Hydroperoxide intermediate

Strong evidence has been provided that the photoxygenation proceeds via a hydroperoxide intermediate which is transformed into an epoxide. The epoxide is then opened by the nucleophilic solvent. 

In the postulated bioluminescence mechanism, firefly luciferin is adenylated in the presence of luciferase, ATP and Mg2+. Luciferyl adenylate in the active site of luciferase is quickly oxygenated at its tertiary carbon (position 4), forming a hydroperoxide intermediate (A). 

Eckstein, J. W., Hastings, J. W., and Ghisla, S. (1993). Mechanism of bacterial bioluminescence. 4a,5-Dihydroflavin analogs as models for luciferase hydroperoxide intermediates and the effect of substituents at the 8-position of flavin on luciferase kinetics. Biochemistry 32 404 111. 

Watanabe, H., et al. (1992). Chemiluminescence in the crude extracts of soybean seedlings. Postulated mechanism on the formation of hydroperoxide intermediates. Biochim. Biophys. Acta 1117 107-113. 

Bashkirov A process for making aliphatic alcohols by oxidizing paraffins. The reaction is conducted in the presence of boric acid, which scavenges the hydroperoxide intermediates. Borate esters of secondary alcohols are formed as intermediates and then hydrolyzed. Developed in the USSR in the 1950s and now operated there and in Japan. 

The source of chemiluminescence in the oxidation of luminol was explored by Merenyi and co-workers in detail (153). The oxidation of luminol yields aminophthalate as a final product and the reaction proceeds via a series of electron transfer steps. The primary oxidation product is the luminol radical which is transformed into either diazaquinone or the a-hydroxide-hydroperoxide intermediate (a-HHP). The latter oxidation step occurs between the deprotonated form of the luminol radical and O -. The chemiluminescence is due to the decomposition of the mono-anionic form of a-HHP into the final products ... 

The peroxide value measurement is a general quantitative measure of peroxide/hydroperoxide intermediates produced during oxidative degradation. 

The mechanism by which the hydroperoxide intermediate, (42) (Scheme 29) is converted into the products of Scheme 28 is not clear. The follow-up reaction of (42) may be diverted by reaction with an enone that undergoes epoxidation in 85 to 90% yield. Scheme 29, [121]. The epoxidation reaction does not take place directly from O2 and 02 but requires the formation of an intermediate of type (42) derived either from the enone or from an external carbon acid as in Scheme 29. Yields are considerably improved using an external carbon acid since the Michael addition between the enone and its anion otherwise competes with the epoxidation. For... 

Ab initio calculations of the transition-state energies in the epoxidation of alkenes by hydrogen peroxide catalysed by titanosilicates have been carried out. They indicate a markedly lower energy barrier for attack of the alkene by the oxygen atom of the titanium(IV) hydroperoxide intermediate that is closer to the metal centre. 

The bleomycins (50) are hardly simple amines, but they do have two NH2 groups and a CONH2 group at the N-terminal domain, as well as potential donor nitrogens in pyrimidine and imidazole, which can complex metal ions." " The complexing of iron to bleomycin" " " has a significant effect on bleomycin-DNA interactions—metal complexes can mediate strand scission—and on alkene oxidation. Both may involve hydroperoxide intermediates." " " " ... 

MCBA enhances the solubility of the cobalt salts in MeCN solution, thereby ensuring better efficiency to a needed redox decomposition of the hydroperoxide intermediate of the substrate en route to the products". By using the HPI/Co(II)/MCBA/02 system in MeCN solution at 25 °C, competitive oxidations of p-X-substituted benzyl alcohols were run pairwise (Scheme 8). From the amount of the aldehydes produced, the relative reactivity (kx/ h) could be reckoned, and the acquired data provided a p = —0.68 in a Hammett plot vs. <7+. ... 

Although the cofacial diporphyrins represent a vibrant and innovative direction in dioxygen activation, simple porphyrins and their derivatives also remain an important research area. The dichlorophenyl-substituted porphyrin tdcpp [5,10,15,20-tetrakis(2,6-dichlorophenyl)-porphyrin] forms a complex with cobalt(II), [Co(tdcpp)], and catalyzes the oxidation of conjugated olefins to (after experimental workup) ketones in the presence of dioxygen and triethylsilane (80) a hydroperoxide intermediate has been isolated from these reactions (81). 

Finally, all the additives prepared by hydroperoxide intermediates increase dramatically the life time (both in photo and thermal ageing) of elastomers such as EPDM(ENB) and polyoctenamer whose the original stabilities are well known to be very low. 

The Merck system can be extended to the asymmetric synthesis of a-hydroxy ketones by using oxygen as electrophile (Scheme 18) (47). The hydroperoxide intermediates are reduced by triethyl phosphite. The sense of asymmetric induction is again consistent with the ion-paired, 7r-stacked assembly model given in Scheme 13. 

Simple alkyl-substituted dihydro-1,4-thiazines are readily converted into the corresponding 5-monoxides atmospheric oxidation is sometimes sufficient, although side reactions may also occur. The cyclohexene derivative (99), for instance, affords not only the oxide (100) but also the spiro compound (101) probably generated by ring contraction of a hydroperoxide intermediate (Scheme 42) <73US(B)(8)34l>. 

The allylic hydroperoxide, 2,3-dimethyl-3-hydroperoxy-l-butene, III, was detected during the oxidation of TME in the presence of [MCl(CO)-(Ph3P)2] (M = Rh, Ir) and reached a maximum yield of 11% after 3.5 hours when the rhodium complex was used (Figure 1). James and Ochiai (13) have cited spectral evidence for hydroperoxide intermediates, and Fusi et ah (14) obtained evidence which supports the intermediacy of an allylic hydroperoxide during cyclohexene oxidation in the presence of metal complexes. The allylic hydroperoxide (III) which is formed during the oxidation of TME in the presence of [MCl(CO) (Ph3P)2]... 

Considerable evidence exists that indicates the selective oxidation of propylene proceeds via the formation of a symmetrical allyl species. Subsequent steps may vary as a function of the catalyst. Some catalyst systems may abstract a second hydrogen atom before the insertion of oxygen. Others may add molecular oxygen, forming a hydroperoxide intermediate, which may then subsequently decompose into acrolein and water. 

Catalytic oxidation ofl-alkenes.2 The Co(II) complex catalyzes the oxygenation of terminal alkenes to the methyl ketone and the corresponding alcohol. The reaction is not a radical-initiated autoxidation it probably involves a hydroperoxide intermediate. 

Oxidation of indoles.5 Indoles react with K02 in conjunction with 18-crown-6 or benzyl(triethyl)ammonium chloride in THF to give products (1, 2, 3) that arise from an indoxyl hydroperoxide intermediate (a). 

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