Preparation of Phase-Pure M1 MoVTeNb Oxide Catalysts by Hydrothermal Synthesis—Influence of Reaction Parameters on Structure and Morphology

This work presents a detailed investigation of the preparation of MoVTeNbO _x catalysts by hydrothermal synthesis. Phase-pure synthesis of M1 has been achieved applying the metals in a molar ratio Mo/V/Te/Nb = 1/0.25/0.23/0.12. Raman, UV/Vis spectroscopy, and SEM/EDX analysis show that the elements are inhomogeneously distributed in the initial suspension that is formed after mixing the metal salts in an aqueous medium. Iso- and heteropoly anions of molybdenum, free telluric acid as well as supra-molecular polyoxometalate clusters are observed in the solution, whereas all metals have been found in the precipitate. Complete rearrangement of molecular building blocks under hydrothermal conditions is essential for formation of phase-pure materials. Optimized synthesis conditions with respect to temperature and time result in the formation of a precursor consisting of nano-structured M1 characterized by an extended periodic organization in the [001] direction and a fairly homogeneous distribution of the elements. Residual ammonium containing supra-molecular species in the precursor result in the formation of phase mixtures during the subsequent crystallization by heat treatment in inert gas. Phase-pure M1 exhibits a distinct degree of flexibility with respect to the chemical composition that becomes obvious by incorporating Nb not exclusively into pentagonal bi-pyramidal units, but also into octahedral coordinated positions as shown by EXAFS. Anisotropic growth of the needle-like M1 crystals has been observed during the final heat treatment performed at 873–923 K in inert atmosphere disclosing a potential method to control the catalytic properties of MoVTeNbO _x catalysts.     

Development of elastic and plastic properties of polyoxymethylene during bending fatigue

The development of the plastic and viscoelastic properties and the corresponding failure limits of the acetal homopolymer polyoxymethylene were studied in unidirectional cyclic fatigue. Samples with molecular weights (MWs) ranging from 90 to 142 kg/kmol were tested in displacement‐controlled conditions, resulting in maximum stress amplitudes between 30 and 59 MPa and strain amplitudes between 35.8 and 92.6 με. The zero‐hour material properties and the cycle‐dependent property development were predominantly dictated by deformations in the crystalline regions and showed a negligible dependence on MW. However, the final failure limits were found to be primarily dependent on the length of the amorphous tie chains that connect the crystallites. As such, fatigue life analysis showed a strong dependence on MW. Results are interpreted in light of the primary mechanical failure mechanisms and the corresponding molecular deformations. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40762.     

Konfiguration und Thermochromie von Benzoinhydrazon-Derivaten

Configuration and Thermochromic Properties of Benzoine Hydrazone Derivatives Z-Benzoine aroylhydrazones ( 2a – d ), E-benzoinephenylether phenylhydrazone ( 4 ) and E-benzoinephenylether p-chlorobenzoylhydrazone ( 5 ), respectively, are produced by acid-catalyzed reaction of benzoine and corresponding hydrazone derivatives. The configuration of these new compounds are proved by their u.v.-spectra and n.m.r.-spectra data. In comparison to the Z-isomers, the E-isomers possess a hypsochromically shifted electron transition. In the n.m.r.-spectra the Z-isomers can be detected by a downfield N–H-signal. Only the aroylhydrazones 2 have thermochromic properties in methanolic solutions, based on a geometrical E/Z-isomerization. The kinetic and thermodynamic data of this reaction agree with an inversion mechanism.     

Untersuchungen zur Spin-Trapping-Kinetik in Systemen von Radikalen unterschiedlicher Reaktivität. Die Photolyse von α-Phenylbenzoin in Gegenwart von Benzyliden-tert.-butylamin-N-oxid

Investigations on Spin-Trapping Kineties in Radical Systems with Different Reactivity. Photolyses of α-Phenylbenzoine in the Presence of Benzylideneter. -butylamine N-oxide As a model system to study the spin-trapping kinetics of systems forming two radicals of different reactivity α-phenylbenzoine (PhB) was chosen. The photolysis of PhB forms benzoyl (B·) and diphenylketylradikals (K·), respectively, which can be trapped by benzylidene-tert-butyl-amine N-oxide (PBN), as a spin trap. The rate constants of radical addition to PBN and their reactions with the spin adducts were determined by means of flash photolysis and kinetic calculations of the PBN concentration dependence. For B· and K· addtion rate constants to PBN of k₁ = 8,1 × 10⁵ M⁻¹s⁻¹, and k₂ = 5,8 · 10⁴ M⁻¹s⁻¹, respectively, were found. The rate constants for the reactions of B· and K· with the spin adducts are in the order of 10⁹…10¹⁰ M⁻¹s⁻¹.     

Lichtinitiierte Polymer- und Polymerisationsreaktionen. 14. Radikalische Photopolymerisation mit Kaliumtrisoxalatocobaltat-Aryloniumsalz-Systemen

Light Induced Polymer and Polymerization Reactions. 14. Radical Photopolymerization by Potassium Trisoxalato Cobaltate Arylonium Salts Systems. The photopolymerization of acrylamide (AA) by trisoxalato cobaltate ([Co(ox)₃]³⊖) is inefficient because the produced nucleophilic ·CO₂⊖-radicals are oxidized or they terminate with polymer radicals. If onium compounds are added to this system the initiation efficiency is increased as follows : p-CH₃OC₆H₄N₂⊕>Ph₂I⊕>PhCOCH₂S(CH₃)₂⊕>Ph₃S⊕. By means of quantum yield measurements a mechanism was proposed including the electron transfer from ·CO₂⊖ to onium compounds. The produced radicals also initiate the polymerization of AA. The exponent m of the polymerization rate (v_p ≈︁ [AA]^m) is decreased from 1.4 to 1.1 in the presence of Ph₂I⊕, deciding the decrease of termination reaction between ·CO₂⊖ and polymer radicals. In comparison with K₃[Fx(ox)₃] the corresponding cobalt complex possesses higher polymerization quantum yields for AA.     

Reaktionen von zwitterionischen s-Triazolo[4,3-b]pyridazinen mit elektrophilen Reagentien

Reactions of Mesoionic s-Triazolo[4,3-b] pyridazines with Electrophilic Reagents The redox-properties of zwitterionic s-triazolo [4, 3-b]pyridazines 1–3 depend on the heteroatom: products with S-atoms can easily be oxidated. O-Zwitterions 1 and 2 react with diazoniumsalts under azocoupling, while S-zwitterions 3 lead to a dediazonation. The O-zwitterions 1 and 2 can also be bromated, nitrated and hydroxylated electrophilicably. A reaction with dithioliumsalts is not possible. S-Zwitterions 3 react in a more complicated way in the electrophilic reactions mentioned.     

Photoinitiierte Polymerisation mit Dialkoxythiocarbonyldisulfiden – eine Polymerisationsreaktion mit Primärradikalabbruch

Photoinitiated Polymerization with Dialkoxy Thiocarbonyl Disulfides – a Polymerization Reaction with Primary Radical Termination The photoinduced free radical polymerization of methyl methacrylate (MMA) and some other vinyl monomers using dialkoxy thiocarbonyl disulfides ( 1 – 4 ) as photoinitiators was studied. The photolysis of these initiators leads to cleavage of the S S bond, which was determined by spin trapping experiments with phenyl tert-butyl nitrone. No evidence was found for a further thermal decomposition of the primary alkoxy thiocarbonyl sulfide radicals (R·) at room temperature. In the absence of scavengers the primary radicals react back exclusively to the initial compounds, due to a strong cage effect. By means of UV spectroscopic measurements and in the presence of MMA the quantum yields of the initiator decomposition were detected to be 0.8. The polymerization of acrylic and methacrylic derivatives can be initiated by the R·, contrary to the situation with fumarates and maleates. The mechanism of MMA polymerization depends on the light intensity absorbed by the initiators. At high intensities the combination of primary and polymer radicals terminates the chain reaction. This follows from the measured monomer exponent of α = 2, the light intensity exponent of β = 0,2 and the number of thiocarbonyl end groups of 2 in the polymers isolated. Contrary to this, in the low intensity region the experimental data obey the ideal kinetic equation. Kinetic modelling gives evidence for an interaction of the monomer with the cage radicals.