Primary Hydroperoxides

Primary alkyl hydroperoxides are decomposed in the presence of many metal salts to give mainly alcohols, aldehydes and in some cases carboxylic acids [326]. Cobalt(II) octanoate catalyzes the decomposition of w-butyl hydroperoxide in pentane at 38 °C to give -butyl alcohol (67%), oxygen (70%) and w-butyraldehyde (32%) [328], equation (215). 

The decomposition of -decyl hydroperoxide in the presence of cobalt complexes has been studied in detail by Bulgakova, Skibida and Maizus [363,364] and found to proceed via a radical pathway at 50 °C. The reaction mechanism depended on the nature of the anionic ligand in this case. Thus, when cobalt(II) acetylacetonate was used as the catalyst a linear dependence on [Co(acac)2] concentration was observed. This and other evidence suggested to these authors [364] that decomposition of -decyl hydroperoxide in the presence of [Co(acac)2] proceeds via monomolecular decomposition of a mononuclear complex [Co(acac)2(ROOH)], equations (216) and (217). Inhibition studies indicated that while decomposition of n-decyl hydroperoxides gave radicals, a chain mechanism was not involved. 

A7-C10H21OOH + Co(acac)2 / -CioH2iOOH Co(acac)2 ------- Co(acac)20H +a -CioH2iO  

When cobalt(II) stearate was used as the catalyst, however, the rate of hydroperoxide decomposition was a linear function of the square of the [CoSt2] concentration. [364]. Thus, the pathway shown in equations (218) and (219) was proposed [364]. 

In the decomposition of w-decyl hydroperoxide catalyzed by copper(II) stearate, the formation of radicals was preceded by the formation of the complex [CuSt2(ROOH)2] [365]. 

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Under the action of heat and free radicals, hydroperoxides are decomposed into alcohols and carbonyl compounds. The primary hydroperoxide RCH2OOH is an unstable molecule and is decomposed into aldehyde, acid, and dihydrogen through the interaction with formed aldehyde [111]. 

As a result, the primary hydroperoxide is decomposed into aldehyde, carbonic acid, ester, and dihydrogen. 

As alkylaromatic hydrocarbon (toluene, p-xylene, etc.) is oxidized, aldehydes appear radicals and peracids formed from them play an important role. First, aldehydes react rapidly with the Co3+ and Mn3+ ions, which intensifies oxidation. Second, acylperoxyl radicals formed from aldehydes are very reactive and rapidly react with the initial hydrocarbon. Third, aldehydes form an adduct with primary hydroperoxide, which decomposes to form aldehyde and acid. 

Co-oxidation of indene and thiophenol in benzene solution is a free-radical chain reaction involving a three-step propagation cycle. Autocatalysis is associated with decomposition of the primary hydroperoxide product, but the system exhibits extreme sensitivity to catalysis by impurities, particularly iron. The powerful catalytic activity of N,N -di-sec-butyl-p-phenylenediamine is attributed on ESR evidence to the production of radicals, probably >NO-, and replacement of the three-step propagation by a faster four-step cycle involving R-, RCV, >NO, and RS- radicals. Added iron complexes produce various effects depending on their composition. Some cause a fast initial reaction followed by a strong retardation, then re-acceleration and final decay as reactants are consumed. Kinetic schemes that demonstrate this behavior but are not entirely satisfactory in detail are discussed. 

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. 

When the oxidation moves by the intermolecular path and the reaction is applied to n-hexane, the sequence of steps may be written as indicated below. This sequence, for steps 2 to 5, inclusive, is analogous to the sequence used by Walsh (J ) for the oxidation of iso-octane. Step 1 is different, in that Walsh used the tertiary hydrogen atom as a preferred point of attack. This sequence is also analogous to the one used by Bailey and Norrish (4), except that these authors seemed to prefer to start with the methyl group. They were careful to point out that much, possibly more, of the oxidation would be initiated at methylene groups and that the alkylhydroperoxides involved in the repeating sequences of the decadent reaction chain would all be primary hydroperoxides. 

Hydrogen was observed among reaction products of primary hydroperoxide decomposition). 

In the first steps of irradiation, the BR moieties have to be considered as the prime reason for the photooxidation of ABS. Primary hydroperoxidation occurs in the a-position to the double bond of BR units leading to the formation of a, P-unsaturated hydroperoxides [14-16]. The two mechanisms reported below are proposed to account for the photochemical and thermal homolysis of a, P-unsaturated hydroperoxides ... 

The high reactivity of the primary hydroperoxide product toward chaincarrying peroxyl radicals readily explains the relatively high yields of alcohol... 

Hydrocarbon autoxidation takes place via a complex set of radical reactions, some of which were only recently identified. One of the mechanistic difficulties is that the reactions can only be indirectly investigated by monitoring the evolution of stable products. The input of quantum-chemical calculations, in combination with theoretical kinetics, turned out to be a crucial tool to construct a generic mechanism. One of the new insights is the importance of the copropagation of the primary hydroperoxide product. A solvent-cage reaction, activated by the exother-micity of this secondary step, leads to the formation of the desired alcohol and... 

Amaud R., J.Y. Moisan, and J. Lemaire. 1984. Primary hydroperoxidation in low density polyethylene. Macromolecules 17 332-336. 

Many of the classical mechanistic concepts of lipid oxidation were formulated on the basis of kinetic studies. Later developments in support of the general free radical mechanism of oxidation were based on structural studies of the primary hydroperoxide products. To simplify the kinetics of linoleate oxidation, the reactions were studied at early stages of oxidation, at low levels of conversion, at lower temperatures and in the presence of an appropriate initiator. Under these conditions, the propagation reactions producing hydroperoxides in high yields are emphasized, and the decomposition of hydroperoxides is minimized... 

In summary, alkyl hydroperoxides are readily decomposed in the presence of catalytic quantities of transition metal complexes. In most cases the predominant reaction products are the corresponding alcohol and oxygen. Carbonyl compounds are formed in varying yields depending on the nature of the hydroperoxide. Tertiary alkyl hydroperoxides often decompose by a radical chain process, but non-chain radical processes as well as molecular processes which do not liberate large numbers of radicals occur frequently when secondary or primary hydroperoxides are cata-lytically decomposed. It appears that in many cases, a metal hydroperoxide complex is formed prior to decomposition. 

Primary hydroperoxides (CH2—O—OH) show distinct satellite bands at 1488 and 1435 cm on either side of the 1465 cm band while most corresponding alcohols have only the 1465 cm band. Secondary hydroperoxides (CH—O—OH) have a band at 1352-1334 cm (CH wag). The comparable band in secondary alcohols is shifted from this position owing to interaction with the deformation of the adjacent OH group. 

ZnO accelerates photo-oxidation of polyolefins [145, 1272, 1273, 1275, 1314, 1708], poly(ethylene-co-propylene) [1275, 1996], poly(vinyl chloride) [687, 805, 1667] and polyamides [1314, 1854, 2093]. UV excitation of the ZnO dispersed in atactic polypropylene induces a primary hydroperoxidation and decomposition of the formed hydroperoxides into alcohols and ketones [1708] ... 

The decrease in the diffusion coefficients for different gases through UV irradiated polymeric membranes (films) can be interpreted by the formation of chemical crosslinks and the decrease of free volumes. In the case of photo-oxidative degradation the decrease in diffusion through an irradiated membrane can be the result of physical interactions between primary hydroperoxide photoproducts, and can be used as a sensitive criterion to characterize the photo-oxidative evolution of polymers [1717]. 

Acids are produced by scission of the polymeric chain, with a mechanism that has not yet been elucidated [21, 28-29]. The alkoxy radical formed through Reaction 21 can decompose via (3-scission, according to Reactions 28 and 29 (Scheme 10), with the formation of a methyl chain end, whose increase has been observed in the post-irradiation oxidation process, and of a carbonyl radical, which in turn decomposes giving a primary macroalkyl radical and carbon monoxide (CO), commonly found among the products of irradiation or thermo-oxidation of PE [2, 30]. Primary alkyl macroradicals react with oxygen to form primary hydroperoxides, then the hydroperoxides decomposition results in the formation of acids, as already stated in the literature [28]. 

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