Cyclohexene reaction + peroxy radicals

As illustrated in Scheme 3.26, the role of the Pd(II) porphyrin complex is the photochemically sensitized generation of singlet oxygen Oj), which forms the allylic hydroperoxide 14. Subsequent Fe3+ porphyrin-catalyzed hydrogen abstraction from 14 yields the peroxy radical 16, while the catalytic Fe3+ species is recycled by homolytic 0—0 bond cleavage of 14 to give the alkoxy radical 17. Both radicals 16 and 17 are involved in the dark reaction where the remaining cyclohexene is consumed. 

The values obtained for the rate coefficients of these reactions were (1.6 0.6) x 106 and (3 1) x 106 l.mole 1.sec 1 respectively. Similar values of the rate coefficients for the recombination of peroxy radicals were obtained from studies of the photooxidation of cyclohexene and other olefins by the rotating sector technique75. Production of peroxy radicals was presumably via the reactions... 

Let us consider as an example the reaction of cyclohexene with ozone in the atmosphere. This reaction has been studied in laboratory chamber experiments by Kalberer et al. (2000). A potential reaction mechanism is depicted in Figure 14.11. The first steps of the reaction are the formation of an initial molozonide M, its transformation to a peroxy radical intermediate, and then to a dioxyrane-type intermediate, and finally to an excited Criegee biradical [CHO(CH2)4CHO O ]. A series of reactions then lead from the Criegee biradical to stable products, some with five and some with six carbon atoms (Figure 14.11). This rather complicated series of reactions leads to the stable gas-phase products listed in Table 14.10. 

An example of this reaction is the reaction of cyclohexene with t-butyl perbenzoate, which is mediated by Cu(I)." The initial step is the reductive cleavage of the peroxy ester. The t-butoxy radical then abstracts hydrogen from cyclohexene to give an allylic radical. The radical is oxidized by Cu(II) to the carbocation, which captures benzoate ion. 

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