Oxidation of Benzene to Phenol by

An ideal solution would be the direct oxidation of benzene to phenol by dioxygen  

However, many attempts to accomplish this reaction have failed. The interaction with 02 leads to destruction of the aromatic nucleus and low phenol selectivity. 

Oxidation over vanadia catalyst In 1983, Iwamoto and co-authors [58] were the first to use N20 for the oxidation of benzene to phenol  

This reaction over vanadia catalyst showed much better selectivity than before. At 823 K the selectivity exceeded 70%. This result was recognized as a promising lead to a long awaited direct process. However, a pilot test did not meet expectation since the selectivity proved to be too low for commercialization of the process. 

Selectivity is among the most important parameters for the partial oxidation, especially in the case of non-02 oxidants. Usually, for 02 oxidations, the selectivity is considered only with respect to the organic reagent. But this approach is not acceptable with monooxygen donors, the cost of which may be of the same order as that of the organic reagent. In this case, selectivity based on the oxidant becomes an equally important parameter for estimating process efficiency. Thus, in the case of 

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Pd(II) Wacker-type catalysts were also studied.146 Selective oxidation of benzene to phenol by molecular oxygen in the presence of Pd and heteropolyacids have been published.147... 

The ce-pyrrolidonate Pt(2.5 + )4 (19) was also found to catalyze the oxidation of benzene to phenol by hydrogen peroxide (121). By HPLC, ESR, and UV-Vis absorption spectroscopy, the main reaction pathway was confirmed to be Eq. (13). 

S. (2008) liquid phase oxidation of benzene to phenol by molecular oxygen over La catalysts supported on HZSM-5. Top. Catal, 47, 98-100. 

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. 

Considerable efforts have been made to understand ZSM-5-based catalysts for the selective oxidation of benzene to phenol by nitrous oxide. However, the nature of the active species remains unclear. The most important proposals for the active species are extraframework Fe species [101], Bronsted add sites [102] and Lewis and A1 sites [103, 104]. The activity is usually interpreted in terms of very small, possibly... 

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. 

The oxidation of benzene to phenol can also be achieved using nitrous oxide as an oxidant in the presence of a catalytic system such as vanadium, molybdenum or tungsten oxides at 550 °C, and after addition of 30% of water to afford phenol in 10% yield . More effective catalytic systems have been investigated and zeolites show promise to be good catalysts for the oxidation of benzene to phenol with nitrous oxide . The use of zeolite catalysts has led to a reduction in the reaction temperature to 300-400°C, to the exclusion of water addition to the reaction mixture and to an increase in the yields up to 25-30% . Recently, direct oxidation of benzene to phenol by nitrous oxide has been commercialized . 

The oxidation of benzene to phenol by means of oxygen or air lias been carried out successfully in the liquid phase by a number of investigators but as far as can be learned from a review of the general literature, the percentage yields have, in most cases, been exceedingly low. It was observed, for example, as early as 1878, that aluminum chloride causes... 

FeUah MF, van Santen RA, Onal I (2009) Oxidation of benzene to phenol by N2O on tm Fe " " ZSM-5 cluster a density functional theory study. J Phys Chem C 113 15307... 

Panov, G. (2000). Advances in Oxidation Catalysis Oxidation of Benzene to Phenol by Nitrous Oxide, Cattech, 4, pp. 18-32. 

Ye X, Cui Y, Qiu X, Wang X (2014) Selective oxidation of benzene to phenol by Fe-CN/TS-1 catalysts under visible light irradiation. Appl Catal B 152 383-389... 

Forced-flow polymeric membrane reactors have also been successfully tested for the oxidation of benzene to phenol by Molinari and co-workers. Mixed-matrix membranes consisting of CuO powder or CuO nanoparti-cles dispersed in PVDF were prepared by the inversion phase method, by using dimethylacetamide (DMAc), dimethylformamide (DMF) or N-methyl-2-pyrrolidone (NMP) as solvents and water as non-solvent. The membranes were assembled in a ultraliltration unit to which a solution of acetonitrile/benzene and hydrogen peroxide (HjOj) was fed. The best results were obtained with a PVDF membrane hlled with CuO nanoparticles, with a phenol yield of 2.3% at 35°C and a contact time of 19.4 s in a single pass, in the presence of ascorbic acid. 

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