Alkyl hydroperoxides, detection

Such a rearrangement was detected only in the presence of sulfuric acid, and furthermore at 100°C. it was supplanted by a homolytic breakdown. The products found in the purely thermal decomposition—methyl vinyl ketone and methyl vinyl carbinol—are in fact consistent with the behavior of alkyl hydroperoxides and are analogous to the products produced from the cyclic allylic hydroperoxide from cyclohexene (2). 

In vivo, thymine glycol may be one of the most interesting biomarkers of non-enzymatic aromatic hydroxylation, for it can be detected by non-invasive analysis of urine [46], As shown in the upper part of Fig. 2, the one-electron reductive cleavage observed in the Fenton reaction can be extended to alkyl hydroperoxides, ROOH, yielding alkoxyl radicals, RO , whose oxidizing power, although smaller than that of OH , is still considerable [20,24,47] ... 

Total concentrations of detectable stable products (cyclohexanol and cyclohexanone) in the chromatogram of the sample unreduced with PPhj will be (C. + ACoiT" and (Cam ACo, ) " , respectively. Triphenylphosphine reduces the alkyl hydroperoxide to yield, quantitatively, cyclohexanol. So the concentrations of ol and one determined by GC in the sample treated with PPhj will be (C , + Cpnd) and (Co e)" , respectively. The real amount of ketone present in the reaction mixture may thus be determined by measuring the concentration (Cone) " of this product in the reduced sample. 

In general, the yields of hydroperoxides decrease as the starting alkene becomes larger. This may simply reflect the greater number of reaction pathways open to larger molecules our analysis detects only hydroperoxides, and in some of the experiments only primary linear alkyl hydroperoxides. 

The first step of peroxidase catalysis involves binding of the peroxide, usually H2C>2, to the heme iron atom to produce a ferric hydroperoxide intermediate [Fe(IE)-OOH]. Kinetic data identify an intermediate prior to Compound I whose formation can be saturated at higher peroxide concentrations. This elusive intermediate, labeled Compound 0, was first observed by Back and Van Wart in the reaction of HRP with H2O2 [14]. They reported that it had absorption maxima at 330 and 410 nm and assigned these spectral properties to the ferric hydroperoxide species [Fe(III)-OOH]. They subsequently detected transient intermediates with similar spectra in the reactions of HRP with alkyl and acyl peroxides [15]. However, other studies questioned whether the species with a split Soret absorption detected by Back and Van Wart was actually the ferric hydroperoxide [16-18], Computational prediction of the spectrum expected for Compound 0 supported the structure proposed by Baek and Van Wart for their intermediate, whereas intermediates observed by others with a conventional, unsplit Soret band may be complexes of ferric HRP with undeprotonated H2O2, that is [Fe(III)-HOOH] [19]. Furthermore, computational analysis of the peroxidase catalytic sequence suggests that the formation of Compound 0 is preceded by formation of an intermediate in which the undeprotonated peroxide is coordinated to the heme iron [20], Indeed, formation of the [Fe(III)-HOOH] complex may be required to make the peroxide sufficiently acidic to be deprotonated by the distal histidine residue in the peroxidase active site [21],... 

As indicated in Scheme VII/32, cyclononanone (VII/165) is transformed into hydroperoxide hemiacetal, VII/167, which is isolated as a mixture of stereoisomers. The addition of Fe(II)S04 to a solution of VII/167 in methanol saturated with Cu(OAc)2 gave ( )-recifeiolide (VII/171) in quantitative yield. No isomeric olefins were detected. In the first step of the proposed mechanism, an electron from Fe2+ is transferred to the peroxide to form the oxy radical VII/168. The central C,C-bond is weakened by antiperiplanar overlap with the lone pair on the ether oxygen. Cleavage of this bond leads to the secondary carbon radical VII/169, which yields, by an oxidative coupling with Cu(OAc)2, the alkyl copper intermediate VII/170. If we assume that the alkyl copper intermediate, VII/170, exists (a) as a (Z)-ester, stabilized by n (ether O) —> <7 (C=0) overlap (anomeric effect), and (b) is internally coordinated by the ester to form a pseudo-six-membered ring, then only one of the four -hydrogens is available for a syn-//-elimination. [111]. This reaction principle has been used in other macrolide syntheses, too [112] [113]. 

Another example of highly effective melt stabilizers are the thiolate metal complexes (e.g. MDRC, MDRP, MRX, M = Ni, Zn) which are also thermal and UV stabilizers for polyalkenes (see Section 19.3.3.1.V, 19.4.2.2.i and 19.4.2.2.ii) and no hydroperoxides can be detected in polymers containing them after processing. In addition to their peroxidolytic function dithiolates have the ability to trap alkyl peroxyl radicals The contribution of this trapping mechanism to... 

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