Methyl peroxy radical, hydrogen

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... 

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

However in low NOx conditions peroxy radicals primarily react through self and cross peroxy-peroxy reactions to form methyl hydrogen peroxide (CH3OOH) and hydrogen peroxide (H202). H02 is also recycled back to OH through the reaction with 03 (Reaction 9). 

The effect of the medium on the rates and routes of liquid-phase oxidation reactions was investigated. The rate constants for chain propagation and termination upon dilution of methyl ethyl ketone with a nonpolar solvent—benzene— were shown to be consistent with the Kirkwood equation relating the constants for bimolecular reactions with the dielectric constant of the medium. The effect of solvents capable of forming hydrogen bonds with peroxy radicals appears to be more complicated. The rate constants for chain propagation and termination in aqueous methyl ethyl ketone solutions appear to be lower because of the lower reactivity of solvated R02. .. HOH radicals than of free RO radicals. The routes of oxidation reactions are a function of the competition between two R02 reaction routes. In the presence of water the reaction selectivity markedly increases, and acetic acid becomes the only oxidation product. 

Pathway (a) proceeds via hydrogen atom abstraction by the OH radical from the methyl group of NMP. This leads to the formation of an alkyl radical, which then reacts with dissolved oxygen to form a peroxy radical. By analogy with the aqueous phase behaviour of other peroxy radicals (Von Sonntag and Schuchmann, 1997), it can self-react to form a tetroxide which rapidly decomposes, leading to the formation of FP and NHMP. 

Oxidation of methyl ethyl ketone with a mixture of oxygen and ozone in CC14 at 20—50° C yields acetic acid, diacetyl (intermediate) and hydrogen peroxide [280]. The reaction is second order with a rate coefficient, k = 3.6 X 109 exp(—17,000/RT) 1 mole 1 s 1. The oxidation of the ketone under these conditions is a radical non-chain reaction. Peroxy radicals react faster by a termination reaction than by a propagation reaction at these temperatures. In aqueous solution, ozone oxidizes the ketone as well as the enol form of methyl ethyl ketone [281] and therefore acid accelerates the rate of oxidation. 

Percent product distribution butanone 80.8 1.46, 2-hydroxy-2-methyl-butanal 4.6 0.1, l,2-dihydroxy-2-methyl-butane 14.3 0.3. The addition of OH at the double bond of 2-methyl-1-butene occurs to 10.5 % at the inner and to 89.5 % at the outer position. This results mainly in the formation of a tertiary hydroxyalkyl peroxy radical, which carries no abstractable hydrogen at the... 

Figure 3 shows the reaction sequence for the OH radical-induced oxidation of methane. The first product following hydrogen atom abstraction is a methyl radical. Rapid addition of oxygen converts the methyl radical to methyl peroxy... 

Hydrogen abstraction by polymer alkoxy (PO ) and hydroxyl (HO ) radicals from the photocleavage of polymer hydroperoxy groups (POOH) in polypropylene occurs with 50% probabiUty at methyl groups. This means that up to 25% of the polymer peroxy radical (POO ) pairs produced in the initiation process may be pairs of primary peroxy radicals and the remaining 75% would be pairs between secondary, tertiary and mixed peroxy radicals. Due to the high radical concentration within such pairs of immediately adjacent radicals, the termination processes would be favoured over the slow hydrogen abstraction reaction of these radicals. 

There are additionally a few studies that directly address biodiesel-related esters. Hayes and Burgess " " in 2009 explored hydrogen transfer reactions of the alpha peroxy radicals of MB and methyl pentanoate. Such reactions had been suggested by Herbinet et al. to be important in the early CO2 formation seen in methyl ester combustion. Hayes and Burgess were able to derive high-pressure rate expressions and considered a number of competing reactions as well. They also reported that composite G3B3 calculations matched available benchmark data on related reaction barriers with better accuracy than DFT approaches. 

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