The Experts below are selected from a list of 14208 Experts worldwide ranked by ideXlab platform
Gregory B Boursalian - One of the best experts on this subject based on the ideXlab platform.
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palladium catalysed electrophilic aromatic c h Fluorination
Nature, 2018Co-Authors: Gregory B Boursalian, Kumiko Yamamoto, Jiakun Li, Jeffrey Garber, Julian David Rolfes, Jannik C BorghsAbstract:An approach for the direct electrophilic C–H Fluorination of arenes is reported, using a palladium catalyst and mild fluorinating reagents. In the pharmaceutical industry, fluorine has long been added to organic molecules to improve the bioavailability of drugs. These molecules are also important in positron-emission tomography (PET) imaging and in the agrochemical industry. Although aryl fluorides are an important class of such molecules, general methods for the direct C–H Fluorination of aromatic compounds are lacking. Here, Tobias Ritter and colleagues report that electrophilic fluorinating agents react with palladium(II) to generate a more active catalytic fluorinating agent. This agent can react with a range of unfunctionalized aromatic compounds directly, including several pharmaceuticals, and so provides access to a range of fluorinated compounds that were otherwise not readily accessible. Aryl fluorides are widely used in the pharmaceutical and agrochemical industries1,2, and recent advances have enabled their synthesis through the conversion of various functional groups. However, there is a lack of general methods for direct aromatic carbon–hydrogen (C–H) Fluorination3. Conventional methods require the use of either strong fluorinating reagents, which are often unselective and difficult to handle, such as elemental fluorine, or less reactive reagents that attack only the most activated arenes, which reduces the substrate scope. A method for the direct Fluorination of aromatic C–H bonds could facilitate access to fluorinated derivatives of functional molecules that would otherwise be difficult to produce. For example, drug candidates with improved properties, such as increased metabolic stability or better blood–brain-barrier penetration, may become available. Here we describe an approach to catalysis and the resulting development of an undirected, palladium-catalysed method for aromatic C–H Fluorination using mild electrophilic fluorinating reagents. The reaction involves a mode of catalysis that is unusual in aromatic C–H functionalization because no organometallic intermediate is formed; instead, a reactive transition-metal-fluoride electrophile is generated catalytically for the Fluorination of arenes that do not otherwise react with mild fluorinating reagents. The scope and functional-group tolerance of this reaction could provide access to functional fluorinated molecules in pharmaceutical and agrochemical development that would otherwise not be readily accessible.
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A Fluoride-derived Electrophilic Late-Stage Fluorination Reagent for PET Imaging
'American Association for the Advancement of Science (AAAS)', 2018Co-Authors: Lee E, Gregory B Boursalian, Adam S Kamlet, Dc Powers, Cn Neumann, Furuya T, Dc Choi, Jm Hooker, Ritter T.Abstract:The unnatural isotope fluorine-18 (F-18) is used as a positron emitter in molecular imaging. Currently, many potentially useful F-18-labeled probe molecules are inaccessible for imaging because no Fluorination chemistry is available to make them. The 110-minute half-life of F-18 requires rapid syntheses for which [F-18]fluoride is the preferred source of fluorine because of its practical access and suitable isotope enrichment. However, conventional [F-18]fluoride chemistry has been limited to nucleophilic Fluorination reactions. We report the development of a palladium-based electrophilic Fluorination reagent derived from fluoride and its application to the synthesis of aromatic F-18-labeled molecules via late-stage Fluorination. Late-stage Fluorination enables the synthesis of conventionally unavailable positron emission tomography (PET) tracers for anticipated applications in pharmaceutical development as well as preclinical and clinical PET imaging.X11225220sciescopu
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a fluoride derived electrophilic late stage Fluorination reagent for pet imaging
Science, 2011Co-Authors: Eunsung Lee, Gregory B Boursalian, Adam S Kamlet, David C Powers, Constanze N Neumann, Takeru Furuya, Daniel C Choi, Jacob M Hooker, Tobias RitterAbstract:The unnatural isotope fluorine-18 ( 18 F) is used as a positron emitter in molecular imaging. Currently, many potentially useful 18 F-labeled probe molecules are inaccessible for imaging because no Fluorination chemistry is available to make them. The 110-minute half-life of 18 F requires rapid syntheses for which [ 18 F]fluoride is the preferred source of fluorine because of its practical access and suitable isotope enrichment. However, conventional [ 18 F]fluoride chemistry has been limited to nucleophilic Fluorination reactions. We report the development of a palladium-based electrophilic Fluorination reagent derived from fluoride and its application to the synthesis of aromatic 18 F-labeled molecules via late-stage Fluorination. Late-stage Fluorination enables the synthesis of conventionally unavailable positron emission tomography (PET) tracers for anticipated applications in pharmaceutical development as well as preclinical and clinical PET imaging.
Yewen Zhang - One of the best experts on this subject based on the ideXlab platform.
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modulation of surface electrical properties of epoxy resin insulator by changing Fluorination temperature and time
IEEE Transactions on Dielectrics and Electrical Insulation, 2015Co-Authors: Qianqian Yin, Feihu Zheng, Yaqiang Liu, Qingquan Lei, Yewen ZhangAbstract:In order to systematically investigate the modulating role of Fluorination temperature and time on surface electrical properties of the epoxy resin insulator, epoxy resin sheets were surface fluorinated in a laboratory vessel using a F22/N22 mixture with 12.5% F22 by volume at 0.1 MPa and different temperatures of 25–95 °C for different times of 5–120 min. Conductivity measurements have shown that the intrinsic surface conductivity of the epoxy resin insulator could be modulated from an even lower value to a nearly four orders of magnitude higher value than the value prior to Fluorination by changing the Fluorination temperature and time. Surface conductivity increased with increasing Fluorination temperature at the same Fluorination time, while decreased to some extent with increasing Fluorination time at a given Fluorination temperature. Surface potential decay measurements showed consistent results with the surface conductivity measurements. ATR-IR analyses revealed substantial changes in surface chemical composition and structure, depending on the Fluorination temperature and time. SEM images clearly showed an increase of the fluorinated layer thickness with increasing Fluorination temperature and time. Surface cracks appeared only at elevated Fluorination temperatures and increased with Fluorination temperature, while the surface became compact with the duration of the Fluorination. These results, compared with the previous results on an epoxy resin insulator made of DGEBA epoxy resin with a lower epoxy value, also indicated a significant influence of the epoxy resin insulator itself or the epoxy resin raw material on surface electrical properties and surface physicochemical characteristics after Fluorination.
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characteristics and electrical properties of epoxy resin surface layers fluorinated at different temperatures
IEEE Transactions on Dielectrics and Electrical Insulation, 2013Co-Authors: Yaqiang Liu, Feihu Zheng, Qianqian Yin, Qingquan Lei, Yewen ZhangAbstract:Epoxy resin sheets were surface fluorinated in a laboratory vessel using a F2/N2 mixture with 12.5% F2 by volume at the different temperatures of 25, 55, 75, and 95 °C for the same time of 30 min, to investigate the effect of Fluorination temperature on surface electrical properties. ATR-IR analyses indicate that Fluorination led to substantial changes in surface chemical composition and structure, depending on Fluorination temperature, and SEM surface and cross section images show an evolution of surface morphology and an increase of thickness of the fluorinated layer with Fluorination temperature. Conductivity measurements reveal that the surface fluorinated samples have higher surface conductivities than the unfluorinated sample, and surface conductivity significantly increases with Fluorination temperature. Surface potential measurements, performed about 10 s after corona charging, indicate lower initial surface potentials for the surface fluorinated samples than the unfluorinated sample, and a decrease of the initial surface potential with surface conductivity. The initial surface potential was found to decrease dramatically above a critical surface conductivity (3.0×10-14 S), and almost to zero when surface conductivity increased to 10-12 S. Contact angle measurements and surface energy calculations show a much higher surface polarity of the surface fluorinated samples compared to the unfluorinated sample and a dramatic increase of the surface polarity with Fluorination temperature. An increase in degree of chain scission is considered to be the main cause for the increases of surface conductivity and surface polarity with Fluorination temperature.
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suppression effect of surface Fluorination on charge injection into linear low density polyethylene
Journal of Applied Physics, 2009Co-Authors: Q. Yang, Yue Jiang, Feihu Zheng, Chen Xie, Yewen ZhangAbstract:To suppress charge injection from electrodes, direct Fluorination using fluorine gas was used for linear low density polyethylene (LLDPE) since it is one of the most effective methods of the polymer surface modification. Surface Fluorination of the LLDPE plates was obtained as indicated by attenuated total reflection infrared spectroscopy. Remarkable suppression of charge injection by the surface Fluorination was observed by space charge distribution measurements using the pressure wave propagation method. Comparing with the remarkable bipolar charge distribution in bulk of the original LLDPE, there is less space charge in bulk and it mostly exists in the fluorinated surface layers. The possible mechanisms of the charge injection suppression are discussed, one of which, the effect of Fluorination on the charge traps in surface layer was investigated by the thermally stimulated discharge technique. The results indicate that Fluorination has charge traps in the surface layer remarkably deepened and charges ...
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suppression effect of surface Fluorination on charge injection into linear low density polyethylene
Journal of Applied Physics, 2009Co-Authors: Q. Yang, Yue Jiang, Feihu Zheng, Chen Xie, Yewen ZhangAbstract:To suppress charge injection from electrodes, direct Fluorination using fluorine gas was used for linear low density polyethylene (LLDPE) since it is one of the most effective methods of the polymer surface modification. Surface Fluorination of the LLDPE plates was obtained as indicated by attenuated total reflection infrared spectroscopy. Remarkable suppression of charge injection by the surface Fluorination was observed by space charge distribution measurements using the pressure wave propagation method. Comparing with the remarkable bipolar charge distribution in bulk of the original LLDPE, there is less space charge in bulk and it mostly exists in the fluorinated surface layers. The possible mechanisms of the charge injection suppression are discussed, one of which, the effect of Fluorination on the charge traps in surface layer was investigated by the thermally stimulated discharge technique. The results indicate that Fluorination has charge traps in the surface layer remarkably deepened and charges captured in the deep traps can block or shield the further charge injection.
Tobias Ritter - One of the best experts on this subject based on the ideXlab platform.
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a fluoride derived electrophilic late stage Fluorination reagent for pet imaging
Science, 2011Co-Authors: Eunsung Lee, Gregory B Boursalian, Adam S Kamlet, David C Powers, Constanze N Neumann, Takeru Furuya, Daniel C Choi, Jacob M Hooker, Tobias RitterAbstract:The unnatural isotope fluorine-18 ( 18 F) is used as a positron emitter in molecular imaging. Currently, many potentially useful 18 F-labeled probe molecules are inaccessible for imaging because no Fluorination chemistry is available to make them. The 110-minute half-life of 18 F requires rapid syntheses for which [ 18 F]fluoride is the preferred source of fluorine because of its practical access and suitable isotope enrichment. However, conventional [ 18 F]fluoride chemistry has been limited to nucleophilic Fluorination reactions. We report the development of a palladium-based electrophilic Fluorination reagent derived from fluoride and its application to the synthesis of aromatic 18 F-labeled molecules via late-stage Fluorination. Late-stage Fluorination enables the synthesis of conventionally unavailable positron emission tomography (PET) tracers for anticipated applications in pharmaceutical development as well as preclinical and clinical PET imaging.
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Catalysis for Fluorination and trifluoromethylation
Nature, 2011Co-Authors: Takeru Furuya, Adam S Kamlet, Tobias RitterAbstract:Recent advances in catalysis have made the incorporation of fluorine into complex organic molecules easier than ever before, but selective, general and practical Fluorination reactions remain sought after. Fluorination of molecules often imparts desirable properties, such as metabolic and thermal stability, and fluorinated molecules are therefore frequently used as pharmaceuticals or materials. But the formation of carbon-fluorine bonds in complex molecules is a significant challenge. Here we discuss reactions to make organofluorides that have emerged within the past few years and which exemplify how to overcome some of the intricate challenges associated with Fluorination.
Magnus Rueping - One of the best experts on this subject based on the ideXlab platform.
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metal free catalytic asymmetric Fluorination of keto esters using a combination of hydrogen fluoride hf and oxidant experiment and computation
ACS Catalysis, 2018Co-Authors: Roman Pluta, Patricia E. Krach, Luigi Cavallo, Laura Falivene, Magnus RuepingAbstract:A chiral iodoarene organocatalyst for the catalytic asymmetric Fluorination has been developed. The catalyst was used in the asymmetric Fluorination of carbonyl compounds, providing the products with a quaternary stereocenter with high enantioselectivities. Chiral hypervalent iodine difluoride intermediates were generated in situ by treatment of the catalyst with an oxidant and hydrogen fluoride as fluoride source. As such, the α-Fluorination of a carbonyl compound was achieved with a nucleophilic fluorine source. A combined computational and experimental approach provided insight into the reaction mechanism and the origin of enantioselectivity.
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Metal-Free Catalytic Asymmetric Fluorination of Keto Esters Using a Combination of Hydrogen Fluoride (HF) and Oxidant: Experiment and Computation
2018Co-Authors: Roman Pluta, Patricia E. Krach, Luigi Cavallo, Laura Falivene, Magnus RuepingAbstract:A chiral iodoarene organocatalyst for the catalytic asymmetric Fluorination has been developed. The catalyst was used in the asymmetric Fluorination of carbonyl compounds, providing the products with a quaternary stereocenter with high enantioselectivities. Chiral hypervalent iodine difluoride intermediates were generated in situ by treatment of the catalyst with an oxidant and hydrogen fluoride as fluoride source. As such, the α-Fluorination of a carbonyl compound was achieved with a nucleophilic fluorine source. A combined computational and experimental approach provided insight into the reaction mechanism and the origin of enantioselectivity
Katia Guérin - One of the best experts on this subject based on the ideXlab platform.
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Rhombohedral iron trifluoride with a hierarchized macroporous/mesoporous texture from gaseous Fluorination of iron disilicide
Materials Chemistry and Physics, 2016Co-Authors: Katia Guérin, André Hamwi, Delbègue Diane, Nicolas Louvain, Doubtsof Léa, Barbara Laik, Jean Pierre Pereira-ramos, Moulay Tahar Sougrati, Jean-claude Jumas, Patrick WillmannAbstract:Stable low temperature rhombohedral iron trifluoride has been obtained by the Fluorination under the pure fluorine gas of iron disilicide. The combination of both unusual Fluorination process and precursor avoids to get unhydrated crystalline FeF3 particles and allows the formation of hierarchized channels of mesoporous/macroporous texture favorable for lithium diffusion. The Fluorination mechanism proceeds by temperature steps from the formation, for a Fluorination temperature below 200 °C, of an amorphous phase and an intermediate iron difluoride identified mainly by 57Fe Mössbauer spectroscopy before getting, as soon as a Fluorination temperature of 260 °C is reached, the rhombohedral FeF3. Both amorphous and crystallized samples display good ability for electrochemical process when used as cathode in lithium-ion battery. The low diameter of rhombohedral structure channels is balanced by an appropriate mesoporous texture and a capacity of 225 mAh.g−1 after 5 cycles for a discharge cut-off of 2.5 V vs. Li+/Li at a current density of C/20 has been obtained and stabilized at 95 mAh.g−1 after 116 cycles.
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modification of ultra high molecular weight polyethylene by various fluorinating routes
Journal of Polymer Science Part A, 2011Co-Authors: A P Kharitonov, Katia Guérin, Marc Dubois, André Hamwi, Hayat Kharbache, Galina V Simbirtseva, Vyacheslav V M Bouznik, Maxim M G Chepezubov, Francis MasinAbstract:Chemical-physical properties of ultra-high-molecular weight polyethylene (UHMWPE) treated by direct Fluorination, direct Fluorination accompanied with UV irradiation, by XeF2 and by TbF4, were tested by FTIR spectroscopy, visible spectroscopy, 19F and 13C NMR, scanning electron microscopy, XRD, and EPR. Surface energy measurements were carried out. The direct fluo- rination of UHMWPE is a diffusion-controlled process, but treat- ment with XeF2 is a kinetically controlled one. Direct Fluorination and direct Fluorination accompanied with UV irradiation results mainly in a formation of ACF2A groups. On the contrary, ACHFA groups are prevailing in UHMWPE treated with XeF2 and TbF4. Surface texture of UHMWPE treated with XeF2 and with F2 is quite different. Direct Fluorination results in a higher polarity of the polymer surface when compared with treatment with XeF2. For the case of direct Fluorination, both long-lived peroxy and flu- oroalkylradicals are formed. For the case of treatment with XeF2, only fluoroalkylradicals were detected. V C 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 49: 3559-3573, 2011
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New synthesis methods for fluorinated carbon nanofibres and applications
Journal of Fluorine Chemistry, 2010Co-Authors: W. Zhang, Katia Guérin, Marc Dubois, André Hamwi, Francis Masin, L. Spinelle, Hayat Kharbache, Alexander P. Kharitonov, Jérôme Brunet, Christelle VarenneAbstract:Several new synthesis methods of fluorinated carbon nanofibres, such as controlled Fluorination using fluorinating agent (TbF4 or XeF 2), or assisted Fluorination under UV and gamma irradiation, are reviewed and compared with the direct Fluorination using undiluted fluorine gas. The results highlight the different Fluorinationmechanisms for the direct Fluorination and the new methods. The other advantage of those alternative Fluorination routes is the possibility to provide fine tuning of the Fluorination level, i.e. from F/C atomic ratio close to zero, as a functionalization, to the unity (CF1) according to the required application, electrochemical or tribological. Two applications are described in this paper as a function of the fluorine content: protection against ozonation and use as solid lubricants. © 2010 Elsevier B.V. All rights reserved.
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carbon nanofibres fluorinated using tbf4 as fluorinating agent part i structural properties
Carbon, 2008Co-Authors: W. Zhang, Katia Guérin, Marc Dubois, Ziad Fawal, Dimitri A Ivanov, Loic Vidal, André HamwiAbstract:Abstract Fluorination of carbon nanofibres (CNFs) under fluorine gas at 480 °C leads to high fluorine content but also to some partial exfoliation. In order to avoid such phenomenon, an alternative route has been performed at temperatures ranged between 420 and 500 °C using a fluorinating agent, i.e. terbium tetrafluoride. The structural properties of the fluorinated CNFs are discussed taking into account the data of 13 C solid state NMR, Raman spectroscopy, SEM, TEM and XRD. Whatever the Fluorination temperature, a fluorinated phase of (CF) n structural type, is formed contrary to the direct process using F 2 gas for which a (C 2 F) n -type fluorinated phase appeared for Fluorination temperatures lower than 450 °C. The progressive release of fluorine atoms from the thermal decomposition of TbF 4 allows an homogenous distribution of the fluorinated part into the CNFs matrix and the formation of a unique (CF) n type structure. Moreover, for high Fluorination temperatures (480 and 500 °C), the Fluorination leads to some nanofibres breaking but in no way to exfoliation.
