Oxygen peroxo compounds

Oxides of Platinum Metals Anodes of platinum (and more rarely of other platinum metals) are used in the laboratory for studies of oxygen and chlorine evolution and in industry for the synthesis of peroxo compounds (such as persulfuric acid, H2S2O8) and organic additive dimerization products (such as sebacic acid see Section 15.6). The selectivity of the catalyst is important for all these reactions. It governs the fraction of the current consumed for chlorine evolution relative to that consumed in oxygen evolution as a possible parallel reaction it also governs the current yields and chemical yields in synthetic electrochemical reactions. 

Oxidized impurities in the fuel are also adsorbed and oxidized by the reactor which has U.S. Patent 6,068,943. Suitable oxygen-containing compounds include peroxo monosulfuric acid, a peroxide of the alkali or alkaline earth metals in an acid solution. These oxygen-containing compounds can be catalytically decomposed to release oxygen. Liquid... 

During the last three decades, peroxo compounds of early transition metals (TMs) in their highest oxidation state, like TiIV, Vv, MoVI, WV1, and Revn, attracted much interest due to their activity in oxygen transfer processes which are important for many chemical and biological applications. Olefin epoxidation is of particular significance since epoxides are key starting compounds for a large variety of chemicals and polymers [1]. Yet, details of the mechanism of olefin epoxidation by TM peroxides are still under discussion. 

An important finding is that all peroxo compounds with d° configuration of the TM center exhibit essentially the same epoxidation mechanism [51, 61, 67-72] which is also valid for organic peroxo compounds such as dioxiranes and peracids [73-79], The calculations revealed that direct nucleophilic attack of the olefin at an electrophilic peroxo oxygen center (via a TS of spiro structure) is preferred because of significantly lower activation barriers compared to the multi-step insertion mechanism [51, 61-67]. A recent computational study of epoxidation by Mo peroxo complexes showed that the metallacycle intermediate of the insertion mechanism leads to an aldehyde instead of an epoxide product [62],... 

Despite of the common reaction mechanism, peroxo complexes exhibit very different reactivities - as shown by the calculated activation energies -depending on the particular structure (nature of the metal center, peroxo or hydroperoxo functionalities, type and number of ligands). We proposed a model [72, 80] that is able to qualitatively rationalize differences in the epoxidation activities of a series of structurally similar TM peroxo compounds CH3Re(02)20-L with various Lewis base ligands L. In this model the calculated activation barriers of direct oxygen transfer from a peroxo group... 

Early work on peroxo compounds of molybdenum has been reviewed.286 The stoichiometri-cally simplest Mo peroxo complex is the red-brown Mo(02)4 ion formed by the reaction of MoO2- with H202. Although the complex is not stable in solution and decomposes slowly with the evolution of 02, the anion can be crystallized as the Zn(NH3)4+ salt whose structure has been determined. In a sense, Mo(02)4 is an intermediate in the thermodynamically favored decomposition of hydrogen peroxide to water and oxygen. 

Titanium containing materials have been investigated for various reactions, but selective oxidations with H202 as the oxidant have attracted the most interest. For these reactions, the formation of surface titanium peroxo compounds with H202 and the subsequent transfer of the peroxidic oxygen to the organic reactants have been proposed to explain the mechanism by which titanium participates in the catalytic cycle (Notari, 1988). 

Concerted mechanisms have been proposed on the basis of work carried out with soluble Movl, Wvl and TiIV peroxo compounds. The experimental evidence is consistent with the hypothesis that these compounds act as oxidants in stoichiometric epoxidations and that the reactions involve electrophilic attack of the peroxo compound on the organic molecule or, what is equivalent, a nucleophilic attack of the organic molecule on the peroxidic oxygen, in a butterfly transition state. The reaction product is formed and, after desorption, the peroxo compound is regenerated by reaction of TiIV with H202 this accounts for the catalytic nature of the reaction (Amato et al, 1986). The same type of mechanism... 

It is somewhat surprising that Mn compounds with 02 moieties appear to have such limited existence peroxo compounds of the higher oxidation states are an important feature of the earlier transition metals (and we shall notice a few, poorly characterized, examples for Mn in Section 41.5.3) and the metals which follow manganese—Fe and Co—have an extensive and important chemistry of reversible combination with the oxygen molecule. It is perhaps pertinent to recall that some Mn11 species are very efficient catalysts for the decomposition of hydrogen peroxide (Section 41.3.3.7). 

Organic peroxo compounds are also obtained by autooxidation of ethers, unsaturated hydrocarbons, and other organic materials on exposure to air. A free-radical chain reaction is initiated almost certainly by radicals generated by the interaction of oxygen and traces of metals such as copper, cobalt, or iron. The attack on specific reactive C—H bonds by a radical X" gives first R, then hydroperoxides, which can react further ... 

Figure 2 Peroxidation of oolyunsaturated fatty acids exemplified with a -linolenic acid (=0 -lin). In this scheme radicals are produced by the presence of protoporphyrin IX. In the light, either singlet oxygen may be generated or a superoxide anion provided a suitable redox reaction occurs in case an appropriate reductant is available (part A II, reactions 1,2). Singlet oxygen may lead to formation of a peroxo compounds (of --linolenic acid, part B 1/1) the protoporphyrin IX-radical may form a hydroxy radical HO via superoxide, see part 1/2 (41,42). Both, peroxo linolenic acid and the hydroxy radical will initiate a radical chain reaction (part B, II, III) with linolenic acid leading to the OJ-lin radical possibly in two ways as indicated by the arrows numbered (1) and (2). This radical supports the chain reaction.

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