Alkylarene oxidation

This procedure illustrates a general method for the preparation of aromatic carboxylic acids by oxidation of the corresponding alkylarenes.2 For example, 2-naphthoic acid (360 g., 93% yield m.p. 184-185°) was obtained from 2-methylnaphthalene (320 g., 2.25 moles), sodium dichromate (975 g., 3.26 moles, 45% excess), and water (1.81.). 

Oxidation, of acids to peroxy acids by hydrogen peroxide, 43, 96 of alkylarenes to aromatic carboxylic acids, 43, 80... 

Ambulgekar GV, Samant SD, Pandit AB (2004) Oxidation of alkylarenes to the corresponding acids using aqueous potassium permanganate by hydrodynamic cavitation. Ultrason Sonochem 11 191-196... 

Oxidation with peroxydisulfate in AcOH in the presence of catalytic amounts of iron and copper salts gives benzylic acetates in good yields.785,861 The reaction of lead tetraacetate with alkylarenes in AcOH provides benzylacetates in moderate yields.693 Most of these oxidations usually involve methyl-substituted benzenes since aromatics with longer chain produce different side products. 

Uncatalysed oxidation of cycloalkanes and alkylarenes by molecular oxygen with acetaldehyde as sacrificial co-reductant occurs efficiently in supercritical carbon dioxide under mild multiphase conditions.252... 

Despite the ionic reactions, other reactions (presented in Scheme 44) show that free-radical mechanisms can also take place. Catalyzed by ebselen, TBHP oxidation of alkylarenes to alkyl aryl ketones (141) [240], anthracene to anthraquinone (142), 1,4-dimethoxyarenes to 1,4-quinones (e.g., menadione 143) [244], and oxidative coupling of 2-aminophenol to phenoxazinone (144) [245] gave results similar to these when one-electron oxidants such as Ce(IV), Ag(II), or Mn(III) were the reagents. Moreover, oxidation of azine derived from 2-acetylpyridine gave a mixture of ketone (145) and condensed triazole (146) [240], The same result was found when cerium ammonium nitrate was used as the reagent. This suggests that the... 

Oxidation. This reagent is prepared by reaction of CAN with K2C03 (2 equiv.) to form Ce(C03)2, which is then treated with trifluoromethanesulfonic acid (4 equiv.). This oxidant is effective for oxidation of benzylic alcohols to aldehydes (72-92% yield), and of alkylarenes to aldehydes or ketones (65-70% yield). 

Shi and coworkers found that vinyl acetates 68 are viable acceptors in addition reactions of alkylarenes 67 catalyzed by 10 mol% FeCl2 in the presence of di-tert-butyl peroxide (Fig. 15) [124]. (S-Branched ketones 69 were isolated in 13-94% yield. The reaction proceeded with best yields when the vinyl acetate 68 was more electron deficient, but both donor- and acceptor-substituted 1-arylvinyl acetates underwent the addition reaction. These reactivity patterns and the observation of dibenzyls as side products support a radical mechanism, which starts with a Fenton process as described in Fig. 14. Hydrogen abstraction from 67 forms a benzylic radical, which stabilizes by addition to 68. SET oxidation of the resulting electron-rich a-acyloxy radical by the oxidized iron species leads to reduced iron catalyst and a carbocation, which stabilizes to 69 by acyl transfer to ferf-butanol. However, a second SET oxidation of the benzylic radical to a benzylic cation prior to addition followed by a polar addition to 68 cannot be excluded completely for the most electron-rich substrates. 

Minisci s group developed homolytic substitution reactions of electron-poor arenes or hetarenes providing alkylarenes and -hetarenes extensively (see also Part 2, Sect. 2.5). The state of the art was reviewed thoroughly, so that the methodology is illustrated only by selected examples [435, 436, 437]. A protocol using silver nitrate as the catalyst and sodium peroxydisulfate as the stoichiometric oxidant proved to be very useful for the catalytic oxidative generation of radicals [438]. 

The silica-supported benzisoselenazol-3(277)-one 117 (Scheme 42) was used as a heterogenous catalyst for hydrogen peroxide oxidation of sulfides to sulfoxides and sulfones, alkylarenes to the ketones and aromatic aldehydes to the arenecarboxylic acids. It exhibited appreciable activity and the results were similar to these when ebselen was a homogenous catalyst. It can be recovered from the reaction mixture simply, and reused <2004MI148>. 

Low-valent nickel species catalyze the reaction between Grignard reagents and aryl or alkenyl sulfide in the preparation of alkylarenes, biaryls, and alkenes (see citations in Ref. ///). Wenkert et al. recently isolated compounds 132 and 133 to show that an oxidative addition occurs between diaryl sulfides and tris(tri-/ -butyl)phosphinonickel (77/). 

However, the promptness with which the oxidations start and their ease of propagation are not only dependent on the alkyl substituents which are to be oxidized, but also very much on the type and the position of the substituents in the aromatic system. The first, rate-determining step of the alkylarene oxidation - either the formation of a radical cation via an electron-transfer mechanism, or the direct formation of a benzylic radical by a-hydrogen abstraction - is increased with the electron density of the aromatic system supported by the substituents present. 

Li12[Mnn2ZnW (ZnW90 34)2] Alkanes, alkylarenes Ketones, a-oxidation products Ozone h2o Likely metal-ozonide intermediate 461... 

Sulfoxides C1CH2CH2C1 A good correlation of heterolytic benzylic C—H bond energies and alkylarene oxidation rates the formation of 9-phenylfluorene from triphenylmethane and other data imply rate-limiting hydride abstraction by POM-sulfoxide complex 536... 

The selective oxidation of hydrocarbons into hydroperoxides, primary products of oxidation is the most difficult problem because of the high catalytic activity of the majority of applied catalysts in ROOH decomposition. At the same time, the problem of selective oxidation of alkylarens (ethylbenzene and cumene) with molecular 02 in ROOH, is of current importance from the practical point of view in connection with ROOH use in large-tonnage productions such as production of propylene oxide and styrene (a-phenylethylhydroperoxide, PEH), or phenol and acetone (cumyl hydroperoxide) [1],... 

The oxidation of cycloalkanes or alkylarenes with molecular oxygen and acetaldehyde as a co-reductant takes place efficiently in scC02 under mild conditions. No catalyst is required and high-pressure ATR-FTIR online measurements showed that a radical reaction pathway was heterogeneously initiated by the stainless steel of the reactor walls (Equation 4.34) [67]. 

Much higher yields are found for the oxidation of alkylarenes to aldehydes, ketones and carbon acids by oxygen in the presence of transition metal compounds (MnBr2, CoBr2, CuBr) as catalysts [57]. For example, a yield of 30 % benzaldehyde and only 10 % benzoic acid was found for the oxidation of toluene. Also the dehydrogenation of cyclohexene and cyclohexane to benzene with Pt02 as catalyst was investigated at 375 °C [34]. 

Scheme 4. Selective radical decay in the oxidation of alkylarene with 2...

The interaction of arenes or alkylarenes, ArCH2R, with some oxidants, Ox, [27] for example, with cerium(IV) salts [27c] or photoactivated quinones [27d], gives rise to the formation of the ion-radical pair ... 

Alkylarenes can be oxidized with molecular oxygen at 70-140° C if ion Br" and tertiary ammonium salts are present in the solution [36]. The oxidation of p-xylene has been proposed to be initiated by arylalkyl hydroperoxide ... 

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