Oxidation reactions general mechanisms

Primary amines are oxidized to hydroxlyamines, which in turn are oxidized to ni-troso compounds, which are oxidized to nitro compounds. Hydrogen peroxide, peroxy-acids, and other common oxidizing agents are used to oxidize amines. The oxidation reactions generally take place by mechanisms that involve radicals, so they are not well characterized. 

Degradation of polyolefins such as polyethylene, polypropylene, polybutylene, and polybutadiene promoted by metals and other oxidants occurs via an oxidation and a photo-oxidative mechanism, the two being difficult to separate in environmental degradation. The general mechanism common to all these reactions is that shown in equation 9. The reactant radical may be produced by any suitable mechanism from the interaction of air or oxygen with polyolefins (42) to form peroxides, which are subsequentiy decomposed by ultraviolet radiation. These reaction intermediates abstract more hydrogen atoms from the polymer backbone, which is ultimately converted into a polymer with ketone functionahties and degraded by the Norrish mechanisms (eq. 

At least two pathways have been proposed for the Nenitzescu reaction. The mechanism outlined below is generally accepted." Illustrated here is the indolization of the 1,4-benzoquinone (4) with ethyl 3-aminocrotonate (5). The mechanism consists of four stages (I) Michael addition of the carbon terminal of the enamine 5 to quinone 4 (II) Oxidation of the resulting hydroquinone 10 to the quinone 11 either by the starting quinone 4 or the quinonimmonium intermediate 13, which is generated at a later stage (HI) Cyclization of the quinone adduct 11, if in the cw-configuration, to the carbinolamine 12 or quinonimmonium intermediate 13 (IV) Reduction of the intermediates 12 or 13 to the 5-hydroxyindole 6 by the initial hydroquinone adduct 7 (or 8, 9,10). 

The general mechanism of coupling reactions of aryl-alkenyl halides with organometallic reagents and nucleophiles is shown in Fig. 9.4. It contains (a) oxidative addition of aryl-alkenyl halides to zero-valent transition metal catalysts such as Pd(0), (b) transmetallation of organometallic reagents to transition metal complexes, and (c) reductive elimination of coupled product with the regeneration of the zero-valent transition metal catalyst. 

There is an extensive literature on the use of 2,1,3-benzoxadiazole 1-oxide [often called benzofuroxanie) (BFO) (462)] as a substrate for the primary synthesis of quinoxaline 1,4-dioxides and occasionally quinoxaline mono-A -oxides or even simple quinoxalines. Very few substituted derivatives of the parent substrate (462) have been employed in recent years. The general mechanism clearly involves a fission (usually amine-catalyzed) of the oxadiazole ring followed by reaction with an ancillary synthon. The following examples are divided according to the type of synthon employed. 

We have previously considered the mechanism of electrospray ionization in terms of the charging of droplets containing analyte and the formation of ions as the charge density on the surface of the droplet increases as desolvation progresses. The electrospray system can also be considered as an electrochemical cell in which, in positive-ion mode, an oxidation reaction occurs at the capillary tip and a reduction reaction at the counter electrode (the opposite occurs during the production of negative ions). This allows us to obtain electrospray spectra from some analytes which are not ionized in solution and would otherwise not be amenable to study. In general terms, the compounds that may be studied are therefore as follows ... 

In terms of gross features of mechanism, a redox reaction between transition metal complexes, having adjacent stable oxidation states, generally takes place in a simple one-equivalent change. For the post-transition and actinide elements, where there is usually a difference of two between the stable oxidation states, both single two-equivalent and consecutive one-equivalent changes are possible. 

The oxidation of alcohols to the corresponding carbonyl compounds is one of the key reactions in organic synthesis and nnmerous methods have been developed over the years to accomplish this transformation [16], A general mechanism for Pd-catalysed aerobic oxidation is shown below (Scheme 10.5). 

Within the general mechanism for the oxidation of Ci molecules, proposed by Bagotzsky, formic acid is one of the simplest cases, since it requires only the transfer of two electrons for the complete oxidation to CO2 [Bagotzky et al., 1977]. In fact, it has the same oxidation valency as CO both require two electrons for complete oxidation to CO2. When compared with CO, the reaction mechanism of formic acid is more complex although the catalysis of the oxidation reaction is much easier. In fact, formic acid can be readily oxidized at potentials as low as 0.2 V (vs. RHE). Its reaction mechanism takes place according to the well-established dual path mechanism [Capon and Parsons, 1973a, b] ... 

Ertl and his colleagues in 1997 reported detailed STM data for the oxidation of CO at Pt(l 11) surfaces, with quantitative rates extracted from the atomically resolved surface events.27 The aim was to relate these to established macroscopic kinetic data, particularly since it had been shown that no surface reconstruction occurred and the reaction was considered to obey the Langmuir-Hinshelwood mechanism, where it is assumed that the product (C02) is formed by reaction between the two adsorbed reactants, in this case O(a) and CO(a). Nevertheless, it was well known that for many features of the CO oxidation reaction at Pt(lll) there is no mechanism that is consistent with all features of the kinetics the inherent problem is that in general a reaction mechanism cannot be uniquely established from kinetics because of the possible contribution of intermediates or complications for which there might be no direct experimental evidence. 

Scheme 8. General mechanism of the copper-catalyzed allylic oxidation of alkenes (Kharasch-Sosnovsky reaction).

Also autooxidation or auto-oxidation. A slow, easily initiated, self-catalyzed reaction, generally by a free-radical mechanism, between a substance and atmospheric oxygen. Initiators of autoxidation include heat, light, catalysts such as metals, and free-radical generators. Davies (1961) defines autoxidation as interaction of a substance with molecular oxygen below 120°C without flame. Possible consequences of autoxidation include pressure buildup by gas evolution, autoignition by heat generation with inadequate heat dissipation, and the formation of peroxides. 

Abstract The basic principles of the oxidative carbonylation reaction together with its synthetic applications are reviewed. In the first section, an overview of oxidative carbonylation is presented, and the general mechanisms followed by different substrates (alkenes, dienes, allenes, alkynes, ketones, ketenes, aromatic hydrocarbons, aliphatic hydrocarbons, alcohols, phenols, amines) leading to a variety of carbonyl compounds are discussed. The second section is focused on processes catalyzed by Pdl2-based systems, and on their ability to promote different kind of oxidative carbonylations under mild conditions to afford important carbonyl derivatives with high selectivity and efficiency. In particular, the recent developments towards the one-step synthesis of new heterocyclic derivatives are described. 

The mechanism of the reaction was first described by Harrod and Chalk [10], It involves the general mechanism of H-X additions to unsaturated organic compounds, starting with an oxidative addition of HX to a zerovalent platinum complex. The process is the same as that of addition of HCN to double bonds (Chapter 11). 

Fig. 9.5. The reaction of organic nitrites with thiols (Reaction a), and a general mechanism for the release of nitric oxide from S-nitroso thiols (Reactions b and c) [31]...

Although no reported work is available on vinyl acetylene oxidation, oxidation by O would probably lead primarily to the formation of CO, H2, and acetylene (via an intermediate methyl acetylene) [37], The oxidation of vinyl acetylene, or the cyclopentadienyl radical shown earlier, requires the formation of an adduct [as shown in reaction (3.142)]. When OH forms the adduct, the reaction is so exothermic that it drives the system back to the initial reacting species. Thus, O atoms become the primary oxidizing species in the reaction steps. This factor may explain why the fuel decay and intermediate species formed in rich and lean oxidation experiments follow the same trend, although rich experiments show much slower rates [65] because the concentrations of oxygen atoms are lower. Figure 3.13 is a summary of the reaction steps that form the general mechanism of benzene and the phenyl radical oxidation based on a modified version of a model proposed by Emdee et al. [61, 66], Other models of benzene oxidation [67, 68, which are based on Ref. [61], place emphasis on different reactions. 

The general mechanism of MeOH on Pt and PtRu is well established. First, MeOH is adsorbed and subjected to multiple dehydrogenation steps to give adsorbed CO. This dehydration step is known to occur at low potentials. The adsorbed CO is then oxidized by active OH species produced by the dissociation of H2O. This is fhe pofenfial-driven rate-determining step because OH formation does not occur on Pt until higher potentials. The addition of Ru pro-mofes fhe reaction because it is able to produce OH species at lower potentials. This promotional effect is known as the "bifunctional" mechanism ... 

Chromium produces some of the most interesting and varied chemistry of the transition elements. Chromium(O) and chromium(I) are stabilized in organometallics (Prob. 8). There have been extensive studies of the redox chemistry of Cr(II), Cr(III) and Cr(VI). Generally the Cr(IV) and Cr(V) oxidation states are unstable in solution (see below, however). These species play an important role in the mechanism of oxidation by Cr(VI) of inorganic and organic substrates and in certain oxidation reactions of Cr(II) and Cr(III). Examination of the substitution reactions of Cr(III) has provided important information on octahedral substitution (Chap. 4). 

The title system in AN forms a homogeneous solution. The generation of NO cation takes place. As known, NO is a remarkable, diverse reagent not only for nitrosation and nitration but also for oxidation. Kochi et al. (1973) christened a new general mechanism oxidative aromatic substitution to describe aromatic snbstitntion reactions (Kochi 1990, Bosch and Kochi 1994). This mechanism incorporates ground-state electron transfer before the substitution step (see also Skokov and Wheeler 1999). 

Strong reducing agents like sodium borohydride and lithium aluminum hydride are capable of reducing aldehydes to primary alcohols and ketones to secondary alcohols. The general reaction is the reverse of the reactions used to form aldehydes and ketones by the oxidation of primary and secondary alcohols, respectively (to review, see the earlier section Oxidation reactions ). However, the mechanisms for reduction are different. 

Oxidation by molecular oxygen most likely occurs via a radical mechanism 10-13 and the reaction rates are generally slow unless traces of metal ions are present which are known to drastically affect the reaction rate 14 thus making control of the air-oxidation reaction rather difficult. The rates can also be significantly enhanced by adding charcoal to induce a surface-assisted catalysis of the intramolecular disulfide bond formation 15 Nonetheless the difficult control of this oxidation procedure can lead to partial oxidation of Met and Trp residues when peptides are exposed for longer periods of time to air oxygen 16 ... 

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