Alkyl hydroperoxides functionalization

The largest number of hydrogen bonds in crystal structures of alkyl hydroperoxides refer to intermolecular bonds between the hydroperoxide proton and functionalities of the type 0=X, where X denotes a sulfur (e.g. 27), carbon (e.g. 30) or a phosphorous atom (e.g. 32, Figure 14, Table 7)93,108,115 geometry of [l,2-bis(diphenylphosphinoyl)ethane] bis(2,2-dihydroperoxypropane) (32) in the solid state is a rare example of a bifurcated hydrogen bond between an OOH donor and an 0=X proton acceptor. 

There is reported enthalpy of formation data for methyl hydroperoxide. The enthalpy of formation of the methyl derivative for any functional group, MeZ, is expected to deviate somewhat from the linear relationship established by the n-alkyl members of the homologous series with the same Z. It is unclear where the best straight line lies for the n-alkyl hydroperoxides and so the extent of deviation for methyl hydroperoxide is likewise unclear. However, methyl hydroperoxide, like other methyl derivatives with electron-withdrawing functional groups, should exhibit an enthalpy of formation that is more positive than other members of the series. 

The involvement of transition metal peroxo species in the oxidative functionalization of alkanes and arenes has been postulated for several metals with both hydrogen peroxide and alkyl hydroperoxides. 

When the alkyl hydroperoxide has been fully formed, only one half of the oxidizing power of the oxygen has been utilized. Alkyl hydroperoxides are therefore unstable, the stability being dependent upon the structure. Tertiary hydroperoxides are the most, and primary hydroperoxides the least, stable. The degradation reaction, which is essentially a second stage in the oxidation, may be either inter- or intramolecular the degradation may be either bi- or monomolecular. The rate of degradation is a function of the temperature and is easily subject to catalysis. 

It is noteworthy that cytochrome P-450 can also function with peroxide oxygen sources other than 02 + 2e, viz, iodosylbenzene,81 alkyl hydroperoxides,78 or percarboxylic acids.82... 

A density functional study of the transition structures of Ti-catalyzed epoxidation of allylic alcohol was performed, which mimicked the dimeric mechanism proposed by Sharpless et al.5 Importance of the bulkiness of alkyl hydroperoxide to the stereoselectivity, the conformational features of tartrate esters in the epoxidation transition structure, and the loading of allylic alcohol in the dimeric transition structure model were pointed out. 

Kundu and Ball developed a method for remote functionalization of alkyl hydroperoxides 321 via 1,5-hydrogen transfer reactions (Fig. 88) [421]. When treated... 

Some stereospecific epoxidations such as the Katsuki-Sharpless system only function with alkyl hydroperoxides. 

Lipoxygenases (LOs) are nonheme, mononuclear iron enzymes that catalyze the regio- and stereoselective conversion of polyunsaturated fatty acids with a di.di-1,4-diene functionality into products having a l-hydroperoxy-tra 5, cM-2,4-diene functionality. The mammalian LOs typically act on arachidonic acid and produce alkyl hydroperoxides that are converted into leukotrienes and lipoxins, which are involved as messengers in the inflammatory response. Plant enzymes act on linoleic acid, but the role of the product alkyl hydroperoxide is less well understood. 

Conversely the reaction of the ferric compounds will be potentially less exothermic, or endothermic and hence slower. In this respect the coordination of the iron atom appears to make possible a new reaction path in the case of hydrogen peroxide and alkyl hydroperoxides involving at first complex formation with the peroxide molecule and then the production of further complexes of unknown structure but which function as electron or hydrogen acceptors. 

This fact illustrates the point where the functions of metal salt catalysts become apparent. If oxidation to the alcohol, ketone or carboxylic acid (i.e. beyond the hydroperoxide stage) is the objective, metal catalysts should be used to promote decomposition of the hydroperoxide. The metal ion (complex) catalyzed decomposition of hydroperoxides is responsible for the sustained and rapid formation of radicals participating in a chain reaction. The most effective are metals with at least two accessible oxidation states. Both components of a redox couple may be capable of reacting with alkyl hydroperoxides ... 

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