Peroxy radical generation mechanism

Perhydroxyl radical, 75 thermal generation from PNA of, 75 Peroxy radical generation, 75 Peroxide crystal photoinitiated reactions, 310 acetyl benzoyl peroxide (ABP), 311 radical pairs in, 311, 313 stress generated in, 313 diundecanyl peroxide (UP), 313 derivatives of, 317 EPR reaction scheme for, 313 IR reaction scheme for, 316 zero field splitting of, 313 Peorxyacetyl nitrate (PAN), 71, 96 CH3C(0)00 radical from, 96 ethane oxidation formation of, 96 IR spectroscopy detection of, 71, 96 perhydroxyl radical formation of, 96 synthesis of, 97 Peroxyalkyl nitrates, 83 IR absorption spectra of, 83 preparation of, 85 Peroxymethyl reactions, 82 Photochemical mechanisms in crystals, 283 atomic trajectories in, 283 Beer s law and, 294 bimolecular processes in, 291 concepts of, 283... 

A detailed reaction mechanism has been presented for the 2-methylphenyl radical + 02 reacting system, which generates the 2-methylphenylperoxy radicals (MPP). The MPP radical, depicted in the general scheme, is the key intermediate, lying 48.7 kcal/mol below the reactants MP + 02. The peroxy radical MPP, which is... 

The mechanism shown in Scheme 5 postulates the formation of a Fe(II)-semi-quinone intermediate. The attack of 02 on the substrate generates a peroxy radical which is reduced by the Fe(II) center to produce the Fe(III) peroxide complex. The semi-quinone character of the [FeL(DTBC)] complexes is clearly determined by the covalency of the iron(III)-catechol bond which is enhanced by increasing the Lewis acidity of the metal center. Thus, ultimately the non-participating ligand controls the extent of the Fe(II) - semi-quinone formation and the rate of the reaction provided that the rate-determining step is the reaction of 02 with the semiquinone intermediate. In the final stage, the substrate is oxygenated simultaneously with the release of the FemL complex. An alternative model, in which 02 attacks the Fe(II) center instead of the semi-quinone, cannot be excluded either. 

A mechanism has been proposed for chain-generation catalyzed by metal compounds in which oxygen is incorporated into the coordination-unsaturated complex and the metal-dioxygen complex forms a peroxy radical ROO by opening a C-H bond." ... 

A computer model has been developed which can generate realistic concentration versus time profiles of the chemical species formed during photooxidation of hydrocarbon polymers using as input data a set of elementary reactions with corresponding rate constants and initial conditions. Simulation of different mechanisms for stabilization of clear, amorphous linear polyethylene as a prototype suggests that the optimum stabilizer would be a molecularly dispersed additive in very low concentration which can trap peroxy radicals and also decompose hydroperoxides. 

The mechanism for these metal-catalyzed, 02 promoted oxidations was proposed to be metal-catalyzed 02 oxidation of the aldehyde 55 to form a peroxy radical species 56 which adds to ketone 60 to provide a radical variant of a Criegee intermediate, 57. This intermediate would then extract a proton from the aldehyde 55 to provide the normal Criegee intermediate 58. Alternatively, the generated peroxy radical intermediate 56 abstracts a proton from an aldehyde molecule providing peracid 59 which attacks the ketone 60 to provide the Criegee intermediate 58. 

Peroxy radicals can react by yet other competing routes. For example, evidence for lipid peroxy radical combination through a tetraoxide has been reported recently (8). Such tetraoxides could generate singlet oxygen and nonradical products by the Russell mechanism (9) as shown in Reaction D. 

It is well known that molecular oxygen inhibits free-radical polymerization by scavenging the initiator radicals, which not only reduces the polymerization rate but also affects the mechanical, optical, and structural properties of the cured systems. The mechanism of O2 inhibition is represented in Figure 6(a). As a result of a photooxidation reaction, peroxy radicals (or hydroperoxides or alcoxy radicals) are generated, which are less reactive toward monomer to initiate... 

The first step of the mechanism involves generation of peroxy radicals through thermal decomposition of a peroxide ... 

Consistent with a radical chain mechanism, the rate of O2 insertion was found to be sensitive to light, and the addition of radical initiator AIBN was required in order to observe reproducible reaction rates. Based on analysis of the kinetics of O2 insertion into the Pd-C bond of 24, a mechanism involving mononuclear Pd(III) intermediates was proposed (Fig. 16). Palladium(III) intermediate 27, formed by the combination of dimethyl Pd(II) complex 24 with peroxy radical 26 [84], generates the observed Pd(II) peroxide 25 by homolytic Pd-C cleavage to reduce Pd(III) complex 27 and generate radical chain carrier Me. ... 

It is well established that in the presence of certain transition metal complexes or peroxides, that phosphines will be oxidized in the presence of oxygen via peroxy radicals to generate their thermodynamically stable phosphine oxides, the driving force being the formation of the strong phosphorus-oxygen bond. However, in the absence of such reagents, there are remarkably few studies on the oxidation of phosphines by air. There appears to be no common consensus on the first step in the mechanism of... 

Oxidation reactions are chain reactions which follow a free radical mechanism. In chain reactions three distinct steps are present initiation, propagation and termination. During initiation a free macroradical (P") is generated in the polymer by heating, radiation or stress. This reacts readily with oxygen to yield a peroxy radical (POO"), the peroxy free-radical abstracts hydrogen from another polymer molecule (PH) creating a new macroradical and a hydroperoxide (POOH). Then the hydroperoxide decomposes to two new free radicals, which are also initiators of the chain reaction. These chain reactions have severe consequences for the polymer, and cause extensive localized oxidation. 

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