Reactions of Oxygen and Hydrogen Peroxide

Many of the studies undertaken recently have centred on the reversibility of the oxygen binding and on the nature of the adducts formed. Using the isomeric diethyl-enetriaminemonoacetic acids (L) as ligands, stable cobalt(n) complexes are formed which on oxygenation show no measurable tendency towards irreversible oxidation to the cobalt(m) state. Thermodynamic equilibrium constants may be defined by the equation 

The rate scheme envisaged is similar to that proposed by Wilkins for dioxygen complexes without hydroxo-bridges  

The reaction is catalysed by H+ and by halide ions. Several reaction pathways are proposed involving an initial dissociation of one of the axial water molecules. The product is a cobalt(iii) complex and the fact that HgOg is not detected is interpreted in terms of a mechanism similar to that for Fe -oxygen carrying systems (see p. 110). 

An unusual cobalt-dioxygen adduct is formed in the reaction of O2 with [Co -(CN)a(PMe2Ph)3], in that during the course of reaction a dimeric complex is formed with the exclusion of only a single mole of dimethylphenylphosphine. The rate law of the form 

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Bagotskii VS, Tarasevich MR, Fihnovskii VY. 1969. Calculation of the kinetic parameters of conjugated reactions of oxygen and hydrogen peroxide. Elektrokhimiya 5 1218. 

The effect of oxygen and hydrogen peroxide on the reaction of carbonyl sulfide on primary amines is discussed in Section 3. 

Substitutionally labile metal complexes often generate hydroperoxides by direct substitution with H202 (86 90) or in the reactions between 02 and the reduced metal (91). These mechanisms are commonly observed in naturally occurring molecules and their mimics in the processes of activation of oxygen and hydrogen peroxide (92-98). 

In alkaline solutions D-glucose forms 3-deoxy-D-en/f/iro-hexosulose and 4-deoxy-D-gft/cero-2,3-hexodiulose which yield saccharinic acids. Machell and Richards (57) have shown that 3-deoxy-D-en/fhro-hexosulose (14) is oxidized by 30% hydrogen peroxide to formic acid and 2-deoxy-D-erythro-pentonic acid (15). Recently Rowell and Green (58) found that 14 in the presence of oxygen also forms 15 in addition to the saccharinic acids. They inferred that the reactions with oxygen and hydrogen peroxide are very similar, but they did not present reaction mechanisms. 

The products of the photochemical reaction of oxygen and hydrogen in a flow system are ozone, hydrogen peroxide, and water. Mechanisms for the formation of these products are discussed below. 

Presumably, peroxycarboximidic acid (26) is formed by the reaction of carbodiimides and hydrogen peroxide. This is eventually converted to the urea derivative during epoxidation after transfer of oxygen to the substrate. 

The concentrations of iron as simple solvated ions, Fe2+aq or Fe3+aq, are maintained at extremely low levels because of their damaging ability in the presence of oxygen and hydrogen peroxide. In transferrin, an important iron scavenger, the iron is well-protected and is not involved in redox chemistry. Also, in the major storage proteins, ferritin and haemosiderin, the iron is present in crystalline material inside the protein shell, and is well protected from reaction. 

Reaction of periodate and hydrogen peroxide to form iodate and oxygen has been reported , but the kinetic studies are far from complete. Reproducible initial rates of reaction were observed only in the presence of low concentrations e.g. 10 M) of iodate, but even then the kinetic orders were not simple. 

FIGURE 11.38 Reaction scheme showing the formation of hydroxyquinone structures on treatment of quinones with alkali and with alkali in the presence of oxygen and hydrogen peroxide. 

Ozone can be determined by its reaction with an adsorbed layer of the dye rhodamine B with a silica gel. Another reaction frequently used in chemical sensors is the reaction of oxygen or hydrogen peroxide with luminol (Fig. 2.21). In combination with enzymatic reactions, highly sensitive and extremely selective sensors can be manufactured. Examples are given in Chap. 8. 

Petoxycatboxyhc acids have been obtained from the hydrolysis of stable o2onides with catboxyhc acids, pethydtolysis of acyhinida2ohdes, reaction of ketenes with hydrogen peroxide, electrochemical oxidation of alcohols and catboxyhc acids, and oxidation of catboxyhc acids with oxygen in the presence of o2one (181). 

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