Oxidation Reactions with Dioxygen

The order of the catalytic reaction with respect to oxygen pressure was determined by using oxygen-nitrogen mixtures of various O2/N2 ratios. Anthralur was chosen as the catalyst because it has an extended mesoporosity, making 

The results in Table 7.6 confirm that the catalytic activity of carbon blacks in the oxidation of sulfurous acid is inferior to that of activated carbons. Carbon blacks that had been extracted with hot xylene to remove adsorbed organic molecules and subsequently heat-treated under Ar at 873 K were catalytically inactive. However, weak catalytic activity was observed after heat treatment of these carbon blacks at 1473 K, with the notable exception of an acetylene black that is free of nitrogen. Catalytic activity was also observed with the as-delivered carbon blacks after heat treatment at 973 to 1073 K. 

Sample Treatment Surface Area (m /g) N Content (qmol/g) Catalytic Activity (qmol/g-s) Acidic Surface Groups (qmol/g) 

mol/g s at pH 2.0, and 0.77 ftmol/g-s at pH 1.0. This effect seems to be related to the oxidizing properties of HNO3. Also, KNO3 and Ca(N03)2 have an inhibiting effect at a concentration as low as 1 mmol/L [94]. Reduced activity was also observed on addition of NaOH to establish a pH of 3.0 or 

Addition of soluble organic compounds had an inhibiting effect, not surprisingly. A strong effect was observed with small amounts of hydroquinone or pyrocatechol (2.7 ftmol/L of H2SO3 solution), decreasing the oxidation rate to 

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Apart from the above-mentioned theoretical applications, there is also the possibility of practical applications. The octacyano complexes of Mo(V) and W(V), for example, find excellent use in the oxidation of organic substances which require a mild oxidizing agent. It was also recently observed that derivatives of the dioxotetracyano complexes of Mo(IV) and W(IV) can take up dioxygen, which leads to the activation of the O2 molecule. The complexes are thus candidates as catalysts in oxidation reactions with dioxygen as well as oxygen-transfer reactions. 

III.B.2), complexes with manganese, chromium, as well as second- and third-row transition metal ions (e.g., ruthenium) oxidation reactions with dioxygen alone or with other peroxides (e.g., ferf-butyl-peroxide) the stabilization and spectroscopic characterization of mononuclear superoxo, peroxo, and oxo complexes other catalytic processes (e.g., the iron-catalyzed aziridination), enantioselective reactions with chiral bispidine ligands and the iron oxidation chemistry continues to produce novel and exciting results. 

In the present paper we would like to present the results of synthetic experiments on semiquinone and catechol complexes of copper, with characterization that may provide insights on the extent to which redox activity at both the metal and the quinone ligand contributes to the synthetic course of oxidation reactions with dioxygen. 

Another variation of the oxidation reaction with dioxygen can be efficiently accomplished by a catalytic condensation of amines and isonitriles using a palladium complex catalyst and iodine at 100 °C to give dialkylcarbodirmides in yields of 35-86% [1283]. Dicyclohexylcarbodirmide was obtained in 67% yield from cyclo-hexylisonitrile 1748 and cyclohexylamine 1749 (see Section 4.5.3.5, Table 4.48). 

Finally, it should be noted that there are a large number of irreversible H(G) dioxygen complexes (see Refs. 1, 77) which undergo a whole range of oxidative reactions with a variety of substrates. For instance, M(Ph3P)4, where M = Ni, Pd, Pt, react with O2 in solution as follows (194). 

Since the rate of chain oxidation of hydrocarbon is v v,1/2 and does not depend on [02] (see Chapter 2), the catalyst initiates the chains via two parallel reactions by the reaction with ROOH and by the reaction with dioxygen. The following mechanism was proposed ... 

Lifetime of nitric oxide is an important parameter of its reactivity. Measurement of NO in intact tissue yielded a value in the order of 0.1 s [35] although preliminary estimates gave a much bigger lifetime. It has been accepted that the main reason for the rapid disappearance of NO in tissue is its reaction with dioxygen, which proceeds in aqueous solution with the following overall stoichiometry ... 

Thus the competition between stimulatory and inhibitory effects of NO depends on the competition between two mechanisms the direct interaction of NO with free radicals formed in lipid peroxidation and the conversion of NO into peroxynitrite or other reactive NO metabolites. Based on this suggestion, Freeman and his coworkers [42-44] concluded that the prooxidant and antioxidant properties of nitric oxide depend on the relative concentrations of NO and oxygen. It was supposed that the prooxidant effect of nitric oxide originated from its reaction with dioxygen and superoxide ... 

Thus, LOX-catalyzed oxidative processes are apparently effective producers of superoxide in cell-free and cellular systems. (It has also been found that the arachidonate oxidation by soybean LOX induced a high level of lucigenin-amplified CL, which was completely inhibited by SOD LG Korkina and TB Suslova, unpublished data.) It is obvious that superoxide formation by LOX systems cannot be described by the traditional mechanism (Reactions (1)-(7)). There are various possibilities of superoxide formation during the oxidation of unsaturated compounds one of them is the decomposition of hydroperoxides to alkoxyl radicals. These radicals are able to rearrange into hydroxylalkyl radicals, which form unstable peroxyl radicals, capable of producing superoxide in the reaction with dioxygen. 

Reaction with Dioxygen and Electrochemical Oxidation of OH- in Acetonitrile... 

These complexes combine a central metal in a high oxidation state with a redox active ligand (catechol). This combination arises from the idea that the electronic perturbation induced in the metal complex by reaction with dioxygen can discharge itself ... 

Introduction of mesityl groups at the porphyrin ring can prevent the formation of the dimeric products and the reaction with dioxygen now leads to ruthenium(VI)-dioxo complexes of TMP (tetramesitylporphyrin) [35], The tram-Ru(VI)02-TM P species can catalyse the epoxidation of alkenes as well as whole range of other oxidation reactions. After transfer of one oxygen atom to an organic substrate Ru(IV)0-TMP is formed, which disproportionates to an equilibrium of Ru02 and llu ). 

Reactions with dioxygen generally afford the corresponding metal carbonyl derivatives, with loss of organic aldehyde or acid. This reaction can be expressed as an analog of multiple bond metathesis and corresponds to oxidation of vinylidene to CO [46]. Oxidation of OsHCl(=C=CHPh)(L)2 affords the styryl complex 0sC102( -CH=CHPh)(L)2 [243]. 

There are various possibilities of superoxide formation during the oxidation of unsaturated compounds one of them is the decomposition of hydroperoxides to alkoxyl radicals. These radicals are able to rearrange into hydroxylalkyl radicals, which form unstable peroxyl radicals, capable of producing superoxide in the reaction with dioxygen. 

The metals which form this type of complex by reaction with dioxygen are mainly the later second and third row transition series metals, notably Ru°, Os°, Rh1, Ir1, Pt° and Pd°. It is not surprising to see metals noted for their ability to undergo oxidative addition reactions amongst those which form this type of mononuclear dioxygen complex as a formal two-electron reduction of dioxygen is required for complex formation. The other metals known to form mononuclear peroxo-type complexes with dioxygen are Ni°, Co1 and one example of Co . 

Some of the early transition metals are known to form mononuclear peroxo complexes. These complexes are not formed by reacting a metal complex in a low oxidation state with dioxygen, as this usually results in the formation of metal oxo species, but rather by reaction of a metal complex in a high oxidation state, eg. TiIV, Nbv or MoVI, with the peroxide anion. This frequently leads to more than one peroxide ligand per metal centre. 

Kinetic studies with laccase have shown that the enzyme must be reduced by the organic substrate before reaction with dioxygen occurs. The first electron from the substrate is accepted by the type 1 Cu2+, and the second by the type 2 Cu2+. The electrons from these reduced sites are then transferred to the type 3 copper pair, which then binds dioxygen with reduction to peroxide. It is possible that the type 2 and type 3 centres are in the same cavity, which only becomes accessible to the solvent when the type 1 Cu+ is oxidized. 

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