Methyl peroxy radical

It is important to examine more closely reaction (3.72), which proceeds [18, 19] through a metastable intermediate complex—the methyl peroxy radical—in the following manner ... 

The overall selectivity to C2 compounds is thus determined by the relative rates of the combination of CH3 radicals [Eq. (3.35)] and their reaction with oxygen molecules [Eq. (3.36)] or with surface O- [Eq. (3.37)] to form methyl peroxy radical and surface methoxy species, respectively ... 

The methyl peroxy radical that is formed converts to H02 in the sequence for primary peroxy radicals shown in equations 30 and 31. The chain reaction is subject to termination steps that include the following ... 

The addition reaction between methyl radicals and oxygen to give methyl peroxy radicals is well established as a third-order reaction and... 

The method by which methoxy radicals are formed from methyl peroxy radicals was originally suggested by Raley and co-workers106... 

More recently, Barber et al.10 have suggested that methanol can be produced by the reaction of hydroxyl radicals with methyl peroxy radicals... 

The absence of methyl hydroperoxide in the results of Hanst and Calvert38 cannot be considered conclusive and it is very likely that methyl radicals will be oxidized to methyl hydroperoxide, in this system as in other systems (e.g., CH3I photooxidation), where a readily available hydrogen atom is present. Decomposition to give methanol and/or formaldehyde might quickly follow and Hanst and Calvert say that under their conditions formaldehyde would quickly be converted to formic acid. The chain ending steps that they postulate [(96) and (21)] are quite possible, but if one accepts the reaction between hydroxyl radicals and methyl peroxy radicals as put forward for CHSI photooxidation,10 one might equally accept a similar reaction... 

Their work seems to contradict that of Subbaratnam and Calvert122 and shows that methyl peroxy radicals can abstract from a hydrogen-containing species at room temperature... 

Methyl peroxy radicals evidently do not give methanol and formaldehyde in equal quantities when hydrogen iodide is added, so it seems that they must give formaldehyde by a different reaction... 

Methanol can scarcely be chiefly formed from methoxy radicals since these would abstract from hydrogen iodide to give methane and water in the same way as methyl and hydroxyl radicals. Therefore, methanol must be produced from methyl peroxy radicals by the reaction... 

Most methyl radicals will not react according to reaction (18) in this system but will form methyl peroxy radicals. If reaction (27) is to... 

Fig. 3 Atmospheric degradation mechanism of methane showing the central role played by the methyl peroxy radical (CH3O2). Values in parentheses are order of magnitude estimates for the lifetimes of the various species...

The second phase is a quasi-stationary chain-branched process with a quadratic radical termination, which proceeds mainly via the recombination of methyl-peroxy radicals... 

As in the case of the hydrogen atom, the methyl radical, CH3, reacts virtually instantaneously with 02 to yield the methyl peroxy radical, CH302... 

Under tropospheric conditions, the methyl peroxy radical can react with NO, N02, H02 radicals, and itself the reactions with NO and H02 are the most important. The reaction with NO leads to the methoxy radical, CH30, and N02 ... 

HO2 -F NONO2 + OH-The methyl peroxy radical can also react with NO.,... 

In the case of the methyl peroxy radical, for example, the presence of an F atom, Cl atom (s), or OH group, increases the rate constant by more than a factor of 10. The effect of bromine, on the contrary seems smaller. The enhancement is even larger with the presence of a carbonyl group e.g. acetonylperoxy) or an aromatic ring e.g, benzylperoxy). 

To complement the studies of the interaction between RO2 and NO3 radicals, we have carried out some studies on RO2 + RO2 systems, because this reaction, at least, must always compete with the reaction RO2 + NO3. We have probed the processes by following the second-order decays of RO2 for several partially and fully halogenated methyl peroxy radicals. Allowance is made in the analysis for the reaction RO2 + HO2 in those cases where HO2 is a secondary product. The preliminary rate coefficients obtained are displayed in Table 2. 

Fig. 21. EPR spectra of the radicals formed over MgO (a) methyl radical (CH3O (b) methyl peroxy radical (CH3O2 ) spectrum. Reprinted from Ref 140, copyright 1985, with kind permission from American Chemical Society.

Matrix isolation was also used to identify the radical intermediates in the partial methanol oxidation reaction over a Pt/Si02 catalyst. Methyl peroxy radicals (CH3OO ) and methyl oxy radicals (CH3OO ) were discriminated between, based on their different stability to photolysis (142). By combining EPR and in situ IR spectroscopy, it was shown that the radical species form super equilibrium concentrations under reaction conditions at the platinum/support interface region (143). 

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