Oxidations with O2 and

In reactions catalyzed by peroxidases one cannot easily avoid the presence of hydrogen peroxide as this is the natural oxidant employed by the enzyme. However, it is necessary to maintain the steady-state concentration of hydrogen peroxide as 

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Mn and Fe chemistry has shown that zeolites are excellent supports for anchoring of metallophthalocyanines. There is a report of n-hexane oxidation with O2 and zeolite-supported Cu-perchlorophthalocyanine catalyst (189) ... 

Supported Initiators of Oxidations with O2 and a Sacrificial Aldehyde... 

A further problem arises from the fact that catalysts Vork by forming chemical bonds with the substrate molecules. Thus metals form hydrides with H2 and H donors such as CH4 or NH3, or oxides with O2 and 0 donors such as CO2 or NO2. It is presumably these surface compounds that play the role of active intermediates in the catalytic reaction. Under slightly different conditions, however, it is possible to extend the catalyst-adsorbate reaction to produce bulk compounds, e.g., hydrides and oxides. In view of this ability of the surface phase to propagate into the bulk in many instances, it is not at all clear that only the surface of the solid catalyst is active in the reaction. Such complexities add enormously to the difficulty of interpreting the kinetic data from heterogeneously catalyzed reactions. 

Fig. 8. Electron energy loss spectra of 15 ML thick MgO layers, (a) as grown (b) after Ar sputtering (c) after additional deposition of 4 ML of Mg (d) after deposition of 4 ML of Mg and post oxidation with O2 and consequent annealing. Reproduced from ref. [128], Copyright 1999 Elsevier.

An alternative oxidation using O2 and a RuCls catalyst converted pyridine to pyridine A-oxide. Bromamine-T and RuCls in aq. acetonitrile also oxidizes pyridine to the A-oxide. Tertiary amines are oxidized to the A-oxide with O2 and Fe203 in the presence of an aliphatic aldehyde. " Oxygen and a cobalt-Schiff base complex also oxidzes tertiary amines, including pyridine. ... 

Reaction condition 80 ml of 0.38 mol/1 2-ethylanthrahydroquinone (EAHQ) solution was oxidized with O2, and 30 mmol of H2O2 was formed. The reaction was maintained at the temperature for 8 h. 

Reaction conditions (1) 75.0 ml of 0.42 mol/1 EAHQ solution was oxidized with O2, and 31.5 mmol H2O2 is formed. 

Reaction conditions (1) 70 ml of 0.32 mol/1 EAHQ solution produced in a fixed-bed reactor with a Pd/Al203 catalyst was oxidized with O2, and 20 mmol H2O2 was formed. (2) EAHQ fresh catalyst = 300 1. At the end of each cycle, the catalyst was separated by centrifugation, washed with toluene, and used in the next reaction wilii addition of fresh catalyst to make up for losses. 

COMPARISON OF Pt/MnOx/SiOj AND Pt/Co0x/Si02 CATALYSTS FOR THE CO OXIDATION WITH O2 AND THE NO REDUCTION WITH CO... 

With plahnum and palladium catalysts, supported on siUca, alumina and active carbon, both H2, O2 and CO probe molecules are available for dispersion measurements. For rhodium, the various values are taken from the work of Ferretti et al. [102]. For ruthenium and iridium, O2 cannot be used as a probe molecule for dispersion measurements, because there is formahon of bulk oxides. With nickel, only H2 gives reUable results, O2 and CO cannot be used as probe molecules for dispersion measurements, because there is formation of bulk oxides with O2 and metal-carbonyls with CO, but the dispersion of the sample can be additionally measured by magnetic measurements. 

Barbaux, Y., Elamrani, A., and Boimelle, J.-P. Catalytic oxidation of methane on Mo03-Si02 mechanism of oxidation with O2 and N2O studied by surface potential measurements. Catal. Today 1987,1, 147-156. 

A thiol can be protected by oxidation (with O2 H2O2 I2. - ) to the corresponding symmetrical disulfide, which subsequently can be cleaved by reduction [Sn/HCl Na/xylene, Et20, or NH3 LiAlH4 NaBH4 or thiols such as HO(CH2)2SH]. Un-symmetrical disulfides have also been prepared and are discussed. 

The deposition of thin films of the high-temperature superconductor yttrium-barium-copper oxide, YBa2Cu307, is obtained from the mixed halides, typically YCI3, Bal2, and CUCI2, with O2 and H2O as oxygen sources. Deposition temperatures are 870-910°C.f ]... 

In the absence of O2, NO reduction continued, however at a rate about ten times lower than that in the presence of O2. During 20 h experiments NO conversion remained constant. On O2 addition, the catalytic activity increased with O2 content in the mixture up to about 1000 ppm, and changed little thereafter. We noticed that increasing the O2 concentration caused NO conversion to become lower than that of NH3, probably due to changes in the stoichiometry of the overall reaction (the NO/NH3 ratio passed from 1.5 to 1). Catalytic tests of NH3 oxidation with O2 yielded high selectivity to N2 (66-90%), which decreased with the higher loading catalysts. 

An alternative approach (Matveev et al., 1995), which avoids the selectivity problem mentioned above, is shown in Fig. 2.19. In this route, 1-naphthol is selectively methylated at the 2-position using methanol over a solid catalyst in the vapour phase. The product undergoes selective oxidation to menadione with O2 and a heteropolyanion catalyst. 

Similarly, 2,3,5-trimethyl-1,4-hydroquinone (TMHQ), a key intermediate in the synthesis of vitamin E, is produced via oxidation of 2,3,6-trimethylphenol to the corresponding benzoquinone. Originally this was performed by reaction with chlorine followed by hydrolysis, but this process has now been superseded by oxidation with O2 in the presence of a Cu2Cl2/LiCl catalyst (see Fig. 2.20) (Mercier and Chabardes, 1994). Alternatively, this oxidation can also be cataly.sed by a heteropolyanion (Kozhevnikov, 1995). 

Jacobsen (1999) has carried out carbomethoxylation of asymmetric epoxides. Thus, the carbomethoxylation of (R)-propylene oxide with CO and methanol yields 92% of (3R)-hydroxybutanoic acid in greater than 99% ee. Similarly, the reaction of (/ )-epichlorohydrin gives 96% of 4-chloro-(3R)-hydroxybutanoic acid in greater than 99% ee. The catalyst consists of dicobalt octacarbonyl and 3-hydroxy pyridine. A continuous process for making enantiomeric 1-chloro-2-propanol has been suggested. With a suitable catalyst propylene reacts with O2, water, cupric and lithium chloride to give 78% of (S)-l-chloro-2-propanol in 94% ee. 

Figure 2.14 A possible scheme for the reactions of diiron centres with O2 and substrates. Formal oxidation states, ground spin states and shorthand letter designations are listed below each diiron species. Reprinted from Kurz, 1997, by courtesy of Marcel Dekker, Inc.

The common method of 2 generation is by bubbling O2 through the catholyte during reduction, and an excess of O2 is therefore present. Car-banions formed by proton transfer to 02 may therefore react with O2, and many synthetically interesting reactions involve not only deprotonation but also oxidative follow-up reactions of the deprotonated substrate (cf. Sect. 14.8.7). Eor several base-catalyzed reactions (Sect. 14.9) the O2 present in... 

Figure 9.1 compares the synthesis of acetophenone by classic oxidation of 1-phenylethanol with stoichiometric amounts of chromium oxide and sulphuric acid, with an atom efficiency of 42%, with the heterogeneous catalytic oxidation with O2, with an atom efficiency of 87%, and with water as the only by-product. This is especially important if we consider the environmental unfriendliness of chromium salts the potential environmental impact of reactions can be expressed by the environmental quotient (EQ), where E is the E-factor (kg waste/kg product) and Q is the environmental unfriendliness quotient of the waste. If Q is... 

Trace metals are introduced to the ocean by atmospheric feUout, river runoff, and hydrothermal activity. The latter two are sources of soluble metals, which are primarily reduced species. Upon introduction into seawater, these metals react with O2 and are converted to insoluble oxides. Some of these precipitates settle to the seafloor to become part of the sediments others adsorb onto surfaces of sinking and sedimentary particles to form crusts, nodules, and thin coatings. Since reaction rates are slow, the metals can be transported considerable distances before becoming part of the sediments. In the case of the metals carried into the ocean by river runoff, a significant fraction is deposited on the outer continental shelf and slope. Hydrothermal emissions constitute most of the somce of the metals in the hydrogenous precipitates that form in the open ocean. 

For example, in oxic natural waters the principal oxidant is O2 and in agreement with expectations the pe of such waters is generally poised in the range expected for the O2-H2O couple (Morel and Herring, 1993). Thns for water at pH = 7 in eqnilibrinm with atmospheric Pq2 (= 10 atm), the half reaction is... 

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