Oxidation by Oxygen Atom Transfer

This conclusion is in agreement with experiments in which a smootb quartz and cellulose were used as substrates. For above materials the transfer of excitation energy of the dye into the substrate is low which is confirmed by intensive luminescence of adsorbed tripaflavine. Note, that the activation energy of emission of singlet oxygen is close for zinc oxide oxidized by oxygen atoms, quartz and cellulose and amounts to 5-10 kcal/mol [83]. 

The formation of compound I is thought to depend upon aspartate-43 and arginine-38, as detailed in the mechanism shown in Figure 63.1362 Two-electron oxidations of substrate may occur by oxygen atom transfer, but formation of compound II could proceed by reaction (74). 

The possible role of oxygen atom transfer in molybdenum enzyme catalysis was recognized in the early 1970s (190-194). In the ensuing years, a wealth of chemistry has established molybdenum as the premier exponent of such reactions (7, 195). Importantly, related dioxo-Mo(VI) and oxo-Mo(IV) complexes are interconverted by oxygen atom transfer reactions (Eq. (13)). These reactions are effected by reductants (X) such as tertiary alkyl and aryl compounds of the group 15 elements (especially phosphines) and oxidants (XO) such as S- and N-oxides. In many cases, however, the Mo(VI) and Mo(IV) compounds participate in a comproportionation reaction yielding dinuclear Mo(V) complexes (Eq. (15)). 

The metal-catalyzed reaction of an aldehyde with molecular oxygen affords the corresponding peracid. The reaction of low-valent ruthenium catalyst with the peracid thus formed would give an oxo-mthenium intermediate, followed by oxygen atom transfer to afford the corresponding alcohols. The alcohol is further oxidized to the corresponding ketone under the reaction conditions. 

Regarding substrate oxidations, reductive oxygen atom transfer is given by the reverse of this reaction. In marked contrast to the oxotransferases, substrate hydroxylations (formal insertion of an O atom into a substrate C-H bond) follow the reaction stoichiometry given below ... 

Khenkin and Neumann discovered that SET from polycyclic arenes to a mixed-addenda heteropoly acid (HPA), Hj[PV2M0jj 0 (j], can be followed by oxygen atom transfer from the HPA to the radical cation (Scheme 14.7) [38], This type of reactivity is well known in the area of heterogeneous gas-phase oxidation as a Mars-van Krevelen mechanism, whereby a metal oxide at high temperature transfers oxygen atom from the lattice to an activated hydrocarbon substrate, but in homogeneous catalysis, it is veiy rare. 

We examined the epoxidation of carbon-carbon double bonds by oxygen atom transfer reactants. We used the competition between cinnamic acid derivatives and crotonic acid in water (D2O) and water with added 2-propanol. There was no selectivity when the oxidant... 

---