Hydroperoxide formation yields

Table 6b Hydroperoxide formation yields (%) of O3 reactions with alkenes (mol % of reacted alkene).

The now classic Farmer-type hydrogen-abstraction Initiation of free radical autoxldatlon accounts for a large portion of the nonenzymlc oxidations of n-3 fatty acids (45). Because fish lipids contain substantial concentrations of EPA and DHA (47-48), they provide many allowed sites (18, 22, 45, 46, 49) of hydroperoxide formations, and thus can account for a large array of decomposition products. Oxidizing model systems of unsaturated methyl esters of fatty acids yielded monohydroperoxides, but also produce dlhydroperoxldes that are formed by cycllzatlon of Intermediate hydroperoxy radicals when suitable H-donatlng antioxidants are not present to quench the free radical reaction (45, 50, 51). Decomposition of monohydroperoxides of fatty acids In model systems yields a very different profile of lower molecular weight products than observed for similar decompositions of dlhydroperoxldes of the same fatty acids (45, 46). 

The reaction is not "clean." Hydroperoxide decomposition yields aldehyde and ketone. Moreover, at other than quite low conversion, further oxidation leads to scission of carbon-carbon bonds and formation of acids [63], However, if a boric-acid ester or boroxine is added, secondary alcohol can be obtained in good yield (see Example 5.5 in Section 5.4). 

With chiral ligands, the transition-metal catalyst-hydroperoxide complex yields optically active oxiranes. " One of the most significant advances in the formation of chiral epoxides from allyl alcohols has recently been reported by the Sharpless group. Using (-l-)-tartaric acid, ferf-butylhydroperoxide, and titanium isopropoxide, they were able to obtain chiral epoxides in very high enantiomeric excess. The enantiomeric epoxide can be obtained by employing (—)-tartaric acid (Eq. 33a). 

Two process routes to propylene oxide are commercially practiced hydroperoxide formation and then use of this to oxidize propylene, and formation of propylene chlorohydrin followed by treatment with a base to form propylene oxide [22, 23]. It has not been possible to produce adequate yields of propylene oxide via the direct oxidation of propylene with air in the manner in which ethylene oxide is now produced, although attempts to come close to this continue [24]. 

The details of the complicated mechanism of this rearrangement were only discovered some time after the startup of commercial facilities (Eig. 19.4). Distillation is used to recover the 90+% yield of the rearrangement products. Unreacted cumene is recycled after careful purification to remove any traces of phenol, which would be a powerful inhibitor of hydroperoxide formation. 

Organosulphur compounds are the main source for the formation of the acid catalyst. Compounds such as XIII react with hydroperoxides to yield sulphoxides, XIV, as key intermediates for the stabilisation of the lubricant [58-60], (Reaction 4.47) ... 

A number of hindered and relatively unreactive alkenes such as adamanty-lideneadamantane (30) undergo reaction with 02(1Ag) to yield the corresponding dioxetane. This clearly reflects the fact that, for non-activated alkenes of this type, allylic hydroperoxide formation is sterically impossible. Several papers [139-142] have reported the concomitant formation of the corresponding epoxide and this has been assumed [143] to indicate the intermediacy of a perepoxide (Eq. (53)). 

Formation of a-ketohydroperoxide in the course of an oxidation is observed for cyclohexanone [130] and /Jj3 -dimesitylpropiophenone [137]. Hydrogenation of the hydroperoxides formed yields a-ketoalcohols. a-Ketohydroperoxides decomposes to acid and aldehyde according to Rieche [138], viz. 

Yields have been determined for hydroperoxide formation from the alkyl side-groups ethylbenzene-2-hydroperoxide, 17 % C from OH + ethylbenzene benzyl-hydroperoxide, 5 % C from OH + toluene (Bachmann). Low yields of methylhydroperoxide are reported for both systems, and ethylhydroperoxide was also observed in the reaction of OH with ethylbenzene. 

The quantum yield of hydroperoxide formation is < pooh = 8.6x 10 (253.7 nm). The yield of hydroperoxides is much smaller than the amount of oxygen absorbed because most of them are decomposed during photooxidation to yield secondary oxidation products. 

Autoxidation of alkanes generally promotes the formation of alkyl hydroperoxides, but d4-tert-huty peroxide has been obtained in >30% yield by the bromine-catalyzed oxidation of isobutane (66). In the presence of iodine, styrene also has been oxidized to the corresponding peroxide (44). 

The kinetics of formation and hydrolysis of /-C H OCl have been investigated (262). The chemistry of alkyl hypochlorites, /-C H OCl in particular, has been extensively explored (247). /-Butyl hypochlorite reacts with a variety of olefins via a photoinduced radical chain process to give good yields of aUyflc chlorides (263). Steroid alcohols can be oxidized and chlorinated with /-C H OCl to give good yields of ketosteroids and chlorosteroids (264) (see Steroids). /-Butyl hypochlorite is a more satisfactory reagent than HOCl for /V-chlorination of amines (265). Sulfides are oxidized in excellent yields to sulfoxides without concomitant formation of sulfones (266). 2-Amino-1, 4-quinones are rapidly chlorinated at room temperature chlorination occurs specifically at the position adjacent to the amino group (267). Anhydropenicillin is converted almost quantitatively to its 6-methoxy derivative by /-C H OCl in methanol (268). Reaction of unsaturated hydroperoxides with /-C H OCl provides monocyclic and bicycHc chloroalkyl 1,2-dioxolanes. 

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