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Articles de revues sur le sujet "Ether oxygenation"

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Howell, Bob A., et Yoseph G. Daniel. « The impact of sulfur oxidation level on flame retardancy ». Journal of Fire Sciences 36, no 6 (novembre 2018) : 518–34. http://dx.doi.org/10.1177/0734904118806155.

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Compounds containing sulfur in various forms may be used as flame retardants or as adjuvants to promote the activity of other flame-retarding elements, most notably phosphorus. To gain a better understanding of the nature of the sulfur moiety in a flame retardant on performance, a series of phosphorus esters derived from isosorbide containing sulfur at various levels of oxygenation (sulfide, sulfoxide, sulfone) have been prepared and evaluated for flame-retardant impact in diglycidyl ether of bis-phenol A epoxy. In all cases, the presence of sulfur positively impacts flame retardancy. In general, the impact on flame retardancy increases as the level of oxygenation at sulfur increases (sulfone > sulfoxide > sulfide).
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Sundaram, Rajyashree M., Takeo Yamada, Ken Kokubo, Kenji Hata et Atsuko Sekiguchi. « Commercial Wet-Spun Singlewall and Dry-Spun Multiwall Carbon Nanotube Fiber Surface O-Functionalization by Ozone Treatment ». Journal of Nanoscience and Nanotechnology 21, no 12 (1 décembre 2021) : 6151–59. http://dx.doi.org/10.1166/jnn.2021.19536.

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In this work, we demonstrate controlled introduction of O-functional groups on commercial carbon nanotube fibers (CNTFs) with different nanotube morphologies obtained by dry- and wet-spinning by treatment with gaseous ozone (O3(g)). Our test samples were (1) wet-spun fibers of smalldiameter (1–2 nm) singlewall (SW)-CNTs and (2) dry-spun fibers containing large-diameter (20 nm) multiwall (MW)-CNTs. Our results indicate that SW-CNTFs undergo oxygenation to a higher extent than MW-CNTFs due to the higher reactivity of SW-CNTs with a larger curvature strain. Oxygenation resulting from O3 exposure was evidenced as increase in surface O atomic% (at% by X-ray photoelectron spectroscopy, XPS) and as reductions in G/D (by Raman spectroscopy) as well as electrical conductivities due to changes in nanotube graphitic structure. By XPS, we identified the emergence of various types of O-functionalities on the fiber surfaces. After long duration O3 exposure (>300 s for SW-CNTFs and >600 s for MW-CNTFs), both sp2 C═O (carbonyl) and sp3 C–O moieties (ether/hydroxy) were observed on fiber surfaces. Whereas, only sp3 C–O (ether/hydroxy) components were observed after shorter exposure times. O3 treatment led to only changes in surface chemistry, while the fiber morphology, microstructure and dimensions remained unaltered. We believe the surface chemistry controllability demonstrated here on commercial fibers spun by different methods containing nanotubes of different structures is of significance in aiding the practical application development of CNTFs.
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Aly, Hamdy A. H., Nguyen B. Huu, Victor Wray, Howard Junca et Dietmar H. Pieper. « Two Angular Dioxygenases Contribute to the Metabolic Versatility of Dibenzofuran-Degrading Rhodococcus sp. Strain HA01 ». Applied and Environmental Microbiology 74, no 12 (25 avril 2008) : 3812–22. http://dx.doi.org/10.1128/aem.00226-08.

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ABSTRACT Rhodococcus sp. strain HA01, isolated through its ability to utilize dibenzofuran (DBF) as the sole carbon and energy source, was also capable, albeit with low activity, of transforming dibenzo-p-dioxin (DD). This strain could also transform 3-chlorodibenzofuran (3CDBF), mainly by angular oxygenation at the ether bond-carrying carbon (the angular position) and an adjacent carbon atom, to 4-chlorosalicylate as the end product. Similarly, 2-chlorodibenzofuran (2CDBF) was transformed to 5-chlorosalicylate. However, lateral oxygenation at the 3,4-positions was also observed and yielded the novel product 2-chloro-3,4-dihydro-3,4-dihydroxydibenzofuran. Two gene clusters encoding enzymes for angular oxygenation (dfdA1A2A3A4 and dbfA1A2) were isolated, and expression of both was observed during growth on DBF. Heterologous expression revealed that both oxygenase systems catalyze angular oxygenation of DBF and DD but exhibited complementary substrate specificity with respect to CDBF transformation. While DfdA1A2A3A4 oxygenase, with high similarity to DfdA1A2A3A4 oxygenase from Terrabacter sp. strain YK3, transforms 3CDBF by angular dioxygenation at a rate of 29% ± 4% that of DBF, 2CDBF was not transformed. In contrast, DbfA1A2 oxygenase, with high similarity to the DbfA1A2 oxygenase from Terrabacter sp. strain DBF63, exhibited complementary activity with angular oxygenase activity against 2CDBF but negligible activity against 3CDBF. Thus, Rhodococcus sp. strain HA01 constitutes the first described example of a bacterial strain where coexpression of two angular dioxygenases was observed. Such complementary activity allows for the efficient transformation of chlorinated DBFs.
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Wu, Wencheng, Yinying Pu, Han Lin, Heliang Yao et Jianlin Shi. « Starvation-Sensitized and Oxygenation-Promoted Tumor Sonodynamic Therapy by a Cascade Enzymatic Approach ». Research 2021 (3 juin 2021) : 1–17. http://dx.doi.org/10.34133/2021/9769867.

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The therapeutic outcomes of noninvasive sonodynamic therapy (SDT) are always compromised by tumor hypoxia, as well as inherent protective mechanisms of tumor. Herein, we report a simple cascade enzymatic approach of the concurrent glucose depletion and intratumoral oxygenation for starvation-sensitized and oxygenation-amplified sonodynamic therapy using a dual enzyme and sonosensitizer-loaded nanomedicine designated as GOD/CAT@ZPF-Lips. In particular, glucose oxidase- (GOD-) catalyzed glycolysis would cut off glucose supply within the tumor, resulting in the production of tumor hydrogen peroxide (H2O2) while causing tumor cells starvation. The generated H2O2 could subsequently be decomposed by catalase (CAT) to generate oxygen, which acts as reactants for the abundant singlet oxygen (1O2) production by loaded sonosensitizer hematoporphyrin monomethyl ether (HMME) upon the US irradiation, performing largely elevated therapeutic outcomes of SDT. In the meantime, the severe energy deprivation enabled by GOD-catalyzed glucose depletion would prevent tumor cells from executing protective mechanisms to defend themselves and make the tumor cells sensitized and succumbed to the cytotoxicity of 1O2. Eventually, GOD/CAT@ZPF-Lips demonstrate the excellent tumoral therapeutic effect of SDT in vivo without significant side effect through the cascade enzymatic starvation and oxygenation, and encouragingly, the tumor xenografts have been found completely eradicated in around 4 days by the intravenous injection of the nanomedicine without reoccurrence for as long as 20 days.
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Zeng, Wei, Jianzhang Li, Zhihua Mao, Zhou Hong et Shengying Qin. « Synthesis, Oxygenation and Catalytic Oxidation Performance of Crown Ether-Containing Schiff Base-Transition Metal Complexes ». Advanced Synthesis & ; Catalysis 346, no 11 (septembre 2004) : 1385–91. http://dx.doi.org/10.1002/adsc.200404094.

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Fan, Mao Yan, Li Fang Zhang, Hong Xiao et Tian Tian Xie. « Preparation and Electrical Properties of Multilayer Zinc Oxide Varistor by Gelcasting ». Advanced Materials Research 852 (janvier 2014) : 285–90. http://dx.doi.org/10.4028/www.scientific.net/amr.852.285.

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Multilayer ZnO varistors were prepared by aqueous gel tape casting with water-soluble acrylamide as binder. 0.8wt% PAA dispersant was found to be the optimum concentration needed to prepare stable slurry. Plasticizer glycerol has a positive effect on the fluidity of the suspension and oxygen anti-polymerizing inhibitor PEG 2000 deteriorated the fluidity. The addition of 15wt. % PEG2000 eliminates the surface exfoliation absolutely due to the oxygenation of ether units. The solid loading of the slurry was about 71wt% compared to the custom acrylic formulation binder 60wt%. The multilayer ZnO varistors prepared by aqueous gel tape casting display comparable good electrical properties to those prepared by water-based tape casting using custom acrylic formulation binder which is attributed to the high solid loading of slurry.
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Leimanis-Laurens, Mara L., Karen Ferguson, Emily Wolfrum, Brian Boville, Dominic Sanfilippo, Todd A. Lydic, Jeremy W. Prokop et Surender Rajasekaran. « Pediatric Multi-Organ Dysfunction Syndrome : Analysis by an Untargeted “Shotgun” Lipidomic Approach Reveals Low-Abundance Plasma Phospholipids and Dynamic Recovery over 8-Day Period, a Single-Center Observational Study ». Nutrients 13, no 3 (27 février 2021) : 774. http://dx.doi.org/10.3390/nu13030774.

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Lipids are molecules involved in metabolism and inflammation. This study investigates the plasma lipidome for markers of severity and nutritional status in critically ill children. Children with multi-organ dysfunction syndrome (MODS) (n = 24) are analyzed at three time-points and cross-referenced to sedation controls (n = 4) for a total of N = 28. Eight of the patients with MODS, needed veno-arterial extracorporeal membrane oxygenation (VA ECMO) support to survive. Blood plasma lipid profiles are quantified by nano-electrospray (nESI), direct infusion high resolution/accurate mass spectrometry (MS), and tandem mass spectrometry (MS/MS), and compared to nutritional profiles and pediatric logistic organ dysfunction (PELOD) scores. Our results show that PELOD scores were not significantly different between MODS and ECMO cases across time-points (p = 0.66). Lipid profiling provides stratification between sedation controls and all MODS patients for total lysophosphatidylserine (lysoPS) (p-value = 0.004), total phosphatidylserine (PS) (p-value = 0.015), and total ether-linked phosphatidylethanolamine (ether-PE) (p-value = 0.03) after adjusting for sex and age. Nutrition intake over time did not correlate with changes in lipid profiles, as measured by caloric and protein intake. Lipid measurement in the intensive care environment shows dynamic changes over an 8-day pediatric intensive care unit (PICU) course, suggesting novel metabolic indicators for defining critically ill children.
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Latté, Klaus Peter, Oliver Kayser, N. Tan, Macki Kaloga et Herbert Kolodziej. « Unusual Coumarin Patterns of Pelargonium Species Forming the Origin of the Traditional Herbal Medicine Umckaloabo ». Zeitschrift für Naturforschung C 55, no 7-8 (1 août 2000) : 528–33. http://dx.doi.org/10.1515/znc-2000-7-809.

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Abstract The coumarin patterns of Pelargonium sidoides DC. and Pelargonium reniforme CURT., forming the origin of the herbal medicine “umckaloabo”, were analysed and compared for therapeutic equivalence. For both species, members of tri- and tetraoxygenated coumarins almost exclusively were present in the respective metabolic pools. However, the roots of P. sidoides and P. reniforme expressed conspicuously distinct coumarin variations, with umckalin, its 7-O-methyl ether, 7-acetoxy-5,6-dimethoxycoumarin, 6,8-dihydroxy-7-methoxycoumarin, 6,8-dihydroxy-5,7-tetramethoxycoumarin, artelin and three unique coumarin sulfates as uncommon metabolites of this class of secondary products of P. sidoides. Furthermore, the highly oxygenated but known coumarins fraxinol, isofraxetin and fraxidin were associated with the new 8-hydroxy-5,6,7-trimethoxycoumarin as representatives of P. reniforme. Of the twelve identified coumarins only the two species shared the ubiquitous scopoletin and the unique 6,7,8-trihydroxycoumarin. From the oxygenation patterns it is evident that the majority of these Pelargonium coumarins match the recently established basic structural requirements for marked antibacterial activity, i.e. the presence of a methoxy function at C-7 and an OH group at either the C-6 or C-8 position. The current data on the coumarin profiles of each Pelargonium species also indicate a previous erroneous identification of the plant material claimed to be P. reniforme. Absence and presence of umckalin and its 7-O-methyl ether defines P. reniforme and P. sidoides, respectively.
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Eke, Joyner, Lillian Banks, M. Abdul Mottaleb, Andrew J. Morris, Olga V. Tsyusko et Isabel C. Escobar. « Dual-Functional Phosphorene Nanocomposite Membranes for the Treatment of Perfluorinated Water : An Investigation of Perfluorooctanoic Acid Removal via Filtration Combined with Ultraviolet Irradiation or Oxygenation ». Membranes 11, no 1 (25 décembre 2020) : 18. http://dx.doi.org/10.3390/membranes11010018.

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Nanomaterials with tunable properties show promise because of their size-dependent electronic structure and controllable physical properties. The purpose of this research was to develop and validate environmentally safe nanomaterial-based approach for treatment of drinking water including removal and degradation of per- and polyfluorinated chemicals (PFAS). PFAS are surfactant chemicals with broad uses that are now recognized as contaminants with a significant risk to human health. They are commonly used in household and industrial products. They are extremely persistent in the environment because they possess both hydrophobic fluorine-saturated carbon chains and hydrophilic functional groups, along with being oleophobic. Traditional drinking water treatment technologies are usually ineffective for the removal of PFAS from contaminated waters, because they are normally present in exiguous concentrations and have unique properties that make them persistent. Therefore, there is a critical need for safe and efficient remediation methods for PFAS, particularly in drinking water. The proposed novel approach has also a potential application for decreasing PFAS background levels in analytical systems. In this study, nanocomposite membranes composed of sulfonated poly ether ether ketone (SPEEK) and two-dimensional phosphorene were fabricated, and they obtained on average 99% rejection of perfluorooctanoic acid (PFOA) alongside with a 99% removal from the PFOA that accumulated on surface of the membrane. The removal of PFOA accumulated on the membrane surface achieved 99% after the membranes were treated with ultraviolet (UV) photolysis and liquid aerobic oxidation.
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Mignion, Lionel, Julie Magat, Olivier Schakman, Etienne Marbaix, Bernard Gallez et Bénédicte F. Jordan. « Hexafluorobenzene in comparison with perfluoro-15-crown-5-ether for repeated monitoring of oxygenation using19F MRI in a mouse model ». Magnetic Resonance in Medicine 69, no 1 (22 mars 2012) : 248–54. http://dx.doi.org/10.1002/mrm.24245.

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Thèses sur le sujet "Ether oxygenation"

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Kinne, Matthias. « The extracellular peroxygenase of the agaric fungus Agrocybe aegerita : catalytic properties and physiological background with particular emphasis on ether cleavage ». Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2010. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-62076.

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Litter-decay fungi have recently been shown to secrete heme-thiolate peroxygenases that oxidize various organic chemicals, but little is known about the physiological role or the mechanism of these enzymes. The aromatic peroxygenase of Agrocybe aegerita (AaeAPO) was purified and catalytically characterized. An overall reaction mechanism was proposed. The results show that AaeAPO catalyzed diverse H2O2-dependent monooxygenations (two-electron oxidations) including (a) the cleavage of aliphatic and aromatic ethers, (b) the regio- and enantioselective hydroxylation of aromatic compounds, (c) the stepwise oxygenation of benzylic compounds, (d) the N-dealkylation of secondary amines and (e) the dehalogenation of halogenated aliphatic compounds as well as typical peroxidase reactions (suggested to involve one-electron oxidation) such as (f) oxidation and polymerization of phenols and (g) halogenations. The enzyme failed to oxidize polymers such as polyethylene glycol (PEG). Mechanistic studies with several model substrates provided information about the reaction cycle of AaeAPO: (1) stoichiometry of tetrahydrofuran cleavage showed that the reaction was a two-electron oxidation that generated one aldehyde group and one alcohol group, yielding the ring-opened product 4-hydroxybutanal, (2) steady-state kinetics results with methyl 3,4-dimethoxybenzyl ether, which was oxidized to 3,4-dimethoxybenzaldehyde, gave parallel double reciprocal plots suggestive of a ping-pong mechanism, (3) the cleavage of methyl 4-nitrobenzyl ether, the hydroxylation of aromatics such as diclofenac and nitrophenol and the oxygenation of benzylic compounds, resulted in incorporation of 18O into the reaction product in the presence of H218O2, and (4) the demethylation of 1-methoxy-4-trideuteromethoxybenzene showed an distinct observed intramolecular deuterium isotope effect. These results support a mechanism similar to that envisaged for the peroxygenase activity of P450s in which the enzyme heme is oxidized by H2O2 to give an iron species that carries one of the peroxide oxygen. This intermediate then abstracts a hydrogen from the substrate, which is followed by rebound of an •OH equivalent to produce the monooxygenated reaction product (hydrogen abstraction and oxygen rebound mechanism). AaeAPO may accordingly have a role in the biodegradation of natural and anthropogenic low molecular weight compounds in soils and plant litter. Moreover, the results raise the possibility that fungal peroxygenases may be useful for versatile, cost-effective, and scalable syntheses of drug metabolites and herbicide precursors
Die Peroxygenase des Südlichen Ackerling (Agrocybe aegerita, AaeAPO) wurde gereinigt, ihr Katalysepotential ermittelt und ein allgemeiner Reaktionsmechanismus postuliert. Die AaeAPO katalysiert sowohl H2O2-abhängige Monooxygenierungen (Zwei-Elektron Oxidationen) wie (a) die Spaltung aliphatischer und aromatischer Ether, (b) die regio- und enantioselektive Hydroxylierung von Aromaten, (c) die schrittweise Monooxygenierung von Toluolderivaten, (d) die N-Dealkylierung sekundärer Amine und (e) die Dehalogenierung chlorierter Aliphaten als auch typische Reaktionen bekannter Peroxidasen (vermutlich Ein-Elektron-Oxidation) unter anderem (f) die Oxidation/ Polymerisierung von Phenolen und (g) die Halogenierung von Aromaten. Polymere Verbindungen wie Polyethylenglycol (PEG) werden nicht oxidiert. Mechanistische Untersuchungen zur Etherspaltung am Beispiel der AaeAPO haben Einblick in den generellen Reaktionsmechanismus dieses neuen Enzymtyps ermöglicht: (1) die Stöchiometrie der Spaltung von Tetrahydrofuran entspricht der einer zwei-Elektron-Oxidation, (2) die Spaltung von Methyl-3,4-Dimethoxybenzylether zu 4-Dimethoxybenzaldehyd und Methanol ergaben parallele Verläufe für die ermittelten Ausgleichsgeraden in der doppelt reziproken Darstellung, was einem „Ping-Pong“-Reaktionsmechanismus entspricht (3) die Monooxygenierungen haben stets den Einbau eines aus dem Peroxid (H2O2) stammenden Sauerstoffatoms in das Produkt zur Folge, (4) die O-Dealkylierung von 1-Methoxy-4-Trideuterummethoxybenzol zeigt einen ausgeprägten Deuterium Isotopen Effekt, was auf die primäre Abspaltung eines Wasserstoffatoms vom Substratmolekül hindeutet. Demnach verläuft die Peroxygenase-katalysierte Monooxygenierung über Wasserstoffabstraktion und eine unmittelbar anschließende Sauerstoffrückbindung (hydrogen abstraction - oxygen rebound mechanism). Diese Reaktionsabfolge ähnelt dem sogenannten peroxide "shunt" pathway, der von einer Reihe Cytochrom-P450-abhängiger Monooxygenasen her bekannt ist. Die physiologische Funktion der AaeAPO besteht möglicherweise in der extrazellulären Transformation und Detoxifikation niedermolekularer Pflanzeninhaltsstoffe, mikrobieller Metabolite und anthropogener Xenobiotika. Aufgrund der Stabilität und Unabhängigkeit der AaeAPO von teuren Kofaktoren ergeben sich vielversprechende biotechnologische Möglichkeiten zum Einsatz isolierter Biokatalysatoren in selektiven (bio)chemischen Synthesen monooxygenierter Metabolite
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SUAREZ, BERTOA RICARDO. « Sustainable procedures in organic synthesis ». Doctoral thesis, Università degli Studi di Milano-Bicocca, 2009. http://hdl.handle.net/10281/7474.

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O-acyl-N-benzyllactamides are obtained in good yield by reaction of 4-benzyl-5-methyl-1,3-oxazolidine-2,4-diones with Grignards reagents and with lithium alkyls. Three alkanes and two ethers were oxidised with ozone in dichloromethane solution or in aqueous pH 3 suspension. Cyclodecane and cyclododecane were converted into the corresponding cycloalkanones. n-decane was converted into a mixture of isomeric n-decanones and carboxylic acids. An ester was formed from the ethers. Hence, one of the methylene groups of these substrates is generally converted into a carbonyl group. Some of these reactions have preparative value. The oxidation of naphthalene in dichloromethane or acetonitrile with excess ozone gives phthalic aldehyde, 2-formyl benzoic acid and phthalic anhydride. Small amounts of the (E)- and (Z)-isomer of 3-phenyl-(2-formyl)-propenal and are also observed in some cases. The reaction is faster in acetonitrile than in dichloromethane owing to the higher solubility of ozone in the former solvent. The reaction is faster on lowering the temperature because of the increase of the concentration of ozone in solution at lower temperature. With a 1:1 or a 1:2 naphthalene:ozone ratio high conversion and low selectivity for the anhydride is observed. The ozonation of cyclohexane in dichloromethane or acetonitrile gives cycloxexanone, cyclohexanol and acidic material. The influence of solvent, reactant concentration, amount of ozone, temperature, reaction time is studied. A reaction mechanism is proposed based on the results of a simulation of the reaction energetics. The ozonation of N-phenylmorpholine in dichloromethane or acetonitrile produced a lactame and a diformylderivative. These products derive from the attack of ozone at the heterocyclic ring. The reaction mechanism has been investigated by DFT calculations which show that the reaction occurs through the insertion of ozone at the carbon-hydrogen bond of a methylenic group of the morpholine ring. The regioselectivity is due to the to the significantly lower energy barrier calculated for the attack of ozone in α to nitrogen than in α to oxygen. Also, the energy barrier decreases with increasing the polarity of the solvent, accounting for the higher reaction rate observed for the reaction carried out in acetonitrile than in dichloromethane. The ozonation of trans- and cis-decalin in dichloromethane or acetonitrile gives the corresponding 9-hydroxydecalinns, 2- and 3-decalones and acidic material. The influence of solvent, reactant concentration, amount of ozone, temperature, reaction time is studied. A reaction mechanism is proposed based on the results of a simulation of the reaction energetics. The N,N bis(salicylidene)ethylenediaminocobalt(II) catalysed oxidative carbonylation of para-substituted aromatic primary amines at 100 °C in methanol gives carbamates in high yields. In presence of excess dimethylamine also N-aryl-N’,N’-dimethylureas are formed. In methylene chloride moderate yields in isocyanate are obtained. 1-methylbenzylamine gives the carbamate and the urea in high yield. i-propylamine gives only the urea. An α-aminoalcohol gives a 1,3-oxazolidin-2-one. Aliphatic secondary amines react faster and give carbamates in methanol and ureas in methylene chloride. The turnover frequency is also measured in two cases.
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Chapitres de livres sur le sujet "Ether oxygenation"

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Taber, Douglass F. « The Sato/Chida Synthesis of Paclitaxel (Taxol®) ». Dans Organic Synthesis. Oxford University Press, 2017. http://dx.doi.org/10.1093/oso/9780190646165.003.0104.

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Paclitaxel (Taxol®) 3 is widely used in the clinical treatment of a variety of cancers. Takaaki Sato and Noritaka Chida of Keio University envisioned (Org. Lett. 2015, 17, 2570, 2574) establishing the central eight-membered ring of 3 by the SmI2-mediated cyclization of 1 to 2. The starting point for the synthesis was the enantiomerically-pure enone 5, pre­pared from the carbohydrate precursor 4. Conjugate addition to 5 proceeded anti to the benzyloxy substituent to give, after trapping with formaldehyde and protection, the ketone 6. Reduction and protection followed by hydroboration led to 7, that was, after protection and deprotection, oxidized to 8. The second ring of 3 was added in the form of the alkenyl lithium derivative 9, prepared from the trisylhydrazone of the corresponding ketone. Hydroxyl-directed epoxidation of 10 proceeded with high facial selectivity, leading, after reduction and protection, to the cyclic carbonate 11. Allylic oxidation converted the alkene into the enone, while at the same time oxidizing the benzyl protecting group to the ben­zoate, to give 12. Reduction of the ketone 12 led to a mixture of diastereomers. In practice, only one of the diastereomers of 1 cyclized cleanly to 2, as illustrated, so the undesired diastereomer from the NaBH4 reduction was oxidized back to the enone for recycling. For convenience, only one of the diastereomers of 2 was carried forward. To establish the tetrasubstituted alkene of 3, the alkene of 2 was converted to the cis diol and on to the bis xanthate 13. Warming to 50°C led to the desired tet­rasubstituted alkene, sparing the oxygenation that is eventually required for 3. For convenience, to intercept 16, the intermediate in the Takahashi total synthesis, both xanthates were eliminated to give 14. Hydrogenation removed the disubsti­tuted alkene, and also deprotected the benzyl ether. Oxidation followed by Peterson alkene formation led to 15, that was carried on to the Takahashi intermediate 16 using the now-standard protocol for oxetane construction. It is a measure of the strength of the science of organic synthesis that Masahisa Nakada of Waseda University also reported (Chem. Eur. J. 2015, 21, 355) an elegant synthesis of 3 (not illustrated).
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Taber, Douglass. « Enantioselective Assembly of Alkylated Stereogenic Centers ». Dans Organic Synthesis. Oxford University Press, 2011. http://dx.doi.org/10.1093/oso/9780199764549.003.0037.

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Oxygenated secondary stereogenic centers are readily available. There is a limited range of carbon nucleophiles that will displace a secondary leaving group in high yield with clean inversion. Teruaki Mukaiyama of the Kitasato Institute has described (Chem. Lett. 2007, 36, 2) an elegant addition to this list. Phosphinites such as 1 are easily prepared from the corresponding alcohols. Quinone oxidation in the presence of a nucleophile led via efficient displacement to the coupled product 2. The sulfone could be reduced with SmI2 to give 3. Enantioselective reduction of trisubstituted alkenes is also a powerful method for establishing alkylated stereogenic centers. Juan C. Carretero of the Universidad Autonoma de Madrid has found (Angew. Chem. Int. Ed. 2007, 46, 3329) that the enantioselective reduction of unsaturated pyridyl sulfones such as 4 was directed by the sulfone, so the other geometric isomer of 4 gave the opposite enantiomer of 5. The protected hydroxy sulfone 5 is a versatile chiral building block. Samuel H. Gellman of the University of Wisconsin has reported (J. Am. Chem. Soc. 2007, 129, 6050) an improved procedure for the aminomethylation of aldehydes. L-Proline-catalyzed condensation with the matched α-methyl benzylamine derivavative 7 gave the aldehyde, which was immediately reduced to the alcohol 8 to avoid racemization. The amino alcohol 8 was easily separated in diastereomerically-pure form. In the past, aldehydes have been efficiently α-alkylated using two-electron chemistry. David W. C. Macmillan of Princeton University has developed (Science 2007, 316, 582; J. Am. Chem. Soc. 2007, 129, 7004) a one-electron alternative. The organocatalyst 9 formed an imine with the aldehyde. One-electron oxidation led to an α-radical, which was trapped by the allyl silane (or, not pictured, a silyl enol ether) leading to the α-alkylated aldehyde 10. This is mechnistically related to the work reported independently by Mukund P. Sibi (J. Am. Chem. Soc. 2007, 129, 4124; OHL Feb. 11, 2008) on one-electron α-oxygenation of aldehydes. Secondary alkylated centers can also be prepared by SN2’ alkylation of prochiral substrates such as 11. Ben L. Feringa of the University of Groningen has shown (J. Org. Chem. 2007, 72, 2558) that the displacement proceeded with high ee even with conventional Grignard reagents.
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Taber, Douglass F. « The Trost Synthesis of (-)-Pseudolaric Acid B ». Dans Organic Synthesis. Oxford University Press, 2013. http://dx.doi.org/10.1093/oso/9780199965724.003.0085.

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(-)-Pseudolaric acid B 3, isolated from the bark of the golden larch Pseudolarix kaempferi, shows potent antifungal activity. A key step in the total synthesis of 3 described (J. Am. Chem. Soc. 2008 , 130 , 16424) by Barry M. Trost of Stanford University was the free radical cyclization of 1 that established the angular ester and the trans ring fusion of 2 and thus of 3. To prepare the bicyclic skeleton of 1, the authors envisioned the Rh-mediated intramolecular addition of the alkyne of 11 to the alkenyl cyclopropane. The acyclic centers of 11 were established by Noyori hydrogenation of (equilibrating) racemic 4. One enantiomer reduced much more quickly than the other, leading to 5. The absolute configuration of the cyclopropane was set by Charette cyclopropanation of the monosilyl ether of the inexpensive diol 8. The two components were then coupled using a Corey-Schlosser protocol. Alkylation of the ylide 10 with 7 gave a new phosphonium salt, which in situ was deprotonated and condensed with the aldehyde 9 . The resulting betaine was deprotonated and quenched, then exposed again to base to give the trans alkene 11. It is important in this procedure to use PhLi as the base, because the alkyl lithium can displace the alkyl group on phosphorus. The product from Ru-catalyzed cyclization was the expected 1,4-diene 12 . Fortunately, it was found that TBAF desilylation led to concomitant alkene migration, to give the more stable conjugated diene 13. Selective epoxidation of the more electron-rich alkene fol lowed by exposure to strong base then delivered 14 , with the requisite angular oxygenation established. Pseudolaric acid B 3 would be derived from cyclization of the selenocarbonate of a tertiary alcohol. In fact, however, attempted cyclization of such selenocarbonates led only to decarboxyation and reduction. Even with the selenocarbonate 1 prepared from the secondary alcohol, the cyclization to 2 required careful optimization, including using not AIBN but azobis(dicyclohexylcarbonitrile) as the radical initiator. Acetylide addition to the ketone 15 could be effected with high diastereocontrol, but lactone construction proved elusive. Alkaline conditions led quickly to addition of the angular hydroxyl to the activated alkene in the seven-membered ring.
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Bressan, M., et A. Morvillo. « Ruthenium (II) Catalysts for the Homogeneous Oxygenation of Aliphatic Hydrocarbons and Ethers ». Dans New Developments in Selective Oxidation, 119–24. Elsevier, 1990. http://dx.doi.org/10.1016/s0167-2991(08)60140-8.

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Actes de conférences sur le sujet "Ether oxygenation"

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Gonzalez, Uriel, et Isaac Schifter. « Oxygenated fuels properties and its relationship with engine performance in port fuel injection engines. » Dans ILASS2017 - 28th European Conference on Liquid Atomization and Spray Systems. Valencia : Universitat Politècnica València, 2017. http://dx.doi.org/10.4995/ilass2017.2017.4855.

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Gasoline oxygenating agents (alcohols, ethers and a carbonate) were used to formulate gasoline at different oxygencontents up to 20 wt.% and compared with commercial Premium gasoline.The performance of each fuel was investigated in a port fuel injected, single cylinder, spark-ignited engine at different stages i.e. air fuel mixture preparation, combustion behavior and exhaust emissions. In all cases, the intake cooling effect (related mainly to fuel properties like latent heat of vaporization and Reid Vapor Pressure), shows an important relationship with engine performance and emissions, probably due to reductions in heat losses associated with decreases in charge temperature at compression stroke before ignition. This results was confirmed by means of vehicle FTP-75 test.The high RVP promotes high intake manifold evaporation rate, and the high HoV is related to important cooling effect as the fuel absorbs heat during evaporation. If the fuel evaporates faster upstream intake valves, the advantages of high HoV as a way to reduce compression work and heat transfer fallen.The quantification of the charge cooling effect was done by means of precision intake air temperature control and the instrumentation of a temperature downstream the injector at intake port and as close as possible to the intake valves.The use of oxygenates reduce the hydrogen and carbon fuel contents as a result of fuel dilution. For a given level of oxygenation as lower is the molecular oxygen content in the additive, higher will be the fuel dilution.For 10 wt.% oxygen and more, fuel performance in port engines depends mainly on oxygenate contents and its relationship with HoV and RVP. For oxygenated gasolines, fuel sensitivity have a direct relationship with latent heatls increase RON. In the other hand, MON is almostinsensible to high heat of vaporization, because the intake air is heated to 159 C as a test requirement.DOI: http://dx.doi.org/10.4995/ILASS2017.2017.4855
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