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  • 1
    Electronic Resource
    Electronic Resource
    Thermal and Photochemical Rearrangement of 3-Substituted 2-Methylbenzofuran Epoxides and Their Valence-Isomeric Quinone Methides (1994)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 127 (1994), S. 433-436 
    Details
    ISSN: 0009-2940
    Keywords: Epoxidation ; Dioxirane, dimethyl- ; Benzofurans, 2-methyl- ; Benzofuran epoxides ; Quinone methides ; Photoisomerization ; Chromenes ; 3-Benzofuranones ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The dimethyldioxirane oxidation of the 3-substituted 2-methylbenzofurans 1 [1a: 3(E)-styryl, 1b: 3-acetoxy, 1c: 3-(tert-butyldimethylsilyloxy)] is reported. Only quinone methide 3a, none of the benzofuran epoxides 2a-c, could be detected by 1H- and 13C-NMR spectroscopy at low temperature (-30°C), which on photoisomerization led to chromene 7a. The benzofuran-3-ones 5b, c and the α-diketone 6c are presumably formed by thermal isomerization of the transient benzofuran epoxides 2b, c and quinone methide 3c.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cber.19941270220
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  • 2
    Electronic Resource
    Electronic Resource
    Preparation of 2H-Benzoxetes by Photoinduced [2 + 2] Cycloaddition of Quinone Methides, Accessible by Dimethyldioxirane (DMD) Oxidation of 2,3-Dimethylbenzofurans (1994)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 127 (1994), S. 1115-1118 
    Details
    ISSN: 0009-2940
    Keywords: Epoxidation ; Dioxirane, dimethyl- ; Benzofurans, 2,3-dimethyl- ; Benzofuran epoxides ; Quinone methides ; [2 + 2] Photocycloaddition ; Benzoxetes ; Hetero-Diels-Alder reaction ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Irradiation (λ 〉 366 nm) of the quinone methides 3, which were formed by valence isomerization of the methyl-, chloro-, and tert-butyl-substituted 2,3-dimethylbenzofuran epoxides 2, afforded the novel 2H-benzoxetes 4 by photochemical [2 + 2] cycloaddition. These strained and highly labile benzoxetes 4 were spectrally (1H and 13C NMR) characterized at subambient temperatures. On prolonged storage (2-3 d) at -20 to -10°C, the benzoxetes 4 reverted to the quinone methides 3 and/or benzofuran epoxides 2.
    Additional Material: 1 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cber.19941270622
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  • 3
    Electronic Resource
    Electronic Resource
    Epoxidation of 2,3-Dimethylbenzofurans by Dimethyldioxirane (1992)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 125 (1992), S. 231-234 
    Details
    ISSN: 0009-2940
    Keywords: Epoxidation ; Dioxirane, dimethyl ; Benzofurans, 2,3-dimethyl- ; Benzofuran epoxides ; Quinone methides ; Methanol addition ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The synthesis of epoxides 2 by the reaction of the chloro- and methyl-substituted 2,3-dimethylbenzofurans 1 with dimethyl-dioxirane at low temperature is reported. These labile epoxides were spectroscopically characterized (1H and 13C NMR) at subambient temperatures. Epoxidation of benzofuran 1c affords a 31:69 mixture of epoxide 2c and quinone methide 3c, the latter presumably being produced by valence isomerization of the epoxide. On warming up above -10°C, the epoxides 2 suffer decomposition. Treatment of epoxide 21 with methanol yields the tautomeric mixture of adducts 4i and 4i′.
    Additional Material: 2 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cber.19921250136
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  • 4
    Electronic Resource
    Electronic Resource
    Photochemical and Thermal Rearrangement of Acyl-Substituted Quinone Methides, Accessible by Dimethyldioxirane Oxidation of Benzofurans and Subsequent Valence Isomerization of the Resulting Epoxides (1993)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 126 (1993), S. 2697-2699 
    Details
    ISSN: 0009-2940
    Keywords: Epoxidation ; Dioxirane, dimethyl- ; Benzofurans, 2-methyl-3-phenyl ; Benzofuran epoxides ; Quinone methides ; (Z/E) Photoisomerization ; Norcaradiene ; Benzocycloheptafuran ; Thermal rearrangement ; Xanthenes, 9-acetyl- ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The photoisomerization of quinone methides 3 to benzocycloheptafuran 4 and the thermolysis of the latter to xanthenes 5 are reported. The quinone methides 3 are accessible by dimethyldioxirane oxidation and subsequent valence isomerization of the resulting benzofuran epoxides 2. On irradiation (λ 〉 400 nm), the quinone methides 3 rearrange by cyclization to the corresponding norcaradiene, and ring enlargement affords the benzocycloheptafurans 4. Thermolysis of the cycloheptatrienes 4 leads to the xanthenes 5, first by cycloreversion to the norcaradienes, followed by electrocyclization to the chromenes and tautomerization of the latter. The new cycloheptatrienes 4 and xanthenes 5 were fully characterized.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cber.19931261220
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  • 5
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    Laboruntersuchungen zur Freisetzung von Unat aus einem Gestein unter oxischen naturnahen Bedingungen (2018)
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    Publication Date: 2021-03-29
    Description: Im Labor wurden verschiedene Größen (pH-Wert, HCO3 --Gehalt, Präsenz von Fe(OH)3) untersucht, von denen angenommen werden konnte, dass sie die umweltrelevante Freisetzung von Uran aus Gesteinen (z.B. Haufwerken, Halden, Tailings) im neutralen und schwach basischen pH-Bereich (6 bis 9) beeinflussen. Hierzu wurde der Austrag von Unat aus einem schwach vererzten Urangestein (2.31 %) in Batchversuchen untersucht. Diese Versuche wurden mit 8, 10 oder 40 g/L Gestein und Leitungs- bzw. Mineralwasser durchgeführt. Zum Vergleich wurden parallele Standversuche in deionisiertem Wasser, 0,1 M Na2CO3 und 0,1 M H2SO4 durchgeführt. Die Ergebnisse zeigen eine Begünstigung der Uranfreisetzung in Anwesenheit von Carbonat (gelöst oder in-situ durch Dolomitauflösung entstanden), während die Rolle des Pyrits auf die Freisetzung deutlich komplexer ist. Das Erreichen eines Gleichgewichtszustands kann unter Umständen durch sorptive Einflüsse verzögert werden.
    Description: The effects of carbonate concentration and the presence of iron hydroxide phases on uranium release into the environment were investigated under oxic conditions and in the pH range from 6 to 9. For this purpose not-shaken batch experiments were conducted with a constant amount (8, 10 or 40 g/L) of a uranium bearing rock and different types of water (deionised, tap and mineral water). For comparison parallel experiments were conducted with 0.1 M Na2CO3 and 0.1 M H2SO4. The use of dolomite confirmed the favourable role of carbonate bearing minerals for U transport while the presence of pyrite on Uranium mobilisation was shown to be considerably more complex. This study shows that the approach of equilibrium conditions can be strongly delayed by sorption processes.
    Keywords: Unat; Urangestein, Batchversuche ; 551
    Language: German
    Type: article , submittedVersion
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  • 6
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    Testing the Suitability of Zerovalent Iron Materials for Reactive Walls (2018)
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    Publication Date: 2021-03-29
    Description: Zerovalent iron (ZVI) has been proposed as reactive material in permeable in-situ walls for contaminated groundwater. An economically feasible ZVI reactive wall requires cheap but efficient iron materials. From an uranium treatability study and results of iron dissolution in 0.002 M EDTA by five selected ZVI materials, it is shown that current research and field implementation is not based on a rational selection of application-specific iron metal sources. An experimental procedure is proposed which could enable a better material characterization. This procedure consists in mixing ZVI materials and reactive additives including contaminant releasing materials (CRM) in long term batch experiments and characterise the contaminant concentration over the time.
    Keywords: contaminant; groundwater; in-situ remediation; zerovalent iron; uranium ; 551
    Language: English
    Type: article , submittedVersion
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  • 7
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    Airborne Thermal Data Identifies Groundwater Discharge at the North-Western Coast of the Dead Sea (2018)
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    Publication Date: 2021-03-29
    Description: A qualitative and quantitative monitoring of groundwater discharge was conducted based on an airborne thermal campaign undertaken along the north-western coast of the Dead Sea in January 2011 to contribute to the relatively scarce information on groundwater discharge to date in the region. The application of airborne thermal data exploits thermal contrasts that exist between discharging groundwater and background sea surface temperatures of the Dead Sea. Using these contrasts, 72 discharge sites were identified from which only 42 were known from previous in situ measurements undertaken at terrestrial springs by the Israel Hydrological Service. Six of these sites represent submarine springs and at a further 24 locations groundwater appears to seep through the sediment. Although the abundance of groundwater seepage sites suggests a significant, but so far unknown groundwater source, the main contribution appears to originate from terrestrial springs. In an attempt to provide a quantitative approach for terrestrial springs, a linear bootstrap regression model between in situ spring discharge and respective thermal discharge plumes (r2 = 0.87 p 〈 0.001) is developed and presented here. While the results appear promising and could potentially be applied to derive discharge values at unmonitored sites, several influence factors need to be clarified before a robust and reliable model to efficiently derive a complete quantitative picture of groundwater discharge can be proposed.
    Keywords: thermal discharge plume; groundwater discharge; ; 551
    Language: English
    Type: article , publishedVersion
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  • 8
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    Microbial and Chemical Characterization of Underwater Fresh Water Springs in the Dead Sea (2018)
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    Publication Date: 2021-03-29
    Description: Due to its extreme salinity and high Mg concentration the Dead Sea is characterized by a very low density of cells most of which are Archaea. We discovered several underwater fresh to brackish water springs in the Dead Sea harboring dense microbial communities. We provide the first characterization of these communities, discuss their possible origin, hydrochemical environment, energetic resources and the putative biogeochemical pathways they are mediating. Pyrosequencing of the 16S rRNA gene and community fingerprinting methods showed that the spring community originates from the Dead Sea sediments and not from the aquifer. Furthermore, it suggested that there is a dense Archaeal community in the shoreline pore water of the lake. Sequences of bacterial sulfate reducers, nitrifiers iron oxidizers and iron reducers were identified as well. Analysis of white and green biofilms suggested that sulfide oxidation through chemolitotrophy and phototrophy is highly significant. Hyperspectral analysis showed a tight association between abundant green sulfur bacteria and cyanobacteria in the green biofilms. Together, our findings show that the Dead Sea floor harbors diverse microbial communities, part of which is not known from other hypersaline environments. Analysis of the water’s chemistry shows evidence of microbial activity along the path and suggests that the springs supply nitrogen, phosphorus and organic matter to the microbial communities in the Dead Sea. The underwater springs are a newly recognized water source for the Dead Sea. Their input of microorganisms and nutrients needs to be considered in the assessment of possible impact of dilution events of the lake surface waters, such as those that will occur in the future due to the intended establishment of the Red Sea - Dead Sea water conduit.
    Keywords: Dead Sea; Archaeal community ; 551
    Language: English
    Type: article , publishedVersion
    Format: 21
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  • 9
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    Simulation of saturated and unsaturated flow in karst systems at catchment scale using a double continuum approach (2018)
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    Publication Date: 2021-03-29
    Description: The objective of this work is the simulation of saturated and unsaturated flow in a karstified aquifer using a double continuum approach. The HydroGeoSphere code ( Therrien et al. , 2006 ) is employed to simulate spring dis- charge with the Richards equations and van Genuchten pa- rameters to represent flow in the (1) fractured matrix and (2) conduit continuum coupled by a linear exchange term. Rapid vertical small-scale flow processes in the unsaturated conduit continuum are accounted for by applying recharge boundary conditions at the bottom of the saturated model do- main. An extensive sensitivity analysis is performed on sin- gle parameters as well as parameter combinations. The tran- sient hydraulic response of the karst spring is strongly con- trolled by the matrix porosity as well as the van Genuchten parameters of the unsaturated matrix, which determine the head dependent inter-continuum water transfer when the con- duits are draining the matrix. Sensitivities of parameter com- binations partially reveal a non-linear dependence over the parameter space. This can be observed for parameters not belonging to the same continuum as well as combinations, which involve the exchange parameter, showing that results of the double continuum model may depict a certain de- gree of ambiguity. The application of van Genuchten pa- rameters for simulation of unsaturated flow in karst systems is critically discussed.
    Keywords: saturated unsaturated flow; karst systems; catchment scale; double continuum ; 551
    Language: English
    Type: article , publishedVersion
    Format: 15
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  • 10
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    Development of a numerical workflow based on μ-CT imaging for the determination of capillary pressure–saturation-specific interfacial area relationship in 2-phase flow pore-scale porous-media systems: a case study on Heletz sandstone (2018)
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    Publication Date: 2021-03-29
    Description: In this case study, we present the implementation of a finite element method (FEM)-based numerical pore-scale model that is able to track and quantify the propagating fluid–fluid interfacial area on highly complex micro-computed tomography (μ-CT)-obtained geometries. Special focus is drawn to the relationship between reservoir-specific capillary pressure (pc), wetting phase saturation (Sw) and interfacial area (awn). The basis of this approach is high-resolution μ-CT images representing the geometrical characteristics of a georeservoir sample. The successfully validated 2-phase flow model is based on the Navier–Stokes equations, including the surface tension force, in order to consider capillary effects for the computation of flow and the phase-field method for the emulation of a sharp fluid–fluid interface. In combination with specialized software packages, a complex high-resolution modelling domain can be obtained. A numerical workflow based on representative elementary volume (REV)-scale pore-size distributions is introduced. This workflow aims at the successive modification of model and model set-up for simulating, such as a type of 2-phase problem on asymmetric μ-CT-based model domains. The geometrical complexity is gradually increased, starting from idealized pore geometries until complex μ-CT-based pore network domains, whereas all domains represent geostatistics of the REV-scale core sample pore-size distribution. Finally, the model can be applied to a complex μ-CT-based model domain and the pc–Sw–awn relationship can be computed.
    Keywords: μ-CT imaging; Heletz sandstone ; 551
    Language: English
    Type: article , publishedVersion
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