Oxides reactivity

The dehydrogenation of 2-butanol is conducted in a multitube vapor-phase reactor over a zinc oxide (20—23), copper (24—27), or brass (28) catalyst, at temperatures of 250—400°C, and pressures slightly above atmospheric. The reaction is endothermic and heat is suppHed from a heat-transfer fluid on the shell side of the reactor. A typical process flow sheet is shown in Figure 1 (29). Catalyst life is three to five years operating in three to six month cycles between oxidative reactivations (30). Catalyst life is impaired by exposure to water, butene oligomers, and di-j -butyl ether (27). 

Finally, we want to compare the main mechanistic findings of our study with the classic bifunctional mechanism, which is generally used to explain the improved CO oxidation reactivity of PtRu surfaces and catalyst particles [Watanabe and Motoo, 1975]. According to that mechanism, Ru acts as a promotor for the formation of oxygenated adspecies on bimetallic PtRu surfaces, which can then react with CO... 

Volume 436. Globins and Other Nitric Oxide-Reactive Proteins, Part A (in preparation)... 

Thus, radicals are the most reactive and destructive of protein structure, followed by peroxy derivatives, singlet oxygen, and other oxygen compounds. The oxidative reactivity of some of these oxygen species is so high that just contact of the pure compound with paper or cotton fabrics can cause combustion (e.g., superoxide). 

Almeida IF, Fernandes E, Lima JLFC, Costa PC and Bahia, MF. 2008. Walnut (Juglans regia) leaf extracts are strong scavengers of pro-oxidant reactive species. Food Chem 106(3) 1014-1020. 

Since for an endothermic reaction the activation energy E > AH, all such reactions cannot explain the experimental value of the activation energy (see Chapter 4). The following mechanism seems to be the most probable now. Hydrogen peroxide is protonized in a polar alcohol solution. Protonization of H202 intensifies its oxidizing reactivity. Protonized hydrogen peroxide reacts with alcohol with free radical formation. 

The work on the electrochemical generation of a solution of ceric sulphate from slurry of cerous sulphate in 1-2 M sulphuric acid was abandoned by BCR due to difficulties encountered in handling slurried reactants. A 6kW pilot reactor operated at 50 °C using a Ti plate anode and a tungsten wire cathode (electrolyte velocity about 2ms 1) produced 0.5 M Ce(S04)2 on the anode with a current efficiency of 60%. The usefulness of Ce(IV) has been limited by the counter anions [131,132], Problems include instability to oxidation, reactivity with organic substrates and low solubility. Grace found that use of cerium salts of methane sulfonate avoids the above problems. Walsh has summarized the process history, Scheme 6 [133],... 

The binding of a reductant or oxidant species to form an inner-spheric surface complex changes its electronic structure and thus influences its reductive and oxidative reactivity. As a consequence the following differences in thermodynamic and kinetic properties between dissolved and adsorbed species may be observed (Wehrli et al., 1989). 

The Sc -promoted photoinduced electron transfer can be generally applied for formation of the radical cations of a variety of fullerene derivatives, which would otherwise be difficult to oxidize [135]. It has been shown that the electron-transfer oxidation reactivities of the triplet excited states of fullerenes are largely determined by the HOMO (highest occupied molecular orbital) energies of the fullerenes, whereas the triplet energies remain virtually the same among the fullerenes [135]. 

Crystalline packing is an important parameter for auto-oxidation in the sohd state, as molecular oxygen must be able to access susceptible moieties in the molecule. Lyn et al. [63] showed that only one (hexagonal form) of the five different polymorphic forms of prednisolone tert-butylacetate were susceptible to oxidation, yielding the 11-ketone product. The authors attributed this oxidative reactivity to channels in the crystal structure allowing access to the labile 11-alcohol position. Bryn et al. [64] also identified a similar phenomenon in the photo-mediated oxidation of 21-cortisol tert-butylacetate to the corresponding ketone. 

Clay et al. [65] showed clear correlation between the oxidative reactivity of dialuric acid monohydrate and prevailing moisture contents. Below 93% relative humidity the drug was reasonably stable, oxidation occurring over a 2-month period, whereas the same reaction took less than a day at humidities in excess... 

From the aforementioned, it should be evident that the amino group is one of the most reactive functionalities towards dioxirane oxidation consequently, to achieve a chemo-selective oxidation of a multi-functionalized substrate that possesses an amino group, the latter must be protected. This may be accomplished by masking the amino substituent in the form of its ammonium salt ", or BF3 complex ", even better as an amide functionality (iV-phenylacetamide resists TFD oxidation at room temperature""). This will reduce sufficiently the oxidative reactivity of the amino group, such that another less reactive group may be selectively oxidized" ... 

A triple-bonded nitrogen functionality (a ip-hybridized nitrogen atom), namely the cyano group, is resistant towards dioxirane oxidation. The fact that acetonitrile is widely used as a solvent for dioxirane oxidations " amply substantiates the lack of oxidative reactivity of cyano compounds. 

Among the CH oxidations, a most impressive case, for example, concerns the quantitative TFD oxidation of cyclohexane to cyclohexanone at —22° C in only 18 min (equation 26) There exists no other chemical oxidant, even metal-catalyzed systems, that may compete with this astounding oxidative reactivity of TFD. Whether the oxidation of an amine to a hydroxylamine involves the direct insertion of an oxygen atom into the N—H bond is mechanistically still uncertain, since alternatively (more probably the case on... 

When the C—H bond to be oxidized is proximate to a functional group, as we have stated already, its reactivity depends on the type of functional group. In the case of the hydroxy group, especially in secondary alcohols, these are more prone to dioxirane oxidation than their alkane precursors and, consequently, usually carbonyl products are obtained as the final product. Primary alcohols are less reactive, but may still be converted slowly to the corresponding aldehydes or carboxylic acids (due to the facile further oxidation of aldehydes)The functional-group transformation of the alcohols to ethers or acetals reduces the oxidative reactivity " but these C—H bonds are still more reactive than unfunctionalized ones. Thus, dioxirane oxidation of benzyl ether or acetal may... 

The oxidative reactivity of peroxynitrite as a function of pH. The data are plotted as the percentage of the maximal yield under optimal conditions. Data were originally reported in Beckman et al. (1990, 1992) Radi et al (1991a,h). 

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