Oxidation by Electron Transfer

A good example is the oxidation of aromatic compounds by manganic or cobaltic acetates in acetic acid, in particular the oxidation of arylmethanes to arylmethyl acetates, which takes place as follows  

Manganic acetate is not a sufficiently powerful oxidizing agent to attack toluene in this way, but it will attack derivatives of toluene in which the ionization potential has been lowered by introduction of — E substituents (e.g., p-methoxytoluene). Cobaltic acetate, being a more powerful oxidizing agent than manganic acetate, will also attack toluene. 

An interesting example seems to be provided by the Shell process for 

The final step is undoubtedly a typical radical chain autooxidation (p. 274), involving the propagation steps 

The oxidation of arylmethanes to carboxylic acids can also be brought about by alkaline ferricyanide, probably by a similar electron transfer mechanism i.e., 

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Electron transfer of the glucose oxidase/polypyrrole on the electrode surface was confirmed by differential pulse voltammetiy and cyclic voltammetry. The glucose oxidase clearly exhibited both reductive and oxidative current peaks in the absence of dissolved oxygen in these voltammograms. These results indicate that electron transfer takes place from the electrode to the oxidized form of glucose oxidase and the reduced form is oxidized by electron transfer to the electrode through polypyrrole. It may be concluded that polypyrrole works as a molecular wire between the adsorbed glucose oxidase and the platinum electrode. 

A similar oxidation by electron transfer from phenolate anion to Cu(II) is also an important step in... 

In the direct method substrates are oxidized by electron transfer from the substrate to the anode, while in the indirect method they are oxidized in solution by the oxidized form of a mediator that is generated from the reduced form at the anode. Thus, efficiencies in direct and indirect methods are largely dependent on the oxidation potentials of substrates and mediators, respectively. 

Oxidation of guanine and 8-oxo-7,8-dihydroguanine with a Mn(IV)=0 species, a two-electron oxidant and riboflavin, a known photosensitizer and a one-electron oxidant, was studied. A quantification of the ratio between one- and two-electron oxidation mechanisms of guanine oxidation by electron transfer led to the conclusion that one-electron oxidation predominates and the two-electron oxidation process is a minor pathway.288... 

This is a very reactive radical which can abstract H atoms, add to double bonds, or oxidize by electron transfer quite rapidly. A few examples of rate constants for its reactions are given in Table 3 rate constants for over a hundred reactions of S0 are given in a recent compilation (21)... 

With excess base the dianion is formed, which is easily oxidized by electron transfer or reaction with 02 ... 

Enzymes catalyzing redox reactions in which oxygen serves as the electron acceptor may be divided in two groups those that catalyze substrate oxidation by electron transfer to the acceptor (oxidases and peroxidases) and those that catalyze substrate... 

HRP compound II is further oxidized by electron transfer with [Ru(bpy)3] + to afford compound I (Scheme 11) [168]. Compound II was generated spontaneously after photolysis of the HRP-[Ru(bpy)3] +-[Co(NH3)5Cl] + system [168], The rate of formation of compound I obeys second-order kinetics, being first order in each reactant, as given by Eq. 11 [168],... 

Oxidation by electron transfer of the a-methylenic group by the metal ion. 

Cl2. —This radical may abstract hydrogen, add to unsaturated compounds, or oxidize by electron transfer. Extensive measurements of rate constants for its reaction with aliphatic, aromatic, and inorganic compounds have helped to clarify the relative importance of these reaction modes. 

The reaction of Cl 2 with aromatic compounds can occur through addition to the benzene ring (A < 10 but the important reaction is direct oxidation by electron transfer which becomes possible when the ring is substituted with OH, OMe, NHg, or related groups (A >10 s ). ... 

There have been several papers dealing with the oxidation reactions of nitrogen and sulfur-based compounds. Hindered amines, such as substituted 2,2,6,6-tetramethylpiperidines, are easily oxidized by electron-transfer reactions to the corresponding cation, by the sulfate radical anion, and by sensitized electron transfer to carbonyl triplets. Radicals derived from tertiary piperidines were observed directly by optical spectroscopy and deprotonated to a-alkylamine radicals. The amine radical cation derived from secondary piperidines deprotonated to give aminyl radicals. In the presence of oxygen, both classes were oxidized to give nitroxyl radicals, but by different proposed mechanisms. Both oxidation and fragmentation pathways have been observed in the photochemical reaction of alkyl phenyl sulfides with tetranitromethane. The oxidation of various A-(arylthio)-4-substituted-2,6-diarylanilines (18) with PbOa yielded, in most cases, persistent radicals that could... 

The transition metals mentioned are present in particulates emitted from the combustion plant, and are active in promoting the subsequent SO2 oxidation (by electron transfer). 

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