Bestimmung von Sauerstoff in Molybd?n, Wolfram und Rhenium nach dem Wasserstoffreduktionsverfahren

Zusammenfassung Gegenüber dem universell einsetzbaren Hei\extraktionsverfahren besteht der Hauptvorteil des Wasserstoffreduktionsverfahrens in dem geringen apparativen Aufwand. Aus der Umsetzung des bei der Reduktion gebildeten Wassers mit Calciumhydrid resultiert obendrein eine hohe Empfindlichkeit des Wasserstoffreduktionsverfahrens. Dies bedeutet, da\ — im Gegensatz zu den anderen Varianten des Wasserstoff-reduktionsverfahrens — auch für Sauerstoffgehalte unter 0,01% Probenmengen von etwa 1 g ausreichend sind.

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Summary A method is described for the determination of oxygen in molybdenum, tungsten, and rhenium by reduction with hydrogen. The water formed is then reacted with calcium hydride to give hydrogen which is determined by gas volumetry. In contrast to the generally applicable hot-extraction the main advantage of the reduction procedure is the less expensive equipment. Moreover, the reaction of the water with calcium hydride results in a high sensitivity of the method. Sample weights of about 1 g are sufficient, also for oxygen contents below 0.01%.

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Teil der Dissertationsarbeit von K. Friedrich.

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Herrn Prof. Dr. habil. E. Rexer möchten wir für die Förderung der Arbeit danken. Weiterhin sind wir besonders Herrn Dr. rer. nat. G. Ehrlich für anregende Diskussionen zu Dank verpflichtet.     

Synthese und Oxidation von14C-kernmarkierten Bikreosolen

Bicreosol, labelled with¹⁴C in ring position 1.1-, 4.4-, 5.5-, in the methyl- or in the methoxy substituent was oxygenated in 0.25m-NaOH. Isolation of low molecular fragments and determination of their specific activities indicate that at least two fragmentation pathways take place simultaneously: one with ring opening between the oxygen substituted carbon atoms, and one in which the bond between these atoms is not cleaved.

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Meinem Lehrer, Herrn Prof. Dr. Dr. h.c. mult.H. Mark, zum 80. Geburtstag gewidmet.

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3. Mitt.:K. Kratzl, P. Claus undf. W. Vierhapper, Mh. Chem.103, 100 (1972).     

Thalliumverbindungen als Katalysatoren für Umesterungen mit Glycidol und für Esteraustauschreaktionen mit Glycidylacetat

Thallium compounds as catalysts for transesterifications and ester exchange reactions The transesterification of di-, tri- and tetracarboxylic alkyl esters with 2,3-epoxy-propanol was investigated in the presence of various metal compounds as catalysts. It was found that only thallium compounds catalyse the reactions under mild conditions without decomposition of 2,3-epoxypropanol. Many thallium compounds also proved to be very good catalysts for the reactions of 2,3-epoxypropanol with alkoxysilanes and the ester exchange reactions of di-, tri- and tetracarboxylic alkyl esters with 2,3-epoxypropyl-acetate.     

Thermogravimetric and differential thermal analytical investigations on sewage farm soils

Soil substrates of sewage farms (inflow of sewage areas) and of closed sewage farms were investigated by means of thermogravimetry and differential thermal analysis. The results were compared with those obtained for control samples from outside the sewage farms.The organic matter of actively used sewage areas (inflow) contains a remarkable amount of easily oxidizable compounds brought to the inflows by suspended matter.Beside these compounds, macromolecular organic substances predominate in the composition of the organic matter and are responsible for an immense heat release in the high temperature range of the thermal studies.In the substrates of closed sewage farm inflows or of other sewage farm areas which do not belong to the inflows, the amounts of volatile and easily oxidizable compounds decrease rapidly. The substrates hardly differ in their reaction temperatures from control samples. The influence of single macromolecules on the exothermic oxidation is reduced with increasing humification.     

Preparation of alpha-aminobenzylphosphonic acids with a stereogenic quaternary carbon atom via microscopically configurationally stable alpha-aminobenzyllithiums

The enantiomers of 1-phenylethylamine were phosphorylated with diethyl chlorophosphate/Et(3)N and then Boc-protected (Boc=tert-butoxycarbonyl) at the nitrogen atom. These phosphoramidates were metalated by using sBuLi/N,N,N',N'-tetramethylethylenediamine (TMEDA) to give alpha-aminobenzyllithiums that isomerised to alpha-aminophosphonates in yields of up to 80 % with retention of the configuration at the carbon atom. The intermediate tertiary organolithiums were found to be microscopically configurationally stable from -78 to 0 degrees C in Et(2)O. The protected alpha-aminophosphonates were deblocked by using boiling 6 M HCl or preferably Me(3)SiBr/(allyl)SiMe(3). When the Boc group was replaced by the diethoxyphosphinyl group, the alpha-aminobenzyllithium intermediate partially enantiomerised even at -78 degrees C and rearranged to yield an alpha-aminophosphonate with 50 % ee (ee=enantiomeric excess). Similarly, N-Boc-protected phosphoramidates derived from racemates and/or enantiomers of 1-(1-naphthyl)ethyl-, 1-indanyl- and 1,2,3,4-tetrahydro-1-naphthylamine or 1-azidoindan- and 1-azido-1,2,3,4-tetrahydronaphthalene were converted to aminophosphonates in good yields. Deblocking gave alpha-aminophosphonic acids of excellent enantiomeric excess (97-99 %), as determined by means of HPLC on a chiral ion-exchange stationary phase based on quinine carbamate. When racemic Boc-protected diethyl phosphoramidate derived from 1,2,3,4-tetrahydro-1-naphthylamine was metalated with LiTMP/TMEDA (TMP=2,2,6,6-tetramethylpiperidine), 1-hydroxyethylphosphonamidates resulted. The configuration of the main isomer was determined by means of a single-crystal X-ray structure analysis.     

2]borametallocenophanes of group 4 metals: synthesis and structure

We report a series of [2]borametallocenophanes of Ti, Zr, and Hf with various ligand systems. The ligands have been synthesized in high yields starting from 1,2-dibromo-1,2-bis(dimethylamino)diborane(4) upon reaction with Na[C5H5] and Li[C13H9], respectively. All compounds were fully characterized by multinuclear NMR spectroscopy and, for selected examples, by X-ray analysis.     

Darstellung und Kristallstruktur von Diamminmagnesiumdiazid Mg(NH3)2(N3)2

Preparation and Crystal Structure of Diammin Magnesium Diazide Mg(NH₃)₂(N₃)₂ Diammin magnesium diazide was synthesized from Mg₃N₂ and NH₄N₃ in liquid ammonia and crystallized at 150 °C under autogenous atmosphere of HN₃ and NH₃ using sealed ampoules. Mg(NH₃)₂(N₃)₂ is a colorless, microcrystalline powder which can detonate above 180 °C. Caution, preparation and manipulation of Mg(NH₃)₂(N₃)₂ is very dangerous! The crystal structure was solved from powder data using the Patterson method and a Rietveld refinement was performed (Mg(NH₃)₂(N₃)₂, I 4/m, no. 87; a = 6.3519(1), c = 7.9176(2) Å; Z = 2, R(F²)= 0.1162). The crystal structure of Mg(NH₃)₂(N₃)₂ is related to that of SnF₄. It consists of planes built up from corner sharing Mg(NH₃)₂(N₃)₄ octahedra connected equatorially over their four azide bridges with the ammonia ligands being in trans position. IR data were collected and interpreted in accordance with the structural data.     

Microstructure and fracture mechanical properties of short fiber reinforced thermoplastic P.E.T.

Summary This report contains results of fracture mechanics tests and corresponding observations of the fracture behavior of short fiber reinforced, thermoplastic polyethylene terephthalate (P.E.T.) depending on microstructural parameters. Injection molded plaques of this composite material possess across their thickness individual layers of different fiber orientation which induce different crack propagation behavior transvers and longitudinal to the mold fill direction. The fracture toughness is higher for cracks perpendicular to the main fiber orientation and increases more general with the weight fraction of fibers. Fatigue cracks indicate the same tendency, i. e. their growth rate is lower for cracks transvers to the mold fill direction in samples with highest fiber fraction. Additional influences on fracture behavior due to differences in matrix toughness and adhesive strength of the fiber/matrix interface are discussed.The work was carried out by the author during a research study at the Center for Composite Materials, University of Delaware, Newark, Del. 19711, USA.     

On the hyperbolicity of Einstein's and other gauge field equations

It is shown that Einstein's vacuum field equations (respectively the conformal vacuum field equations) in a frame formalism imply a symmetric hyperbolic system of reduced propagation equations for any choice of coordinate system and frame field (and conformal factor). Certain freely specifiable gauge source functions occurring in the reduced equations reflect the choice of gauge. Together with the initial data they determine the gauge uniquely. Their choice does not affect the isometry class (conformal class) of a solution of an initial value problem. By the same method symmetric hyperbolic propagation equations are obtained from other gauge field equations, irrespective of the gauge. Using the concept of source functions one finds that Einstein's field equation, considered as second order equations for the metric coefficients, are of wave equation type in any coordinate system.Work supported by a Heisenberg-Fellowship of the Deutsche Forschungsgemeinschaft     

On factor refinement in number fields

Let be an order of an algebraic number field. It was shown by Ge that given a factorization of an -ideal into a product of -ideals it is possible to compute in polynomial time an overorder of and a gcd-free refinement of the input factorization; i.e., a factorization of into a power product of -ideals such that the bases of that power product are all invertible and pairwise coprime and the extensions of the factors of the input factorization are products of the bases of the output factorization. In this paper we prove that the order is the smallest overorder of in which such a gcd-free refinement of the input factorization exists. We also introduce a partial ordering on the gcd-free factorizations and prove that the factorization which is computed by Ge's algorithm is the smallest gcd-free refinement of the input factorization with respect to this partial ordering.