Hydroperoxy groups

The ff-oxidation of carbonyl compounds may be performed by addition of molecular oxygen to enolate anions and subsequent reduction of the hydroperoxy group, e.g. with triethyl phosphite (E.J. Bailey, 1962 J.N. Gardner, 1968 A,B). If the initially formed a-hydroperoxide possesses another enolizable a-proton, dehydration to the 1,2-dione occurs spontaneously, and further oxidation to complex product mitctures is usually observed. 

Ketone Peroxides. These materials are mixtures of compounds with hydroperoxy groups and are composed primarily of the two stmctures shown in Table 2. Ketone peroxides are marketed as solutions in inert solvents such as dimethyl phthalate. They are primarily employed in room-temperature-initiated curing of unsaturated polyester resin compositions (usually containing styrene monomer) using transition-metal promoters such as cobalt naphthenate. Ketone peroxides contain the hydroperoxy (—OOH) group and thus are susceptible to the same ha2ards as hydroperoxides. 

Photolytic cleavage of hydroperoxy groups to give macroxy radical has been reported [112-114]. They sug-... 

Such a reciprocal motion of the kinetic chain (or back reaction) results in the decomposition of hydroperoxide groups without any interruption of kinetic chains and leads to the decrease in hydroperoxy groups. It has... 

The OH radical formed during the decomposition of hydroperoxy groups is very reactive and can either terminate a reaction (39) or may attack the weak bond of the backbone polymer resulting in the formation of a new radical (40). 

O Protonation of the hydroperoxy group on the terminal oxygen atom gives an oxonium ion. . . ... 

The reactivity order of alkenes is that expected for attack by an electrophilic reagent. Reactivity increases with the number of alkyl substituents.163 Terminal alkenes are relatively inert. The reaction has a low AHl and relative reactivity is dominated by entropic factors.164 Steric effects govern the direction of approach of the oxygen, so the hydroperoxy group is usually introduced on the less hindered face of the double bond. A key mechanistic issue in singlet oxygen oxidations is whether it is a concerted process or involves an intermediate formulated as a pcrcpoxide. Most of the available evidence points to the perepoxide mechanism.165... 

The peroxyl radical formed from this alkyl radical attacks the a-C—H bond, which is weak due to the dual influence of the adjacent oxo and hydroperoxy groups. 

During PP oxidation, hydroxyl groups are formed by the intramolecular isomerization of alkyl radicals. Since PP oxidizes through an intense intramolecular chain transfer, many of the alkyl radicals containing hydroperoxy groups in the 0-position to an available bond can undergo this reaction. An isomerization reaction has also been demonstrated for the liquid-phase oxidation of 2,4-dimethylpentane [89], Oxidation products contain, in addition to hydroperoxides, oxide or diol. 

The data described above proved that isomerization of alkyl and peroxyl radicals plays a very important role in polymer oxidation. They influence the composition of products of polymer oxidation including the structure of hydroperoxy groups. The competition between reactions of alkyl radical isomerization and addition of dioxygen appeared to be very important for the self-initiation and, hence, autoxidation of PP (see later). 

Suppression of the Pummerer reaction (Fig. 24) could also be a manifestation of the stabilization of the persulfoxide which prevents its interconversion to the hydro-peroxysulfonium ylide, HPSY (Fig. 25), which is the intermediate that has been suggested to undergo a 1,2-shift of the hydroperoxy group and ultimately produces the SC bond cleavage products.92 However, the situation is probably more complex since the intrazeolite reaction of /1-chlorosulfide, 29 (Fig. 28A), requires 7-hydrogen abstraction. The complexation motif (Fig. 28B) which favors the extended rather than folded M+-PS may also play an important role. A complete understanding of these reactions will require additional studies. 

The three solid phase tetralin and decalin hydroperoxides have enthalpies of reaction that are surprisingly comparable, —93.9 6.4 kJmoR, despite the sometimes large error bars associated with either the peroxide or corresponding alcohol and their differences in structure. Notably, the gas phase reaction enthalpy for the cumyl hydroperoxide is nearly identical to the solid phase reaction enthalpy for the 1-methyl-1-tetralin hydroperoxide, —87.0kJmoR, for these structurally similar compounds and supports the hypothesis that the gas and condensed phase formal reaction enthalpies are nearly the same for all compounds. Flowever, for 2,5-dimethylhexane-2,5-dihydroperoxide, the enthalpies of reaction 5 per hydroperoxy group for the solid and gaseous phase are not close —57 and —76 kJmoR, respectively. Compare them with the enthalpies of reaction for ferf-butyl hydroperoxide of —66 (Iq) and —67 or —78 (g) kJmoR. For the unsaturated counterpart, 2,5-dimethylhex-3-yne-2,5-dihydroperoxide, the solid and gas phase enthalpies of reaction per hydroperoxy group are —64.2 kJmoR and —74.6 kJmoR, respectively. 

Dimethyl-2-hydroperoxide-5-ierr-butylperoxyhexane contains both a peroxy and a hydroperoxy group. The enthalpy of reaction 5, to give 2,5-dimethyl-2-hydroxy-5-f-butylperoxyhexane, is —59.9kJmoR (Iq) and —58.8kJmol (g), comparable to those obtained from 1-methylcyclohexane hydroperoxide and f-butyl hydroperoxide. If the mixed peroxide were to undergo the formal reactions 5 and 6 simultaneously, the alcohol product would be 2,5-dimethylhexane-2,5-diol, for which there is only an enthalpy... 

Reviews appeared on the following subjects Analysis of lipid hydroperoxides , the difficulties encountered for hydroperoxide analysis in a plasma matrix , post-column derivatization after GLC of lipid hydroperoxides and methods for detection and characterization of hydroperoxy groups in oxidized polyolefins . 

The negative ion electrospray MS of fatty acid hydroperoxides exhibits various typical features that may be useful for characterization of this type of compounds, such as loss of small neutral molecules and fragmentation associated with the position of the OOH group. The [M — H] and [M — H2O peaks are usually most abundant and cleavage of the double bond allylic to the hydroperoxy group is also observed. The features of the fragmentation after loss of H2O in the MS of a fatty acid hydroperoxide are the same as those observed in the MS of the analogous keto acid . ... 

Treatment of compound 222, containing a 1,2,4-trioxane ring fused to a cyclopentene ring, with O2 leads to formation of a hydroperoxide (223) with ene displacement, as shown in equation 76. The structure of 223 was determined by single-crystal XRD analysis. A contact of the hydroperoxy group with the endocyclic ether O atom of a neighboring molecule (287.4 pm) points to weak H-bonding. ... 

The preceding discussions have clearly shown that type II photosensitized oxygenation of olefins is a powerful tool for the preparation of allyl hydroperoxides and allyl alcohols. The introduction of a hydroxyl group into an olefin occurs under mild conditions and can even be achieved at very low temperatures if the instability of the starting material or the expected allyl hydroperoxides requires such conditions. In many cases a stereoselective introduction of a hydroperoxy group occurs which makes this method even more valuable, especially since hydroperoxides can easily be reduced with retention of configuration. 

Reaction 8 may, therefore, be the major chain-propagating reaction of H02 between 250° and 400°C. The radicals produced will, of course, undergo the same fates as those produced in Reaction 4, regenerating (eventually) alkyl radicals. The main difference between the alkene-H02 addition route and the alkylperoxy radical isomerization route is that in the former case the hydroperoxyalkyl radicals formed are necessarily a-radicals—i.e., radicals in which the unpaired electron is borne by a carbon atom adjacent to that bearing the hydroperoxy group, such as... 

Jp many cases, stereoselective introduction of a hydroperoxy group occurs jjjdlich makes this reaction very valuable in synthetic organic chemistry. 

Whereas several X-ray structural analyses prove the endo orientation of the oxygen atom of the oxaziridine ring, the assumption of an exo oriented hydroperoxy group in 83 is based solely on the opposite sense of asymmetric induction observed for 82 and 83. 

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