Of aromatic compounds Hydroxylation

Hydroxylation of aromatic compounds 3.3.1 Overview Target products and oxidants 

In the commercially relevant reports of benzene oxidation catalyzed by framework metal-containing zeotype materials hydrogen peroxide or nitrous oxide (N2O) are used as oxidants. Thus phenol is produced without major by-product formation. 

Phenol can be produced directly from benzene by use of N2O as an oxidizing agent in the gas phase. Catalysts are modified ZSM-5 or ZSM-11 materials, containing elements such as antimony, arsenic, beryllium, boron, cobalt, chromium, copper, gaUium, indium, iron, nickel, scandium, vanadium or zinc. (208) 

Fe-MFI is among the reported (209) catalysts for the oxidation of benzene to phenol with reactants in the gas phase. At a benzene 

The possible formation and activity of a-oxygen, defined as the active oxygen that is formed when N2O reacts with ZSM-5 (212), in Fe-MFI was proposed by Yang et al. (213) On the basis of DFT calculations. Fellah 

---

The most commonly employed reagent for the hydroxylation of aromatic compounds is that consisting of ferrous ion and hydrogen peroxide. The suggestion that hydroxyl radicals are intermediates in this reaction was first made by Haber and Weiss, who proposed the following radical-chain mechanism for the process ... 

The hydroxylation of C-H bonds by radicals, in contrast to the case of electrophilic oxidants, leads to alcohols without retention of stereochemical configuration. H202, activated by strong acids (superacids (277), HF-BF3 (272), A1C13 (213), and CF3COOH (214)) have been used for the hydroxylation of aromatic compounds. These acid-catalyzed hydroxylations cannot be applied for aliphatic reactants because the hydroxylated products are more reactive than the starting compounds and, hence, they are oxidized further. 

The hydroxylation of aromatic compounds using microorganisms is more predictable and a number of processes have been adapted to large scale, for example the preparation of 6-hydroxynicotinic acid1781 and (R)-2-(4-hydroxy-phenoxy)propanoic acid1791, important intermediates to pesticides and herbicides respectively. 

Scheme 37 Hydroxylation of aromatic compounds mediated by Fenton s reagent.

Mason and coworkers [44,45] have for the first time observed that HRP catalyzes the hydroxylation of aromatic compounds by molecular oxygen in the pre-... 

Halfpenny, E., and Robinson, P. L. (1952a). The nitration and hydroxylation of aromatic compounds by pernitrous acid. J. Chem. Soc., 939-946. 

One-step electrophilic hydroxylation of aromatic compounds using various peroxide reagents in the presence of acid catalysts has been achieved. The systems studied include hydrogen peroxide in the presence of sulfuric acid,766 hydrogen fluoride,767 Lewis acids,768 769 and pyridinium poly(hydrogen fluoride).770 Lewis acid-promoted electrophilic hydroxylation with peracids,771,772 di-tcrt-butyl peroxide,773 and diisopropyl peroxydicarbonate774 775 were also described. A common feature of these reagents is the formation of monohydroxylated compounds in low yields. 

Lead(IV) trifluoroacetate is a strong electrophilic and oxidizing reagent It is a valuable reagent for the hydroxylation of aromatic compounds [5S, 59] Lead(IV) trifluoroacetate also reacts with silylated benzenes with the exclusive formation of the corresponding trifluoroacetate esters [59] (equation 28)... 

Hydroxylation reaction has been observed for several semiconductors in aqueous suspensions. Matthews found that benzoic acid can be hydroxylated in Ti02 aqueous suspension.783 Fujihira et al. reported the Ti02-photocatalyzed hydroxylation of benzene and toluene in water.793 In these systems, the OH radical, which is obtained as the result of the reaction between photogenerated holes and water or oxygen and photogenerated electrons, is an important reactant for the hydroxylation of aromatic compounds. 

Institute of Health) shift.80,110,111 Originally, the term NIH shift was used as a phenomenological description of the consequence of hydroxylation of aromatic compounds by mixed-function oxygenases. These enzymes catalyze the oxidation of aromatic substrates by deriving oxygen from molecular oxygen and not from water.80,110,111 Later studies narrowed the term to include arene oxide involvement.80... 

Metelitsa, D.I., Mechanism of the hydroxylation of aromatic compounds, Russian Chem. Rev., 40, 7, 1971. 

The NIH Shift Recent Experiments Reveal an Unexpected and General Result of Enzymatic Hydroxylation of Aromatic Compounds. Science. 1967,157, 1524-1530. 

Oxidation/hydroxylation of aromatic compounds by OH and HOONO is expected to enhance their degradation rate and hence decrease their lifetime on particulate matter, which in the case of pollutants is beneficial from the point of view of human health. Oxidation of PAHs could also lead to the production of photosensitizers such as quinones and aromatic carbonyls [10, 40, 41]. These compounds, if present in the gas phase, are also able to form aggregates and are therefore involved in the formation of secondary organic aerosol [42]. In contrast, nitration induced by OH + N02 or HOONO could lead to highly mutagenic nitro-PAHs [43] or phytotoxic nitrophenols [44, 45], in which case the health and environmental impact of the reaction intermediates is not negligible and is sometimes higher than that of the parent molecules. 

Ullrich R, Flofrichter M (2007) Enzymatic hydroxylation of aromatic compounds. Cell Mol Life Sci 64 271-293... 

Klibanov AM, Berman Z, Alberti BN (1981) Preparative hydroxylation of aromatic compounds catalyzed by peroxidase. J Am Chem Soc 103 6263-6264... 

A general review on oxygenase-catalyzed hydroxylation of aromatic compounds has appeared, which discusses this area in greater detail. ... 

Hydroxylation. The main general method for the hydroxylation of aromatic compounds is the alkali fusion of sulfonic acids ... 

---