Dihydroperoxides, formation

A similar mechanism of chain oxidation of olefinic hydrocarbons was observed experimentally by Bolland and Gee [53] in 1946 after a detailed study of the kinetics of the oxidation of nonsaturated compounds. Miller and Mayo [54] studied the oxidation of styrene and found that this reaction is in essence the chain copolymerization of styrene and dioxygen with production of polymeric peroxide. Rust [55] observed dihydroperoxide formation in his study of the oxidation of branched aliphatic hydrocarbons and treated this fact as the result of intramolecular isomerization of peroxyl radicals. 

Previous work by Sahetchian et al. [177] on the oxidation of n-heptane and n-butane in a motored CFR engine, with particular attention to the isomerization reactions and the autoignition delay, showed that the concentration of the hydroperoxide formed in the isomerization reaction reaches a maximum concentration just preceding autoignition at a compression ratio of CR = 9.6 1 (T = 640 K). However, in similar experiments on n-butane oxidation no hydroperoxide was formed and autoignition was not observed for compression ratios up to 16 1. This may be regarded as a consequence of the different chain lengths of the two hydrocarbons, and probably relates to the different tendencies for isomerization reactions, and dihydroperoxide formation to occur. 

Resorcinol or hydroquinone production from m- or -diisopropylben2ene [100-18-5] is realized in two steps, air oxidation and cleavage, as shown above. Air oxidation to obtain the dihydroperoxide (DHP) coproduces the corresponding hydroxyhydroperoxide (HHP) and dicarbinol (DC). This formation of alcohols is inherent to the autooxidation process itself and the amounts increase as DIPB conversion increases. Generally, this oxidation is carried out at 90—100°C in aqueous sodium hydroxide with eventually, in addition, organic bases (pyridine, imidazole, citrate, or oxalate) (8) as well as cobalt or copper salts (9). 

Gem-dihydroperoxide (2), > /O-OH C no-oh W sol and decomp slowly with evoln of 02 and formation of expl polymeric peroxides can be reduced and hydrolyzed thermal decompn leads to pro- orpccivp Vinn/1 plptivacrp nf —0—0—, C—0— and then C—C bonds Polymeric peroxides formed as a decompn product are extremely expl... 

Rust [55] studied the oxidation of branched alkanes and was the first to observe the formation of dihydroperoxides as primary products of the hydrocarbon oxidation [55], Dihydroperoxide was found to be the main product of 2,4-dimethylpentane oxidation by dioxygen at 388 K ... 

The formation of dihydroperoxides as the primary products of hydrocarbon oxidation is the result of peroxyl radical isomerization (see Chapter 2). 

The formation of large yields of acetone from n-pentane, however, has led to the suggestion that decomposition analogous to that of the of-dihydroperoxides is important... 

Table 1.20 lists Arrhenius parameters for a number of secondary initiators. When acting as a secondary initiator in an autocatalytic reaction, the time to maximum rate is comparable with the half-life of the initiator. Thus the half-life of H2O2 at 60Torr (mostly N2 and O2) and 753 K is about 60 sec, consistent with the induction period shown in the oxidation of butene-2 (see later). The half-life of alkyl peroxides is much shorter, but in the high pressure rapid combustion observed in gasoline engines this rate of initiation is too slow and only radical branching is sufficiently fast to explain the observed phenomena. The formation of dihydroperoxide... 

There is ample experimental evidence for the formation of alkyldihydro-peroxides, especially from the longer chain n-alkanes (Section 6.5) but, as noted in Chapter 1, the rate of chain branching which arises from the homolysis of molecular hydroperoxides, regardless of whether they are alkyl hydroperoxides or dihydroperoxides, is too slow to account for the short duration of ignition delays in high-pressure gases at low-temperature. There is also experimental evidence for the formation of alkylketohydro-peroxy radicals of the form... 

In the oxidation of hydrocarbons such internal isomerization leads to the formation of unusual products. Thus, in the oxidation of 2,4-di-methylpentane (59), the major product is the 2,4-dihydroperoxide obtained by the route ... 

The unusual feature of the oxidation of 2,4-dimethylpentane is the formation, even at the lowest measurable conversions, of the dihydroperoxide in yields of over 90%, viz. 

Figure 4.5. Formation of dihydroperoxides from autoxidized methyl linolenate (Neff et al., 1981).

Coxon, D.T., Peers, K.E. and Rigby, N.M. Selective formation of dihydroperoxides in the alpha-tocopherol inhibited autoxidation of methyl linolenate. J. Chem. Soc. Chem. Comm. 67-68 (1984). 

Sumitomo of Japan has developed a commercially alternative process that avoids the use of sulfuric acid and the concomitant undesired salt formation (see reaction sequence below). This alternative route is analogous to the cumene process for phenol production. Diisopropylbenzene (m-DIPB) can be manufactured by the catalytic dialkylation of benzene with two equivalents of propylene. The resulting m-DIPB is then catalytically hydroperoxidized to the corresponding dihydroperoxide (DHP). Upon acidification the dihydroperoxide (DHP) is cleaved cleanly to give resorcinol and acetone. It is worth noting that the Sumitomo process not only provides a cleaner alternative route for the production of resorcinol,... 

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