Fries over zeolits

The reactivity of acetic acid is much weaker than that of AA and the aromatic ring can generally be acetylated with acetic acid over zeolite catalysts only at high temperatures (gas phase reactions).[62,63] This acetylation appears also at low temperatures (liquid phase reactions), but only with hydroxyarene substrates as a secondary transformation of aryl acetates rapidly formed through O acylation. This section will be split into two parts gas phase acetylation of aromatic substrates without hydroxyl substituents and transformation of aryl acetates, the so-called Fries rearrangement. 

Table 3.6 Gas phase Fries rearrangement of phenyl acetate and phenol acetylation over zeolite and mesoporous molecular sieves. All the reactions were carried out in fixed bed...

Table 3.7 Liquid phase Fries rearrangement of phenyl acetate (PA) over zeolite catalysts...

Reaction scheme The Fries rearrangement of phenyl acetate (PA) was first mentioned as occurring over zeolites in the review paper published in 1968 by Venuto and Landis.[64] This rearrangement was afterwards investigated at 673 K over HFAU and HMFI zeolites.[65] The reaction was not selective the expected o-and p-hydroxyacetophenones (o- and p-HAP) were minor components and phenol the main component. With both zeolites, o-HAP was highly favoured over the para isomer. 

Vogt, A., Kouwenhoven, H. W., Prins, R. Fries rearrangement over zeolitic catalysts. Appl. Cat. A 1995,123, 37-49. 

Balkus, K. J., Jr., Khanmamedova, A. K., Woo, R. Fries rearrangement of acetanilide over zeolite catalysts. J. Mol. Catal. A Chemical... 

The propionylation of phenol with propionyl chloride can be carried out over zeolite-H-beta, Re-Y, H-Y, mordenite, H-ZSM-5 and AICI3 at 140 °C to give para-hydroxypropiophenone and ortto-hydroxypropiophenone as the major products. Among these catalysts, the zeolite-H-beta is the most efficient. The product distribution depends upon the reaction conditions and acidity of the zeolite catalysts. The reaction involves the initial O-propionylation of the phenol followed by its rapid Fries rearrangement. 

The Fries rearrangement is specific in that published results are not always consistent, and that there is a dehate on intra-Zintermolecular reactivity. In the Fries rearrangement of phenyl acetate over zeolites (Eq. 16) it was first shown that the reaction is initiated by protonation of the aromatic ester, leading then to the formation of the acylium ion (Scheme 1) [33]. 

Heidekum, A., Harmer, M. A., and Hoelderich, W. F. 1998. Highly selective Fries rearrangement over zeolites and Nafion in silica composite catalysts a comparison. /. Catal. 176 260-263. 

Heitling, E., Roessner, F., and van Steen, E. 2004. Origin of catalyst deactivation in Fries rearrangement of phenyl acetate over zeolite H-Beta. ]. Mol. Catal. A Chem. 216 61-65. 

Prior to solving the structure for SSZ-31, the catalytic conversion of hydrocarbons provided information about the pore structure such as the constraint index that was determined to be between 0.9 and 1.0 (45, 46). Additionally, the conversion of m-xylene over SSZ-31 resulted in a para/ortho selectivity of <1 consistent with a ID channel-type zeolite (47). The acidic NCL-1 has also been found to catalyze the Fries rearrangement of phenyl acetate (48). The nature of the acid sites has recently been evaluated using pyridine and ammonia adsorption (49). Both Br0nsted and Lewis acid sites are observed where Fourier transform-infrared (FT IR) spectra show the hydroxyl groups associated with the Brpnsted acid sites are at 3628 and 3598 cm-1. The SSZ-31 structure has also been modified with platinum metal and found to be a good reforming catalyst. 

The consecutive formation of o-hydroxybenzophenone (Figure 3) occurred by Fries transposition over phenylbenzoate. In the Fries reaction catalyzed by Lewis-type systems, aimed at the synthesis of hydroxyarylketones starting from aryl esters, the mechanism can be either (i) intermolecular, in which the benzoyl cation acylates phenylbenzoate with formation of benzoylphenylbenzoate, while the Ph-O-AfCL complex generates phenol (in this case, hydroxybenzophenone is a consecutive product of phenylbenzoate transformation), or (ii) intramolecular, in which phenylbenzoate directly transforms into hydroxybenzophenone, or (iii) again intermolecular, in which however the benzoyl cation acylates the Ph-O-AfCL complex, with formation of another complex which then decomposes to yield hydroxybenzophenone (mechanism of monomolecular deacylation-acylation). Mechanisms (i) and (iii) lead preferentially to the formation of p-hydroxybenzophenone (especially at low temperature), while mechanism (ii) to the ortho isomer. In the case of the Bronsted-type catalysis with zeolites, shape-selectivity effects may favor the formation of the para isomer with respect to the ortho one (11,12). 

The Fries rearrangement of PA over H-BEA zeolites, which is a simple reaction, was chosen to introduce the competition for adsorption on the zeolite catalysts and its role on the reaction rate. Ortho- and para-hydroxyacetophenones (o- and p-HAP), para-acetoxyacetophenone (p-AXAP) and phenol (P) are the main products o-HAP, P and p-AXAP, which are directly formed (primary products),... 

Table 3.8 Influence of the reaction temperature on the gas phase Fries rearrangement of phenyl acetate over a HBEA zeolite. Values of conversion obtained after 1 and 10 h reaction (Xi, Xio) and of selectivity and yield to hydroxyacetophenones after lh reaction...

The Fries rearrangement of phenyl acetate (PA) over solid-acid catalysts was first studied in a fixed bed reactor at 400 °C by Pouilloux et al. [9,10]. o- and p-Hydro-xyacetophenone (o- and p-HAP), p-acetoxyacetophenone (p-AXAP), and phenol (P) were the main reaction products. Fluorinated alumina and H-FAU zeolites afforded approximately the same product distribution, o-HAP being highly favored over the para isomer. The reaction scheme proposed was that PA dissociates into phenol (P) and ketene and that o-HAP results partly from an intramolecular rearrangement of PA and partly from transacylation (Eq. 2) whereas p-HAP results from the latter reaction only [10]. 

In the Fries liquid-phase rearrangement of PA carried out in the presence of ZSM-5(41) zeolite at 170°C, a good shape selectivity (ortho/para = 0.17) can be reached after 24 h by keeping modest the conversion of the starting ester (- 20%). When the reaction is repeated over Nu-10 zeolite, a 1 1 mixture of ortho- and para-products is isolated this different behavior can be ascribed to the smaller pore dimension of Nu-10 zeolite, which hampers the entrance of the reagents producing both isomers. 

Jayat, R, Sabater Picot, M. J., and Guisnet, M. 1996. Solvent effects in liquid phase Fries rearrangement of phenyl acetate over a HBea zeolite. Catal. Lett. 41 181-187. 

The exclusive selectivity towards nitrogen in the NH3 oxidation with oxygen is striking, considering the fact that NO or N2O production is observed with many other catalysts [13]. A reaction patliway of ammonia oxidation over cerium zeolite remains to be elucidated. Tlie comparison of ammonia conversions in its oxidation and in the NO reduction illustrates a characteristic of tlie NO reduction with ammonia over cerium zeolite. At lower temperatures, NH3 appears to be activated more easily under NO reduction conditions tlian witli oxygen only. This picture of reductant activation differs fonn tliat assumed for hydrocarbons, where the activation of hydrocarbons is regarded as an important factor for NO reduction [3, 27]. fri a previous paper, we have proposed the intermediacy of NO2 in the NO reduction with ammonia at lower temperatures (e.g. 300 °C) [23]. Tliis intennediate NO2 can probably oxidize ammonia more efficiently than oxygen. 

Chamoumi and Brunei investigated the liquid phase rearrangement of 1,2-epoxyalkenes over various zeolites [96]. H-Offretite gave the best selectivity for the formation of octanal in the reaction with 1,2-epoxyoctane. The esterification of resorcinol with benzoic acid derivatives is followed by a Fries rearrangement to give benzophenones [97]. The reaction is catalysed by Amberlyst-15 ion-exchange resin or Nafion-17 acidic exchange resin. 2,4-Dihydroxybenzophenone has been synthesised in 88% yield by this method. 

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