Hydrogen peroxide catalytic oxygen reduction

It is important to compare the catalytic properties of Prussian blue with known hydrogen peroxide transducers. Table 13.2 presents the catalytic parameters, which are of major importance for analytical chemistry selectivity and catalytic activity. It is seen that platinum, which is still considered as the universal transducer, possesses rather low catalytic activity in both H202 oxidation and reduction. Moreover, it is nearly impossible to measure hydrogen peroxide by its reduction on platinum, because the rate of oxygen reduction is ten times higher. The situation is drastically improved in case of enzyme peroxidase electrodes. However, the absolute records of both catalytic activity... 

Initial halogenation of the oxime can use chlorine, hypobromite, bromine, or A-bromoacetamide. " Oxidation of the a-halonitrosoalkane can be achieved with nitric acid, nitric acid-hydrogen peroxide, " atmospheric oxygen, ozone, or a peroxyacid. Reduction of thea-halonitroalkaneis achieved with sodium borohydride or by catalytic hydrogenation, although potassium hydroxide in ethanol has been used for the conversion. 

SCHEME 2.5 Wroblowa s oxygen electroreduction mechanism with electrochemical rate constants k3 forthe direct reduction to water, k2 and k 2 for the parallel electrochemical reduction and oxidation of adsorbed hydrogen peroxide, k3 for the electrochemical decomposition of hydrogen peroxide to water, k4 for the chemical catalytic decomposition of hydrogen peroxide to oxygen, and ks and fc 5 for the parallel adsorption/desorption of the adsorbed hydrogen peroxide. The species with the super index and ° are located at the interface and in the bulk of the solution, respectively. The sub index ads refers to the adsorbed state, and the term dif symbolizes the diffusion to the bulk of the solution and vice versa. 

List and coworkers reported an oxa-Michael reaction with aliphatic acyclic enones 94 using hydrogen peroxide as oxygen source [111]. Treatment of enones with catalytic amounts of cinchona alkaloid derived primary amine 33 (as its salt), followed by excess hydrogen peroxide furnished the intermediate peroxy-hemiketals with high yields and stereoselectivities. Subsequent reduction of these compounds led to the corresponding p-hydroxyketones 124 without loss of enantioselectivity (Scheme 33.36). The same research group developed the asymmetric epoxidation of enones with excellent results [112],... 

Scheme 10.27 Catalytic cycle of HppE. Dashed arrows indicate electron transport. In this scheme HPP binds to iron1". After a one-electron reduction, dioxygen binds and reoxidizes the iron center. The peroxide radical is capable of stereospecifically abstracting the (pro-R) hydrogen. Another one-electron reduction is required to reduce one peroxide oxygen to water. Epoxide formation is mediated by the resulting ironlv-oxo species.

For catalytic oxidations opt for hydrogen peroxide or molecular oxygen as oxidant for catalytic reductions opt for molecular hydrogen as reductant. 

Nitrite can also be catalytically reduced by the Mb-CMC film electrode. When an Mb-CMC film electrode was placed in a pH 5.5 buffer containing N02, a new reduction peak appeared at about -0.8 V while the original Mb Fem/Fen peak pair at about -0.25 V was intact. This new peak increased with the concentration of N02 and the catalytic reduction peak of nitrite increased linearly with nitrite concentration in the range of 0.6-8mM with a detection limit of 0.32mM. Oxygen and hydrogen peroxide are also often detected by biosensors based on the direct electrochemistry of Mb in the Mb-CMC film electrode. 

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