resin system Araldite CY 225/HY 225/filler. In particular, the decisive role of the heating rate on the evaluation of the kinetic parameters from dynamic DSC-experiments is discussed.

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Zusammenfassung Mit Hilfe der Mikrokalorimetrie wurden thermodynamische (Reaktionsenthalpien) und kinetische (Arrhenius-Konstanten, Reaktionsordnung) Parameter eines gefüllten Epoxid/Anhydrid-Giessharz-Systems (Araldit CY 225/HY 225/Quarzmehl) bestimmt.Die Eignung dieser Parameter zur praxisrelevanten Simulation der HÄrtungsreaktion in Giessformen wird demonstriert. Es zeigt sich, dass die Heizrate im dynamischen DSC-Experiment bei der Bestimmung der kinetischen Parameter eine entscheidende Rolle spielt.

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We wish to thank Dr. P. Bujard, Ciba-Geigy SA, for the measurement of the thermal conductivity data, and Mrs. Emmi Stoisser for technical assistance.     

Untersuchungen an oxidischen Katalysatoren. XLII. Redoxverhalten des Nickels in NiNa?Y-Zeolithen 4. Einfluß der Zusammensetzung auf die Reduzierbarkeit von Nickel in NiNa?Y-Zeolithen

Studies on Oxide Catalysts. XLii. Redox Behaviour of Nickel in Zeolites NiNa? Y. 4. Influence of Composition on the Reducibility of Nickel in Zeolites NiNa? Y By chemical analysis (reaction with K₂Cr₂O₇) and ESCA investigations we determined the degree of reduction in reduced samples NiNa-Y as function of the mole ratio SiO₂/Al₂O₃ (module), of the Ni²⁺ degree of exchange and the kind of the second cations. (NH₄₊, Ca²+, Co²+, and Nd³+) in the temperature region of 620–770 K. The degree of nickel reduction increases with increasing module, decreasing degree of exchange and decreasing number of Brönsted acidic centres. This behaviour is caused by the influence of the interaction between cations Ni²⁺ and zeolite lattice on the reduction equilibrium.