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Oxidation System (oxidation + system)
Selected AbstractsSelective Aerobic Oxidation of Benzylic Alcohols Catalyzed by Carbon-Based Catalysts: A Nonmetallic Oxidation System,ANGEWANDTE CHEMIE, Issue 2 2010Yongbo Kuang Anstelle von Übergangsmetallen kann Kohlenstoff zur selektiven aeroben Oxidation von Benzylalkoholen eingesetzt werden. Das Additiv HNO3 aktiviert einen Kohlenstoffkatalysator mit Nanoschalenstruktur (NSC), der als primäres Oxidationsmittel für den Alkohol dient, und wird durch O2 regeneriert. [source] A New and Highly Effective Method for Catalytic Oxidation of Alcohols to the Corresponding Carbonyl Compounds Using the Tris[(2-oxazolinyl)phenolato] manganese(III)/Oxone®/n-Bu4NBr Oxidation System.CHEMINFORM, Issue 12 2004Mojtaba Bagherzadeh Abstract For Abstract see ChemInform Abstract in Full Text. [source] Catalytic cleavage of methyl oleate or oleic acidEUROPEAN JOURNAL OF LIPID SCIENCE AND TECHNOLOGY, Issue 1 2010Angela Köckritz Abstract Different reaction pathways are discussed for the Os-catalyzed oxidation of methyl oleate and oleic acid using O2/aldehyde as oxidation system. Monomethyl azelate and pelargonic acid were the main products obtained in yields of approximately 50,70% starting from methyl oleate. Besides, varying amounts of methyl 9,10-epoxystearate and methyl 9,10-dihydroxystearate were found as by-products. Azelaic acid and pelargonic acid were obtained exclusively from oleic acid used as reactant. Some mechanistic considerations led to the conclusion that the observed products are formed in parallel reaction paths. The effective oxidant for the scission of the C=C double bond seems to be very likely an in situ formed peracid generated by Os-catalysis from O2/aldehyde. Additional investigations concerning the cleavage of oleic acid and methyl oleate with in situ formed performic acid from H2O2/formic acid corroborate this assumption. [source] Inhibition of lipid peroxidation by anthocyanins, anthocyanidins and their phenolic degradation productsEUROPEAN JOURNAL OF LIPID SCIENCE AND TECHNOLOGY, Issue 1 2007Jonathan E. Brown Abstract Food components that delay or prevent biomolecule oxidation may be relevant in shelf life extension as well as disease prevention. Anthocyanins are a potentially important group of compounds, but they are prone to degradation both in vitro and in vivo, producing simple phenols. In this study, eight structurally related (poly)phenols [anthocyan(id)ins and phenolic acids] were examined for their ability to inhibit lipid oxidation at physiologically relevant concentrations (100,1000,nM) using the Cu2+ -mediated low-density lipoprotein oxidation model. Interaction between each (poly)phenol and Cu2+ ions was also investigated. (Poly)phenols with an ortho -dihydroxy group arrangement, i.e. cyanidin-3-glucoside, cyanidin and protocatechuic acid, were the most effective within their class, extending the lag phase to oxidation by 137, 255 and 402%, respectively (at 1000,nM). At the same concentration, trihydroxy-substituted compounds (delphinidin and gallic acid) were of intermediate efficacy, extending the lag phase by 175 and 38%, respectively. Compounds with the 4'-hydroxy-3',5'-methoxy arrangement (i.e. malvidin-3-glucoside and malvidin) were the least effective (3 and 58% extension, respectively), while syringic acid (4-hydroxy-3,5-dihydroxy benzoic acid) was pro-oxidant (lag phase shortened by 31%). (Poly)phenols with the ortho -dihydroxy arrangement chelated Cu2+ ions, which in part explains their greater efficacy over the other (poly)phenols in this model oxidation system. However, differences in their hydrogen-donating properties and their partitioning between lipid and hydrophilic phases are also relevant in explaining these structure-activity relationships. [source] Role of phenoxy radicals in PCDD/F formationINTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 9 2002Sukh Sidhu In this work, the role of phenoxy radicals in polychlorinated dibenzo- p -dioxins and polychlorinated dibenzofurans (PCDD/F) formation was investigated by studying the slow oxidation of 2-chlorophenol (2-CP) and 2-chloroanisole (2-CA) at a gas-phase concentration of 4 ppm (,2.1 × 104 ,g/m3) over a temperature range of 400,800°C. Residence times were maintained at 2.0 ± 0.10 s. PCDD/F reaction products were dibenzofuran, dibenzo- p -dioxin, 4-chlorodibenzofuran, 1-chlorodibenzo- p -dioxin, 4,6-dichlorodibenzofuran, and 1,6-dichlorodibenzo- p -dioxin (1,6-DCDD). Major products observed in these experiments were 2,6-dichlorophenol, 3-phenyl-2-propenal, 1-indanone, 1,3-isobenzofurandione, and 3-phenyl-2-propenoyl chloride. The 2-CP and 2-CA experiments, along with the variable concentration 2-CA experiments, showed that the concentration of radicals present in the oxidation system has a significant effect on the PCDD/F product distribution and ultimately the PCDD/PCDF ratio. Also, the observation of dichlorinated phenoxy phenol and dichlorinated dihydroxybiphenyl, the proposed intermediate species in the radical,radical mechanism, suggests that radical,radical mechanism dominates gas-phase PCDD/F formation. This information will be helpful in constructing a detailed kinetic mechanism of PCDD/F formation/destruction in combustor postcombustion zone. © 2002 Wiley Periodicals, Inc. Int J Chem Kinet 34: 531,541, 2002 [source] Degradation of isooctane by Mycobacterium austroafricanum IFP 2173: growth and catabolic pathwayJOURNAL OF APPLIED MICROBIOLOGY, Issue 3 2004F. Solano-Serena Abstract Aims:, Isooctane (2,2,4-trimethylpentane), a major component of gasoline formulations, is recalcitrant to biodegradation probably because of the quaternary carbon group it contains. Information on the biodegradability of this hydrocarbon is essential to evaluate its fate in the environment. For these reasons, the degradation kinetics and the catabolic pathway of isooctane were investigated in Mycobacterium austroafricanum IFP 2173, the only strain characterized to use it as sole carbon and energy source. Methods and Results:, The selected strain exhibited a rather moderate maximum growth rate (,max = 0·053 h,1) but degraded isooctane up to 99% with a mineralization yield of 45%, indicating attack of the quaternary carbon group. The GC/MS identification of metabolites, 2,4,4-trimethylpentanoic and dimethylpropanoic (pivalic) acids, which transiently accumulated in the cultures indicated that degradation started from the isopropyl extremity of the molecule and subsequently proceeded by catabolism of the tert -butyl moiety. The degradation of putative metabolic intermediates was investigated. The initial isooctane oxidation system was tentatively characterized. Conclusions:, The isooctane-degrading strain harboured two candidate systems for initial alkane oxidation. Although a cytochrome P450 was induced by isooctane degradation, the functional oxidation system was probably a nonheme alkane monooxygenase as indicated by PCR amplification and RT-PCR expression of an alkB gene. Significance and Impact of the Study:, Isooctane is a recalcitrant branched alkane. A plausible pathway of its degradation by Myco. austroafricanum was put forward. [source] The influence of selenium on the antioxidant activity of green teaJOURNAL OF THE SCIENCE OF FOOD AND AGRICULTURE, Issue 5 2003Juan Xu Abstract This study was aimed at determining the effects of selenium on the contents of vitamin C, amino acid, total water-soluble solids and tea polyphenol, and whether the antioxidant activity of selenium-enriched green tea is enhanced compared with regular green tea by linoleic acid oxidation and the lard oxidation method. The contents of selenium, vitamin C and tea polyphenol in green teas were greatly increased by foliar application of selenium-enriched fertilizer. No significant differences of the contents of vitamin C, amino acid and tea polyphenol were observed between green tea treated with sodium selenite and that without selenium. The selenium-enriched green tea exhibited significantly higher antioxidant activity than regular green tea, both in linoleic acid oxidation and in the lard oxidation system. These results suggest that the antioxidant activity of green tea is significantly enhanced by the combination of selenium and green tea constituents compared with that of regular green tea. Copyright © 2003 Society of Chemical Industry [source] Ionic liquid-H2O Resulting in a Highly Chemoselective Oxidation of Benzylic Alcohols in the Presence of Aliphatic Analogues Catalyzed by Immobilized TEMPOCHINESE JOURNAL OF CHEMISTRY, Issue 3 2009Ruijun HU Abstract In ionic liquid 1-butyl-3-methylimidazolium hexafluorophosphate ([bmim][PF6])-H2O, a highly chemoselective oxidation of benzylic alcohols in the presence of aliphatic ones to the corresponding hydroxyl benzyl aldehydes and ketones was allowed in high yields using N -chlorosuccinimide (NCS)/NaBr/IL-TEMPO (ionic liquid immobilized 2,2,6,6-tetramethylpiperidine-1-oxyl) as a facile and effective catalytic oxidation system. The medium, [bmim][PF6], together with the catalyst IL-TEMPO could be easily recycled for ten runs without any influence on the efficacy of the reaction in terms of yield and selectivity of the product. [source] Comparison between photocatalytic ozonation and other oxidation processes for the removal of phenols from waterJOURNAL OF CHEMICAL TECHNOLOGY & BIOTECHNOLOGY, Issue 9 2005Fernando J Beltrán Abstract Photocatalytic ozonation (1O3 + VUV + TiO2), ozonation (O3), catalytic ozonation (O3 + TiO2), ozone photolysis (O3 + VUV), photocatalysis (TiO2 + VUV) and photolysis (VUV) have been compared in terms of formation of intermediates, extent of, mineralization (TOC, COD, chloride, nitrate) and kinetics in the aqueous treatment of three phenols (phenol, p -chlorophenol and p -nitrophenol). In all cases, photocatalytic ozonation led to lower degradation times for chemical oxygen demand and total organic carbon removal. Intermediates formed were similar in the different oxidation systems with some exceptions. They can be classified into three different types: polyphenols (resorcinol, catechol, hydroquinone), unsaturated carboxylic acids (maleic and fumaric acids) and saturated carboxylic acids (glyoxylic, formic and oxalic acids). First order kinetic equations have been checked for the oxidation processes studied in the case of the parent compound. Rate constants of these systems have also been calculated. Copyright © 2005 Society of Chemical Industry [source] Highly Efficient Biomimetic Oxidation of Sulfide to Sulfone by Hydrogen Peroxide in the Presence of Manganese meso -TetraphenylporphyrinCHINESE JOURNAL OF CHEMISTRY, Issue 6 2008Xian-Tai ZHOU Abstract Low amount of manganese meso -tetraphenyl porphyrin [Mn(TPP)] was used for highly efficient selective oxidation of sulfide to sulfone by hydrogen peroxide at room temperature. Sulfones were produced directly with yields generally around 90% while the catalyst concentration was only 4×10,5 mol·L,1. In a large-scale experiment of thioanisole oxidation, the isolated yield of sulfone (87%) was obtained and the turnover number (TON) reached up to 8×106, which is the highest TON for the oxidation systems of sulfide to sulfone catalyzed by metalloporphyrins. [source] | |||||||||||||