Phenol iron complex catalyzed

In addition to nonheme iron complexes also heme systems are able to catalyze the oxidation of benzene. For example, porphyrin-like phthalocyanine structures were employed to benzene oxidation (see also alkane hydroxylation) [129], Mechanistic investigations of this t3 pe of reactions were carried out amongst others by Nam and coworkers resulting in similar conclusions like in the nonheme case [130], More recently, Sorokin reported a remarkable biological aromatic oxidation, which occurred via formation of benzene oxide and involves an NIH shift. Here, phenol is obtained with a TON of 11 at r.t. with 0.24 mol% of the catalyst. 

Phthalocyanine complexes of cobalt(II), copper(II), manganese(11), and iron(II) catalyze the oxidation of substituted phenols to the corresponding benzoquinones and diphenoquinones. Typical selectivity data are listed in Table III. 

Aerobic oxidation of aromatics (benzene, toluene, chlorobenzene) at room temperature in the presence of zinc powder as reducing agent and a p-oxo binuclear iron complex as catalyst in CH Clj led to phenols as major products [63]. Co-oxidation of benzene and crotonaldehyde catalyzed by VO(dpm)j [dmp = l,3-bis(p-methoxyphenyl)-l,3-propanedionato] gave phenol in a 21% yield (Eq. 14.19) [64]. 

MnP is the most commonly widespread of the class II peroxidases [72, 73], It catalyzes a PLC -dependent oxidation of Mn2+ to Mn3+. The catalytic cycle is initiated by binding of H2O2 or an organic peroxide to the native ferric enzyme and formation of an iron-peroxide complex the Mn3+ ions finally produced after subsequent electron transfers are stabilized via chelation with organic acids like oxalate, malonate, malate, tartrate or lactate [74], The chelates of Mn3+ with carboxylic acids cause one-electron oxidation of various substrates thus, chelates and carboxylic acids can react with each other to form alkyl radicals, which after several reactions result in the production of other radicals. These final radicals are the source of autocataly tic ally produced peroxides and are used by MnP in the absence of H2O2. The versatile oxidative capacity of MnP is apparently due to the chelated Mn3+ ions, which act as diffusible redox-mediator and attacking, non-specifically, phenolic compounds such as biopolymers, milled wood, humic substances and several xenobiotics [72, 75, 76]. 

The bis-hydroxylamine adduct [Fe (tpp)(NH20H)2] is stable at low temperatures, but decomposes to [Fe(tpp)(NO)] at room temperature. [Fe(porphyrin)(NO)] complexes can undergo one-and two-electron reduction the nature of the one-electron reduction product has been established by visible and resonance Raman spectroscopy. Reduction of [Fe(porphyrin)(NO)] complexes in the presence of phenols provides model systems for nitrite reductase conversion of coordinated nitrosyl to ammonia (assimilatory nitrite reduction), while further relevant information is available from the chemistry of [Fe (porphyrin)(N03)]. Iron porphyrin complexes with up to eight nitro substituents have been prepared and shown to catalyze oxidation of hydrocarbons by hydrogen peroxide and the hydroxylation of alkoxybenzenes. ... 

Recently, syntheses of the model compounds 156 and 157 were reported [107,108], which are closely related to earlier approaches [103,109] (Fig. 25). In agreement with theoretical calculations the CO complexes of the Fe(II)por-phyrins 156 and 157 display a split Soret band at 370/446 nm and 383/456 nm, respectively, but no experiments with molecular oxygen were reported. But it was demonstrated that 157 catalyzed the formation of stable aryloxy radicals from the corresponding phenols in the presence of e.g. feri-butylhydroperoxide (TBHP). These results indicate a thiolate mediated 0-0 bond cleavage of TBHP accelerated 240 fold in comparison to iron(III)tetraphenylporphyrin [108],... 

Model complexes of peroxidase were used as catalysts for the oxidative polymerization of phenols. Hematin, a hydroxyferriprotoporphyrin, catalyzed the polymerization of />ethylphenol in an aqueous DMF.63 Iron—A/,A/ -ethylenebis(salicylideneamine) (Fe—salen) showed high catalytic activity for oxidative polymerization of various phenols.64 The first synthesis of crystalline fluorinated PPO was achieved by the Fe—salen-catalyzed polymerization of 2,6-difluorophenol. Cardanol was polymerized by Fe— salen to give a cross-linkable polyphenol in high yields. 

Copper, titanium, cobalt and iron substituted mesoporous silicas (Cu-, Ti-, Co-, and Fe-HMS) were synthesized with dodecylamine surfactant as templating reagent. Three assembled pathways were used to bond Ti tartrate complex over mesoporous silicas (HMS). The above described catalysts were characterized by XRD and FT-IR, their metal loadings were measured by chemical analysis method. In catalytic testing, Cu-HMS and especially Fe-HMS show the best catalytic activity for hydroxylation of phenol with H2O2 in the presence of water. Ti-HMS and especially Ti tartrate complex assembled HMS catalysts exhibit the best epoxidative activity for catalyzing epoxidation of styrene with rcrt-butyl hydroperoxide. 

The reaction was catalyzed by a complex of iron with -ethylene bis(sallicylidene amine) as well as a horseradish peroxidase enzyme to carry out oxidative coupling of phenols using hydrogen peroxide as an oxidizing agent. The product is a new type of plastic. 

C atalytic site of peroxidase is a heme, which is rapidly oxidized in its free form to hematin. p-Ethylphenol was polymerized using hematin as catalyst in an aqueous DMF (325). Iron-)VA -ethylenebis(salicyhdeneamine) (Fe-salen) also can be regarded as model complex of peroxidase. Fe-salen catalyzed an oxidative polymerization of various phenols such as 2,6-dimethylphenol, bisphenol A, cardanol, and urushiol analogues (251,293,326-329). The polymerization of 2,6-difluorophenol by Fe-salen produced a crystalline fluorinated PPO derivative (330). 

Tonami, H., Uyama, H., Kobayashi, S., Higashimura, H., and Oguchi, T. (1999) Oxidative Polymerization of 2,6-disubstituted Phenols Catalyzed by Iron-Salen Complex. J. Macrom. ScL-Pure Appl Chem., A36,719— 730. 

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