Hydroperoxides reduction with

Metallation of a-substituted a,P-unsaturated nitriles followed by introduction of dry oxygen gas results in the regioselective trapping of the delocalized anion at the a carbon to produce the hydroperoxide. Reduction with aqueous NujSO, and exposure of the cyanohydrin to NaOH affords the p.y-unsaturated ketones in good yields (Scheme 6.57).- 5 ... 

The intermediate hydroperoxide is sufficiently stable to be isolated, and reduction with any one of a number of reagents (zinc-acetic acid is preferred) then gives the 17a-hydroxy-20-keto compound. 

Extensive studies have established that the catalytic cycle for the reduction of hydroperoxides by horseradish peroxidase is the one depicted in Figure 6 (38). The resting enzyme interacts with the peroxide to form an enzyme-substrate complex that decomposes to alcohol and an iron-oxo complex that is two oxidizing equivalents above the resting state of the enzyme. For catalytic turnover to occur the iron-oxo complex must be reduced. The two electrons are furnished by reducing substrates either by electron transfer from substrate to enzyme or by oxygen transfer from enzyme to substrate. Substrate oxidation by the iron-oxo complex supports continuous hydroperoxide reduction. When either reducing substrate or hydroperoxide is exhausted, the catalytic cycle stops. 

Many different analytical techniques were developed for the estimation of hydroperoxides. Among them, the iodometric technique has been used for a long period of time [60]. According to this method, peroxide is reduced by HI, and diiodine is formed in stoichiometric quantity. The amount of the formed I2 is measured by reduction with thiosulfate using any titrometric technique or photometrically. 

In the case of cobalt ions, the inverse reaction of Co111 reduction with hydroperoxide occurs also rather rapidly (see Table 10.3). The efficiency of redox catalysis is especially pronounced if we compare the rates of thermal homolysis of hydroperoxide with the rates of its decomposition in the presence of ions, for example, cobalt decomposes 1,1-dimethylethyl hydroperoxide in a chlorobenzene solution with the rate constant kd = 3.6 x 1012exp(—138.0/ RT) = 9.0 x 10—13 s—1 (293 K). The catalytic decay of hydroperoxide with the concentration [Co2+] = 10 4M occurs with the effective rate constant Vff=VA[Co2+] = 2.2 x 10 6 s— thus, the specific decomposition rates differ by six orders of magnitude, and this difference can be increased by increasing the catalyst concentration. The kinetic difference between the homolysis of the O—O bond and redox decomposition of ROOH is reasoned by the... 

The carbanions take up 02 and these take up protons to give hydroperoxides in good yields. But because they are explosive in nature, they are not usually isolated and on reduction with sodium sulphite on trialkyl phosphite give alcohols. Alcohols can also be prepared via hydroperoxy molybdenum complexes and alkyl boranes. These reactions are summarized as follows ... 

Regioselective [4-1-2] cycloadditions to Cjq are also possible with 2,3-dimethyl-buta-1,3-diene (4) and with the monoterpene 7-methyl-3-methylideneocta-l,6-diene (5, myrcene) [22]. These monoadduct formations proceed under mild and controlled conditions. Most of these addition products of 1,3-butadiene derivatives (e.g. 4, 5, 8-12) are unstable against air and light [25]. The dihydrofuUerene moiety in the Diels-Alder adducts act as a 02-sensitizer and promotes the oxidation of the cyclohexene moiety to the hydroperoxide. Reduction of the hydroperoxide with PPhj yields the corresponding allylic alcohols [25]. 

Hydroperoxides undergo reduction with aqueous Fe(II), which turns to aqueous Fe(III). The reaction can be followed at 305 nm (e = 2095 M cm ) ° . Although the stoichiometry of this process is straightforward, with two Fe(II) ions being consumed per molecule of hydroperoxide, the mechanism involves an alkoxide free radical, RO", that may undergo -elimination, H abstraction from R—H, or a 1,2-H-shift and reaction with other components in the system. A case in point is the determination of f-butyl hydroperoxide which consumes under 1 mol of Fe(II) per mol of analyte under inert gas cover, while in the presence of O2 four mols are consumed, pointing to extensive side reactions of the RO" free radical, both without and with O2 in the system. ... 

All the complexes in Table I have the ability to serve as immediate or indirect precursors to high valent species. The hydroperoxides react with one-electron reductants in Fenton-type chemistry to generate... 

The sulfur oxidation is carried out at pressure higher than 8 atm and below 180 °C, with a proprietary supported-Mo oxide-based catalyst, for example, an alpha alumina-supported MgMo04 catalyst, operating at 110 °C and 17 atm [59c]. All the products produced by oxidation side reactions and by hydroperoxide reduction are separated from the gas oil stream together with the sulfones. This operation may result in diesel yield loss therefore, the valorization or upgrade of this oxidized stream affects the process economics. This stream can be blended into the heating oil pool or treated in a hydrocracking unit to recover valuable products. 

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