Oxygen atom transfer hydroperoxides

One further recent preliminary report describes the preparation of reactive hydroperoxide compounds [M(OEP)(Me)(OOH)] (M = P, As, Sb) and their oxygen atom transfer chemistry with triphenylphosphine, indicating that further interesting chemical applications of organoelement Group 15 porphyrins might be expected. 

VII. OXYGEN ATOM TRANSFER FROM SELECTED HYDROPEROXIDES 67... 

In the past decade more efficient code and faster computers have allowed the use of electron-correlated methods of calculation and this has opened this area of theoretical chemistry to a wide range of research groups. The present sequel will be focused mainly on recent theoretical studies on a variety of oxidative processes involving oxygen atom transfer. We will include an extensive description of the very recent chemistry of peroxyni-trous acid (HO—ONO), dioxiranes, peracids and alkyl hydroperoxides. Since chemically realistic molecular systems can now be treated at an adequate level of electron-correlated... 

FIGURE 32. Mechanistic pathway for oxygen atom transfer from peroxyformic acid (a) and alkyl hydroperoxides (b) to trimethylamine... 

However, these reactions can actually be considered as electron transfer or oxygen atom transfer reactions, as in the case of the ozone reactions with the hydroxyl and hydroperoxide ions or with the nitrite ion, respectively ... 

S-oxidation of thioxane by 4a-FlEtOOH in anhydrous dioxane is first order in the flavin hydroperoxide (35). Apparently the oxygen atom transfer potential of 4a-FlEtOOH is such that general-acid-catalyzed assistance of oxygen transfer is not required. 

Many compounds have been synthesized, characterized, and studied as models for proposed intermediates in various homogeneous catalytic reactions. Here we discuss two examples. Complex 2.4 is proposed as a model that shows the mode of interaction between an organic hydroperoxide and high-valent metal ions such as Ti4+, V5+, and Mo6+. This type of interaction is considered to be necessary for the oxygen atom transfer from the hydroperoxide to an alkene to give an epoxide (see Chapter 8). 

Figure 8.5 Catalytic cycle for the molybdenum-catalyzed oxidation of propylene by r-butyl hydroperoxide. Paths A and B are the two proposed alternative mechanisms for oxygen atom transfer. No evidence has been found for 8.26.

The evidence for the proposed mechanism comes from kinetic, spectroscopic (multinuclear NMR), X-ray structure, and theoretical calculations. The kinetic rate law under optimum catalytic conditions is very complex. Under pseudo-first-order conditions, where the concentrations of both 9.35 and the hydroperoxide are much greater than that of allyl alcohol, the rate expression 9.5 is obeyed. In this expression the inhibitor alcohol is an inert alcohol such as isopropanol or f-butanol that is deliberately added to slow down the reaction for convenient rate measurements. The inert alcohol acts as an inhibitor, since it competes with both hydroperoxide and allyl alcohol for coordination to the Ti center. Note that expression 9.5 is consistent with the formation of an intermediate like 9.36, before the rate-determining oxygen atom transfer step. 

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