Panov reaction

The catalytic oxidation of benzene to phenol in iron-containing zeolites is known as the Panov reaction The ZSM-5 zeolitic system is the preferred matrix. There are several ways in which the catalyst can be activated for this reaction. 

It is now well established that the active component of the catalytic reaction is monomeric Fe +. The Panov reaction consists of two reaction steps ... 

Figure 4.29. (a) The speculated reaction path for the oxidative transformation of benzene to phenol in the Panov reaction , (b) Rates of phenol formation and N2O decomposition as a function of Fe content in ZSM-5... 

Iron-modified zeolites (Fe/ZSM-5) are highly efficient catalysts for a wide range of important processes than include the selective oxidation of benzene with N O (the Panov reaction) [37], catalytic decomposition of N O [38], selective catalytic reduction (SCR) of NOx [39], and many others. These unique properties stem from the presence of specific extra-framework iron-containing cationic species in the micropores of ZSM-5 zeolite [40]. Because of a very heterogeneous iron speciation in the zeolite catalyst, the direct determination of the catalytically active iron species and the mechanism of the catalytic reaction by experimental methods was not possible. The exact speciation will obviously depend on such parameters as the Fe loading, the method of iron introduction, and the history of the sample (calcination, reduction, etc.). Many studies have indicated that the reactivity of Fe/ZSM-5 for the selective benzene oxidation is mainly associated with the presence of highly dispersed Fe + extraframework cations [41]. On the contrary, the high catalytic activity in the N O decomposition... 

Another example of heterogeneous catalysis by oxo-ions is the one-step oxidation of benzene to phenol with nitrous oxide, N2O. Fe/MFI catalysts have, again been found to be very active. This catalysis was discovered by Iwamoto and has been extensively studied by the group of G. Panov in Novosibirsk. " Preparations of Fe/MFI which appear highly active for this reaction display poor activity for NOj reduction and those which are optimum for that process, are poor for benzene oxidation. This shows that different sites are used. Work by Jia et al. revealed that the active sites for benzene oxidation appear to be Fe-oxo-ions containing only one Fe ion. This does not necessarily mean that the sites are mononuclear. A recent work by Zhu et al. has rather suggested that the site consists of one Fe and one Al + ion, the latter ion having left the zeolite framework. ... 

Tuulmets, A. Nguyen, B. T. Panov, D. Sassian, M. Jarv, J. Kinetics of the Grignard Reaction with Silanes in Diethyl Ether and Ether-Toluene Mixtures. J. Org. Chem. 2003, 68, 9933-9937. 

In 2002, this type of N20 oxidation was re-discovered by Panov et al. [168]. Being guided by quite a different idea, the authors [168] used milder conditions and obtained much better selectivity, which in many cases exceeded 90%. Such a high selectivity was shown to relate to a non-radical type reaction mechanism as well as to a remarkable feature of the oxidant. N20 reacts solely with alkene C=C bonds and is inert towards all other bonds. Therefore, reaction products having no double bonds are not subjected to overoxidation. Only non-oxidation side processes maybe a reason for decreasing selectivity. 

In 1958, Panov and Kocheshkov1216 found another route to the formation of the C—Pb bond, namely the interaction of tetraacyloxyplumbanes with aromatic and heteroaromatic compounds (the plumbylation reaction). They showed that the reaction of thiophene with Pb(OCOPr-i)4 at room temperature during 10 days led to unstable RPb(OCOR/)3 (R = 2-thienyl R = i-Pr), which was disproportionated to R2Pb(OCOR/)2 and Pb(OCOR/)4-... 

In 1952, Panov and Kocheshkov employed the reaction of trialkylacyloxyplumbane cleavage by mercury salts of carboxylic acids Hg(OOCR )2 for the synthesis of R2Pb(OOCR )2- Triethylacetoxyplumbane was also obtained by Razuvaev and CO workers using EtsPbPbEts cleavage of Pb(OOCMe)4 in benzene media. 

Synthetic zeolites have gained importance as industrial catalysts for cracking and isomerization processes, because of their unique pore structures, which allow the shape-selective conversion of hydrocarbons, combined with their surface acidity, which makes them active for acid-catalyzed reactions. Many attempts have been made to introduce redox-active TMI into zeolite structures to create catalytic activity for the selective oxidation and ammoxidation of hydrocarbons as well as for SCR of nitrogen oxides in effluent gases (69-71). In particular, ZSM-5 doped with Fe ions has attracted attention since the surprising discovery of Panov et al. (72) that these materials catalyze the one-step selective oxidation of benzene to phenol... 

The selective insertion of an oxygen atom into a benzene carbon-hydrogen bond to yield phenol is not a classical organic chemistry reaction. The first process for such a reactions was the Solutia process, based on discoveries by Panov and coworkers at the Boreskov Institute of Catalysis in Novosibirsk and then developed in close cooperation with Monsanto. In this process, the oxidant is nitrous oxide, N2O, while an iron-containing zeolite is used as the catalyst (Equation 13.4) ... 

Our quantum-chemical simulation of benzene oxidation reaction based on pseudospinel iron center (see Fig. 20.36, bottom) reveals the same structure. The characteristic feature of such intermediate is the presence of C(sp )-H bond. The presence of the C(5/7 )-H bond intermediate was confirmed by in-situ IR experiment of Panov et al. [84]. The IR band at 2874 cm appeared immediately after benzene was fed to the FeO catalyst. At the same time no phenol signals were detected. Heating of the sample resulted in complete disappearance of this band. According to our quantem-chemical simulation only the a-complex structure has the characteristic of this IR band. For benzene oxide, which also has two C(sp )-H bonds, this band is not present, since all of the vibrational frequencies are within narrow range of 3182-3218 cm . In the case of the benzene o-complex the calculated IR frequency for the C(sp )-H vibration is 2930 cm , while the other C-H vibrations are within 3178-3215 cm . Applying anharmonic scaling factor/= 0.96 one may obtain quite reasonable agreement 2813 em and 3050-3086 cm (theory estimation) versus 3037-3090 cm and 2874 em (experimental data). 

Dubkov KA, Paukshtis EA, Panov GI (2001) Stoichiometry of oxidation reactions involving a-oxygen on FeZSM-5 zeolite. Kinet Catal 42 205... 

An important difference between the benzene oxidation reaction and methane activation, is the absence of an isotope effect in the benzene oxidation reaction. In the enzyme, CH4 activation is initiated by hydrogen abstraction. This initiates a radical-type reaction. Benzene oxidation in the Panov stem, however, follows a very different reaction path. 

Panov s group in collaboration with Monsanto researchers contributed significantly to the development and implementation of this process in a pilot scale (nowadays, the Solutia process) [59, 85]. The reaction is performed in the gas phase at 350°C. The selectivity toward phenol attains 97-98% at 27% benzene conversion and 100% N O conversion. Dihydroxy benzenes (ca. 1%, mainly hydroquinone (HQ)) and carbon monoxide (0.2-0.3%) are main by-products. The catalyst half-life is restricted by a few days, but catalytic activity can be easily restored by buming-off coke deposits. The catalyst can thus sustain more than 100 regeneration cycles. The manufacture of adipic acid provides a cheap technical access to N O. More information about the Solutia process can be found in the two book chapters [58, 59]. Unfortunately, its commercialization has been postponed on the score of economics [9b]. 

Diphenyldiacetoxyplumbane in dry acetone treated with a little water followed by ethereal diazomethane during 6 min., and the product isolated after several hrs. bis(diphenylacetoxy)plumboxane. Y 96%. F. e. and reverse reaction s. E. M. Panov, N. N. Zemlyanskii, and K. A. Kocheshkov, Dokl. Akad. Nauk SSSR U3, 603 (1962) C. A. 57, 12521d. 

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