Hydroperoxy! radical aldehyde reactions

The hydroxyl groups may be formed along the polymer chain or on its end groups. The carbonyl and aldehyde groups are formed from the scission of alkoxy radicals or by the decomposition of hydroperoxy radicals. The reaction between two polymer alkoxy radicals also produces a carbonyl and hydroxyl group by disproportionation ... 

Further reaction with the HO2 radical (reactions 5.55 and 5.56) gave a hydro-tetraoxide that decomposed to dialdehydes and/or to dicarboxylic acids. In aliphatic hydrocarbons, the OH radical first abstracts a hydrogen atom from the chain. Subsequent addition of O2 and further reaction with the hydroperoxy radical from reaction 5.52 led to formation of ketones and aldehydes (reactions 5.55 and 5.56 Heller, 1995). 

Alkyl radicals, R, react very rapidly with O2 to form alkylperoxy radicals. H reacts to form the hydroperoxy radical HO2. Alkoxy radicals, RO, react with O2 to form HO2 and R CHO, where R contains one less carbon. This formation of an aldehyde from an alkoxy radical ultimately leads to the process of hydrocarbon chain shortening or clipping upon subsequent reaction of the aldehyde. This aldehyde can undergo photodecomposition forming R, H, and CO or, after OH attack, forming CH(0)00, the peroxyacyi radical. 

A closer examination by ex situ analysis using NMR or gas chromatography illustrates that intrazeolite reaction mixtures can get complex. For example photooxygenation of 1-pentene leads to three major carbonyl products plus a mixture of saturated aldehydes (valeraldehyde, propionaldehyde, butyraldehyde, acetaldehyde)38 (Fig. 33). Ethyl vinyl ketone and 2-pentenal arise from addition of the hydroperoxy radical to the two different ends of the allylic radical (Fig. 33). The ketone, /i-3-penten-2-one, is formed by intrazeolite isomerization of 1-pentene followed by CT mediated photooxygenation of the 2-pentene isomer. Dioxetane cleavage, epoxide rearrangement, or presumably even Floch cleavage130,131 of the allylic hydroperoxides can lead to the mixture of saturated aldehydes. 

Although the above reactions generate a few fi radicals, most of the oxidation of nitric oxide to nitrogen dioxide is carried out by the alkyl-peroxy, RO, and hydroperoxy radicals that are formed in later reactions involving reactive hydrocarbons, aldehydes, or even carbon monoxide. One such example is shown in Figure 2-7. There is still considerable uncertainty as to the mechanism of these secondary reactions. The modeling studies should be consulted for details. ... 

Reaction (4.7) leads to a proliferation of hydroxy radicals, which non-selectively abstract hydrogen atoms, see Reactions (4.8) and (4.9). Acids are formed by the following two reactions, which start from a hydroperoxy-peroxy radical, see Reaction (4.4), and an aldehyde [9, 10]. Carboxylic acids (RCOOH), formed according to Reaction sequences (4.18) and (4.19), represent one of the principal products under these oxidation conditions. In a subsequent step they can react with alcohols R OH, produced by Reactions (4.10) and (4.14), to form esters, RCOOR. In addition, when the rate of oxidation becomes limited by diffusion, ethers are formed. Reaction sequence (4.20) ... 

Further reaction of the alkoxy radicals, formed in this step, with O2 affords aldehydes and hydroperoxy radicals (also capable of oxidizing NO with regeneration of OH) ... 

At first, the /7-toluic acid was esterified with methanol in a separate step before final oxidation to monomethyl terephthalic acid. Alternatively, if methanol was used as a solvent for the /7-xylene, both methyl groups were esterified in a single step, if the residence time was longer than 20 h. The reaction mechanism involved the conversion of the methyl group to a benzyl radical by reaction with trivalent cobalt ions. The benzyl radical then reacts with oxygen and forms a peroxy species that decomposes to the oxidation product. Trivalent cobalt ions are regenerated as aldehydes from the peroxy or hydroperoxy species. 

Under relatively low NOx conditions in the atmosphere, a part of alkyl peroxy radicals, and hydroxyalkyl peroxy radicals react with HO2 to give hydroperoxy butane (pathways (f), (k)), and hydroxyhydroperoxy butane (pathway (q)). Thus, in oxidation reactions of alkane in the atmosphere, hydroperoxides, hydoxyhydor-peroxides, and hydroxyalkyl nitrate, could also be produced in addition to the normal aldehydes, ketones and alkyl nitrates. 

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