Cyclic hydroperoxides

The rt,/3-unsaturated linear carbonyl compound 39 is obtained by the decomposition of the cyclic hydroperoxide 38 with PdCl2,[35]. The a, 0-epoxy ketone 40 is isomerized to the /3-diketone 41 with Pd(0) catalyst[36]. The 1,4-epiperoxide 42 is converted into the /3-hydroxy ketone 43 and other products[37]. 

The alkenyl hydroperoxides and polymeric dialkyl peroxides are fairly stable at ambient temperature but decompose appreciably at the reaction temperatures studied. Thermal stabilities of the alkenyl hydroperoxides and dialkyl peroxides in the olefin solution were determined by heating the solution at 110°C. under nitrogen. The peroxide numbers were plotted vs. time to estimate the half-lives in solution. The thermal decomposition half-lives of these alkenyl hydroperoxides are compared with values from the literature for acyclic and cyclic hydroperoxides in Table IV. Secondary acyclic alkenyl hydroperoxides appear to be less... 

Decomposition of cyclic hydroperoxides. Cyclohexyl hydroperoxide (1) is decomposed mainly to (E)-2-hexenal by this salt and a trace of FeSO -VHaO in a two-phase system of water and an organic solvent. Highest yields (58%) are obtained with nitrobenzene. Na2PdCl4 is the most satisfactory water-soluble eomplexof PdX, for this purpose. The reaction is general, but yields are low from Cg-Ci2 cyclic hydroperoxides. Cyclopentyl hydroperoxide is converted into the corresponding enal in 73.6% yield. 

Ozone adds directly to double bonds in fatty acids to form ozonides (183-185). These decompose to lipid alkoxyl and peroxyl radicals that abstract hydrogens to initiate radical chains (186). In the process, internal rearrangements within the original lipid molecule(s) yield hydroxy epoxides and hydroxy epidioxides with 1,3- and 1,4-cyclic hydroperoxides ... 

It has been demonstrated, not only with linolenate (18 3) aqueous solutions but also with linoleate (18 2), and more recently with arachidonate (20 4) solutions [18], that the hydroperoxides were composed of two different kinds of molecules according to the concentration of PUFA in the irradiated medium. Indeed, for a given PUFA, above the critical micellar concentration, namely when micelles are formed, one type of hydroperoxide predominates, whereas when monomers (or very small aggregates) are dispersed in solution (below the cmc), other types of hydroperoxide are formed. This phenomenon is illustrated in Figure 5 for arachidonate. We can see that monohydroperoxides are produced in micelles whereas in monomers, either a cyclic hydroperoxide or an aliphatic dihydroperoxide is obtained [18]. 

Ferrous sulfate/cupric sulfate Oxidation of free radicals as a preparative method Ring opening of cyclic hydroperoxides... 

Cyclic hydroperoxides have been characterised by chemical ionisation MS with a direct exposure probe [262]. 

Aromatic aldehydes and cyclic perfluoroketones are oxidized to a-hydroxy hydroperoxides or bis(a-hydroxy) peroxides, aliphatic ketones are converted to esters, and ketenes are converted to a-lactones... 

Aldehydes Propionates Cyclic polyethers a-Amino acids Hydroperoxides C2H5, CHO... 

Another useful oxidative reaction in aqueous medium is the cleavage of cyclic ketones by hydrogen peroxide in the presence of Fe(II) salts (Eq. 8.25). The reaction proceeds through an a-hydroxy hydroperoxide, leading to a variety of products.50 The presence of Fe(II) salts decomposes the intermediate, generating a radical. In the presence of halide ions, the radical leads to synthetically useful halocarboxylic acids.51... 

Many ethers, either of open chain (diethyl or diisopropyl ether) or cyclic type (tetrahydrofuran, dioxane), are readily autoxidised on exposure to air or oxygen in presence of light. The hydroperoxides formed are less volatile than the parent ether and may be concentrated to a dangerous extent if distillation of peroxidised material is attempted. 

In addition to the classification of inhibitors according to their mechanisms of the action on oxidation, they can be classified into consumable and long-lived inhibitors. A consumable inhibitor is irreversibly consumed in its reactions with free radicals (R or RCV) or hydroperoxide. The stoichiometric coefficient of inhibition of such inhibitors is typically equal to one or two per inhibitory functional group. However, in some systems (for example RH 02 InH), an inhibitor can act cyclically so that, getting repeatedly regenerated, the... 

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. 

Kinetic Parameters of Inhibitors of Cyclic Chain Termination in PP Containing Hydroperoxide Groups and Reacting with H02 Radicals... 

FIGURE 25.3 The formation of linear hydroperoxides and cyclic prostanoids during peroxidation of unsaturated acids with bisallylic positions. 

The cyclic carbonate could also be synthesized directly from the alkenes in the same reactor by reacting the alkenes in the presence of Ti-MCM-41 with a mixture of an epoxidizing agent (such as H202 or tert-butyl hydroperoxide) and... 

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