Oxidation-reduction reaction with oxygen

There existed oxidation-reduction reactions with the same reaction speed on the sulphide mineral surface in water. One is the self-corrosion of sulphide mineral. Another is the reduction of oxygen. If the equilibrium potential for the anodic reaction and the cathodic reaction are, respectively, E and, and the mineral electrode potential is E, the relationship among them is as follows ... 

A point that seems to have been coming out of all of our work is that in interactions, especially oxidation-reduction reactions involving oxygenated species, we have to consider such condensations as this. I shouldn t be surprised if they were involved in a lot of the reactions involving simple metal ions which are hydrated. A recent article (2) states that bichromate also condenses with an aquo complex of cobalt with a much higher formation constant than that for CrSCV2 and with... 

Lead appears to be able to interact with complex small biomolecules as well, such as flavins for example, bis(lO-methylisoalloxazine) perchlorate tetrahy-drate (223). IsoaUoxazine is a planar three-ringed heterocychc amino cofactor associated with riboflavin and is active in oxidation-reduction reactions with metals such as Mo and Fe. Lead binds to bis(lO-methylisoalloxazine) in a 1 1 metal-ligand complex, with two additional waters bound resulting in a four coordinate molecule with a total of four oxygen donors. An active lone pair results in a distorted square-pyramidal structure. As is the case for citrate, extensive hydrogen bonding was observed in the crystal lattice. 

As we have just seen the reaction of alkanes with oxygen to give carbon dioxide and water IS called combustion A more fundamental classification of reaction types places it m the oxidation—reduction category To understand why let s review some principles of oxidation-reduction beginning with the oxidation number (also known as oxidation state)... 

Hydroxylamine sulfate is produced by direct hydrogen reduction of nitric oxide over platinum catalyst in the presence of sulfuric acid. Only 0.9 kg ammonium sulfate is produced per kilogram of caprolactam, but at the expense of hydrogen consumption (11). A concentrated nitric oxide stream is obtained by catalytic oxidation of ammonia with oxygen. Steam is used as a diluent in order to avoid operating within the explosive limits for the system. The oxidation is followed by condensation of the steam. The net reaction is... 

The standard reduction potential of Cr " (Table 2) shows that this ion is a strong reducing agent, and Cr(II) compounds have been used as reagents in analytical chemistry procedures (26). The reduction potential also explains why Cr(II) compounds are unstable in aqueous solutions. In the presence of air, the oxidation to Cr(III) occurs by reaction with oxygen. However, Cr(II) also reacts with water in deoxygenated solutions, depending on acidity and the anion present, to produce H2 and Cr(III) (27,28). 

The radicals that are formed from the enolate in this process are rapidly destroyed so that only the stable semidione species remains detectable for EPR study. Semidiones can also be generated oxidatively from ketones by reaction with oxygen in the presence of base. The diketone is presumably generated oxidatively and then reduced to the semidione via reduction by the enolate derived from the original ketone. 

In addition to simple dissolution, ionic dissociation and solvolysis, two further classes of reaction are of pre-eminent importance in aqueous solution chemistry, namely acid-base reactions (p. 48) and oxidation-reduction reactions. In water, the oxygen atom is in its lowest oxidation state (—2). Standard reduction potentials (p. 435) of oxygen in acid and alkaline solution are listed in Table 14.10- and shown diagramatically in the scheme opposite. It is important to remember that if or OH appear in the electrode half-reaction, then the electrode potential will change markedly with the pH. Thus for the first reaction in Table 14.10 O2 -I-4H+ -I- 4e 2H2O, although E° = 1.229 V,... 

Is this an oxidation-reduction reaction Historically, it surely is, for the term oxidation originally referred specifically to reactions with oxygen. Yet our electron-transfer view of oxidation-reduction reactions provides no help in deciding so. Where in reaction (76) is there any evidence of electrons being gained or lost In such a doubtful case, our oxidation number scheme provides an answer. Applying the same assumptions used in treating the HSOf-HSOi"... 

Fig. 3-4 Electron transport process schematic, showing coupled series of oxidation-reduction reactions that terminate with the reduction of molecular oxygen to water. The three molecules of ATP shown are generated by an enzyme called ATPase which is located in the cell membrane and forms ATP from a proton gradient created across the membrane.

Reduced nicotinamide-adenine dinucleotide (NADH) plays a vital role in the reduction of oxygen in the respiratory chain [139]. The biological activity of NADH and oxidized nicotinamideadenine dinucleotide (NAD ) is based on the ability of the nicotinamide group to undergo reversible oxidation-reduction reactions, where a hydride equivalent transfers between a pyridine nucleus in the coenzymes and a substrate (Scheme 29a). The prototype of the reaction is formulated by a simple process where a hydride equivalent transfers from an allylic position to an unsaturated bond (Scheme 29b). No bonds form between the n bonds where electrons delocalize or where the frontier orbitals localize. The simplified formula can be compared with the ene reaction of propene (Scheme 29c), where a bond forms between the n bonds. 

Electron-transfer reactions occur all around us. Objects made of iron become coated with mst when they are exposed to moist air. Animals obtain energy from the reaction of carbohydrates with oxygen to form carbon dioxide and water. Turning on a flashlight generates a current of electricity from a chemical reaction in the batteries. In an aluminum refinery, huge quantities of electricity drive the conversion of aluminum oxide into aluminum metal. These different chemical processes share one common feature Each is an oxidation-reduction reaction, commonly called a redox reaction, in which electrons are transferred from one chemical species to another. 

Apart from reactions involving the oxidative addition of oxygen, the usual oxidation-reduction reactions have also been observed for binuclear technetium clusters with multiple M-M bonds (in this case they must be accompanied by a change in the multiplicity of the Tc-Tc bonds up to their complete dissociation)11 (15,16) [11,80],... 

Reduction reactions of metal oxides by hydrogen start with the dissociative adsorption of H2, which is a much more difficult process on oxides than on metals. Atomic hydrogen takes care of the actual reduction. Depending on how fast or how slow the dissociative adsorption is in comparison to the subsequent reduction reactions which comprise diffusion of atomic hydrogen into the lattice, reaction with oxygen and removal of the hydroxyl species formed, two limiting cases are distinguished [1,7]. 

Metals react with nonmetals. These reactions are oxidation-reduction reactions. (See Chapters 4 and 18). Oxidation of the metal occurs in conjunction with reduction of the nonmetal. In most cases, only simple compounds will form. For example, oxygen, 02, reacts with nearly all metals to form oxides (compounds containing O2-). Exceptions are the reaction with sodium where sodium peroxide, Na202, forms and the reaction with potassium, rubidium, and cesium where the superoxides, K02, Rb02, and Cs02 form. 

Schematic representation of the various reaction modes for the dissolution of Fe(III)(hydr)oxides a) by protons b) by bidentate complex formers that form surface chelates. The resulting solute Fe(III) complexes may subsequently become reduced, e.g., by HS c) by reductants (ligands with oxygen donor atoms) such as ascorbate that can form surface complexes and transfer electrons inner-spheri-cally d) catalytic dissolution of Fe(III)(hydr)oxides by Fe(II) in the presence of a complex former e) light-induced dissolution of Fe(III)(hydr)oxides in the presence of an electron donor such as oxalate. In all of the above examples, surface coordination controls the dissolution process. (Adapted from Sulzberger et al., 1989, and from Hering and Stumm, 1990.)...

Fire is a self-sustaining, exothermic oxidation-reduction reaction. The fire reaction usually involves oxygen which forms the oxides of the fuel. The most important examples in petrochemical and hydrocarbon processing facilities are combustion reactions of hydrocarbons with oxygen. 

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