Oxidation with dioxygen

Codeposition of silver vapor with perfluoroalkyl iodides at -196 °C provides an alternative route to nonsolvated primary perfluoroalkylsilvers [272] Phosphine complexes of trifluaromethylsilver are formed from the reaction of trimethyl-phosphme, silver acetate, and bis(trifluoromethyl)cadmium glyme [755] The per-fluoroalkylsilver compounds react with halogens [270], carbon dioxide [274], allyl halides [270, 274], mineral acids and water [275], and nitrosyl chloride [276] to give the expected products Oxidation with dioxygen gives ketones [270] or acyl halides [270] Sulfur reacts via insertion of sulfur into the carbon-silver bond [270] (equation 188)... 

The stereochemistry of dioxygen oxidation has been studied for the di-f-butyldimesityldisilene (3).93 Oxidation of (E)-3 produced ( )-59a, ( > 60a, and ultimately ( )-61a exclusively, showing that all the steps in the sequence are stereospecific with retention of configuration. (Similar oxidation of a mixture of ( > and (Z)-3 gave isomeric mixtures of 59a, 60a, and 61a having the same proportions of stereoisomers as in the starting material.) Oxidation of 3 was found to be stereospecific both in solution and in the solid state. 

At a molecular level, two mechanistic routes for photosensitized oxidation with dioxygen are usually recognized, termed type I and type II. 

Catalytic oxidation with dioxygen. The well-known aerial oxidation of the nitric oxide (NO ) produced in the stoichiometric oxidations in equation (90) to nitrogen dioxide (NO ) forms the basis for the NO -catalyzed oxidation of various donors with dioxygen251-253 (equation 96). 

Radicals also exhibit high activity in addition reactions. For example, the peroxyl radical of oxidizing styrene adds to the double bond of styrene with the rate constant k = 68 Lmol-1 s-1, and dioxygen adds with k = 5.6x 10-10Lmol-1 s-1 (298 K). As in the case of abstraction reactions, the distinction results from the fact that the first reaction is... 

The trimolecular reaction of two dioxygen molecules with two C—H bonds of one hydrocarbon was observed in ethylbenzene oxidation [43]. 

Scheme A. This scheme is typical of the hydrocarbons, which are oxidized with the production of secondary hydroperoxides (nonbranched paraffins, cycloparaffins, alkylaro-matic hydrocarbons of the PhCH2R type) [3,146]. Hydroperoxide initiates free radicals by the reaction with RH and is decomposed by reactions with peroxyl and alkoxyl radicals. The rate of initiation by the reaction of hydrocarbon with dioxygen is negligible. Chains are terminated by the reaction of two peroxyl radicals. The rates of chain initiation by the reactions of hydroperoxide with other products are very low (for simplicity). The rate of hydroperoxide accumulation during hydrocarbon oxidation should be equal to ...

Like hydrocarbons, ethers are oxidized by dioxygen via the chain mechanism. The mechanism of ether oxidation with initiator I includes the following elementary steps [8,9] ... 

Salts of transition metals are widely used in technological processes for the preparation of various oxygen-containing compounds from hydrocarbon raw materials. The principal mechanism of acceleration of RH oxidation by dioxygen in the presence of salts of heavy metals was discovered by Bawn [46 19] for benzaldehyde oxidation (see Chapter 1). Benzaldehyde was oxidized with dioxygen in a solution of acetic acid, with cobalt acetate as the catalyst. The oxidation rate was found to be [50] ... 

Dioxygen oxidizes transition metal ions in the lower valence state generating the hydroxyperoxyl radicals or superoxide ions [155,156]. The thermodynamic characteristics of these reactions are presented in Table 10.6. It is seen that all cited reactions are endothermic, except for the reaction of the cuprous ion with 02. The reaction of the ferrous ion with dioxygen has a sufficiently low enthalpy (28 kJ mol 3). 

Cobalt bromide is used as a catalyst in the technology of production of arylcarboxylic acids by the oxidation of methylaromatic hydrocarbons (toluene, p-xylene, o-xylene, polymethyl-benzenes). A cobalt bromide catalyst is a mixture of cobaltous and bromide salts in the presence of which hydrocarbons are oxidized with dioxygen. Acetic acid or a mixture of carboxylic acids serves as the solvent. The catalyst was discovered as early as in the 1950s, and the mechanism of catalysis was studied by many researchers [195-214],... 

Catalyst absorbs dissolved dioxygen. Sorbed dioxygen reacts with the oxidized substance with production of free radicals. The free radicals diffuse into solution and initiate the chain oxidation of hydrocarbon or other substances. 

At present, new developments challenge previous ideas concerning the role of nitric oxide in oxidative processes. The capacity of nitric oxide to oxidize substrates by a one-electron transfer mechanism was supported by the suggestion that its reduction potential is positive and relatively high. However, recent determinations based on the combination of quantum mechanical calculations, cyclic voltammetry, and chemical experiments suggest that °(NO/ NO-) = —0.8 0.2 V [56]. This new value of the NO reduction potential apparently denies the possibility for NO to react as a one-electron oxidant with biomolecules. However, it should be noted that such reactions are described in several studies. Thus, Sharpe and Cooper [57] showed that nitric oxide oxidized ferrocytochrome c to ferricytochrome c to form nitroxyl anion. These authors also proposed that the nitroxyl anion formed subsequently reacted with dioxygen, yielding peroxynitrite. If it is true, then Reactions (24) and (25) may represent a new pathway of peroxynitrite formation in mitochondria without the participation of superoxide. 

Conversely, Gourec et al. suggested a mechanism involving a non-metallic active site.85 In the proposed mechanism, based on XPS, SIMS, and CV analysis, dioxygen reacts with protonated nitrogen surface species to form oxidized nitrogen surface species and water. After further reaction with protons and electrons, the oxidized nitrogen is reduced, and water is produced. 

Scheme 11.11 Reaction scheme for glycerol oxidation with dioxygen on Au/C catalysts. (After [84]).

Air or dioxygen can be used as an oxidant with non-chiral DABCO to give a low cost catalyst for dihydroxylation of alkenes into racemic mixtures dihydroquinidine modified catalysts with the air variant give lower e.e. s than the AD-mix catalysts [26],... 

Introduction. The production of terephthalic acid (1,4-benzenedicarboxylic acid) has several interesting features. First, it is one of the examples of a homogeneous, radical-catalysed oxidation with the use of dioxygen and cobalt salt initiators. Secondly, it is an example of a catalyst/product separation involving a filtration of the product from the liquid that contains the catalyst. Crystallisation on such a huge scale is not very attractive, but the low solubility of phthalic acid in many solvents and the high boiling point do not allow any other solution. Theoretically, a solvent-solvent extraction would be an option, but we are not aware of a viable combination of solvents. 

A qualitative and preliminary picture (Fig. 11.16) of the mechanism of oxidation that emerges from our studies is the following Under the reaction conditions (pH = 6.5), the phenols exist in the phenolate form. Two phenolate ions coordinate to the two Cu(II) ions of the copper acetate dimer, reducing them to the Cu(I) oxidation state. Next, dioxygen reacts with the copper-phenolate adduct. The latter undergoes an 0-0 bond scission concomitant with the hydroxylation of the substrate. The acetate... 

The use of six equivalents of dihydrogen peroxide leads to a clean conversion of the dithiolate complex to the disulfonate compound. Earlier studies on oxidation of nickel thiolates showed that oxidations with dioxygen stop at monosulfinates. Our observation and the characterization of the first chelating bis-sulfonato nickel complex formed from the direct oxidation of a mononuclear nickel dithiolate, may also provide new insight into the chemistry of sulfur-rich nickel-containing enzymes in the presence of oxygen. 

Interactions and reactions of iron porphyrins with dioxygen species,with nitric oxide (see Section 5.4.3.8), with nitrite and with nitrate, and also of complexes containing carbon-bonded ligands, have continued to attract considerable interest and be reviewed. 

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