Hydroperoxide radicals

Oxidative degradation of polymers is initiated by radicals (R ) generated in the polymer by heat or mechanical shear during processing or by exposure to UV light. These radicals, in turn, react with 02 to form peroxy and hydroperoxide radicals that promote radical reactions. 

In heterogeneous domains of oxidized PP, terminal dioxetane groups may be formed from 1,3-peroxyl hydroperoxides radicals in the sequence of reactions depicted in Scheme 7. 

Another factor complicating the situation in composition of peroxyl radicals propagating chain oxidation of alcohol is the production of carbonyl compounds due to alcohol oxidation. As a result of alcohol oxidation, ketones are formed from the secondary alcohol oxidation and aldehydes from the primary alcohols [8,9], Hydroperoxide radicals are added to carbonyl compounds with the formation of alkylhydroxyperoxyl radical. This addition is reversible. 

With the formation of free radicals having been initiated, these radicals react with oxygen (Reaction 3) to begin the propagation of the radical chains in forming a peroxy radical. The peroxy radical then attacks the 10-carbon-hydrogen bond to form the hydroperoxide radical (Reaction 4). [The possibility of such an intramolecular attack has been demonstrated in an aliphatic system where two reactive hydrogen atoms are located in the favorable 1,4-positions (9)]. 

The hydroperoxide radical reacts with another molecule of oxygen (Reaction 5) to give the hydroperoxide-peroxy radical. This radical in turn reacts with a molecule of dihydroanthracene (Reaction 6), to give the dihydroperoxide and generate a radical to propagate the chain. However, the hydroperoxide radical formed in Reaction 4 may be decomposed by a carbanion to the anthracene diradical (Reaction 7). [An example of the decomposition of an unstable hydroperoxide by reaction with an anion is found in the basic autoxidation of 2-nitropropane (3).]... 

Supporting Evidence. Reactions 5 and 7 indicate that the hydroperoxide radical can react with either oxygen or a carbanion to give anthraquinone or anthracene, respectively. Thus, high oxygen and low carbanion concentrations would favor the formation of anthraquinone ... 

Subsequent one-electron transfer and intramolecular hydrogen migration lead to radical 102 followed by reaction with 02 to yield hydroperoxide radical 103. Radical 103 is further oxidized to a dihydroperoxide (104), which decomposes to anthra-quinone. Alternatively, 103 may be transformed to a diradical that eventually gives anthracene as a byproduct. The ratio of the two products strongly depends on the solvent used. The highest yield of anthraquinone (85% at 100% conversion) was achieved in 95% aqueous pyridine. 

With the decay of H04° into oxygen and hydroperoxide radical the chain reaction can start anew (see equation 2-1), Substances which convert OH0 into superoxide radicals 02°7H02° promote the chain reaction they act as chain carriers, the so-called promoters. 

This quantum yield corresponds to the overall process where hydrogen peroxide is not just removed by reaction (54), its direct photolysis, but also by parallel reactions involving the hydroxyl and hydroperoxide radicals as shown below ... 

The reaction I is to a certain extent analogous to the reaction of hydrogen atom abstraction by the peroxide ot hydroperoxide radicals from the hydrocarbons ... 

Among protein oxidation products, formation of protein peroxides should be mentioned. Protein peroxidation occurs as a reaction secondary to free-radical attack on amino acid side groups, effecting a carbon-centered free radical of amino acid formation. Such a radical reacts with the oxygen molecule and produces a hydroperoxide radical ... 

The second step, which is also a reaction in the propagation cycle, is the addition of another molecule to the hydroperoxide radical to generate new free radicals. 

Radical from the corresponding hydroperoxide. Radical from the corresponding hydrocarbon. 

In general, alkoxy radicals generated in cellulose are stable as compared to carbon radicals. The carbon radicals readily undergo secondary termination reactions. Carbon radicals in vacuo have an affinity for recombination and hydrogen abstraction to stabilize themselves in the presence of oxygen, and they are transformed rapidly into hydroperoxide radicals to build up hydroperoxide. This rapid oxygenation reaction is further accelerated when excited oxygen is presented (S3). 

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