Peroxide complexes

Benzaldehyde is easily oxidised by atmospheric oxygon giving, ultimately, benzoic acid. This auto-oxidation is considerably influenced by catalysts tiiose are considered to react with the unstable peroxide complexes which are the initial products of the oxidation. Catalysts which inhibit or retard auto-oxidation are termed anti-oxidants, and those that accelerate auto-oxidation are called pro-oxidants. Anti-oxidants find important applications in preserving many organic compounds, e.g., acrolein. For benzaldehyde, hydroquinone or catechol (considerably loss than U-1 per cent, is sufficient) are excellent anti-oxidants. 

E. Vedejs (1978) developed a general method for the sterically controlled electrophilic or-hydroxylation of enolates. This uses a bulky molybdenum(VI) peroxide complex, MoO(02)2(HMPTA)(Py), which is rather stable and can be stored below 0 °C. If this peroxide is added to the enolate in THF solution (base e.g. LDA) at low temperatures, oneO—O bond is broken, and a molybdyl ester is formed. Excess peroxide is quenched with sodium sulfite after the reaction has occurred, and the molybdyl ester is cleaved to give the a-hydroxy car-... 

Minor levels of titanium are conveniently measured by spectrophotometry, eg, by the 410-nm absorbance of the yellow-orange peroxide complex that develops when hydrogen peroxide is added to acidic solutions of titanium. 

Pairing properties of 2-hydroxyadenine and 8-oxoadenine with four standard DNA bases were studied at the Hartree-Fock level [99JST59] and adenine-hydrogen peroxide complexes at the MP2 and DFT levels [99JPC(A)4755]. 

Peroxide complexes which are neither peroxyacids nor their derivatives. These may also be divided into mononuclear and multinuclear compds... 

The mononuclear peroxide complexes can further be divided into three subgroups peroxy-complexes, perhydrocomplexes, and hydro per-... 

Another approach to an oxidative desulphonylation reaction is to oxidize an a-sulphonyl carbanion with an oxidizing agent that is also nucleofugal. An example of this was presented by Little and Sun Ok Myong203 who used a molybdenum peroxide complex (M0O5.Pyridine.HMPA) as the oxidant. However, this reagent is expensive and... 

Oscilloscope traces obtained on mixing Ce(IV) perchlorate and H2O2 in a stopped-flow apparatus reveal an initial build-up of absorption at 350 nm complete within a few msec, suggesting formation of a complex, followed by a first-order decay almost complete within 20 msec and independent of initial [Ce(IV)], [H2O2] and [HjO-"] and of added Ce(III) at 25 °C k, = (2.8+0.2) x 10 sec and a similar value is found over a temperature range of 18-43 °C implying E = 0. Breakdown of a Ce(IV)-peroxide complex to H02 followed by oxidation of H02 to O2 is proposed . 

The latter binding mode has been observed for oxyhemocyanin (77) and in a dicopper(II) peroxide complex (78). Figure 2 illustrates structures for the peroxo intermediate which are most compatible with its spectroscopic parameters, as well as another, less likely, possibility (51). 

Anhydrous peroxytrifluoroacetic acid is not easy to handle, but the procedure has recently been revised.121 Namely, reaction of urea-hydrogen peroxide complex (UHP) with tri-fluoroacetic anhydride in acetonitrile at 0 °C gives solutions of peroxytrifluoroacetic acid, which oxidize aldoximes to nitroalkanes in good yields (Eqs. 2.58 and 2.59). Ketoximes fail to react under these conditions, the parent ketone being recovered. 

Ross, P. K., and E. I. Solomon. 1991. An Electronic Structural Comparison of Cooper-Peroxide Complexes of Relevance to Hemocyanin and Tyrosinase Active Sites. J. Am. Chem. Soc. 113, 3246. 

MnP is the most commonly widespread of the class II peroxidases [72, 73], It catalyzes a PLC -dependent oxidation of Mn2+ to Mn3+. The catalytic cycle is initiated by binding of H2O2 or an organic peroxide to the native ferric enzyme and formation of an iron-peroxide complex the Mn3+ ions finally produced after subsequent electron transfers are stabilized via chelation with organic acids like oxalate, malonate, malate, tartrate or lactate [74], The chelates of Mn3+ with carboxylic acids cause one-electron oxidation of various substrates thus, chelates and carboxylic acids can react with each other to form alkyl radicals, which after several reactions result in the production of other radicals. These final radicals are the source of autocataly tic ally produced peroxides and are used by MnP in the absence of H2O2. The versatile oxidative capacity of MnP is apparently due to the chelated Mn3+ ions, which act as diffusible redox-mediator and attacking, non-specifically, phenolic compounds such as biopolymers, milled wood, humic substances and several xenobiotics [72, 75, 76]. 

Exposure of 93 to dry oxygen furnished the corresponding ethyl peroxide complex, which is highly active for the expoxidation of enones, and crystallizes dimeric with bridging Zn-O bonds.153... 

How does nature prevent the release of hydrogen peroxide during the cytochrome oxidase-mediated four-electron reduction of dioxygen It would appear that cytochrome oxidase behaves in the same manner as other heme proteins which utilize hydrogen peroxide, such as catalase and peroxidase (vide infra), in that once a ferric peroxide complex is formed the oxygen-oxygen bond is broken with the release of water and the formation of an oxo iron(IV) complex which is subsequently reduced to the ferrous aquo state (12). Indeed, this same sequence of events accounts for the means by which oxygen is activated by cytochromes P-450. 

There is an irreversible enzymatic inactivation reaction, which occurs during the oxidation of the cyclizable and noncyclizable diphenols to oquinones. This inactivation process has been interpreted as being the result of a direct attack of an o-quinone on a nucleophilic residue (His) near the active enzyme center or of an attack of a copper-bound hydroxyl radical generated by the Cu(I)-peroxide complex. However, the latter hypothesis seems to be more probable, because inactivation also occurs in the presence of reducing agents that remove the o-quinones generated. 

Burdo and Seitz reported in 1975 the mechanism of the formation of a cobalt peroxide complex as the important intermediate leading to luminescence in the cobalt catalysis of the luminol CL reaction [116]. Delumyea and Hartkopf reported metal catalysis of the luminol reaction in chromatographic solvent systems in 1976 [117], while Yurow and Sass [118] reported on the structure-CL correlation for various organic compounds in the luminol-peroxide reaction. 

Ti and V can be determined simultaneously in steel as their coloured peroxide complexes. 1 mg of each metal in 50 cm3 of solution gave the following absorbances ... 

The mechanism shown in Scheme 5 postulates the formation of a Fe(II)-semi-quinone intermediate. The attack of 02 on the substrate generates a peroxy radical which is reduced by the Fe(II) center to produce the Fe(III) peroxide complex. The semi-quinone character of the [FeL(DTBC)] complexes is clearly determined by the covalency of the iron(III)-catechol bond which is enhanced by increasing the Lewis acidity of the metal center. Thus, ultimately the non-participating ligand controls the extent of the Fe(II) - semi-quinone formation and the rate of the reaction provided that the rate-determining step is the reaction of 02 with the semiquinone intermediate. In the final stage, the substrate is oxygenated simultaneously with the release of the FemL complex. An alternative model, in which 02 attacks the Fe(II) center instead of the semi-quinone, cannot be excluded either. 

Bentley et al.m recently improved upon Julia s epoxidation reaction. By using urea-hydrogen peroxide complex as the oxidant, l,8-diazabicyclo[5,4,0]undec-7-ene (DBU) as the base and the Itsuno s immobilized poly-D-leucine (Figure 4.2) as the catalyst, the epoxidation of a, (3-unsaturated ketones was carried out in tetrahydrofuran solution. This process greatly reduces the time required when compared to the original reaction using the triphasic conditions. 

Some recent advances have been reported in oxime oxidation, including the in situ generation of peroxytrifluoroacetic acid from the reaction of urea hydrogen peroxide complex with TFAA in acetonitrile at 0 °C This method gives good yields of nitroalkanes from aldoximes but fails with ketoximes. 

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