Addition reactions oxygen terminator

There is reason to believe that the rate of addition of oxygen atoms to olefins and the position of addition (orientation) are not governed by the same factors. In the case of 2-pentene the addition takes place at the doubly bonded carbon atom to which the CH3 group is attached and not to the one where the C2HB group is attached. At the same time the rates of addition to propylene and to 1-butene are the same and in both cases terminal addition occurs. Similarly, the rates of addition to 2-butene and 2-pentene are also about the same. If the rates of addition and the orientation were determined by the same factors, approximately equal addition at the two double bond C-atoms would be expected. Since this is not the case, it appears reasonable to conclude that the transition state which determines the rates of addition occurs quite early in the reaction process, before oxygen atoms become localized on either of the two double bond C-atoms. 

Fig. 3. Autoxidation of polyunsaturated fatty acids in phospholipid membranes. Addition of oxygen to lipid free radicals is extremely fast. It yields peroxyl radicals ROO which will tend to capture labile hydrogen atoms of neighbouring polyunsaturated lipids. Accidentally produced free radicals will therefore initiate a chain reaction of lipid peroxidation which will propagate along membranes. This process can result in several dozen propagation steps before it is stopped by a termination reaction. Examples of such termination reactions are the recombination of peroxyl radicals and the formation of a stable free radical from a free radical scavenger (scavH). Termination through recombination of low steady-state concentration of alkyl radicals is unlikely in aerobic medium.

Franchi and coworkers reported on the effect of solvents on hydrogen atom abstraction from phenolic antioxidants by primary alkyl radicals , which could be useful when studying oxidations at low oxygen partial pressures because under those conditions the addition of oxygen to substrate alkyl radicals can be reversible (equation 36) and alkyl radicals could play a role in termination reactions (equation 37)" ... 

Epoxidation of butadiene occurs by addition of dissociatively-adsorbed oxygen to one of the localized C=C bonds to form epoxybutene. The addition of oxygen across the terminal carbon atoms does not occur to any measurable extent. The direct participation of molecular oxygen can be ruled out based both on selectivity arguments as well as the kinetic model for the reaction. The kinetics imply a dual site mechanism. One site, which is unpromoted, serves as the site for butadiene adsorption, while the second site, which is promoted, functions as the site for dissociative oxygen adsorption and epoxybutene formation. 

Addition of the terminal oxygen of phenyl peroxy to the ortho position of the aromatic ring has a barrier that is only 2 - 3 kcal mol lower than the reverse reaction back to ohenvl radical plus O2. Because its transition state structure is tight,... 

As(III) may be oxidized to As(V) by S20 in aqueous alkaline solutions/ At pH > 12.0, the observed rate constant is 1.6 0.3 x 10 M s at an ionic strength of 0.1 M. Sustained oscillations in redox potential, pH, and the concentration of dissolved O2 are reported in the Cu(H)-catalyzed reaction betwen K2S2O8 and Na2S203 in a stirred tank reactor. A free radical mechanism involving Cu(I), Cu(II), and the radicals SO4 and S2O3 may be used to account for the dynamic behavior of this sytem. The kinetics and mechanism of the oxidation of thiosulfate coordinated to cobalt(IH) by peroxymonosulfate have been reported.The reaction proceeds via two consecutive nucleophilic additions of the terminal peroxy oxygen atom to the coordinated S20 . 

The chemistry of carbonyl compounds with transition metal compounds is very rich. The paper by J. Bryan and M. Mayer [22] deserves special attention. It reports on a new type of oxidative addition reaction in which a carbonyl double bond is cleaved to form divalent ligands. The final result is an oxoalkylidene complex (Sch. 6). Such complexes are discussed in a mechanistic study of OM mediated by high-valent group 6 catalysts [23]. Three bimolecular chain termination steps, resulting in olefin, carbonyl compound and singlet oxygen, are proposed. 

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