Alcohols formation from alkyl hydroperoxides

The importance of alkylperoxy radicals as intermediates had long been realized (see Sect. 2) and their subsequent reaction to yield the alkyl-hydroperoxide or decomposition products such as aldehydes and alcohols had been reasonably successful in describing the mechanism of the autocatalytic oxidation of alkanes. However, even though 0-heterocycles (which cannot be derived from intermediate aldehydes) had been found in the products of the oxidation of n-pentane as early as 1935 [66], the true extent of alkylperoxy radical isomerization reactions has been recognized only recently. Bailey and Norrish [67] first formulated the production of O-heterocycles in terms of alkylperoxy radical isomerization and subsequent cyclization in order to explain the formation of 2,5-dimethyl-tetrahydrofuran during the cool-flame oxidation of n-hexane. Their mechanism was a one-step process which involved direct elimination of OH. However, it is now generally formulated as shown in reactions (147) and(I67)... 

Sulfides react faster with hydrogen peroxide and alkyl hydroperoxides than do alkenes. For this reason, transition metal catalysts are rarely necessary, but these reactions are acid catalyzed and first order in both sulfide and peroxide. The acid (HX) can be as weak as alcohol or water but the "effectiveness (of the oxidation) is determined by the pXa of the acid. Sulfides also react faster with peroxides than do ketones (see the Baeyer-Villiger reaction, sec. 3.6). Formation of the sulfone in these reactions is straightforward, but requires more vigorous reaction conditions. It is usually easy to isolate the sulfoxide from oxidation of a sulfide. Direct conversion of a sulfide to a sulfone requires excess peroxide and vigorous reaction conditions (heating, long reaction times, more concentrated peroxide). 

The irradiation of an alkane solution in acetonitrile with visible light in the presence of catalytic amounts of quinone and copper(II) acetate gives rise to the formation of almost pure alkyl hydroperoxide which is decomposed only very slowly under these conditions to produce the ketone and alcohol [64c,d]. It has been proposed [64d] that the first step of the reaction is a hydrogen atom abstraction from the alkane, RH, by a photoexcited quinone species to generate the alkyl radical R and semiquinone. The former is rapidly transformed into ROO and then alkyl hydroperoxide, while the latter is reoxidized by Cu(II) into the initial quinone (Scheme IX. 10). 

The mechanism of aerobic alkane photooxidation catalyzed by metal 0x0 complexes includes the formation of a photoexcited species which is capable of abstracting a hydrogen atom from an alkane. The alkyl radical thus formed rapidly adds a molecule of oxygen. An alkyl hydroperoxide is partially decomposed to produce a ketone and an alcohol ... 

If the crown catalyzed reaction of potassium superoxide with alkyl halide is carried out in dimethylsulfoxide as solvent, the product is the corresponding alcohol [6—9]. The formation of alcohol rather than dialkyl peroxide has been shown to result from reaction of the alkyl hydroperoxide anion with dimethylsulfoxide to form alkoxide and dimethylsulfone (Eqs. 8.3-8.5) [9]. The alkyl hydroperoxide anion is presumably formed by reduction of the initial alkyl hydroperoxide radical by the superoxide anion [8, 9]. 

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