Phenols with hydrogen peroxide

Titanium Silicates. A number of titanium siUcate minerals are known (160) examples are Hsted in Table 19. In most cases, it is convenient to classify these on the basis of the connectivity of the SiO building blocks, eg, isolated tetrahedra, chains, and rings, that are typical of siUcates in general. In some cases, the SiO units may be replaced, even if only to a limited extent by TiO. For example, up to 6% of the SiO in the garnet schorlomite can be replaced by TiO. In general, replacement of SiO by TiO bull ding blocks increases the refractive indices of these minerals. Ti has also replaced Si in the framework of various zeofltes. In addition, the catalytic activity of both titanium-substituted ZSM-5 (TS-1) and ZSM-11 (TS-2) has received attention (161), eg, the selective oxidation of phenol, with hydrogen peroxide, to hydroquinone and catechol over TS-1 has been operated at the 10,000 t/yr scale in Italy (162). 

Yube, K. and Furuta, M. and Mae, K. (2007). Selective oxidation of phenol with hydrogen peroxide using two types of catalytic microreactor, Catalysis Today, 125, 56-63. 

Selective hydroxylation of phenol with hydrogen peroxide was reported on acid zeolite catalysts [91-92]. Peroxonium ions, formed by H2O2 protonation, are the oxidizing species. When the reaction is carried out on a faujasite catalyst, a mixture of hydroxybenzenes and tars is obtained [91]. In the presence of H-ZSM-5 on the other hand, no tar formation was mentioned (which does not necessarily mean that it was absent) and p-selectivities close to 100% were reported for the hydroxylation [92]. These superior selectivities reflect the shape selective properties of ZSM type zeolites. 

The incorporation of vanadium(V) into the framework positions of silicalite-2 has been reported by Hari Prasad Rao and Ramaswamy . With this heterogeneons oxidation catalyst the aromatic hydroxylation of benzene to phenol and to a mixtnre of hydroqninone and catechol conld be promoted. A heterogeneons ZrS-1 catalyst, which has been prepared by incorporation of zirconinm into a silicalite framework and which catalyzes the aromatic oxidation of benzene to phenol with hydrogen peroxide, is known as well in the literature. However, activity and selectivity were lower than observed with the analogous TS-1 catalyst. 

Benzoquinone [106-51-4], C6H402 (quinone) has been reported as a by-product of benzene oxidation at 410—430°C. Benzene can be oxidized to phenols with hydrogen peroxide and reducing agents such as Fe(II) and Ti(II). Frequendy ferrous sulfate and hydrogen peroxide are used (Fenton s reagent), but yields are generally low (12) and the procedure is of limited utility. Benzene has also been oxidized in the vapor phase to phenol in low yield at 450—800°C in air without a catalyst (13). 

To ascertain whether syringyl derivatives IV, V, and VI could be converted to phenoxy radicals under biological conditions, we treated water solutions of the phenols with hydrogen peroxide and peroxidase. All three phenols formed transient green species in contrast to the vanillin compounds (which yielded brown precipitates). The aqueous solutions turned red within a few minutes after initial reaction. If these solutions were quickly frozen in liquid nitrogen a few seconds after the reactants had been mixed, a blue solid was obtained. When the solid was examined by EPR spectrometry, radicals were observed whose half-lives were estimated at 30-60 seconds. The radicals appeared to be identical to those generated in benzene. 

Certain dinuclear iron complexes are found to be efficient catalysts for the oxidation of primary and secondary alcohols with hydrogen peroxide.214 Metalloporphyrins are used as peroxidase mimics in the oxidation of phenol with hydrogen peroxide. 

A catalytic amount of hydrobromic acid with an excess of hydrogen peroxide is found to be an effective reagent for the facile regeneration of carbonyl compounds from their 1,3-dithiane and 1,3-dithiolane derivatives.136 Bromide-assisted oxidation of substituted phenols with hydrogen peroxide, catalysed by heterogenous WO42-ions, resulted in the formation of p-quinols and their ethers in almost quantitative yields.137... 

Table 2 Hydroxylation of phenol with hydrogen peroxide on different catalysts ...

Direct Oxidation of Benzene to Phenol with Hydrogen Peroxide... 

A possible mechanism for the TS-1-catalyzed hydroxylation of phenol with hydrogen peroxide has been proposed [20] it is an ionic mechanism that, with... 

Balducci, L., Bianchi, D., Bortolo, R., D Aloisio, R., Ricci, M., Tassinari, R. and Ungarelli, R. (2003) Direct oxidation of benzene to phenol with hydrogen peroxide over a modified titanium silicalite. Angew. Chem. Int. Ed., 115, 5087-5090. 

The hydroxylation reaction of phenol with hydrogen peroxide and zeolite encapsulated MePc has received considerable attention. With the perchlorinated phthalocyanine (ClnPc) and tetra-nitro ((N02)4Pc) substituted ligands, catalysts with superior activity have been obtained [32], Such catalysts have been prepared via the zeolite synthesis method around the individual complexes. With the former more bulky complex only the slimmer hydroquinone (HQ) has been obtained, while with the encapsulated perchloroPc equal ratios of catechol (CAT) and the para-isomer have been obtained (see table). The unsubstituted Pc in zeolite Y both with Co and Cu as metallating ion, show an excess of the ortho-isomer (CA T) [32J, corresponding to the approximate thermodynamic ratio. This points to the critical importance of the available space close to the encapsulated Pc as selectivity determining parameter when there is more space, the catalyst yields more catechol. 

USE OF OXIDATION OF PHENOLS WITH HYDROGEN PEROXIDE AS AN INDICATOR REACTION FOR DETERMINING SOME METAL IONS... 

Degradation of acylarenes. Such carbonyl compounds are readily converted to phenols with hydrogen peroxide-boric acid. 

Oxidation of phenols. Barton et al. carried out some studies on the oxidation of phenols with hydrogen peroxide and samples of old cerium(IV) oxide. It was later found that the oxidations reported require activation if freshly prepared pure dioxide is used. It is dissolved in hot H2SO4, precipitated at pH 12 with sodium hydroxide, and then heated at ca. 900° for 24 hr. This material in combination with 30% H2O2 oxidizes phenols such as (1) to hydroperoxy-cyclohexadienones (2) in good yield. Other reported reactions are the oxidation of (4) to the oxide (5) and of (6) to juglone (7). This oxidation system probably... 

Oxidation of phenols. Barton et aO carried out some studies on the oxida-lion of phenols with hydrogen peroxide and samples of old cerium(IV) oxide. II was later found that the oxidations reported require activation if freshly pi e pared pure dioxide is used. It is dissolved in hot H2SO4, precipitated at pH... 

Peroxidase Model Catalyst. An iV,iV -bis(salicylidene)ethylenediamino iron [Fe(salen)] complex was found to be a cheap peroxidase model catalyst for oxidative polymerization of phenols with hydrogen peroxide (75-79). Hematin also polymerized ethylphenol in a reaction mechanism similar to that for HRP (80). 

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