Hydroperoxide production

Tertiary A.1 1 Hydroperoxides, Product BuUetin, Atochem North America, Inc., Buffalo, N.Y., Nov. 1991. 

Ethylbenzene Hydroperoxide Process. Figure 4 shows the process flow sheet for production of propylene oxide and styrene via the use of ethylbenzene hydroperoxide (EBHP). Liquid-phase oxidation of ethylbenzene with air or oxygen occurs at 206—275 kPa (30—40 psia) and 140—150°C, and 2—2.5 h are required for a 10—15% conversion to the hydroperoxide. Recycle of an inert gas, such as nitrogen, is used to control reactor temperature. Impurities ia the ethylbenzene, such as water, are controlled to minimize decomposition of the hydroperoxide product and are sometimes added to enhance product formation. Selectivity to by-products include 8—10% acetophenone, 5—7% 1-phenylethanol, and <1% organic acids. EBHP is concentrated to 30—35% by distillation. The overhead ethylbenzene is recycled back to the oxidation reactor (170—172). 

Decomposition of the /rtin -decalyl perester A gives a 9 1 ratio of trans cis hydroperoxide product at all oxygen pressures studied. The product ratio from the cis isomer is dependent on the oxygen pressure. At 1 atm O2, it is 9 1 trans cis, as with the trans substrate, but this ratio decreases and eventually inverts with increasing O2 pressure. It is 7 3 cis trans at 545 atm oxygen pressure. What deduction about the stereochemistry of the decalyl free radical can be made from these data ... 

FIG. 5 Rate of hydroperoxide production in (a, ) lipoxygenation in pure aqueous medium, (b, ) lipoxygenation in biphasic system, (c, x) two-enzyme (lipase-lipoxygenase) system in two-phase medium, determined experimentally, and (d, ) modeled kinetic of the two enzyme system. (From Ref 63.)... 

Tetrahydrofuran has been reported to exhibit an absorption maximum at 280 nm (52,56), but several workers have shown that this band is not produced by the purified solvent (30,41,57). Oxidation products from THF have been invoked in order to account for the appearance of the 280-nm band in PVC films that are solvent-cast from THF in air (57. 581. However, in some reported cases (56,59), this band was undoubtedly produced, at least in part, by a phenolic antioxidant (2.6-di-tert-butyl-p-cresol)(59) in the solvent. Since certain -alkylphenols have now been shown to be powerful photosensitizers for the dehydrochlorination of PVC (60), it is clear that antioxidant photosensitization might well have been responsible for some of the effects attributed previously (56) to THF alone. On the other hand, enhanced rates of photodegradation under air have also been observed for PVC films cast from purified THF (57), a result which has been ascribed to radical formation during the photooxidation of residual solvent (57,61). Rabek et al. (61) have shown that this photooxidation produces a-HOO-THF, a-HO-THF, and y-butyro-lactone, and they have found that the hydroperoxide product is an effective sensitizer for the photodehydrochlorination of PVC at X = 254 nm (61). 

In order to characterize the intermediates leading to the photo-Fries/cleavage and hydroperoxide products shown in Schemes I and II, laser flash photolysis measurements of solutions of both MDI and TDI based polyurethanes were conducted. The results from this study are interpreted by comparison with transient spectra of an aryl monocarbamate and the bispropyl carbamate of MDI. In addition, a dimethylsilicon analog of the MDI bispropyl carbamate is used to... 

Figure 18.13 Effect of fluorescent device exposure on hydroperoxide production in Spectar copolymer [11]. Reprinted from Polymer, 41, Grossetete, T., Riva-ton. A., Gardette, J.-L., Hoyle, C. E., Ziemer, M., Fagerburg, D. R. and Clauberg, H., Photochemical degradation of poly(ethylene terephthalate)-modified copolymer, 3541-3554, Copyright (2000), with permission from Elsevier Science...

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. 

It was initially assumed as in other autoxidation systems, that autocatalysis arose from first- or second-order radical-producing decompositions of the hydroperoxide product of the reaction, and this led to Reaction Scheme 1 (shown below). 

Lipoxygenases, of which the enzyme from soy beans has been studied the most, also catalyze oxidation of polyunsaturated fatty acids in lipids as indicated in Eq. 21-17. Formation of the hydroperoxide product is accompanied by a shift of the double bond and conversion from cis to trans configuration. Soybean lipoxygenase is a member of a family of related lipoxygenases that are found in all eukaryotes. All... 

Although LOX activity is important to the plant s defense against pathogens, there are negative aspects of the enzyme in foods. LOX activity and the resulting fatty acid hydroperoxide products initiate free radical chains that modify proteins (particularly residues of Trp, His, Cys, Tyr, Met, and Lys) as well as vitamins or their precursors (e.g., carotene and tocopherol). Evidence of such free radical reactions is often visibly observed as loss of carotenoid/chlorophyll pigments in improperly blanched frozen foods. Another consequence of these free radical reactions is the development of potent off-flavors, many of which originate from decomposition of the fatty acid hydroperoxide products. 

Figure C4.2.4 (A) SP-HPLC of methyl hydroxyoctadecadienoates obtained from linoleic acid hydroperoxide products. Peak 1, methyl 13-hydroxy-9(Z),11( )-octadecadienoate peak 2, methyl 13-hydroxy-9( ),11(E)-octadecadienoate peak 3, methyl 9-hydroxy-10(E),12(Z)-octadecadi-enoate peak 4, methyl 9-hydroxy-10( ),12( )-octadecadienoate. In this chromatogram, peaks 2 and 4 are more abundant than ordinarily encountered retention times may vary (but not the order of elution) depending on the type of silica HPLC column. (B) CP-HPLC of peak 1 from A. The 13(R)-stereoisomer elutes before the 13(S)-stereoisomer. Elution times may vary. (C) CP-HPLC of peak 3 from A. The 9(S)-stereoisomer elutes before the 9(R)-stereoisomer. Elution times may vary.

The observed lag phase of activity, seen in Figure C4.2.2, is variable in duration and may not be noticed. The lag is generally thought to be due to the time required to convert inactive native Fe2+-LOX into active Fe3+-LOX. Thus, some amount of fatty acid hydroperoxide product is required to prime the pump. As a consequence, relatively long lag phases are often due to either low LOX concentrations, highly purified substrates containing no hydroperoxides from autoxidation, or both. 

In early attempts to produce an iron-oxo species (20) from typical porphyrins like chloro-a,/3,y,8-tetraphenylporphinatoiron(III) [Fe(III)TPP-Cl] and chloroferriprotoporphyrin(IX)[Fe(III)PPIX-Cl], we examined the reaction of t-butyl hydroperoxide and peroxy-acids with alkanes and olefins in the presence of these catalysts. With peroxyacids, decomposition of the porphyrin ring was observed, while with the f-butyl hydroperoxides, product distributions were indistinguishable from free-radical chain reactions initiated photochem-ically in the absence of any metals. 

Grosch, W. 1987. Reactions of hydroperoxides - products of low molecular weight. In Autooxidation of Unsaturated Lipids (H.W.S. Chan, ed.), pp. 95-139, Academic Press, London. 

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