Hydrogen peroxide nucleophilic cleavage

It may be reasonable to argue that this further activation is achieved in several ways. The acid-catalysis required for Gal and de Bruin complex [Rh(/c -bpa)(cod)](PF6) to react with dioxygen can be used to protonate the peroxo compoimd (Scheme 10) to a hydroperoxo species. This is a way to achieve further activation of dioxygen, since it decreases the nucleophilic character of the peroxo hgand and makes interaction with the coordinated olefin easier. Recent works by Moro-oka [88,89] and Braun [90] (Scheme 15) have shown that peroxorhodium complexes can be protonated to hydroperoxo compounds. However, the addition of a second mole of acid leads to hydrogen peroxide ehmination rather than to the highly electrophilic oxo species (M = O) that could result from the heterolytic cleavage of the O - O bond with removal of water. 

The direct use of hydrogen peroxide has rarely been shown to be of practical value in the cleavage of double bonds. However, olefins which are activated towards nucleophilic attack are sometimes cleaved by excess alkaline hydrogen peroxide. For example, a-keto olefins can be cleaved to the aldehydes144 and cinnamaldehyde is cleaved via the epoxide to benzaldehyde (Figure 3.30).145... 

Because the HO-OH bond in hydrogen peroxide is weak (AHdbe = SlkcalmoH vs. 90kcalmoH for the H-OOH bond), there has been a tendency to assnme homolytic cleavage in the reactivity and activation of HOOH. However, a pioneering study established that sulfur dioxide is converted to sulfuric acid through a nucleophilic addition mechanism (equation 79). 

Furthermore, oxidation of fatty acids to vicinal diols, as well as their oxidative cleavage, are important industrial applications. Vicinal diols of unsaturated fatty compounds can be prepared by nucleophilic ring opening of the epoxides after epoxidation, but difficult technical conditions are necessary to achieve this ring opening [9]. The use of Re- [10], W- [11], or Mo [l]-based catalysts with hydrogen peroxide can give a jyn-diol via the epoxide as intermediate (eq. (2)). 

One such experiment involved the introduction of an iron chelate on to a unique residue on the protein human carbonic anhydrase I (HCAI). By labeling the free SH group of Cys-212 of HCAI with (/ -bromoacetamidobenzyl)EDTA, in which the EDTA was loaded with iron(II), the HCAI peptide backbone was cleaved in one place. The cleavage takes place in the presence of ascorbate and hydrogen peroxide. It is believed that the mechanism for cleavage is by nucleophilic attack of an iron-coordinated peroxo group at the carbonyl carbon. This is similar to the hydrolysis of peptides by coordinated water or hydroxide. 

Phenyl esters are suggested for carboxyl protection in peptide synthesis cleavage is achieved under mild conditions without racemization by treatment with hydrogen peroxide. Such enhanced nucleophilicity of peroxy-anions is ascribed to the a-effect of the unshared pair of electrons on the atom adjacent to the nucleophilic atom, and this phenomenon has been studied further. ... 

Substitution reactions on dialkyl peroxides without concurrent peroxide cleavage have been reported, eg, the nitration of dicumyl peroxide (44), and the chlorination of di-/ fZ-butyl peroxide (77). Bromination by nucleophilic displacement on a-chloro- or a-hydroxyalkyl peroxides with hydrogen bromide produces a-bromoalkyl peroxides (78). 

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