O2 as oxidant

This was also accomplished with BaRu(0)2(OH)3. The same type of conversion, with lower yields (20-30%), has been achieved with the Gif system There are several variations. One consists of pyridine-acetic acid, with H2O2 as oxidizing agent and tris(picolinato)iron(III) as catalyst. Other Gif systems use O2 as oxidizing agent and zinc as a reductant. The selectivity of the Gif systems toward alkyl carbons is CH2 > CH > CH3, which is unusual, and shows that a simple free-radical mechanism (see p. 899) is not involved. ° Another reagent that can oxidize the CH2 of an alkane is methyl(trifluoromethyl)dioxirane, but this produces CH—OH more often than C=0 (see 14-4). ... 

Figure 4. Comparison of the behavior of VSil545 in propane oxidative dehydrogenation using N2O or O2 as oxidizing agents. Exp. conditions as in Fig. 1. The dotted lines represent the propane conversion and propylene selectivity observed in the absence of the catalyst (homogeneous gas phase). The activity of the catalyst in the absence of O2 or N2O is similar to that observed in the homogeneous gas phase, but the selectivity to propylene (around 50-60%) is lower.

Pd(II)-catalyzed dialkoxy- or dihydroxycarbonylation of alkynes (Eq. 22, R = alkyl or H, respectively) with formation of maleic and fumaric esters or acids (and, in the case of acetylene, of muconic esters too), has been reported to occur in the presence of CuCl2 and/or O2 as oxidant [73-79] electrochemical reoxidation of Pd(0) has also been described [80]. 

Grunwaldt et al. (2003b) reported XAFS measurements recorded during palladium-catalyzed alcohol oxidation in supercritical CO2. A commercial shell-impregnated catalyst consisting of 0.5 wt% Pd on alumina was used for benzyl alcohol oxidation (to benzaldehyde) in supercritical CO2 with pure O2 as oxidant. The conditions were 353 K and 150 bar. The results are summarized in Table 8. The authors reported only Pd XANES data, not EXAFS data, and thus the analysis is limited to information about the average oxidation state of the palladium. 

Oxidation of a phenol to the corresponding ju-qninone nsing a copper catalyst takes place at room temperatnre nnder similar conditions as those nsed for alcohol oxidation, with O2 as oxidant. Likewise, hydroqninones (22) can be transformed to 3-alkoxy-/7-qninones (23) when reacted in the presence of an alcohol. In the case of 4-substituted phenols (24), polymer-based catalysts composed of ligands (e.g. PVBPy) that chelate copper have been used at elevated temperatures to selectively oxidize a benzylic carbon to yield 4-hydroxybenzaldehydes (25) in good yields. ... 

In vitro a crystalline iron core can be laid down in apoferritin by the addition of an oxidant, such as O2, to an aqueous solution of a ferrous salt and apoferritin (32, 132, 140). The reconstituted core of horse ferritin prepared in the absence of phosphate and with O2 as oxidant is very similar to the native core in terms of its size and Mossbauer properties (85). Electron microscopy, however, reveals that it is less well ordered. Reconstitution in the presence of phosphate leads to smaller cores. Reconstituted A. vinelandii cores in the absence of phosphate were more ordered than were the native cores, and clearly contained ferrihydrite particles and, in some cases, crystal domains (85). Thus the nature of the core is not determined solely by the protein coat the conditions of core formation are also important. This is also indicated by Mossbauer spectroscopy studies of P. aeruginosa cells grown under conditions different than those employed for the large-scale pu-... 

Nevertheless, the use of a supported noble metal catalyst (usually Pt) for soot oxidation under loose contact conditions (proposed to be closer to the practical condition) results in a significant decrease in the soot oxidation temperature.76,94,97,98 Thus, incorporation of the soot in a Pt/SiC foam catalyst allows the soot oxidation rate to be doubled (and also to decrease the maximum rate temperature) with respect to a non-catalysed situation in which the soot is incorporated into the Pt-free SiC foam (with Pt/SiC foam located upstream to promote NO oxidation). In turn, a considerable decrease in the maximum rate temperature is observed when employing NO + O2 instead of O2 as oxidant in the Pt/SiC-soot configuration.98 On the basis mainly of these results, a catalytic role for NO is proposed in a recycle reaction as follows ... 

For the same systems haloperoxidase activity has been reported with H2O2 / O2 as oxidant and HC1 / HBr as halogen source [22]. In this way oxychlorination / oxybromination of benzene, toluene, phenol, aniline, anisolc and resorcinol could be achieved. 

New interesting developments regarding technical processes for the preparation of AA such as biocatalytic oxidation of PA and the two-stage cleavage of oleic acid using H2O2 and O2 as oxidants are reported later in the text. However, ozonolysis coupled with an aerobic oxidative work-up of intermediates is the most important industrial process at the present time [5, 7]. 

From a mechanistic point of view, the direct use of O2 as oxidant has to meet two major problems. These are outlined below, followed by strategies for possible solutions. To this end, two representative case studies are discussed, illustrating the scope and limitations of gas-phase experiments. We omit experimental details and restrict ourselves to the fundamental requirements in the activation of O2 as deduced from model studies conducted with isolated species in the highly diluted gas phase, thus excluding complicating effects due to the presence of solvents, counter ions, aggregation, bulk phe-nomaia etc. (for reviews, see [7]). 

Molten carbonate fuel cells operate at 650 °C with a molten 62 wt. % li2C03-38 wt. % K2CO3-eutectic mixture as the electrolyte, CO2 and O2 as oxidant gases, and H2 as the fuel. The relevant reactions are ... 

Palladium was also investigated for oxidative carbonylation using O2 as oxidant, but now CUCI2 was added to re-oxidize the palladium metal. These reactions were carried out in aqueous trifluoroacetic acid, and led to the formation of a mixture of methanol and its triflate ester. ... 

The synthesis of isoindolinones (128) from IV-tosylbenzamides (129) and t-butyl acrylate was achieved in high yields using O2 as oxidant and Pd(OAc)2 as catalyst in the presence of 4,7-diphenyl-l,10-phenanthroline and toluene. Aliphatic alkenes with electron-rich and electron-deficient alkenes or conjugated alkenes could also be... 

The CDC between A-f-butyl nitrones and terminal alkynes to form alkynylated nitrones in good to excellent yields, catalysed by zinc trifiate, was achieved using 3,3, 5,5 -tetra-tertbutyldipheno-quinone and O2 as oxidants. The alkynylated nitrones were transformed to regioisomerically pure 3,5-disubstituted isoxazoles. Experimental and DFT computational studies of Pd(OAc)2/pyridine-catalysed intramolecular aerobic oxidative amination of alkenes supported a stepwise mechanism that involved (i) the formation of a Pd(ll)-amidate-alkene chelate with release of 1 equiv. of pyridine and AcOH from the catalyst centre, (ii) insertion of alkene into a Pd—N bond. 

Figure 33. Power-current curve of a DMFC single cell at 60 °C using O2 as oxidant and methanol as fuel with various concentrations. The points and lines are experimental and calculated results, respectively.

Table 17. Peak stack power, energy efficiency, energy density and open circuit voltages of a 28-cell DMFC stack with 22 cm electrode area operated at 60 "C using O2 as oxidant and methanol as fuel with different concentrations.

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