Browsing by Subject "Mikrowelle"

Now showing 1 - 4 of 4
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    Influence of microwave irradiation and ionic liquids on multi component reactions
    (2013) Mert-Balci, Fadime; Beifuss, Uwe
    The present thesis focuses on the influence of microwave irradiation and ionic liquids on the outcome of two well-known three component reactions, the Groebke reaction and the Povarov reaction. The first part of the thesis deals with the influence of microwaves and ionic liquids on the Groebke reaction. The reaction of 2-aminopyridines with aldehydes and isocyanides using montmorillonite as a catalyst in toluene under microwave conditions at 160°C delivers the corresponding imidazo[1,2-a]pyridines within only seven minutes with yields ranging from 16 to 98%. The organic solvent can be replaced by ionic liquids like imidazolium and guanidinium salts. With guanidinium salts, it is possible to perform the Groebke reaction in the absence of any other catalyst and solvent under microwave conditions. The second part of this work is about the extension of the scope of typical Groebke reactions by replacing the aldehyde component with a bifunctional 2-carboxybenzaldehyde. The reaction of 2-aminopyridines with isocyanides and 2-carboxybenzaldehydes with 20 mol% methanesulfonic acid as a catalyst in toluene under microwave conditions at 160°C affords the corresponding pyrido[2?,1?:2,3]imidazo[4,5-c]isoquinolin-5(6H)-ones with yields ranging between 35 and 68%. The new method can easily be performed, is robust, and highly efficient. The third part of the thesis is focused on the intermolecular Povarov reaction. Using the reaction between aniline, benzaldehyde, and 2,3-dihydrofuran as a model reaction, the influence of ionic liquids, such as imidazolium and guanidinium salts, and microwaves on the outcome of the Povarov reaction was evaluated. It was established that the model reaction can be promoted by imidazolium salts like [bmim]BF4 under thermal as well as under microwave conditions. The reaction temperature has a strong impact on the chemical yield and the diastereoselectivity of the model reaction. At lower temperatures the formation of the endo-isomer is favored. However, the influence of microwave irradiation on yield and selectivity is not very pronounced. The Povarov reaction can also be promoted by a great number of guanidinium salts. Reactions that were performed under thermal conditions in a sealed vial demonstrated that both the chemical yield and the diastereoselectivity of the reaction are strongly influenced by a) the structure of the guanidinium ion and the nature of the anion of the guanidinium salt, and b) the concentration of the guanidinium salt. Remarkably, the Povarov can also be performed successfully in the presence of only catalytic amounts of a guanidinium salt. Finally, it was demonstrated that the guanidinium salts can be recycled and reused several times without loss of reactivity.
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    Microwave forward model for land surface remote sensing
    (2015) Park, Chang-Hwan; Wulfmeyer, Volker
    In order to improve hydro-meteorological model prediction using remote-sensing measurements the difference between the model world and the observed world should be identified. The forward model proposed in this study allows us to simulate the BT (brightness temperature) from the land surface model to compare with the observed microwave BT. The proposed dielectric mixing model is the key part of the forward model to properly link the model parameters and the BT observed by remote sensing. In this study, it was established that the physically valid computation of the effective dielectric constant should be based on the arithmetic average with consideration of the proposed universal damping factor. This physically based dielectric mixing model is superior to the refractive mixing model or semi-empirical/calibration model with RMSE values of 0.96 and 0.63 for the predicted real and imaginary parts, respectively, compared to the measured values. The RMSE obtained with the new model is smaller than those obtained by other researchers using refractive mixing models for operational microwave remote sensing. Once we determine the model uncertainty using this forward model, we can update the model state using the values obtained from the remote-sensing measurement. The challenging task in this process is to resolve the ill-posed inversion problem (estimation of multiple model parameters from a single BT measurement). This study proposes a simple partitioning factor based on model physics. Again, the forward model is crucial because these factors are required to be computed in BT space. In the case study involving the Schäfertal catchment area, the proposed forward model, including the new dielectric mixing model, and the proper partitioning factors computed from land surface model physics was able to successfully extract the refined soil texture information from the microwave BT measurements. The highly resolved soil moisture variability based on the refined soil texture will allow us to predict convective precipitation with higher spatial and temporal accuracy in the numerical weather forecasting model. Moreover, microwave remote sensing using the developed forward model, which provides the soil texture, soil moisture, and soil temperature with a fine scale resolution, is expected to open up new possibilities to examine the energy balance closure problem with unprecedented realism.
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    Synthesis of N-neterocycles via intramolecular reductive cyclizations of nitroalkenes
    (2007) Merisor, Elena; Beifuss, Uwe
    The current work describes a new triethyl phosphite mediated domino reaction of ω-nitro-alkenes which in one step cyclize to the corresponding saturated N-heterocycles. The one-step domino reaction described in this work includes a three-step reaction, a nitroso-ene reaction being coupled with two reduction reactions. A new C-N bond is formed and saturated N-heterocycles are synthesized. The microwave irradiation of the ω-nitroalkenes has been developed as an alternative protocol, having the advantage that the formation of byproducts can be suppressed and the reaction times reduced. The reductive cyclization reaction mediated by triethyl phosphite allows preparation of a series of saturated N-heterocycles such as substituted 3,4-dihydro-2H-1,4-benzoxazines, 1,2,3,4-tetrahydroquinoxalines and 1,2,3,4-tetrahydroquinolines. The newly developed domino reaction can also occur under CO pressure using metal catalysts, allowing the formation of saturated N-heterocycles. Since the reductive cyclizations reported in this work are transition metal-catalyzed domino processes without precedent, they could be of significant interest to the field of synthetic chemistry and ?Life Sciences?.
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    Untersuchungen zur Inaktivierung von Prionen unter Verwendung einer Thermodruckhydrolyse mit Mikrowellen
    (2022) Schöffler, Marie; Hölzle, Ludwig
    The pathogens that cause TSE, known as prions, are infectious proteins that are responsible for a number of fatal neurodegenerative diseases in humans and animals. In the presented work, inactivation of category 1 and 2 meat mash contaminated with Scrapie 263 K and BSE 301 V were investigated as part of the project "PRIORITY 222887 Protecting the food chain from prions: shaping European priorities through basic and applied research". Category 1 material includes specific risk material that is produced at slaughter and poses a potential TSE risk. Currently this material has to be sterilised and incinerated according to European legislation and thus cannot be put to further use. We were looking for method which, on the one hand, prion proteins are safely inactivated and, on the other hand, a further material use of this inactivated material is made possible. This material could be used, for example, as a source of phosphorus or amino acids in fertilizers or as part of renewable energies such as biogas or biodiesel. Treatment with thermal pressure hydrolysis using microwaves was shown successful in inactivating category 1 and 2 meat mash contaminated with Scrapie 263 K at a temperature of 120°C and a treatment duration of 5 min. For complete inactivation of category 1 and 2 meat mash contaminated with BSE 301 V, a temperature of 120°C and a treatment duration of 10 min are required. Detection was carried out here exclusively by Western blotting. Since detection by Western blotting alone is not reliable, a bioassay was needed. The use of animals was not desired for various reasons, which is why an alternative was sought. With the help of in vitro amplification, the so-called Protein Misfolding Cyclic Amplification (PMCA), a method was found that can replace the bioassay. With PMCA, even small amounts of prions can be amplified identically in such a way that they can be detected by Western blotting. In subsequent inactivation experiments of peptone water spiked with Scrapie 263 K, which served as a meat pulp substitute, complete inactivation (at least 4-5 log10-step reduction) was achieved when treated in thermal pressure hydrolysis with microwaves at a treatment temperature of 120°C and for 15 min. In summary, the results of the work could show that thermal pressure hydrolysis with microwaves is suitable to ensure reliable inactivation of prion proteins in animal by-products.