The oxidation of ethylbenzene and other alkylaromatics by dioxygen catalysed by iron(III) tetrakis(pentafluorophenyl)porphyrin and related iron porphyrins

Abstract

The oxidation of ethylbenzene with dioxygen catalysed by iron() porphyrins in a solvent free system has been studied over the temperature range 30-110 ЊC. The time dependence of the formation of the three main products, 1-phenylethanol, acetophenone and 1-phenylethyl hydroperoxide, and the fate of the iron porphyrin are interpreted in terms of a free radical autoxidation mechanism. The yields of the oxidation products are determined by the rate of reaction and by the lifetime of the catalyst. Catalyst degradation is shown to involve reaction of the porphyrin ligand with 1-phenylethoxyl and 1-phenylethylperoxyl radicals. The disadvantages of increased induction periods and longer reaction times of the oxidations observed at lower reaction temperatures are counter balanced by increased catalyst turnovers. Less extensive studies on the oxidations of toluene, cumene, (2-methylpropyl)benzene and tert-butylbenzene support the overall mechanism proposed for ethylbenzene.A comparative study using the catalysts iron() 2, 3,7,8,12,13,17,18-octachloro-5,10,15,20-tetrakis-(2,6-dichlorophenyl)porphyrin and iron() tetrakis(pentafluorophenyl)porphyrin and five of its derivatives reveals that halogenation of the β-pyrrole positions markedly increases the activity of the catalysts but not the stability of the porphyrin towards degradation. The highest yields were obtained with the µ-oxodimer of iron() tetrakis(pentafluorophenyl)porphyrin and iron() tetrakis(4-dimethylamino-2,3,5,6-tetrafluorophenyl)porphyrin.

Biomimetic Oxidation of Hydrocarbons with Air over Metalloporphyrins

“…[104] is likely operative in isobutane oxidation where the role of metalloporphyrin is to generate radicals by catalyzing the decomposition of alkyl hydroperoxides via Haber-Weiss cycle [103]. (Shceme 18, chemical cycle)This cycle is also present in cycloalkane [109] and alkylaromatics oxidation [112]. Reductive conversion of ferric complexs to ferrous complex in CP-450 catalytic cycle needs for co-reductants, which plays a key role in activation of molecular oxygen.…”

“…The experiments showed that cyclohexanone yield increased when the above reaction was carried out in air [104] at elevated temperature [115]. Moreover, alky radicals could escape more easily from the solvent cage at the higher temperature to participate in the radical-chain autoxidation [112]. …”

Aerobic Oxidation of p-Toluic Acid to Terephthalic Acid over T(p-Cl)PPMnCl/Co(OAc)2 Under Moderate Conditions

“…The result suggested that the reaction proceeded via a radical process. Hydroperoxides could be produced under moderate conditions by the use of metalloporphyrin as catalyst [26]. The changes of peroxides content with reaction time in different catalyst system were investigated and the results were shown in Fig.…”

Hydrocarbon oxidation catalyzed by iron and manganese porphyrins anchored on aminofunctionalized supports

“…Both this substrate and the oxidant have been largely employed in diagnostic reactions to evaluate the catalytic potential of novel systems, so they allow comparison with various other systems studied by our group or described in the literature. 1,7,18,21,25,26 The reaction products were analyzed by gas chromatography, and the yields are based on the oxidant. Results are presented in Table 2.…”

“…Furthermore, literature reports give evidence of the efficiency of these catalysts and consider them good cytochrome P450 biomimetic models, which allows for a comparative evaluation of our results. 18,[20][21][22] The supported catalysts were obtained through the aromatic nucleophilic substitution reaction between the NH 2 functional groups on the surface of the support and the para-fluoro atoms on the pentafluorophenyl substituent in the MePs (Figure 2). …”