Intermediates in oxidations

Oxidation of 4-methylcyclohexanone by addition of nitric acid at about 75°C caused a detonation to occur. These conditions had been used previously to oxidise the corresponding alcohol, but although the ketone is apparently an intermediate in oxidation of the alcohol, the former requires a much higher temperature to start and maintain the reaction. An OTS report, PB73591, mentions a similar violent reaction with cyclohexanone [1], Presence of nitrous acid is essential for the smooth oxidation of cycloalkanones with nitric acid to a, rw-hcxanedioic acids. Because high-purity nitric acid (free of nitrous acid) is now commonly available, addition of a little sodium or potassium nitrite to the acid is necessary before its use to oxidise cycloalkanones [2],... 

Oxidation of 4-methylcyclohexanone by addition of nitric acid at about 75°C caused a detonation to occur. These conditions had been used previously to oxidise the corresponding alcohol, but although the ketone is apparently an intermediate in oxidation of the alcohol, the former requires a much higher temperature to start... 

J. Zhou, H. Xu, G.-H. Wan, C.-F. Duan and H. Cui, Enhancing and inhibiting effects of aromatic compounds on luminol-dimethylsulfoxide-OH chemiluminescence and determination of intermediates in oxidative hair dyes by HPLC with chemiluminescence detection. Talanta, 64 (2004) 467—477. 

These and other interesting results allow quantitative insight into the rate of breakdown of N-(hydroxymethyl) compounds (i.e., carbinolamines (hemi-aminals)), the reaction mechanisms of which we examined in Sect. 8.7.3 (see, in particular, Fig. 8.20) [80 - 82], These carbinolamines, we recall, are major metabolic intermediates in oxidative N-dealkylation reactions resulting from cytochrome P450 catalyzed hydroxylation of the C-atom adjacent to the... 

Epr is most effective for detecting free radicals that may occur as intermediates in oxidation and reduction reactions involving transition metal ions. Since these transients are invariably quite labile, epr is combined with continuous flow, (more conveniently) stopped-flow, flash photolysis, and pulse radiolysis. 

Chromium(IV) and (V) are important intermediates in oxidation by Cr(VI), see next section. Chromium(V) is generally more reactive than Cr(VI). It is believed that Cr(V) is most effective for C —H rupture whereas Cr(IV) best breaks C —C bonds. 

Co(II) acetate in acetic acid with acetaldehyde also gives good selectivity in the formation of adipic acid (73% at 88% conversion at 90oC).200 The role of acetaldehyde is to promote oxidation of Co(II) to Co(III) and maintain a steady-state concentration of Co(III). Later during the reaction, however, cyclohexanone formed as an intermediate in oxidation serves as promoter. Zirconium ions also exhibit a significant promoter effect.201... 

Thiophthalide (452) is the oxo form of l-hydroxybenzo[c]thiophene. It is a stable compound, being intermediate in oxidation level between o-xylene and phthalic acid. It can be formed from o-xylene by oxidation with a mixture of sulfur and water at high temperatures it can also be formed by reduction of phthalic anhydride with H2S + H2 (72AHC( 14)331). It reacts with vinyllithium to form a complex which on hydrolysis undergoes ring expansion to 4,5,6,7-tetrahydro-2//-benzo[c]thiepin-5-one (453), as shown in Scheme 154. 

The reactive intermediates in oxidative coupling of phenols are aryloxy radicals. Growth may occur by the successive addition of aryloxy units as shown in Reaction 5. 

The Griesbaum Coozonolysis allows the preparation of defined, tetrasubsituted ozonides (1,2,4-trioxolanes) by the reaction of O-methyl oximes with a carbonyl compound in the presence of ozone. In contrast to their traditional role as intermediates in oxidative alkene cleavage, 1,2,4-trioxolanes with bulky substituents are isolable and relatively stable compounds. 

The high formal oxidation states of metals in some of these adducts is noteworthy, e.g., Fe(IV) (entries 17 and 18), Ru(IV) (entries 21 and 22), and Pt(IV) (entries 55 and 56). Such adducts are important because they provide definite examples of species often postulated as intermediates in oxidative addition-reductive elimination processes (compare Section II,G,1) and in homogeneous catalysis (134,220a, 410a). In the case of germanium, a tris(germyl) adduct of Pt(IV) has been described (57), but no more than two silyl groups per metal atom are known to result from oxidative addition. 

Mao, Y. Schoeneich, C. Asmus, K. D. Identification of organic acids and other intermediates in oxidative degradation of chlorinated ethanes on Ti02 surfaces en route to mineralization. A combined photocatalytic and radiation chemical study, J. Phys. Chem. 1991, 95, 10080. 

Lee and coworkers117 used lithium enamines as synthetic intermediates in oxidation reactions with perbenzoic acid for the synthesis of 65 as a main intermediate in the synthesis of tansindiol 66 (equation 44). 

Semiquinone Formation Constant.—It was assumed in the foregoing treatment that the two stages of oxidation are fairly distinct, but when this is not the case the whole system behaves as a single two-electron process, as in Fig. 79. In view of the interest associated with the formation of semiquinone intermediates in oxidation-reduction reactions, methods have been developed for the study of systems in which the two stages may or may not overlap. The treatment is somewhat complicated, and so the outlines only will be given here. ... 

Not the papers that reported the discovery and characterization of the phosphohistidine, but the ones that said we thought it was an intermediate in oxidative phosphorylation. That was a learning experience. But I perhaps tend to move ahead to the next possibility more readily than many scientists do. If you want to finish off a research project, make sure that everything seems right in that area, document everything, and so forth, you may never get to the next important aspect. 

Recognition of >j -H2 complexes as likely intermediates in oxidative addition reactions to d ions or reductive eliminations from d metal ions prompts examination of another possible complication to the intimate mechanism of d square-planar metal-ion reactions. Although none have been isolated, it seems reasonable to expect such species as intermediates in reductive eliminations from d complexes also, and a number of site fluxionality cases have been explained this way. 

Free Radicals as Intermediates in Oxidative Transformations of Lower Alkanes. 

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