Aromatic rings oxidation with hydrogen peroxide

In an attempt to protect thiophenols during electrophilic substitution reactions on the aromatic ring, the three substituted thioethers were prepared. After acetylation of the aromatic ring (with moderate yields), the protective group was converted to the disulfide in moderate yields, 50-60%, by oxidation with hydrogen peroxide/boiling mineral acid, nitric acid, or acidic potassium permanganate. ... 

The application of hydrogen peroxide has been controversially discussed.It was shown that oxidation in benzene/acetic acid not only built the desired sulfones of the PASHs but also that the aromatic rings of all types of polycyclic compounds were oxidized. Fow or zero recovery of the analytes is often the result. Oxidation with hydrogen peroxide should therefore be avoided for any samples in which aromatic compounds are to be analyzed. 

Tetracyanoethylene oxide [3189-43-3] (8), oxiranetetracarbonitnle, is the most notable member of the class of oxacyanocarbons (57). It is made by treating TCNE with hydrogen peroxide in acetonitrile. In reactions unprecedented for olefin oxides, it adds to olefins to form 2,2,5,5-tetracyanotetrahydrofuran [3041-31-4] in the case of ethylene, acetylenes, and aromatic hydrocarbons via cleavage of the ring C—C bond. The benzene adduct (9) is 3t ,7t -dihydro-l,l,3,3-phthalantetracarbonitrile [3041-36-9], C22HgN O. 

Co(ni) alkyl peroxides have been prepared and used by Mimoun and coworkers in the hydroxylation of hydrocarbons with this metal a Haber-Weiss type of reactivity is suggested. Square-planar Pt(II) complexes, of the type [(dppe)Pt(CF3)(solv)], used by Strukul in the epoxidation of alkenes and in Baeyer-Villiger oxidations of ketones (Schemes 8 and 9), are effective catalysts also in the direct hydroxylation of aromatics with hydrogen peroxide. The reactivity increases in the presence of electron releasing substituents in the aromatic ring. Ortho and para derivatives are practically the only products observed and interesting selectivity toward the ortho products has been detected (equation 85). 

Treatment of the silyl compound, 61, above with hydrogen peroxide leads to the diol 62 which formally constitutes an oxidation as well as an electrophilic attack on the carbon atom. Classically, oxidation of nonconjugated rings to furnish their conjugated (usually aromatic) analogues is achieved by treatment with nickel(ii) peroxide however, these reactions are common and have been extensively explored for a number of different heterocyclic systems in both GHEC(1984) and CHEC-II(1996) so are not discussed further here. 

Oxidation of alkyl benzene using heteropolycompounds are effective in presence of oxidants like hydrogen peroxide and t-butylhydroperoxide. Vanadium substituted heteropolymolybdates are more effective than unsubstituted heteropoly compounds. Both side chain and products with oxidation in the aromatic ring are observed in presence of heteropoly compound-hydrogen peroxide system whereas only side chain oxidized products were observed in presence of heteropolycompound-t-butyl hydroperoxide system. This difference in activity can be due to the formation of different active intermediate species. 

The synthesis of oxazole A-oxidcs from a-hydroxyimino ketones and aldehydes, and their reductive conversion into oxazoles has already been described (Section II, K). Attempted A-oxidation of 2,5-diphenyloxazole with hydrogen peroxide in acetic acid failed it led to ring-opening.418 Oxazole A-oxides show a strong absorption band around 1240 cm-1 in their infrared spectra, indicative of an aromatic A-oxide group.419 Recently, NMR data for several oxazole A-oxides have been reported.148... 

Oxidation of the parent aromatic heterocycle with hydrogen peroxide at room temperature yields the dioxo compound 8, in line with the susceptibility of the ring system to covalent dihydration. The bromine atom in compound 15 is readily displaced by amines in refluxing ethanol to give... 

Better yields are often obtained when ozone is used for oxidative cleavage of olefins to carboxylic acids or of cycloalkenes to dicarboxylic acids. Olefinic double bonds are very much more easily attacked by ozone than are aromatic systems, so that arylethylene derivatives can be successfully treated with ozone without appreciable effect on the ring. If the ozonide which is formed initially is decomposed with water, the aldehyde is obtained together with hydrogen peroxide and other products ... 

Conversion of Aromatic Rings to Nonaromatic Cyclic Structures. On treatment with oxidants such as chlorine, hypochlorite anion, chlorine dioxide, oxygen, hydrogen peroxide, and peroxy acids, the aromatic nuclei in lignin typically ate converted to o- and -quinoid stmctures and oxinane derivatives of quinols. Because of thein relatively high reactivity, these stmctures often appear as transient intermediates rather than as end products. Further reactions of the intermediates lead to the formation of catechol, hydroquinone, and mono- and dicarboxyhc acids. 

The aromatic ring of a phenoxy anion is the site of electrophilic addition, eg, in methylolation with formaldehyde (qv). The phenoxy anion is highly reactive to many oxidants such as oxygen, hydrogen peroxide, ozone, and peroxyacetic acid. Many of the chemical modification reactions of lignin utilizing its aromatic and phenoHc nature have been reviewed elsewhere (53). 

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