Formation of hydroperoxides

On autoxidation, compounds containing activated C-H bonds (olefins, ethers, alcohols, aldehydes, ketones, and hydrocarbons) always afford in the 

Criegee in Fortschritte Chemische Forschung, Springer-Verlag, Berlin, 1949/50, Vol. 1, p. 508. 

Atmospheric Oxidation and Antioxidants, Elsevier Publ. Co., Amsterdam, 1965. 

Irradiation with ultraviolet light accelerates the uptake of oxygen and is usually essential. Addition of catalytic amounts of heavy-metal salts or other peroxides shortens the induction period and thus the total time for autoxidation. However, traces of heavy metals also lead to more decomposition of the hydroperoxides formed and thus make working up more difficult. It is usually advisable to cease an autoxidation when the peroxide content reaches 5-10%. 

Autoxidation of hydrocarbons 317,318 Saturated hydrocarbons react relatively sluggishly with oxygen. For their autoxidation temperatures of 100-110° are required, also almost always catalysts must be added. Unbranched hydrocarbons give all the possible hydroperoxides in statistical proportions, since the various hydrocarbon groups have almost the same reactivity to oxygen. However, hydrogen on tertiary carbon atoms is preferentially replaced Criegee319 thus obtained decahydro-4a-naphthyl hydroperoxide from decalin  

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As far as oxidation of the polymer with oxygen of the air is concerned, the /3-hydrogen atom in the neighborhood of the C=C double bond is the most likely one to be attacked by oxygen with the formation of hydroperoxide which undergoes further decomposition [19]. OH and CO groups have been detected spectroscopically in the polymer [67,83]. 

Watanabe, H., et al. (1992). Chemiluminescence in the crude extracts of soybean seedlings. Postulated mechanism on the formation of hydroperoxide intermediates. Biochim. Biophys. Acta 1117 107-113. 

The formation of POOH during simultaneous exposure of PP films to ozone and light (LI or L2) can not be obtained kinetically. The experimental results show for rapid formation of hydroperoxide groups which are partially decomposed under UV-irradiation. There is no linear dependence on the ozone concentration. 

Secondly, the interaction of hindered amines with hydroperoxides was examined. At room temperature, using different monofunctional model hydroperoxides, a direct hydroperoxide decomposition by TMP derivatives was not seen. On the other hand, a marked inhibitory effect of certain hindered amines on the formation of hydroperoxides in the induced photooxidation of hydrocarbons was observed. Additional spectroscopic and analytical evidence is given for complex formation between TMP derivatives and tert.-butyl hydroperoxide. From these results, a possible mechanism for the reaction between hindered amines and the oxidizing species was proposed. 

In sum, the results described have led us to postulate the following possible mechanism as explanation of the observed retardation of hydroperoxide formation by TMP derivatives The HALS studied form a complex with the hydroperoxides which is much more efficiently broken down by peroxy and/or alkoxy radicals - with formation of harmless products - than hydroperoxides alone (reaction (26)). The result is a lowering of the rate of formation of hydroperoxides. 

A very serious problem was to clear up the formation of hydroperoxides as the primary product of the oxidation of a linear aliphatic hydrocarbon. Paraffins can be oxidized by dioxygen at an elevated temperature (more than 400 K). In addition, the formed secondary hydroperoxides are easily decomposed. As a result, the products of hydroperoxide decomposition are formed at low conversion of hydrocarbon. The question of the role of hydroperoxide among the products of hydrocarbon oxidation has been specially studied on the basis of decane oxidation [82]. The kinetics of the formation of hydroperoxide and other products of oxidation in oxidized decane at 413 K was studied. In addition, the kinetics of hydroperoxide decomposition in the oxidized decane was also studied. The comparison of the rates of hydroperoxide decomposition and formation other products (alcohol, ketones, and acids) proved that practically all these products were formed due to hydroperoxide decomposition. Small amounts of alcohols and ketones were found to be formed in parallel with ROOH. Their formation was explained on the basis of the disproportionation of peroxide radicals in parallel with the reaction R02 + RH. 

Olefin possesses two reaction centers to be attacked by the peroxyl radical. The peroxyl radicals abstract the hydrogen atom from the weakest C—H bonds in the a-position to the double bond of these compounds with the formation of hydroperoxides. In addition to this reaction, they attack the double bond of the olefin with the formation of oligomeric polyperoxides [12,13,15,137] ... 

The last reaction occurs more rapidly than the reaction of chain termination and as a result two simultaneous chain reactions occur, one with the formation of hydroperoxide and other with alcohol production ... 

Mechanism I. Hydrocarbon oxidizes by consecutive reactions R + 02 and R02 + RH, with the formation of hydroperoxide as the primary product of oxidation. 

The experimental data are in agreement with this equation. In the presence of dioxygen, the alkyl radicals formed from enol rapidly react with dioxygen and thus the formed peroxyl radicals react with Fe2+ with the formation of hydroperoxide. The formed hydroperoxide is decomposed catalytically to molecular products (AcOH and AcH) as well as to free radicals. The free radicals initiate the chain reaction resulting in the increase of the oxidation rate. 

In addition to this reaction, quinones and other alkyl radical acceptors retard polymer oxidation by the reaction with alkyl radicals (see earlier). As a result, effectiveness of these inhibitors increases with the formation of hydroperoxide groups in PP. In addition, the inhibiting capacity of these antioxidants grows with hydroperoxide accumulation. The results illustrating the efficiency of the antioxidants with cyclic chain termination mechanisms in PP containing hydroperoxide groups is presented in Table 19.12. The polyatomic phenols producing quinones also possess the ability to terminate several chains. 

Oxidation to CO of biodiesel results in the formation of hydroperoxides. The formation of a hydroperoxide follows a well-known peroxidation chain mechanism. Oxidative lipid modifications occur through lipid peroxidation mechanisms in which free radicals and reactive oxygen species abstract a methylene hydrogen atom from polyunsaturated fatty acids, producing a carbon-centered lipid radical. Spontaneous rearrangement of the 1,4-pentadiene yields a conjugated diene, which reacts with molecular oxygen to form a lipid peroxyl radical. 

TABLE 2. Enthalpies of formation of hydroperoxides and peroxides containing single-bonded oxygen functional groups (kJ mol )... 

Hi. Lysine. Gamma radiolysis of aerated aqueous solution of lysine (94) has been shown, as inferred from iodometric measurements, to give rise to hydroperoxides in a similar yield to that observed for valine and leucine. However, attempts to isolate by HPLC the peroxidic derivatives using the post-column derivatization chemiluminescence detection approach were unsuccessful. This was assumed to be due to the instability of the lysine hydroperoxides under the conditions of HPLC analysis. Indirect evidence for the OH-mediated formation of hydroperoxides was provided by the isolation of four hydroxylated derivatives of lysine as 9-fluoromethyl chloroformate (FMOC) derivatives . Interestingly, NaBILj reduction of the irradiated lysine solutions before FMOC derivatization is accompanied by a notable increase in the yields of hydroxylysine isomers. Among the latter oxidized compounds, 3-hydroxy lysine was characterized by extensive H NMR and ESI-MS measurements whereas one diastereomer of 4-hydroxylysine and the two isomeric forms of 5-hydroxylysine were identified by comparison of their HPLC features as FMOC derivatives with those of authentic samples prepared by chemical synthesis. A reasonable mechanism for the formation of the four different hydroxylysines and, therefore, of related hydroperoxides 98-100, involves initial OH-mediated hydrogen abstraction followed by O2 addition to the carbon-centered radicals 95-97 thus formed and subsequent reduction of the resulting peroxyl radicals (equation 55). 

There are no available data on the formation of hydroperoxides derived from DNA within cells. This is likely explained, at least partly, by the fact that DNA is a poorer target than proteins for OH radical as observed upon exposure of mouse myeloma cells to ionizing radiation . However, indirect evidence for DNA peroxidation within cells may be inferred from the measurement of final degradation products that may derive from thymine and guanine hydroperoxidation as the result of oxidation reactions mediated by OH radical and O2, respectively (Sections n.A.2 and n.E.2). It may be pointed out that the measurement of oxidized bases and nucleosides within DNA has been the subject of intense research during the last decade and accurate methods are now available . This includes DNA extraction that involves the chaotropic Nal precipitation step and the use of desferrioxamine to chelate transition metals in order to prevent spurious oxidation of overwhelming nucleobases to occur . HPLC coupled to electrospray ionization... 

Of the many studies of the autoxidation of butenes, few (5,11) have emphasized methyl vinyl ketone and methyl vinyl carbinol as major products. In the cumene hydroperoxide-initiated oxidation of 1-butene at 105°C. with 60 atm. of air, Chernyak (5) reported an average hourly rate of production of these two products approximately equal to the combined rates of formation of hydroperoxide and epoxide. The reported rates for hydroperoxide plus vinyl ketone and alcohol indicate that 60% of the products occur by abstraction, in agreement with Van Sickle (17). 

As the quasi-axial hydrogens are in more favorable positions than are the corresponding quasi-equatorial (e ) hydrogens at C3 and C6, the formation of hydroperoxides corresponding to the alcohols 22,26 and 18,21 should be favored over those corresponding to 23,27 and 17,20, respectively. This is the case, as the product distribution... 

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