Oxygen atom transfer mechanism

Oxidation of Fe " aq in solution by ozone, at pH 0 2, showed evidence for an oxygen atom transfer mechanism with as a transient intermediate en route to Fe +. The rate constant at 298 K is... 

X 10 M at 1.0 M ionic strength. A simple outer-sphere mechanism can be ruled out since k is more than two orders of magnitude greater than predicted by the Marcus cross-relation, and an oxygen atom transfer mechanism has been proposed. ... 

Figure 1. Postulated oxygen atom transfer mechanism for the enzymic reduction of nitrate by Mo(H20)63+, assuming NADPH, H+ to be the substrate for reducing Mo02(H20) to Mo(H20)63+...

Subsequently, RR was used to successfully detect structural changes between the oxidized and reduced forms of both DMSOR and BSOR that are consistent with the proposed oxygen atom transfer mechanism of the catalytic reaction (95, 97). These experiments make use of the readily measurable isotopic shifts in vibration frequency between ieO=Mo and lsO=Mo to follow the fate of the oxygen atom removed from DMSO (or BSO) by the Mo. In this way, the clean transfer of 180 from DMSlsO to Mo(IV) to yield the oxidized form of the active site as Mo(VI)=180 was directly observed as well as the substrate-bound intermediate, (DMS180)Mo(IV). Further discussion of the technique of RR applied to metal dithiolenes and dithiolene-containing enzymes is included in Chapter 4 in this volume (98). 

Only in the coupled oxidation of nitrite using glucose oxidase-glucose- 0 (as H 0 0H generating system) and beef liver catalase, which results in the formation of isotopically enriched nitrate (183a), are the results compatible with an oxygen atom transfer mechanism [Eqs.(28) and (29) ]. Even in this case, alternative interpretations are possible, such as oxidation of nitrite via outer or inner sphere electron transfers [Eqs. 

Fig. 21. Mechanism of the oxidative chemistry mediated by high-valent manganese-0x0 porphyrin. A, oxygen atom transfer mechanism B, two-electron abstraction mechanism. The porphyrin ligand is simplified. AH2 is a two-electron donor.

Hamilton GA (1964) Oxidation by Molecular Oxygen. II. The Oxygen Atom Transfer Mechanism for Mixed-Function Oxidases and the Model for Mixed-Function Oxidases. J Am Chem Soc 86 3391... 

A deviation from the oxygen atom transfer mechanism comes from the RDX experiments of Rauch and Fanelli in which they observe the formation of NO2 in addition to the products observed by Robertson and Bulusu. Their results suggest that the NO2 is formed in the gas-phase decomposition of RDX. 

However, substrates with oxidizable lone pairs (such as thioethers, RSR) are usually oxidized through oxygen atom transfer mechanism, eq 5 ... 

Within each group relatively simple molecules will be discussed first. In some cases a given substrate may be reduced by modes (i) and (ii) depending on the reductant and in other cases the mechanism is unknown, for example the reduction of perchlorate ion may involve either electron-acceptance or oxygen atom transfer. 

Importantly, the oxidations in equation (90) are considerably accelerated in the presence of added salt such as n-Bu4N+PF and markedly retarded in nonpolar solvents (such as CCI4 and hexane) as well as in the presence of added nitrate salts, which suggests the critical role of ionic intermediates (viz. NO+NOf).251-253 Accordingly, the ionic mechanism for the oxygen-atom transfer from NO to various donors is outlined in Scheme 24. 

A new generation of oxorhenium compounds has now been prepared. They catalyze oxidation reactions of a different type, and appear to function by a different mechanism. They are oxorhenium(V) compounds that form usually metastable dioxorhenium(VII) intermediates. The mechanisms feature Rev(0)-to-ReVII(0)2 interconversions and catalyze oxygen atom transfer reactions. The mechanisms show a certain diversity as to the steps that enter in a kinetic sense. Yet the schemes presented in this review show a great deal of similarity in their overall mode of action. 

The coordinated dioxygen in 3 -Co(02) is nucleophilic and reacts with electron-poor organic substrates such as benzoyl chloride, malonitrile, and tetracyanoethylene to transfer a single oxygen atom. A mechanism involving a homolytic Co-0 bond cleavage has been proposed (33). The nucleophilic character of 3 -Co(02) was... 

Ruthenium(in) catalyses the oxidative decarboxylation of n-butyric acid and isobutyric acid by ceric sulfate in aqueous acid. A mechanism for the Ru(III)-catalysed oxidation of o-hydroxybenzoic acid by an acidic solution of bromamine-B (PhS02-NNaBr, BAB) has been proposed based on a kinetic smdy. An ionic mechanism is suggested for the ruthenium(III) analogue of the Udenfriend-type system Ru(III)-EDTA-ascorbate-02, for the selective oxygen-atom transfer to saturated and unsaturated hydrocarbons. The kinetics of the oxidation of p-XC6H4CHPhOH(X =... 

Dimesityldioxirane, a crystalline derivative, has been isolated by Sander and colleagues and subjected to X-ray analysis. The microwave and X-ray data both suggest that dioxiranes have an atypically long 0—0 bond in excess of 1.5 A. Those factors that determine the stability of dioxiranes are not yet completely understood but what is known today will be addressed in this review. A series of achiral, and more recently chiral oxygen atom transfer reagents, have been adapted to very selective applications in the preparation of complex epoxides and related products of oxidation. A detailed history and survey of the rather remarkable evolution of dioxirane chemistry and their numerous synthetic applications is presented in Chapter 14 of this volume by Adam and Cong-Gui Zhao. Our objective in this part of the review is to first provide a detailed theoretical description of the electronic nature of dioxiranes and then to describe the nuances of the mechanism of oxygen atom transfer to a variety of nucleophilic substrates. 

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