Oxygen activation, definition

Similarly, a recent study141 of the homogeneous oxidation of cyclohexene by various low-valent phosphine complexes of Group VIII transition metals yielded no definite proof for initiation by oxygen activation. Results were consistent with reactions involving chain initiation via the usual redox reactions of the metal complexes with traces of hydroperoxides. Long induction periods were observed with peroxide-free hydrocarbons. 

Compared with photooxygenation, i.e. the photochemical activation of oxygen, the definition of photoreduction is more difficult. Many photochemical processes involve redox reactions where one part of the substrate (in intramolecular reactions) or a second molecule (in intermolecular reactions) is reduced and the original substrate is oxidized (or... 

The oxygen meter measurements allow for the definition of a threshold value of the oxygen activity. The complex oxide is (only) stable and can be formed at activities above this threshold value. The threshold for the formation of sodium chromite is at relatively low oxygen concentrations in sodium, for instance about 5 wppm at 550 °C The results of such measurements have been used to establish a diagram... 

What do we mean by oxygen activation A reasonable working definition is catalysis of the oxidation of a hydrocarbon substrate by 2 not involving a classical free radical autoxidation mechanism or direct oxidation by a metal salt. The latter stipulation is needed to exclude Wacker-type oxidation processes in which the oxygen in the product is, initially at least, derived from water. On the other hand, it should not matter whether dioxygen complex formation precedes or follows the oxidation of the substrate by an oxometal complex (see Figure 4). The former pertains to liquid and the latter to gas phase processes. 

Chen P, Bell J, Eipper BA, Solomon El. 2004. Oxygen activation by the noncoupled binuclear copper site in peptidylglycine a-hydroxylating monooxygenase spectroscopic definition of the resting sites and the putative Cum(II)-OOH intermediate. Biochemistry 43 5735—5747. 

TS-1 is a material that perfectly fits the definition of single-site catalyst discussed in the previous Section. It is an active and selective catalyst in a number of low-temperature oxidation reactions with aqueous H2O2 as the oxidant. Such reactions include phenol hydroxylation [9,17], olefin epoxida-tion [9,10,14,17,40], alkane oxidation [11,17,20], oxidation of ammonia to hydroxylamine [14,17,18], cyclohexanone ammoximation [8,17,18,41], conversion of secondary amines to dialkylhydroxylamines [8,17], and conversion of secondary alcohols to ketones [9,17], (see Fig. 1). Few oxidation reactions with ozone and oxygen as oxidants have been investigated. 

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