A Mechanistic Study on the Oxidative Degradation of Dibenzazepine Derivatives by Manganese(III) Complexes in Acidic Sulfate Media

The oxidative degradation of tricyclic antidepressants (TCA) was studied in the presence of a large excess of the oxidizing agent manganese(III) and its reduced form manganese(II) sulfate in acidic media. The products were detected and identified using UV–vis, ESI‐MS, IR, and EPR methods. The mechanism of the reaction was studied for the following two classes of TCA: 10,11‐dihydro‐5H‐dibenz[b, f]azepines and dibenz[b, f]azepines. The oxidative degradation between dibenz[b, f]azepines and the manganese(III) ions resulted in the formation of substituted acridine with the same substituent as in the origin dibenz[b, f]azepine derivative. The pseudo–first‐order rate constants (k_obs) were determined for the degradation process. The dependences of the observed rate constants on the [Mn^III] with a zero intercept were linear. The reaction between 10,11‐dihydro‐5H‐dibenz[b, f]azepines, and the manganese(III) sulfate ion resulted in oxidative dehydrogenation, which proceeded via the formation of the following two intermediates: a free organic radical and a dimer. Further oxidation of the second intermediate led to a positively charged radical dimer as the single final product. Linear dependences of the pseudo–first‐order rate constants (k_obs) on the [Mn^III] with a zero intercept were established for the degradation of 10,11‐dihydro‐5H‐dibenz[b, f]azepines. The observed rate constants were dependent on the [H⁺] and independent of the [TCA] within the excess concentration range of the manganese(III) complexes used in the isolation method. The radical product of the degradation of 10,11‐dihydro‐5H‐dibenz[b, f]azepines was not stable in the aqueous solution and was subsequently transformed to a nonradical dimer in the next slower step. The observed rate constants were independent of the [Mn^III], independent of the [H⁺] and increased slightly with increasing TCA concentrations when TCA was used in excess. The mechanistic consequences of all of these results are discussed.     

Neocompact Sets and the Fixed Point Property

We use a newly introduced concept of neocompactness to study problems from metric fixed point theory. In particular, we give a sufficient condition for a superreflexive Banach space X to have the fixed point property and obtain shorter proofs of some well-known results in that theory.     

Reibungsdämpfung durch Scheuerleisten: Ein praxisgerechtes Auslegungskonzept

Übersicht Die Fugen zusammengesetzter Bauteile sind einerseits für eine nachteilige Steifigkeitsminderung verantwortlich, tragen aber andererseits durch Reibungsvorgänge wesentlich zum Dämpfungsvermögen einer Konstruktion bei. Merkliche Reibungsdämpfung ohne gleichzeitigen Steifigkeitsverlust bewirken zusätzliche Fugen, die durch Anbringen sogenannter Scheuerleisten entstehen. Der Autor stellt ein Näherungsverfahren zur dämpfungsoptimalen Auslegung von Scheuerleisten vor. Ausgehend von der zu dämpfenden Schwingungsform liefert dieses Verfahren Kriterien für eine günstige Scheuerleistenanordnung, geeignete Leistenabmessungen und als wichtigstes Ergebnis eine dämpfungsoptimale Fugenpressung, die zu maximaler Energiedissipation führt. Schließlich kann das zu erwartende Dämpfungsmaß berechnet und damit das Ergebnis einer vorgesehenen Dämpfungsmaßnahme abgeschätzt werden.

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Damping by friction ledges: a practical design concept

Summary On the one hand, mating surfaces of structures are responsible for a reduction of stiffness, on the other hand relative motion produces friction, which contributes considerably to the damping. Noticeable friction damping without simultaneous stiffness reduction can be achieved by adding further mating surfaces. Such interfaces are realized by fastening additional elements (e.g. beamlike) onto the structure. An analytic approximation method for these so-called friction ledges is described in this paper. Initiating from the mode shape to be damped the procedure yields criteria for the suitable positioning and design of the ledges. Most important of all is the damping optimized interface pressure, that leads to maximum energy dissipation. Finally, the expected damping rate can be computed, and therefore the result of the proposed measure assessed.

     

Reintroducing anisotropic interactions in magic-angle-spinning NMR of half-integer quadrupolar nuclei: 3D MQMAS

Selective reintroduction of anisotropic interactions such as the chemical shift anisotropy (CSA) and homonucler dipolar (HMD) coupling were implemented in a high-resolution NMR spectroscopy for half-integer quadrupolar nuclei. Rotary resonance recoupling (R(3)) combined with the multiple-quantum magic-angle spinning (MQMAS) in a three-dimensional (3D) experiment provides not only site-specific high-resolution spectra to yield the quadrupolar interaction parameters but also the CSA or HMD interaction parameters. This 3D experiment provides an avenue for the complete local structural information of half-integer quadrupolar nuclei. Three-dimensional MQMAS experiments incorporating R(3) of HMD and CSA interactions were demonstrated on model compounds containing (11)B, (23)Na, and (87)Rb nuclei.     

Mechanism of the thermal decomposition of hydrophosphites of lithium,sodium and potassium

The thermal decomposition of some M ₂ ^I HPO₃ (M-Li, Na, K) phosphites under nitrogen atmosphere was investigated. A stepwise mechanism of thermal decomposition has been proposed.

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Zusammenfassung Es wurde die thermische Zersetzung von Phosphiten M ₂ ^I HPO₃ (M-Li, Na, K) in Stickstoffatmosphere untersucht. Die Schritte des Mechanismus der thermischen Zersetzung wurden vorgeschlagen.

     

Groups of paramagnetic centres in coal samples with different carbon contents

Complex systems of paramagnetic centres existing in demineralised flame coal (71.4 wt% C), medium-rank coal (85.6 wt% C) and anthracite (94.9 wt% C) were analysed by electron paramagnetic resonance spectroscopy (EPR). Different groups of paramagnetic centres were searched in macerals (exinite, vitrinite, inertinite) of coals with carbon contents of 73.8 wt% C and 85.6 wt% C. Experimental EPR spectra were fitted by different superposition of theoretical lines. Total concentration of paramagnetic centres both in coal and macerals increases with carbon content in the sample. Total concentration of paramagnetic centres in macerals increases from exinite to inertinite. Four groups of paramagnetic centres were found in medium-rank coal, and only two groups exist in flame coal and anthracite. The EPR spectrum of medium-rank coal is a superposition of two broad and two narrow lines. Both broad and narrow, and two narrow lines were measured in EPR spectra of flame coal and anthracite, respectively. Two types of paramagnetic centres with broad lines and one group with narrow lines exist in exinite and vitrinite from medium-rank coal. Two narrow components were observed in EPR spectra of its inertinite. Two different broad electron paramagnetic resonance signals were detected for macerals from low-coalificated coal. Paramagnetic centres systems of medium-rank coal samples reveal the most complex character. Broad EPR lines were not observed for the higher coalificated samples, i.e., anthracite and inertinite from medium-rank coal. Narrow lines do not occur in EPR spectra of low-coalificated macerals. Strong dipolar interactions and fast spin-lattice relaxation processes are characteristic for paramagnetic centres with broad lines. Strong exchange interactions and short spin-lattice relaxation time were measured for paramagnetic centres with the narrowest EPR signals.     

Studies of the Factors Controlling Regioselective Nucleophilic Addition to Dienylium-Iron Complexes

Tricarbonyl(4-alkoxyl-1-alkylcyclohexadienylium)iron complexes (I) react with metal-cation enolate nucleophiles to give in most cases a mixture of products (II) and (III), resulting from attack at the C-1 and C-5 termini of the dienylium ring. Factors that control the regioselectivity of nucleophilic addition, including the steric and electronic effects of the 4-alkoxyl and 1-alkyl substituents, the degree of association between the enolate nucleophiles and their counterions, and the polarity of the solvents, were investigated.     

Measurement of γp→K + Λ and γp→K + Σ 0 at photon energies up to 1.47 GeV

The reactions pK ⁺ and pK ^{+ 0} have been measured with the multiparticle detector system SAPHIR at ELSA in Bonn. Besides the differential cross sections the polarization and, for the first time, the ⁰ polarization have been determined in a photon induced reaction. All data are presented as functions of the photon energy (from threshold up to 1.47 GeV) and of the kaon production angle (0°–180°). The polarization of both and ⁰ is substantial at all energies and varies strongly with the production angle.This work is supported by the Bundesminister für Forschung und Technologie (BMFT), FK 06 BN 621 I     

Novel Rearrangements of 2,3-Dimercapto-1-propanol Derivatives: Formation of Dialkyl Sulfide, Dialkyl Disulfide, and 1,2,3-Tris(alkylthio)propane

The base alkylation of 2,3-dimercapto-1-propanol with alkyl halides leads in good yield to 2,3-bis(alkylthio)-1-propanol and dialkyl sulfide. The reaction of 2,3-bis(alkylthio)-1-propanol with catalytic concentrated sulfuric acid proceeds with rearrangement to give 1,2,3-tris(alkylthio)propane and dialkyl disulfide. The rearrangement reaction takes place through a common intermediate thiaranium intermediate 8.     

Effect of extractant on arsenic(V) recovery from sulfuric acid solutions

Extraction of arsenic(V) from sulfuric acid solutions with various extractants in multistage counter-current extraction-stripping systems was compared. The extraction ability of the extractants studied showed the following order: ENIM 100>TBP=CYANEX 923>2-methylhexanol. The extraction depends significantly on the number of extraction stages and the phase ratios in extraction. The effects of the number of stripping stages and the phase ratio in stripping are less important.