Cleavage of the 0-0 bond

Eq. 34). The resultant p-mercurioalkyl peroxides can often be demercurated with sodium borohydride (Eq. 35), or by brominolysis (Eq. 36) without substantial cleavage of the 0-0 bond. Both peroxymercuration and demercurations occur rapidly under mild conditions 48). 

Additional results of the enhancement in phenol conversion (to dihydroxy benzenes) and oxidation of allyl alcohol (to glycidol and allylic oxidation products) catalyzed by TS-1 in various solvents are illustrated in Fig. 46. In solvents with high dielectric constants, the heterolytic cleavage of the 0-0 bond... 

A tentative mechanism involving the heterolytic cleavage of the 0-0 bond along with electron transfer from the alkene to the electrophilic oxygen of the Ti(02H) complex is shown in Scheme 27. 

In the envisaged titanium oxo complex, the Ti atom is side-bound to the peroxy moiety (02H), consistent with all the spectroscopic results mentioned in Section III in Scheme 27, between the two O atoms that are side-bound to Ti4+, the O atom attached to both the Ti and H atoms is expected to be more electrophilic than the O atom attached to only the Ti atom and is likely to be the site of nucleophilic attack by the alkene double bond. The formation of the Ti-OH group (and not the titanyl, Ti=0, as proposed by Khouw et al. (221)) after the epoxidation and its subsequent condensation with Si-OH to regenerate the Ti-O-Si links had been observed (Section III.B) by FTIR spectroscopy by Lin and Frei (133). Because this is a concerted heterolytic cleavage of the 0-0 bond, high epoxide selectivity and retention of stereochemistry may be expected, as indeed has been observed experimentally (204). 

Reaction 13.22 is the net result of two steps, the first being the photochemical cleavage of the 0-0 bond in di-terf-butylperoxide (reaction 13.23), followed by the abstraction of the hydroxylic hydrogen in phenol by the ferAbutoxyl radical (reaction 13.24). 

The rest of the photo-oxidation on the glycol portion is continued in Scheme 18.3. The cleavage of the 0-0 bond should be very facile. Both photolytic and thermal decomposition of these peroxides are possible. 

The cleavage of the 0-0 bond of the hydroperoxide is promoted by the push-pull mechanism shown in Fig. 4, in which the native HRP reacts with the unionized form of the hydroperoxide. Thus, the latter is converted into a much better nucleophile upon transfer of its proton to the distal basic group (His 42). 

The positive charge on the proximal His 170 facilitates the formation of the iron-peroxide bond. Thus, inversion of the charge properties at the active site of HRP facilitates the heterolytic cleavage of the 0-0 bond. The positive charges on His 42 and Arg 38 and the negative charge on His 170 assist the formation of the Fe = 0 species. 

Fig. 9. Possible electron transfer mechanism for NOS utilizing a pterin radical. The oxy-complex in 2 is shown as the ferric (Fe +)-superoxide complex. The role of the pterin then is to donate an electron to the iron, thus giving the peroxy dianion in 3. The dianion is a potent base that abstracts a proton from the substrate, giving 4. The system is now set up for a peroxidase-like heterolytic cleavage of the 0-0 bond to give the active hydroxylating intermediate in 5 and, finally, the first product in 6.

RuCl2(H20) ]+ This species was made from RUCI3 in HCl from pH 0.4-2.0. Kinetic studies suggest that in the epoxidation by [Ru(7l2(H20)4]X02/water-dioxane of cyclo-octene and -hexene homolytic cleavage of the 0-0 bond plays an essential part [771, 772], and that this is so for similar oxidation of alkanes (e.g. of cyclohexane to cyclohexanol) [771],... 

Two extreme mechanisms have been proposed for the unimolecular dioxetane decomposition the concerted mechanism , whereby cleavage of the peroxide and the ring C—C bond occurs simultaneously, and the biradical mechanism whereby the initial cleavage of the 0—0 bond leads to the formation of a 1,4-dioxy biradical whose subsequent C—C bond cleavage leads to the formation of the two carbonyl fragments (Scheme 8). Although the biradical mechanism adequately explains the activation parameters obtained for most of the dioxetanes smdied, it appears not to be the appropriate mechanistic model for the rationalization of singlet and triplet quanmm yields. Therefore, an intermediate mechanism has been proposed, whereby the C—C and 0—0 bonds cleave in a concerted, but not simultaneous, manner (Scheme 8) . 

Iron(n) is known to decompose hydrogen and dialkyl peroxides to free radicals by reductive cleavage of the 0—0 bond and early investigations established the parasite s sensitivity to these species. When treated with radiolabelled C-artemisinin, the hemin-hemozoin fraction of the lysed malaria-infected erythrocytes was shown to contain a radiolabel, though the mechanism of incorporation is not clear. Meshnick and coworkers demonstrated that uninfected cells did not contain radiolabelled proteins whereas six radiolabelled proteins were isolated from cells infected with the Plasmodium falciparum (P. falciparum) strain of the parasite. It was suspected that one of the alkylated proteins was the Histidine Rich Protein (HRP) that was known to bind multiple heme monomers and therefore thought to be instrumental to the parasite s detoxification process. Moreover, iron chelators were found to inhibit the lethal effects of peroxides on the parasite. ... 

The proposed mechanism for the degradation involves SET to the peroxide resulting in homolytic cleavage of the 0—0 bond. An Ol-centred radical led to the formation of the enone, while an 02-centred radical afforded the diol. 

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