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Air Oxidation (air + oxidation)
Kinds of Air Oxidation Selected AbstractsMetal-Free Air Oxidation of Thiols in Recyclable Ionic Liquid: A Simple and Efficient Method for the Synthesis of DisulfidesEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 14 2010Devender Singh Abstract An efficient procedure for the oxidative coupling of alkyl, aryl and heteroaryl thiols with atmospheric oxygen is reported. The methodology utilizes BMIM-BF4 as a recyclable solvent and does not require support materials or metal salts. Symmetric disulfides are obtained in excellent yields. [source] Contact allergy caused by air oxidation of common materials , diagnosis and preventionCONTACT DERMATITIS, Issue 3 2004Ann-Therese Karlberg When considering the allergenic activity of a compound not only the possibility of bioactivation by skin metabolism but also air activation by autoxidation must be taken into account. Natural compounds (terpenes) easily oxidize at air exposure. They are found in products that are common causes of allergic contact dermatitis (ACD) i.e. colophony and fragrances. The introduction of oxygen enables the molecules to form antigens with skin proteins via a nucleophilic- electrophilic interaction or via a radical reaction. The latter mechanism seems to be important since the primary oxidation products, the hydroperoxides, are the most potent sensitizers formed. Oxidative decomposition at air exposure resulting in allergenic oxidation products is observed also for other common compounds e.g. ethoxylated fatty alcohols used as surfactants. It is important to test the patient with the offending compounds for diagnosis of ACD. A negative diagnosis can be due to failure in testing with the correct substances. In the case of air activated compounds, testing should not be performed with the pure substances but rather with the oxidation mixture or the most sensitizing oxidation products (the hydroperoxides). We have in multicenter-studies shown that the common fragrance terpenes, limonene and linalool, are frequent sensitizers when oxidized. This is a challenge in clinical practice since such patch test materials are not easily standardized. Compounds, easily activated at air exposure, should be prevented from oxidative decomposition by addition of antioxidants and proper handling and storage. More research is needed in this area. [source] Synthesis and Characterization of Hypervalent Organoantimony(III) Compounds Containing the [2-(Me2NCH2)C6H4]2Sb FragmentEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 9 2009Laura M. Opris Abstract Compounds containing the [2-(Me2NCH2)C6H4]2Sb moiety were prepared by using R2SbX [X = Cl (1), Br (2)] as starting materials. The reaction of 1 with Me3SiCH2MgCl gave the mixed alkyl,aryl stibine R2SbCH2SiMe3 (3). Reduction of 2 with Mg in thf followed by in situ air oxidation or treatment with S8 resulted in the isolation of (R2Sb)2E [E = O (4), S (5)]. Compound 5 is also formed from R2SbCl and Na2S. The reaction of 4 with [W(CO)5(thf)] gives the unexpected complex [(R2SbOH)W(CO)5] (6). The new compounds were investigated by IR, 1H, and 13C NMR spectroscopy, as well as by mass spectrometry. The structures of 3,6 were determined by single-crystal X-ray diffraction. For compounds 3,5, both nitrogen atoms from the pendant arms are involved in intramolecular N,Sb coordination, which results in distorted square-pyramidal (C,N)2SbC or (C,N)2SbE (E = O, S) cores. By contrast, in 6 only one nitrogen atom is strongly coordinated to the antimony center, whereas the second nitrogen atom is involved in N···H,O bonding. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009) [source] High-Surface-Area Nanoporous Boron Carbon Nitrides for Hydrogen StorageADVANCED FUNCTIONAL MATERIALS, Issue 11 2010David Portehault Abstract Nano- and mesoporous boron carbon nitrides with very high surface areas up to 1560,m2,g,1 are obtained by pyrolysis of a graphitic carbon nitride mpg-C3N4 infiltrated with a borane complex. This reactive hard-templating approach provides easy composition and texture tuning by temperature adjustment between 800 and 1400,°C. The process yields BxCyNzOvHw materials as direct copies of the initial template with controlled compositions of 0.15,,,x,,,0.36, 0.10,,,y,,,0.12, 0.14,,,z,,, 0.32, and 0.11,,,v,,,0.28. The nano and mesoporosities can also be tuned in order to provide hierarchical materials with specific surface areas ranging from 610 to 1560,m2,g,1. Such high values, coupled with resistance against air oxidation up to 700,°C, suggest potential materials for gas storage and as catalyst supports. Indeed, it is demonstrated that these compounds exhibit high and tunable H2 uptakes from 0.55 to 1.07,wt.% at 77,K and 1 bar, thus guiding further search of materials for hydrogen storage. [source] Luminescent Colloidal Dispersion of Silicon Quantum Dots from Microwave Plasma Synthesis: Exploring the Photoluminescence Behavior Across the Visible SpectrumADVANCED FUNCTIONAL MATERIALS, Issue 5 2009Anoop Gupta Abstract Aiming for a more practical route to highly stable visible photoluminescence (PL) from silicon, a novel approach to produce luminescent silicon nanoparticles (Si-NPs) is developed. Single crystalline Si-NPs are synthesized by pyrolysis of silane (SiH4) in a microwave plasma reactor at very high production rates (0.1,10,g,h,1). The emission wavelength of the Si-NPs is controlled by etching them in a mixture of hydrofluoric acid and nitric acid. Emission across the entire visible spectrum is obtained by varying the etching time. It is observed that the air oxidation of the etched Si-NPs profoundly affects their optical properties, and causes their emission to blue-shift and diminish in intensity with time. Modification of the silicon surface by UV-induced hydrosilylation also causes a shift in the spectrum. The nature of the shift (red/blue) is dependent on the emission wavelength of the etched Si-NPs. In addition, the amount of shift depends on the type of organic ligand on the silicon surface and the UV exposure time. The surface modification of Si-NPs with different alkenes results in highly stable PL and allows their dispersion in a variety of organic solvents. This method of producing macroscopic quantities of Si-NPs with very high PL stability opens new avenues to applications of silicon quantum dots in optoelectronic and biological fields, and paves the way towards their commercialization. [source] Catalytic wet air oxidation of phenol using active carbon: performance of discontinuous and continuous reactorsJOURNAL OF CHEMICAL TECHNOLOGY & BIOTECHNOLOGY, Issue 7 2001Frank Stüber Abstract Catalytic wet air oxidation (CWAO) of an aqueous phenol solution using active carbon (AC) as catalytic material was compared for a slurry and trickle bed reactor. Semi-batchwise experiments were carried out in a slurry reactor in the absence of external and internal mass transfer. Trickle-bed runs were conducted under the same conditions of temperature and pressure. Experimental results from the slurry reactor study showed that the phenol removal rate significantly increased with temperature and phenol concentration, whereas partial oxygen pressure had little effect. Thus, at conditions of 160,°C and 0.71,MPa of oxygen partial pressure, almost complete phenol elimination was achieved within 2,h for an initial phenol concentration of 2.5,g,dm,3. Under the same conditions of temperature and pressure, the slurry reactor performed at much higher initial rates with respect to phenol removal than the trickle bed reactor, both for a fresh active carbon and an aged active carbon, previously used for 50,h in the trickle bed reactor, but mineralisation was found to be much lower in the slurry reactor. Mass transfer limitations, ineffective catalyst wetting or preferential flow in the trickle bed alone cannot explain the drastic difference in the phenol removal rate. It is likely that the slurry system also greatly favours the formation of condensation polymers followed by their irreversible adsorption onto the AC surface, thereby progressively preventing the phenol molecules to be oxidised. Thus, the application of this type of reactor in CWAO has to be seriously questioned when aiming at complete mineralisation of phenol. Furthermore, any kinetic study of phenol oxidation conducted in a batch slurry reactor may not be useful for the design and scale-up of a continuous trickle bed reactor. © 2001 Society of Chemical Industry [source] Oxidation of bisnaphthols to spironaphthalenones, revisitedJOURNAL OF HETEROCYCLIC CHEMISTRY, Issue 5 2008Ahmad Khoramabadi-Zad Bis(2-hydroxy-1-naphthyl)methane derivatives have been efficiently converted to their corresponding spirans through three methods, i.e. oxidation by TCCA under mild reaction conditions, Ph3Bi catalyzed air oxidation, and by electrochemical reaction. The first two methods are diastereoselective and give either of the two possible diastereomers, while the electrochemical method produces equal amounts of these diastereomers. [source] The Effect of Adding Phosphate on the Size of Extremely Fine Needle-like Lepidocrocite Particles Prepared by Oxidizing an Aqueous Suspension of Ferrous HydroxideTHE CANADIAN JOURNAL OF CHEMICAL ENGINEERING, Issue 4 2002Naoki Mihara Abstract Extremely fine particles of needle-like lepidocrocite (,-FeOOH) were synthesized by the oxidation of aqueous suspensions of ferrous hydroxide using a bubble column with draft tube at a constant temperature of 30°C, and the effects of the reaction conditions or the oxidation rate were investigated in order to determine the parameters that control the particle size. When the concentration of oxygen in the feed stream was varied under a constant gas velocity, the mean size based on the major axis of a needle-like particle decreased from 0.7 µm to 0.4 µm with increasing oxidation rate. By adding of NaH2PO4 to an aqueous Fe(OH)2 suspension, in concentrations up to 1.0 mol/m3 during the air oxidation, and up to 0.9 mol/m3 during the oxidation with 30% and 50% O2, the major axis could be reduced to ca. 0.3 µm with the minor axis and the oxidation rate remained almost unchanged. Des particules extra fines de lépidocrocite en forme d'aiguilles (,-FeOOH) ont été synthétisées par oxydation de suspensions aqueuses d'hydroxide ferreux à l'aide d'une colonne munie d'un tube d'aspiration à une température constante de 30°C et on a étudié les effets des conditions de réaction et de la vitesse d'oxydation afin de déterminer les paramètres qui contrôlent la taille de particule. Lorsqu'on fait varier la concentration d'oxygène dans le courant d'alimentation à une vitesse de gaz constante, la taille moyenne basée sur l'axe principal d'une particule en forme d'aiguille diminue de 0,7 µm à 0,4 µm avec l'augmentation de la vitesse d'oxydation. En ajoutant du NaH2PO4 à une suspension aqueuse de Fe(OH)2, à des concentrations atteignant 1,0 mol/m3 lors de l'oxydation de l'air et 0,9 mol/m3 lors de l'oxydation avec 30% et 50% de O2, l'axe principal pourrait être réduit à environ 0,3 µm, l'axe secondaire et la vitesse d'oxydation demeurant presque inchangés. [source] Silicon nanoparticles with chemically tailored surfacesAPPLIED ORGANOMETALLIC CHEMISTRY, Issue 3 2010Andrew S. Heintz Abstract Silicon nanoparticles are useful materials for optoelectronic devices, solar cells and biological markers. The synthesis of air-stable nanoparticles with tunable optoelectronic properties is highly desirable. The mechanochemical synthesis of silicon nanoparticles via high-energy ball milling produces a variety of covalently bonded surfaces depending on the nature of the organic liquid used in the milling process. The use of the C8 reactants including octanoic acid, 1-octanol, 1-octaldehyde and 1-octene results in passivated surfaces characterized by strong SiC bonds or strong SiO bonds. The surfaces of the nanoparticles were characterized by infrared spectroscopy and nuclear magnetic resonance spectroscopy. The nanoparticles were soluble in common organic solvents and remarkably stable against agglomeration and air oxidation. The luminescence and optical properties of the nanoparticles were very sensitive to the nature of their passivating surface. Copyright © 2009 John Wiley & Sons, Ltd. [source] N -Malonyl-1,2-dihydroisoquinoline as a Novel Carrier for Specific Delivery of Drugs to the BrainARCHIV DER PHARMAZIE, Issue 1 2010Mohamed Abdel-Aziz Abstract N -Malonyl-1,2-dihydroisoquinoline derivatives were synthesized and investigated as a novel carrier system for site-specific and sustained delivery of drugs to the brain. Such carriers are expected to be stable against air oxidation due to the presence of the carbonyl group close to nitrogen of the dihydroisoquinoline. Reduction of the prepared isoquinolinium quaternary derivatives with sodium dithionite afforded a novel group of N -malonyl-1,2-dihydroisoquinoline chemical delivery systems (CDS). The synthesized N -malonyl-1,2-dihydroisoquinoline chemical delivery systems were subjected to various chemical and biological investigations to evaluate their ability to cross the blood-brain barrier (BBB), and to be oxidized biologically into their corresponding quaternary derivatives. The in-vitro oxidation studies showed that the designed N -malonyl-1,2-dihydroisoquinoline chemical delivery system could be oxidized into its corresponding quaternary derivatives at an adequate rate. The in-vivo distribution studies showed that these N -malonyl-1,2-dihydroisoquinoline chemical delivery systems were able to cross the blood-brain barrier at detectable concentrations. [source] Catalytic wet air oxidation of high-strength organic coking wastewaterASIA-PACIFIC JOURNAL OF CHEMICAL ENGINEERING, Issue 5 2009Lihua Han Abstract Catalytic wet air oxidation (CWAO) treatment of the high-strength organic coking wastewater over CeCu and CeMn catalysts were studied. The main factors affecting the activities of the catalysts were investigated. Experimental results showed that in the absence of rare-earth metal catalysts, CWAO process was also effective for high-strength organic coking wastewater treatment. The catalyst, prepared with the active component CuCe (2:1) and carried by ,-Al2O3/TiO2 calcined at 600 °C, has a higher activity. Up to 95.2% of the initial CODCr was removed at the reaction temperature of 180 °C and oxygen partial pressure of 1.2 MPa. The effect of the catalyst is equivalent to homogeneous catalysis improved by 60% over non-catalytic treatment. Copyright © 2009 Curtin University of Technology and John Wiley & Sons, Ltd. [source] Liquid phase mineralization of gel-type anion exchange resin by a hybrid process of Fenton dissolution followed by sonication and wet air oxidationASIA-PACIFIC JOURNAL OF CHEMICAL ENGINEERING, Issue 1 2009T. L. Gunale Abstract A hybrid process of Fenton dissolution followed by sonication and wet air oxidation (WAO), has been demonstrated to mineralize strongly basic anion exchange resin (gel type). The solid anion exchange resin beads could be dissolved in water by Fenton process wherein the copper-catalyzed hydrogen peroxide (H2O2) reaction makes the resin hydrophilic by the disintegration of polymer matrix. Sonication of the dissolved resin thus obtained made the waste stream more amenable to WAO. Parameters for Fenton dissolution and sonication were studied to aid effective mineralization by WAO. The kinetic studies of WAO were performed using copper sulfate (CuSO4) as the homogeneous catalyst, in the temperature range of 483,523 K. It is thus possible to address the disposal of solid ion exchange resin by the hybrid process, described here. Copyright © 2008 Curtin University of Technology and John Wiley & Sons, Ltd. [source] Effect of green tea catechins on oxidative DNA damage of hamster pancreas and liver induced by N-Nitrosobis(2-oxopropyl)amine and/or oxidized soybean oilBIOFACTORS, Issue 1-4 2004Fumiyo Takabayashi Abstract It has been indicated that high fat diet is a risk factor of the pancreatic cancer by epidemiological studies. We examined whether the oxidized soybean oil (ox-oil) express the synergistic effect on the formation of 8-ox O2,'-deoxyguanosine (8-oxodG) in nuclear DNA of hamster pancreas induced by N-Nitrosobis(2-oxopropyl)amine (BOP) and whether the green tea catechins (GTC) suppressed it. Ox-oil was prepared by air oxidation, and the content of lipid hydroperoxide was 6.22 mg/ml. Hamsters were administered 0.3,ml of ox-oil/day orally for 4 weeks before BOP treatment. GTC was given ad libitum as a 0.1% aqueous solution. Four hours after subcutaneous administration of BOP, hamsters were sacrificed, and the contents of 8-oxodG were measured in nuclear DNA of pancreas and liver. The 8-oxodG content in the pancreas was increased by BOP and/or ox-oil administration. However, it was not suppressed by an intake of GTC. In the liver, though the content of 8-oxodG was increased by ox-oil, it tended to suppress the rise of 8-oxodG by a GTC intake. These results suggested that the long term intake of ox-oil might have the possibility to induce carcinogenesis in hamster pancreas and liver, and an intake of GTC might have the beneficial effect on liver. [source] Synthesis and secondary structure of loop 4 of myelin proteolipid protein: effect of a point mutation found in Pelizaeus-Merzbacher diseaseCHEMICAL BIOLOGY & DRUG DESIGN, Issue 3 2005E. Trifilieff Abstract:, To study the effects of a point mutation found in Pelizaeus-Merzbacher disease (PMD) on the physicochemical and structural properties of the extracellular loop 4 of the myelin proteolipid protein (PLP), we synthesized the peptide PLP(181,230)Pro215 and one mutant PLP(181,230)Ser215 with regioselective formation of the two disulphide bridges Cys200 -Cys219 and Cys183 -Cys227. As conventional amino acid building blocks failed to give crude peptides of good quality we had to optimize the synthesis by introducing pseudoproline dipeptide building blocks during the peptide elongation. In peptide Pro215 the first bridge Cys200,Cys219 was obtained after air oxidation, but in peptide Ser215 because of aggregation, dimethyl sulfoxide (DMSO) oxidation had to be used. The second bridge Cys183,Cys227 was obtained by iodine oxidation of both Cys (acetamidomethyl, Acm)-protected peptides. The secondary structures of the parent and mutant loops were analysed by circular dichroism (CD) in the presence of trifluoroethanol (TFE) and sodium dodecyl sulphate (SDS) as a membrane mimetic. Analysis of the spectra showed that the content of , -helix and , -sheet varied differently for both peptides in TFE and SDS solutions, demonstrating the sensitivity of their conformation to the environment and the differences in their secondary structure. The ability of both peptides to insert into the SDS micelles was assayed by intrinsic tryptophan fluorescence. [source] Hydrolysis of an isolable selenoseleninate under acidic and alkaline conditionsHETEROATOM CHEMISTRY, Issue 4 2001Akihiko Ishii Acid-catalyzed hydrolysis of a selenoseleninate [TripSe(O)SeTrip](Trip = 9-triptycyl) in 2 M HClO4 -1,4-dioxane at room temperature yielded the selenenic acid (TripSeOH). Alkaline hydrolysis of TripSe(O)SeTrip gave the diselenide (TripSeSeTrip) and the seleninic acid (TripSeO2H), where air oxidations of the resulting selenol (TripSeH) and TripSeOH occur at a considerable rate. © 2001 John Wiley & Sons, Inc. Heteroatom Chem 12:198,203, 2001 [source] | |||||||||||||||||||||||||