Zum Mechanismus der Hydrogenolyse aromatisch gebundenen Halogens

The selective chlorination of a m/p-xylene mixture, followed by distillation of the unreacted p-xylene, leaves a residue containing up to 90% of monochlorinated m-xylenes. m-Xylene is recovered from the latter by heterogeneous catalytic hydrogenolysis in the gas-phase. It was found that the hydrogenolysis on certain noble metal catalysts proceeds according to an ionic reaction mechanism at temperatures below a definite temperature range. At temperatures above this range hydrogenolysis follows a radical reaction mechanism.     

Periodic hexagonal mesostructured chalcogenides based on platinum and [SnSe4]4- and [SnTe4]4- precursors. Solvent dependence of nanopore and wall organization

Mesostructured chalcogenide-based materials with long-range order and semiconducting properties can be prepared using suitable molecular building blocks, linkage metal ions and surfactant molecules. In this paper we present surfactant templated, open framework platinum tin selenide and telluride materials assembled using K4SnQ4 (Q = Se, Te) salts and K2PtCl4 as precursors and a study of pore and wall organization. We find that materials prepared in water exhibit disordered pore organization, whereas those prepared in formamide are long-range ordered with hexagonal symmetry. In formamide the [SnQ4]4- anions undergo condensation-oligomerization reactions that produce different chalcogenido molecular species, whereas in water the anions remain intact. In addition to solvent, the pore organization and overall quality of the mesostructured materials strongly depend on the surfactant molecules, i.e., chain length and headgroup size. For example, highly ordered mesostructured platinum tin selenides with hexagonal symmetry were obtained using the hydroxyl-functionalized surfactants CnH2n+1N(CH3)(CH2CH2OH)2Br (n = 16, 18, and 20), but when the headgroup was triethylammonium, hexagonal pore order was achieved only for n = 20 and not for n = 16 and 18. The experimental results imply that in order to achieve highly ordered chalcogenide frameworks a single building anionic block might be insufficient. Finally, we also report the first examples of hexagonal mesostructured Pt/Sn/Te materials based on K4SnTe4 as the precursor. The tellurides behave differently for their selenium analogues and have very low energy band gaps, in the range 0.5-0.7 eV.     

Redetermination of the Crystal Structure of the 1,2,4,7-anti-tetramethylbicyclo[2.2.1]heptan-2-yl cation at 110 K

The structure of the 1,2,4,7-anti-tetramethylbicyclo[2.2.1]heptan-2-yl cation ( 1 ) was redetermined by X-ray crystal structure analysis of its Sb₂F₁₁ salt at 110 K (P2₁/c, R1 = 5.76%). The most important structural features of 1 are: C(1)? C(2) = 1.409(9), C(1)? C(6) = 1.710(8), and C(2)…C(6) = 2.113(9) Å and C(2)? C(1)? C(6) = 84.7(4)°. These results agree with those obtained earlier by other methods for the rapidly equilibrating, partially s?-delocalized 1,2-dimethylbicyclo[2.2.1]heptan-2-yl cation ( 2 ). The detailed experimental procedure for the preparation of crystalline 1 · Sb₂F₁₁ and the crystal selection and mounting are described.     

Phosphides with Zr2Fe12P7-type structure

Twenty-six ternary phosphides Ln₂T₁₂P₇ (Ln = lanthanoid, T = Fe, Co, Ni) were prepared for the first time by reaction of the elemental components in liquid tin or by reaction of the components in evacuated silica tubes. The analysis of their powder patterns indicates their isotypism with Zr₂Fe₁₂P₇. Their lattice constants are reported. Gd₂Ni₁₂As₇ also crystallizes with that structure.     

Metallchelate mit Acetophenon-Benzoylhydrazon und Acetophenon-Salicoylhydrazon

The stoichiometry and structure of acetophenone benzoylhydrazone and acetophenone salicoylhydrazone chelates with some divalent metal ions are studied by conductometric titration and visible and infra-red absorption spectrophotometry. The results are supported by analysis of the solid complexes. The infra-red study revealed that coordination occurs through C=O and C=N groups. The shift in the C=O and C=N bands is utilised for the determination of bond lengths.     

Zur Kenntnis der thermischen Zersetzung von Ammoniumhexafluoroscandat,-titanat,-vanadat und-chromat

Thermal analysis supported by kinetic calculations was applied exhaustively to these compounds. Under dynamic conditions, tetrafluorometallates(III), which as intermediates, could not be isolated, for the first three compounds. In each case, the final step was the pure metal(III) fluoride. Ammonium hexafluorochromate(III) decomposed directly to the pure chromium(III) fluoride. The decomposition rate of all compounds slowed down towards the end, probably for kinetic reasons. Polymorphic transitions of ammonium hexafluorotitanate(III) were observed at 35 and 100°C. Ammoniumhexafluoroscandate(III) underwent polymorphic transition at 47°C. The decomposition patterns for all these compounds were similar. Conditions for the preparation of pure ammonium tetrafluorometallates(III) of Sc, Ti and V are described.     

Untersuchungen zur 3-Phononenabsorption in partiell kristallinen Polymeren

Zusammenfassung In dieser Arbeit wird die Dreiphononenabsorption in Polymeren, die den Hauptanteil an den dielektrischen Verlusten im Millimeterwellengebiet stellt, theoretisch und experimentell untersucht. Aus der Störungsrechnung bis zur 2. Ordnung wird die Temperaturabhängigkeit der Absorption abgeschätzt. Damit ist eine befriedigende Deutung des gesamten Temperaturverlaufs der dielektrischen Verlust-Kurven möglich. Im Hochtemperaturbereich läßt sich die Mehrphononenabsorption eindeutig gegenüber restlichen Relaxationsprozessen abgrenzen. Im Tieftemperaturgebiet konnte erstmals auch für das Millimeterwellengebiet ein temperaturunabhängiger Bestandteil fehlordnungsinduzierter Einphononenabsorption nachgewiesen werden. Im Übergangsbereich durchlaufen die Absorptionskurven einen Wendepunkt bei einer charakteristischen TemperaturT ₀, die dem Schwerpunkt der am Absorptionsprozeß beteiligten Phononenfrequenzen entspricht. Daraus konnten in Übereinstimmung mit dem Experiment die Frequenzen der niedrigsten optisch aktiven Phononen für die verschiedenen Polymeren abgeschätzt werden.

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Summary The 3-phonon absorption in polymers, which gives the main contribution to their dielectric loss in the microwave region, is theoretically and experimentally investigated. Perturbation theory up to the second order is used for the evaluation of its temperature dependence. The theoretical results allow an interpretation of the total absorption-temperature-curves: In the high temperature region 3-phonon absorption can be distinguished from residual relaxation losses (above the glass temperature). In the low temperature region the existence of a low frequency tail of temperature independent disorderinduced one-phonon absorption became evident. At intermediate temperatures (50–150°K) the curves show an inflexion point or plateau at a characteristic temperatureT ₀, which according toT ₀= ⁰, corresponds to the frequencies of those phonons, that mainly contribute to the multiphonon absorption. The plateau gives, in good agreement with the experiment, the frequencies of the lowest optically active phonons in the various polymers.

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Mit 6 Abbildungen in 8 Einzeldarstellungen

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Vorgetragen auf der Arbeitssitzung des Fachausschusses Physik der Hochpolymeren in der Frühjahrstagung 1970 des Regionalverbandes Hessen-Mittelrhein-Saar der Deutschen Physikalischen Gesellschaft in Darmstadt, 10.–13. März 1970.     

Structure des savons alcalins

Summary This is a systematic X-ray diffraction study of the structure of the mesomorphic phases occurring with potassium soaps ranging from C₈ to C₂₂.Four types of structure have been identified. The first is lamellar with both polar groups and paraffin chains in the crystalline state. The second is also lamellar, but with both polar groups and paraffin chains in the liquid state. The third corresponds to the localization of indefinitely long ribbons on a two-dimensional oblique lattice; polar groups are crystalline and paraffin chains desorganized. The fourth corresponds to the localization of discs on a three-dimensionnalB-faces centered orthorhombic lattice; polar groups are crystalline and paraffin chains disorganized.The structural parameters and the polymorphism of the polar groups have been discussed.

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Zusammenfassung Wir beschreiben hier eine systematische Röntgenstrahlendiffraktionsforschung der Struktur der mesomorphen Phasen von Kalium Seifen von C₈ bis C₂₂.Vier Strukturtypen wurden gefunden. Die erste Struktur ist lamellar; beides, die polaren Gruppen und die Paraffinketten sind kristallisiert. Die zweite Struktur ist auch lamellar; aber in diesem Falle sind beides, die polaren Gruppen und Paraffinketten geschmolzen. Die dritte Struktur entspricht einer Lokalisation von Seifenbändern in einem zweidimensionalen monoklinen Gitter; die polaren Gruppen sind kristallisiert und die Paraffinketten geschmolzen. Die vierte Struktur entspricht einer Lokalisation von Seifenscheiben in einemB-flächenzentrierten orthorhombischen Raumgitter; die Polargruppen sind kristallisiert und die Paraffinketten geschmolzen.Wir haben aus den experimentellen Resultaten einige Schlußfolgerungen gezogen.

     

Protection of immobilized sulfhydryl groups against autooxidation by alterations in their microenvironment

Immobilized sulfhydryl groups were prepared by partial thiolation of NH₂-glass beads. The microenvironment of the immobilized SH groups was varied by different chemical modifications of neighboring NH₂ groups. Introduction of a strong charge in the surroundings of immobilized sulfhydryls results in their dramatic stabilization against autooxidation. This effect is due to the salting of O₂ from the surface microlayer of the thiolated beads.