Benzene direct oxidation

Starting from Benzene. In the direct oxidation of benzene [71-43-2] to phenol, formation of hydroquinone and catechol is observed (64). Ways to favor the formation of dihydroxybenzenes have been explored, hence CuCl in aqueous sulfuric acid medium catalyzes the hydroxylation of benzene to phenol (24%) and hydroquinone (8%) (65). The same effect can also be observed with Cu(II)—Cu(0) as a catalytic system (66). Efforts are now directed toward the use of Pd° on a support and Cu in aqueous acid and in the presence of a reducing agent such as CO, H2, or ethylene (67). Aromatic... 

The influence of the conformational factors, which play a decisive role in directing oxide fission in the above cases is no longer operative in the case of 3-keto-5a,6a-epoxides and their 3-ethylene ketals. With these substrates the —I effect of the BFs-complexed 3-keto or 3-ketal grouping predominates leading to the fluorohydrins. Thus, treatment of both 5a,6a-oxidopregnane-3,20-dione (35) and its 3,20-bisethylene ketal with BFg-etherate in benzene-ether affords in 45% yield the 6jff-fluoro-5a-hydroxy-derivative (36) and its 3-ethylene ketal, respectively. which are converted into the 6a-fluoro-A -CH3... 

Nitrous oxide as an efficient oxygen donor was noticed when used in such a delicate reaction as the direct oxidation of benzene to phenol ... 

The anodic reaction used is an indirect oxidation of benzene by Ag(I)/Ag(II) as redox mediator, because of its high faradaic yield. The high yield of BQ of 84% (of the theoretical yield) compared to the yield of the direct oxidation on the Pb02 anode of 62% indicates that some mechanism to minimize side reactions such as formation of o-BQ is operative. The highest yields are achieved with AgC104, (cf. Table 2, Ref. [66]). The use of AgC104 excludes its application in large scale synthesis. 

Quinone is produced in small yield by direct oxidation of benzene itself with silver peroxide, but better by the action of oxidising agents on a large number of its p-disubstitution products. Thus, in addition to quinol, p-aminophenol (experiment, p. 176), p-anisidine, p-toluidine, and sulphanilic acid as well as p-phenylenediamine and many of its derivatives yield quinone in this way. 

Methane to Benzene Both oxidative and nonoxidative routes have been reported. Most attention has been directed at nonoxidative aromatization. In particular, Chinese workers are active in this field. Recently, attractive results have been reported for Mo-loaded HZSM-5 catalysts. 

The fact that an isotope effect of 1.7 0.1 is observed 38) in the benzene/deuterium oxide reaction at 30°C indicates that this reaction is the rate-determining step of the dissociative n complex substitution mechanism. In this respect the result agrees with the direct observations made by other investigators 41, 42), namely that unsaturated hydrocarbons chemisorb at a faster rate than their subsequent interactions with chemisorbed hydrogen. 

In the oxidation of pentafluoroaniline with performic acid, along with the expected pentafluoronitrosobenzene, a 17% yield of decafluoroazoxy-benzene was isolated. Separate experiments showed that the condensation of the nitrosobenzene with the residual amine did not lead to the clean-cut preparation of the azoxy compound, whereas the thermal degradation of the nitroso compound did afford the azoxy compound. The implications of these observations are that either the azoxy product was formed, at least in part, by direct oxidation of the amine or the thermal history of the reaction permitted its formation from the intermediate nitroso compound [29]. 

Oxidation to Quinones. Direct oxidation of arenes to quinones can be accom-plished by a number of reagents. Very little is known, however, about the mechanism of these oxidations. Benzene exhibits very low reactivity, and its alkyl-substituted derivatives undergo benzylic oxidation. Electrochemical methods appear to be promising in the production of p-benzoquinone.797 In contrast, polynuclear aromatic compounds are readily converted to the corresponding quinones. 

Some of the reagents used in olefin epoxidation can be applied in the direct oxidation of arenes to arene oxides. Benzene oxide, however, like other arene oxides, exists in equilibrium with oxepin, its valence tautomer, and has not been isolated. Existence of benzene oxides as intermediates can be concluded from observations like the NIH shift discussed above.752,753... 

Direct polymerization of benzene through oxidative coupling yields polytp-phenylene) (PPP) an insoluble polymer of low molecular weight.427-429 Kovacic s original synthesis430 using a Lewis acid-oxidant combination [Eq. (13.81)] is the most widely employed and still the most effective procedure for the synthesis of PPP ... 

Benzenol and the 2-, 3-, and 4-methylbenzenols (cresols) can be isolated from coal tar (Section 22-11). Benzenol itself is used commercially in such large quantities that alternate methods of preparation are necessary and most of these start with benzene or alkylbenzenes. Direct oxidation of benzene is not satisfactory because benzenol is oxidized more readily than is benzene. 

It was reported independently by three research groups that MFI-type zeolites selectively catalyze the reaction of N20 with benzene to give phenol C6H6 + N20 —> C6H5OH + N2 [93-96]. Fe/ZSM-5 shows remarkable performance in benzene hydroxylation to phenol with N20 as oxidant, which is the first example of a successful gas phase direct phenol synthesis from benzene [97]. No other catalysts show similar high performances to the Fe/ZSM-5 catalyst. At present, iron is the sole element capable of catalyzing the benzene-to-phenol reaction [98]. Direct oxidation of benzene to phenol by N20 has been commercialized in the so-called AlphOx process in Solutia Inc., US A, where N20 is obtained as a by-product in adipic acid production with nitric acid [97, 99, 100] a selectivity >95% to phenol is achieved at >40% conversion at around 4000 C. But the process is cost-effective only if N20 can be obtained cheaply as a by-product in adipic acid production. 

The Fe ion is easily incorporated into zeolites. Ferrosilicates and ferrisilcates are often used as acid catalysts. Direct oxidation of benzene to phenol over Fe-MFI zeolites has been shown to be practical when N20 is used as an oxidant (AlphOx process) [112]. This process is suitable for the abatement ofhighly concentrated N20 (20-40%) gas discharged from adipic acid plants to meet the tightened regulation of emission levels of N20. 

The best known member among the various classes of these iodanes is undoubtedly [hydroxy(tosyloxy)iodo]benzene (HTIB), sometimes called Koser s reagent. It is prepared readily from (diacetoxyiodo)benzene and p-toluenesul-fonic acid monohydrate in acetonitrile. The same method using p-nitroben-zenesulfonic acid or 10-camphorsulfonic acid leads to the corresponding sul-fonyloxy analogs [41,42]. Of special interest are some iodanes of this type coming from a chiral ether. Their preparation was effected by direct oxidation with sodium perborate and the isolated diacetoxy derivatives were separately treated with p-toluenesulfonic acid in acetonitrile (Scheme 8) [43]. 

However, longer reaction times can lead to the corresponding carbonyl compounds as well. An activation of (diacetoxyiodo)benzene 3 with boron trifluoride is also possible and can be used for a direct oxidation of carbazolylmethyl alcohols [72]. 

Although several methods are available for the preparation of the title compounds, in practice the starting material is (diacetoxyiodo)benzene (DIB). The standard method for its preparation is direct oxidation of iodobenzene with either peracetic acid [ 1 ] or sodium perborate in acetic acid [2], The first method appears to be preferable it requires great care in maintaining temperature at exactly 40°C at a lower... 

The preparation of iodylbenzene has been described in Organic Syntheses from (dichloroiodo)benzene [24] an alternative simpler method involved the direct oxidation of iodobenzene using aqueous hypochlorite and phase transfer catalysis. 

Direct oxidation of benzene to phenol is of great interest not only for its industrial importance, but also from a purely scientific point of view. Apart from many earlier reports [35] on the oxidation of benzene to phenol by hydroxyl radicals generated by the reaction of Fe2+ salt (Fenton reagent) with H202 not much is known about the homogeneously catalysed oxyfunctionalization of aromatic C-H bonds. The lack of studies is largely attributable to the fact that the activation of the C-H bond in benzene is difficult owing to its resonance stability and the reactivity of phenol, which is consecutively oxidized to quinones and other by-products. 

Almost all fuel hydrocarbons (including benzene, toluene, ethylbenzene, and the xylene isomers (BTEX)) can be directly oxidized by microorganisms in the groundwater under aerobic conditions [25]. The following stoichiometry illustrates the direct aerobic oxidation of benzene, resulting in production of microbial cells, carbon dioxide, and water ... 

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