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Please use this identifier to cite or link to this item: http://hdl.handle.net/2031/5435

Title: Lewis acid catalyzed oxidation of hydrocarbons by some metal-nitrido, oxo and peroxo complexes
Other Titles: Luyisi suan xie zhu de han dan, han yang ji han guo yang jin shu hua he wu cui hua yang hua tan qing hua he wu
路易斯酸協助的含氮, 含氧及含過氧金屬化合物催化氧化碳氫化合物
Authors: Tai, Kin Ying (戴健英)
Department: Department of Biology and Chemistry
Degree: Master of Philosophy
Issue Date: 2008
Publisher: City University of Hong Kong
Subjects: Polycyclic aromatic hydrocarbons -- Oxidation.
Lewis acids.
Notes: CityU Call Number: QD341.H9 T36 2008
xviii, 162 leaves : ill. 30 cm.
Thesis (M.Phil.)--City University of Hong Kong, 2008.
Includes bibliographical references (leaves 152-162)
Type: thesis
Abstract: This work is divided into four parts. Part I is concerned with the Lewis acids activated oxidation of aromatic hydrocarbons by [nBu4N][Os(N)Cl4]. Part II is concerned with the Lewis acids activated oxidation of alcohols by [nBu4N][Os(N)Cl4]. Part III is concerned with Lewis acid activated oxidation of hydrocarbons by [nBu4N][ReO4]. Part IV is concerned with Lewis acid activated oxidation of hydrocarbons by vanadium peroxo complexes, including K2[VO(O2)2pic] (pic = picolinic acid), K[VO(O2)dipic] (dipic = pyridine-2,6-dicarboxylic acid), K[VO(O2)2phen] (phen = 1,10-phenanthroline) and K[VO(O2)2bipy] (bipy = 2,2’-bipyridine). In Part I, the ion [Os(N)Cl4]- is a stable specie that is not known to act an efficient catalyst for aromatic hydrocarbons. However, addition of just a few equivalents of Sc(CF3SO3)3 to [Os(N)Cl4]- in CH2Cl2/CH3COOH results in a system that can oxidize aromatic hydrocarbons catalytically at room temperature using H2O2 in tributylphosphate as the terminal oxidant. In oxidation of 4-methyl-isopropylbenzene, the products are 4-methyl-isopropylbenzoquinone (53 %) and 5-isopropyl-2-methylphenol (1 %), no oxidation products arising from the methyl side chain were found under standard catalytic oxidation conditions. It is believed that the activating effect comes from the Lewis acidity of Sc(CF3SO3)3. For [nBu4N][Os(N)Cl4]/H2O2/Sc(CF3SO3)3, the KIE values for the competitive oxidation of ethylbenzene and d10-ethylbenzene is 0.94 while a set of para-substituted toluene led to a Hammett ρ value of -5.0. The active intermediate is proposed to be a binuclear μ-nitrido species:[OsVI(N)Cl4]- + Sc(CF3SO3)3 [(Cl)4Os≡N-Sc(CF3SO3)3] The formation of the intermediate (kfor) follows pseudo-first-order kinetics. The rate constant (kfor) is independent of the concentration of 4-methyl-isoporpylbenzene [kfor = (3.36 ± 0.71) x 10-2 s-1]. The decomposition of the active intermediate also obeys pseudo first-order kinetics in the presence of excess 4-methyl-isoporpylbenzene; the rate constant (kdec) increases with [4-methyl-isoporpylbenzene]. The mechanism for the oxidation of aromatic hydrocarbon by [nBu4N][Os(N)Cl4]/H2O2/Sc(CF3SO3)3 has been proposed. In Part II, it was found that the oxidation of alcohols can also be catalyzed by [nBu4N][Os(N)Cl4] effectively at room temperature in the presence of a few equivalents of a Lewis acid, using H2O2 in tributylphosphate as the terminal oxidant. For [nBu4N][Os(N)Cl4]/H2O2/Sc(CF3SO3)3, the KIE values for the competitive oxidation of cyclohexanol and d12-cyclohexanol is 1.8. The decomposition of the active intermediate also obeys pseudo first-order kinetics in the presence of excess cyclohexanol; the rate constant (kdec) increases with [cyclohexanol]. The mechanism for the oxidation of alcohol by [nBu4N][Os(N)Cl4]/H2O2/Sc(CF3SO3)3 has been proposed. In Part III, the ion [ReO4]- is not known to act a good catalyst for hydrocarbons. However, addition of just a few equivalents of Lewis acid to [ReO4]- in CH3CN results in a system that can oxidize hydrocarbons catalytically at 80 ºC using H2O2 as the terminal oxidant. In the absence of Lewis acids, the catalytic activity was negligible. The mechanism for the oxidation of hydrocarbons by [nBu4N][ReO4]/H2O2/BF3 has been proposed. In Part IV, it was found that the oxidation of hydrocarbons can be catalyzed by vanadium peroxo complexes including K2[VO(O2)2pic], K[VO(O2)dipic], K[VO(O2)2phen] and K[VO(O2)2bipy] in the presence of Lewis acid using H2O2 as the terminal oxidant. The mechanism for the oxidation of hydrocarbons by these systems has also been proposed.
Online Catalog Link: http://lib.cityu.edu.hk/record=b2340565
Appears in Collections:BCH - Master of Philosophy

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