Alkoxy radicals oxygen

One decomposition of the tetioxide is not terminating, producing alkoxy radicals and oxygen (eq. 14). 

Mn (IT) is readily oxidized to Mn (ITT) by just bubbling air through a solution in, eg, nonanoic acid at 95°C, even in the absence of added peroxide (186). Apparently traces of peroxide in the solvent produce some initial Mn (ITT) and alkoxy radicals. Alkoxy radicals can abstract hydrogen to produce R radicals and Mn (ITT) can react with acid to produce radicals. The R radicals can produce additional alkylperoxy radicals and hydroperoxides (reactions 2 and 3) which can produce more Mn (ITT). If the oxygen feed is replaced by nitrogen, the Mn (ITT) is rapidly reduced to Mn (IT). 

Diperoxyketals. Some commercially available di(/ f2 -alkylperoxy)ketals and their corresponding 10-h half-life temperatures (deterrnined in dodecane) are hsted in Table 5 (39). Diperoxyketals thermally decompose by cleavage of only one oxygen—oxygen bond initially, usually foUowed by P-scission of the resulting alkoxy radicals (40). For acychc diperoxyketals, P-scission produces an alkyl radical and a peroxyester. 

Diall l Peroxides. Some commercially available diaLkyl peroxides and their corresponding 10-h half-life temperatures in dodecane are Hsted in Table 6 (44). DiaLkyl peroxides initially cleave at the oxygen—oxygen bond to generate alkoxy radical pairs ... 

An important side reaction in all free-radical nitrations is reaction 10, in which unstable alkyl nitrites are formed (eq. 10). They decompose to form nitric oxide and alkoxy radicals (eq. 11) which form oxygenated compounds and low molecular weight alkyl radicals which can form low molecular weight nitroparaffins by reactions 7 or 9. The oxygenated hydrocarbons often react further to produce even lighter oxygenated products, carbon oxides, and water. 

Other miscellaneous compounds that have been used as inhibitors are sulfur and certain sulfur compounds (qv), picryUiydrazyl derivatives, carbon black, and a number of soluble transition-metal salts (151). Both inhibition and acceleration have been reported for styrene polymerized in the presence of oxygen. The complexity of this system has been clearly demonstrated (152). The key reaction is the alternating copolymerization of styrene with oxygen to produce a polyperoxide, which at above 100°C decomposes to initiating alkoxy radicals. Therefore, depending on the temperature, oxygen can inhibit or accelerate the rate of polymerization. 

As shown in Fig. 12-6, hydroxyl radicals primarily add to either of the carbon atoms which form the double bond. The remaining carbon atom has an unpaired electron which combines with molecular oxygen, forming an RO2 radical. There are two types of RO2 radicals labeled C3OHO2 in Fig. 12-6. Each of these RO2 radicals reacts with NO to form NO2, and an alkoxy radical reacts with O2 to form formaldehyde, acetaldehyde, and HOj. 

A possible mechanism for the formation of the furanones 6 and 7 is illustrated in Scheme 2. The initial alkoxy radical generated from the alcohol 5 and lead tetraacetate (LTA) undergoes /3-scission to produce the acyl radical intermediate 9. Subsequent cyclization to 10 proceeds through attack of the radical at the carbonyl oxygen. The resulting Pb(IV) intermediate 11 finally collapses via the reductive... 

Various /-alkoxy radicals may be formed by processes analogous to those described for /-butoxy radicals. The data available suggest that their propensities for addition vs abstraction are similar.72 However, rate constants for [3-scission of /-alkoxy radicals show marked dependence on the nature of substituents a to oxygen (Figure 3.6).210 420,421 Polar, steric and thermodynamic factors are all thought to play a part in favoring this trend.393... 

Figure 17.2 Lipid peroxidation scheme. LH, a polyunsaturated fatty acid LOOM, lipid hydroperoxide LOH, lipid alcohol L, lipid radical LOO, lipid hydroperoxyl radical LO, lipid alkoxyl radical. Initiation the LH hydrogen is abstracted by reactive oxygen (e.g. lipid alkyl radical, lipid alkoxy radical, lipid hydroperoxyl radical, hydroxy radical, etc.) to produce a new lipid alkyl radical, L. Propagation the lipid alkyl, alkoxyl or hydroperoxyl radical abstracts hydrogen from the neighbouring LH to generate a new L radical.

Further oxidation of an alkoxy radical (RO ), via H-atom abstraction at the carbon adjacent to the oxygen s radical center, leads to the formation of an aldehyde. 

The chemical details of the reactions of representative alkyl radicals, alkoxy radicals, and biradicals with oxygen should be established. Both the rate constants and the immediate products are needed to construct realistic mechanisms for the model. 

A recent report by Bartlett and Guaraldi (5) provides convincing evidence for the existence of the tetroxide as an intermediate in the selfreactions of ferf-butylperoxy radicals. They estimate AH for the formation of tetroxide by dimerization of peroxy radicals to be —6 kcal. per mole and AEact for decomposition of the tetroxide to alkoxy radicals and oxygen to be 11 kcal. per mole. 

Another source of the hydroperoxyl radical is the abstraction of a hydrogen atom from alkoxy radicals by molecular oxygen ... 

If the alkoxy radical has four or more carbon atoms and can form a 6-membered transition state via the alkoxy oxygen abstracting H from a C-H bond, an intramolecular isomerization may occur ... 

It should be noted that some alkoxy radicals derived from oxygenated compounds may have some unique chemistry in addition to these reactions. For example, Tuazon et al. (1998b) have shown that alkoxy radicals derived from OH + acetate reactions, i.e., R C(0)0CH(0 )R2> rearrange and decompose to RCO and the acid RC(0)0H. 

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