Transition metals with hydrogen peroxide

Other epoxidizing reagents which have been proposed but have not been extensively employed with olefinic acids include r-butyl hydroperoxide and transition metal salts, hydrogen peroxide and isocyanate, sodium chlorate and osmium tetroxide, iodine and silver oxide and hydrogen peroxide and ortho esters. 

Enthalpies, Entropies, and Gibb s Energies of Transition Metal Ion Oxidation-Reduction Reactions with Hydrogen Peroxide in Aqueous Solution (T = 298 K) [23]... 

The values of the rate constants for the reactions of transition metal ions with hydrogen peroxide in an aqueous solution are presented in Table 10.2. 

Rate Constants of Transition Metal Ion Reactions with Hydrogen Peroxide in Aqueous Solutions... 

Several compounds of tungsten, which is a transition metal closely related to molybdenum, are able to catalyze the selective oxidation of secondary alcohols with hydrogen peroxide as secondary oxidant. These include tris(cetylpyridinium) 12-tungstophosphate,33 peroxotungstopho-sphate (PCWP)34 and Na2W04 in the presence of a phase transfer catalyst.35 Tungstophosphoric acid is able to catalyze the selective oxidation of secondary alcohols in the presence of ferric nitrate as secondary oxidant.36... 

Transition metals have the ability to form a complex with an electron donor. In this complex, the outermost set of five stable d electron orbitals of the transition metal is partially filled. When transition metal salts, such as ferrous sulfate, are combined with hydrogen peroxide, the resulting oxidation power is known as Fenton s reagent. Instead of forming a complex with hydrogen peroxide, the ferrous ion loses one electron to the peroxide bond of hydrogen peroxide. As a result, a hydroxyl radical and a hydroxide ion are formed. 

Martini M, Termini J (1997) Peroxy radical oxidation of thymidine. Chem Res Toxicol 10 234-241 Masarwa M, Cohen H, Meyerstein D, Hickman DL, Bakac A, Espenson JH (1988) Reaction of low-va-lent transition-metal complexes with hydrogen peroxide. Are they,Fenton-like or not 1. The case of Cu+aq and Cr2+aq. J Am Chem Soc 110 4293-4297 Maskos Z, Koppenol WH (1991) Oxyradicals and multivitamin tablets. Free Rad Biol Med 11 609-610... 

Vitamin C (ascorbate) (Fig. 9.5) has the ability to act as a reducing agent, i.e. it will tend to reduce more reactive species. This ability to reduce Fe3+ to Fe2+may be important in promoting iron uptake in the gut. Oxidation of ascorbate by reaction with reactive oxygen species or reactive nitrogen species seems to lead to its depletion. In vitro, vitamin C can also exert pro-oxidant properties. Fe3+ can react with ascorbate to form Fe2+ and the semi-dehydroascorbate or ascorbyl radical. The latter can react with hydrogen peroxide to form Fe3+, the hydroxyl radical and a hydroxide anion. A key question with regard to the pro- or anti- oxidant effects of ascorbate may therefore be the availability of transition metal ions. Neurons main-... 

Selective oxidation of aromatic amines to nitroso-derivatives with hydrogen peroxide and a catalyst is also studied [68, 69], In kinetic systems with transition metal complexes substrate oxidation is accompanied by H202 dissociation to H20 and 02. Therefore, in this case, the occurrence of chemical induction would be expected. 

Use of transition metal catalysts opens up previously unavailable mechanistic pathways. With hydrogen peroxide and catalytic amounts of methyl trioxorhe-nium (MTO), 2-methylnaphthalene can be converted to 2-methylnaphtha-l,4-qui-none (vitamin K3 or menadione) in 58 % yield and 86 % selectivity at 81 % conversion (Eq. 10) [43, 44]. Metalloporphyrin-catalyzed oxidation of 2-methylnaphtha-lene with KHSOs can also be used to prepare vitamin K3 [45]. The MTO-catalyzed process can also be applied to the synthesis of quinones from phenols [46, 47]. In particular, several benzoquinones of cardanol derivatives were prepared in this manner [48], The oxidation is thought to proceed through the formation of arene oxide intermediates [47]. 

The synthesis of peroxo metal complexes with hydrogen peroxide is easily accomplished, normally by one of two methods. Firstly, using early transition... 

A few examples of the use of transition metal catalysis in conjunction with hydrogen peroxide for aldehyde oxidations have also been reported.228,229... 

Photoreduction of ferric ion. Lunck and co-workers observed the enhanced rate of photo-oxidation of salicyclic acid by hydrogen peroxide in the presence of Fe(III) as well as the increased rate of photodecomposition of hydrogen peroxide in the presence of transition metal ions.23 The ferrous ion reacts with hydrogen peroxide, generating a second hydroxyl radical and ferric ion, and the cycle continues. 

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