Nucleophiles hydroperoxide ions

Conjugated unsaturated ketones are unreactive to peracids because of the depletion of electronic charge in the olefiinic bond, but epoxyketones are readily prepared by using the nucleophilic hydroperoxide ion (H02"") [284], In simple aliphatic compounds the epoxidation follows kinetics first order with respect to hydroperoxide ion and unsaturated ketone [28s]- According to House [286], the reaction should be represented as a reversible addition of hydroperoxide ion, followed by closure of the epoxide ring in a slow step, with expulsion of hydroxide ion. The over-all rate will be determined both by the equilibrium constant in the first step and by the rate constant for the second. 

The electrophilic character of boron is again evident when we consider the oxida tion of organoboranes In the oxidation phase of the hydroboration-oxidation sequence as presented m Figure 6 11 the conjugate base of hydrogen peroxide attacks boron Hydroperoxide ion is formed m an acid-base reaction m step 1 and attacks boron m step 2 The empty 2p orbital of boron makes it electrophilic and permits nucleophilic reagents such as HOO to add to it... 

Electron deficient carbon-carbon double bonds are resistant to attack by the electrophilic reagents of Section 5.05.4.2.2(t), and are usually converted to oxiranes by nucleophilic oxidants. The most widely used of these is the hydroperoxide ion (Scheme 79). Since epoxidation by hydroperoxide ion proceeds through an intermediate ct-carbonyl anion, the reaction of acyclic alkenes is not necessarily stereospecific (Scheme 80) (unlike the case of epoxidation with electrophilic agents (Section 5.05.4.2.2(f)) the stereochemical aspects of this and other epoxidations are reviewed at length in (B-73MI50500)). 

Double bonds in a,/3-unsaturated keto steroids can be selectively oxidized with alkaline hydrogen peroxide to yield epoxy ketones. In contrast to the electrophilic addition mechanism of peracids, the mechanism of alkaline epoxidation involves nucleophilic attack of hydroperoxide ion on the con-... 

Early research suggested that the key intermediate in the POCL reaction was 1,2-dioxetandione (structure II in Fig. 5) [2, 3], which is formed following the multistage nucleophilic attack by the hydroperoxide ion on one of the carbonyl carbons in the oxalate compound. This series of reactions is proposed to occur... 

Peroxide and hydroperoxide ions. A patent disclosure h Barueoh and Payne101 has described addition of teri-bntylliydi- peroxide to ethylene oxide, propylene oxide, and isobutylene oxide in ether, in the presence of either basic or acidic catalysts. The <°rt-Imtylperoxide ion, like other nucleophiles, apparently prefers to uttar. c... 

Studies of the reaction between 2,4-dinitrophenyl benzenesulfonate and OH-, CN , and N3- in 20 mol% DMS0-H20 at 25 °C have shown that OH- attacks exclusively at the sulfonyl group, but the softer nucleophiles react - as shown in (40) - to give mixtures of products of S-0 and C-O bond fission, the fraction of the latter being 0.10 for CN- and 0.66 for N3-. 58 The rate of reaction of hydroperoxide ion with 4-nitrophenyl 4-toluenesulfonate was reported.43... 

The normal synthetic pathway for hydroboration is reaction with an ambiphilic nucleophile of which the simplest example is hydroperoxide ion. This elicits a 1,2-migration of an alkyl group from boron to oxygen with concurrent loss of hydroxide ion. The step occurs with essentially complete retention of configuration. In similar vein, ambiphilic species with the structure NH2X may be used in amination, so that the overall reaction is an addition of ammonia to the alkene with the regio- and chemoselectivity driven by the hydroboration step. A majority of reactions of organoboranes can be rationalized in terms of these ionic mechanistic pathways, or closely related protocols (Scheme 2). 

The oxidation occurs by nucleophilic attack of the hydroperoxide ion on the empty orbital of the boron atom followed by a migration of the alkyl chain from boron to oxygen. Do not be alarmed by hydroxide ion as leaving group. It is, of course, a bad leaving group but a very weak bond—the 0-0 <5 bond—is being broken. Finally, hydroxide attacks the now neutral boron to cleave the B-O-alkyl bond and release the alcohol. 

The hydroperoxide ion (HOO ) in aprotic media is an effective nucleophile that (a) oxygenates sulfoxides (equation 69), (b) hydrolyzes nitriles and amides (equations 70-71) and (c) reacts with HOOH to form superoxide ions and hydroxyl radicals (equations 72 and 73). ... 

Hydroperoxide ion (HOO ) is unstable in most aprotic solvents, but persists for several minutes in pyridine ( decomp, 4.6 X 10 s ), which allows studies of its nucleophilic reactivity. In pyridine, HOO is oxi-3S8-i-8HO ----- 8S3 -i-4HOOH (182) dized in a one-electron transfer to give HOO-, which... 

The hydroperoxide ion (HOO ) in aprotic media is an effective nucleophile that (1) oxygenates sulfoxides, ... 

Unionized hydrogen peroxide (HOOH) is a much weaker nucleophile than hydroperoxide ion (HOO ) but, from model compound studies [65], it may be able to react with benzyl carbonium ions in competition with lignin condensation reactions. 

The a-P double bond in hydroxy- or methoxy-substituted stilbenes should also be stable to hydroperoxide ion. It is the electron withdrawing carbonyl group in cinnamaldehydes that makes their double bond susceptible to nucleophilic attack. 

If such reactions were to be coupled with the photochemical generation of organic free radicals or excited molecular states before the H-atoms combined or hydride ions reacted with HaO, the presence of photore-duced products would be explained. The generation of the powerfully nucleophilic peroxy radical-ions and hydroperoxide ions (Equation 8) also could be involved in instances of the oxidative displacement of halide from aromatic rings. 

Despite the numerous and detailed studies concerned with the luminol reaction mechanism, the exact nature of the pathways and intermediates involved are somewhat speculative. However, the most likely starting point appears to be the oxidation of the cyclic diacyl hydrazine moiety to give an azaquinone (Scheme 6). In the presence of basic hydrogen peroxide, nucleophilic attack by the hydroperoxide ion would seem most likely this idea is supported by the luminescence intensity dependence upon hydrogen peroxide concentration. Although there are several possible outcomes from the reaction of the azaquinone with hydroperoxide ion, we shall (for reasons of simplicity) concentrate on that shown in Scheme 6. 

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