Oxidation acetophenone oximes

Kinetic studies of the oxidation of some a-hydroxy acids with pyridinium dichromate (PDC) are consistent with a mechanism involving the loss of H2O from the pro-tonated substrate in the rate-determining step. The oxidation of 8-hydroxyquinoline (oxine) by PDC has been studied. The intermediacy of an acetochromate ion in the oxidation of some acetophenone oximes with PDC is suggested. 

The yield of the reaction (Table 1) clearly depends or the nature of the solid and on the experimental conditions (temperature, time). Thus, with silica and alumina, amorphous solids with a relatively low acidity, the acetophenone oxime molecule reacts with a very low yield, being the only reaction product the hydrolysis one, acetophenone. With the synthetic mixed oxide silica-alumina, that possesses simultaneously BrOnsted and Lewis acidic centres, the conversion is quantitative, being also the major product the hydrolysis one (3), when the reaction is carried out at 160°C. 

Mechanisms have been suggested for the N-bromosuccinimide (NBS) oxidation of cyclopentanol and cyclohexanol, catalysed by iridium(III) chloride,120 of ethanolamine, diethanolamine, and triethanolamine in alkaline medium,121 and for ruthenium(III)-catalysed and uncatalysed oxidation of ethylamine and benzylamine.122 A suitable mechanism has been suggested to explain the break in the Hammett plot observed in the oxidation of substituted acetophenone oximes by NBS in acidic solution.123 Oxidation of substituted benhydrols with NBS showed a C-H/C-D primary kinetic isotope effect and a linear correlation with er+ values with p = —0.69. A cyclic transition state in the absence of mineral acid and a non-cyclic transition state in the presence of the acid are proposed.124 Sulfides are selectively oxidized to sulfoxides with NBS, catalysed by ft-cyclodextrin, in water. This reaction proceeds without over-oxidation to sulfones under mild conditions.125... 

Cleavage of oximes to the parent carbonyl compound may be performed under mild conditions by anodic oxidation in CH3CN/H2O [123]. Thus, anodic oxidation of 4-sub-stituted acetophenone oximes in wet acetonitrile furnishes the corresponding acetophenones in high yields, while the oxidation of benzaldoximes is unselective [124] [Eq. (18)]. By indirect electrochemical oxidation using the Mn(II)/Mn(III) mediator system in the... 

Kinetic studies of oxidation of acetophenone oximes with CBT in aqueous acetic acid were carried out (86MI1). The main reaction products are acetophenones. The scheme of oxidation, complying with the kinetic data and the effects of the acidity of the medium and the addition of chloride ions, proposes that the attack of positively charged chlorine on the oxime group nitrogen is the rate-limiting stage, followed by the fast transformation of the carbocation formed (Scheme 105). 

For oxidation of acetophenone oximes by V03, see under Oximes. Oxidation of thioketones is described later. 

The use of dinitrogen pentoxide in the Ponzio reaction for the oxidation-iutration of oximes to em-dinitro groups has been reported by Russian chemists. Millar and co-workers extensively investigated these reactions and reported the synthesis of 2,4,5,7,9,9-hexanitrofluorene (2), a thermally stable explosive with an oxygen balance better than TNT. Other energetic materials containing gem-dinitro functionality were synthesized from the oximes of acetophenone, 4-nitroacetophenone, a-nitroacetophenone and 2-hydroxyacetophenone. 

Usually, electrochemical oxidative hydrolysis of ketoximes affords the corresponding ketones. Hence, 2-octanone (equation 13) and acetophenone were obtained from the corresponding ketoximes in 90% and 97% yields, respectively. However, camphor oxime was transformed into the ring-cleaved nitrile (equation 14). ... 

CAN-mediated nitration provides a convenient route for the introduction of a nitro group into a variety of substrates. Alkenes on treatment with an excess of sodium nitrite and CAN in chloroform under sonication afford nitroalkenes. When acetonitrile is used as the solvent, nitroacetamidation occurs in a Ritter-type fashion. However, the attempted nitroacetamidation of cyclo-pentene-1 -carboxaldehyde under similar conditions resulted in the formation of an unexpected dinitro-oxime compound. A one-pot synthesis of 3-acetyl- or 3-benzoylisoxazole derivatives by reaction of alkenes (or alkynes) with CAN in acetone or acetophenone has been reported. The proposed mechanism involves a-nitration of the solvent acetone, oxidation to generate the nitrile oxide, and subsequent 1,3-dipolar cycloaddition with alkenes or alkynes. The nitration of aromatic compounds such as carbozole, naphthalene, and coumarins by CAN has also been investigated. As an example, coumarin on treatment with 1 equiv of CAN in acetic acid gives 6-nitrocoumarin in 92% yield. ... 

Mesityl oxide Methyl benzoate Nitroethane Propyl alcohol Propylene dichloride Tetrahydrofurfuryl alcohol Trichloroethylene solvent, cellulose ethers Acetone oxime Acetophenone Butyl benzoate Butyl formate Cyclohexane Cyclohexyl acetate Dibutyl tartrate Diethyl oxalate Epichlorohydrin Ethyl butyrate Ethylene glycol diacetate Ethyl-(S)-lactate Ethyl propionate Isopropyl butyrate Mesityl oxide... 

The kinetics of the oxidation of oximes of substituted acetophenones by vanadium(V) have been measured in aqueous acetic acid, using NaVOsJ A two-electron oxidation to the carbocation is proposed, ultimately yielding the ketone. 

Apparently, the intermediate O-vinyl oxime rearranges to nitrone A [328], which is further fused with acetophenone to generate triene nitrone B (Scheme 1.156). Electrocyclization of the latter gives dihydropyridine-N-oxide C, which rearranges in N-hydroxydihydropyridine D. 1,4-Abstraction of methanol from pyridine D leads to 2,4,6-triphenylpyridine via the intermediate 1,4-biradical E (analog of 1,4-benzoid Bergman biradical [329,330]). 

---