Zeolite Fries rearrangement

Zeolites have also been described as efficient catalysts for acylation,11 for the preparation of acetals,12 and proved to be useful for acetal hydrolysis13 or intramolecular lactonization of hydroxyalkanoic acids,14 to name a few examples of their application. A number of isomerizations and skeletal rearrangements promoted by these porous materials have also been reported. From these, we can underline two important industrial processes such as the isomerization of xylenes,2 and the Beckmann rearrangement of cyclohexanone oxime to e-caprolactam,15 which is an intermediate for polyamide manufacture. Other applications include the conversion of n-butane to isobutane,16 Fries rearrangement of phenyl esters,17 or the rearrangement of epoxides to carbonyl compounds.18... 

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. 

Fries rearrangement, 18 336, 337 isomerization and transalkylation of alky-laromatics, 18 329 epoxide transformations, 18 351-352 hydration and ammonolysis of ethylene oxide, 18 351, 352 isomerization, 18 351 framework composition, 33 226-228 hydrogenation, dehydrogenation, and related reactions, 18 360-365 dehydrocyclization of s-ethylphenyl using zeolites and carbonyl sulfide, 18 364, 365... 

Figure 32 Phenyl phenylacetates examined for photo-Fries rearrangement within zeolites and Nafion membranes.

For samples photolyzed on ZSM-5 zeolite, the product distributions of 31 and 32 are dramatically different from those photolyzed in homogeneous solutions. First, the rearrangement products were totally suppressed. Second, diphenylethane 39 resulted from coupling of benzyl radical was not found. Only phenol 38 and toluene were detected. In contrast, photolyses of 33 and 34 on ZSM-5 follow strikingly different pathways. Both photo-Fries rearrangement 36 and 37 and decarbonylation products 35 and 39 were formed. These results can be understood from consideration of size- and shape-selective sorption combined with restriction on the mobility of the substrates and reaction intermediates imposed by the pentasil pore system. 

Ramamurthy and coworkers studied the photo-Fries rearrangement of phenyl acetate and phenyl benzoate and photo-Claisen rearrangement of allyl phenyl ether (Fig. 34) included in two types of zeolite (faujasites X and Y and pen-tasils ZSM-5 andZSM-11) [192], The photolysis was performed with the zeolite slurry in either hexane or iso-octane. One of the most remarkable observations is that the product distribution is altered within zeolites from that in isotropic solvent. Furthermore, while in solution, nearly a 1 1 mixture of ortho and para isomers 40 and 41 (Fig. 34) was obtained, within zeolites one is able to direct the photoreaction selectively toward either the ortho or the para products by conducting the reaction either within faujasites or pentasils, respectively (Fig. 34). 

Figure 34 Photo-Fries rearrangement of phenyl acetate and phenyl benzoate, and photo-Claisen reaction of allyl phenyl ether in solution and within zeolites.

Recently, Ramamurthy and Weiss and their coworkers reported the photo-Fries rearrangement of three 1-naphthyl phenylacelates (Fig. 36) in cation-ex-changed zeolite Y and high-density polyethylene films [193], When the substrates were irradiated in hexane to <30% conversion, the eight photoproducts in Fig. 36 were detected. The photoproduct distributions from polyethylene or a Y-zeolite are drastically different from those in solution. Cage-escape products (54 and 55) are absent in both constrained media, and in zeolite Y, only 49 was detected. The... 

Figure 36 Photo-Fries rearrangement of 1-naphthyl acetates within Y-zeolite and low-density polyethylene films.

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),... 

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. 

Fries rearrangement and phenol acetylation The Fries rearrangement is the acid catalysed transformation of aryl esters into hydroxyarylketones. Both this rearrangement and the two-step transformation (esterification, Fries rearrangement) in one-pot operation of phenols with carboxylic acid or anhydrides will be examined hereafter. Most studies in which acid zeolites were used as catalysts (Tables 3.6 and 3.7) deal with the synthesis of o- and p-hydroxyacetophenones (o- and p-HAP) either by the Fries rearrangement of phenyl acetate [Reaction (3.5)] ... 

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. 

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...

In the Fries rearrangement of PA, high yield and selectivity for o-HAP can be obtained with large pore zeolites such as HFAU, HBEA and average pore zeolites such as HMFI. HBEA zeolite modified by ion exchange with cerium[77] and especially a commercial HMFI made of primary crystallites and agglomerates joined by finely dispersed alumina[78] were claimed to be particularly stable and selective for the formation of o-HAP. 

Figure 3.8 Liquid phase transformation of phenyl acetate (2.2 mol l-1 in sulfolane solvent) at 433 K. (a) Yield in o-hydroxyacetophenone, o-HAP ( ) and p-hydroxyacetophenone, p-HAP (X) versus reaction time, (b) Effect of the addition of phenol (P) on the p-HAP yield. [P] =0 mol l-1 (x) and [P] =0.6 mol l-1 ( ). Reprinted from Catalysis Letters, Vol. 41, Jayat et al., Solvent effects in liquid phase Fries rearrangement of phenyl acetate using a HBEA zeolite, pp. 181-187, copyright (1996), Kluwer Academic Publishers, with kind permission of Springer Science and Business Media...

Zeolites H-BEA and H-Y were found to be the most active catalysts, however all catalysts readily form the phenyl benzoate (Table 4.1). In the conditions of the reaction, the formation of phenyl benzoate (PB) occurs rapidly via O-acylation of phenol. Direct C-alkylation of phenol with benzoic anhydride (B) and Fries rearrangement of phenyl benzoate results in the formation of 2- and 4-hydroxy-benzophenones (2-HPB and 4-HPB) (Scheme 4.3). 

Another example of the effect of confined medium is found during photo-Fries rearrangement of naphthyl esters in zeolites [103,104]. Upon photolysis in isotropic solution 1-naphthyl benzoate undergoes the photo-Fries rearrangement to yield both ortho (2-) and para (4-) phenolic ketones (Sch. 4). When this ester is included in NaY zeolite and irradiated the main product (96%) is the ortho isomer. This remarkable ortho-selectivity within zeolites has been rationalized on the basis of interactions of the reactant 1-naphthyl benzoate and intermediate radicals with the sodium ion. Due to restrictions imposed by the medium the benzoyl radical, once formed, is compelled to react only with the accessible ortho position. 

Nafion-silica composites were compared with zeolites such as H-Beta, H-USY and H-ZSM-5, in the Fries rearrangement of phenyl acetate (see earlier). The highest conversion was observed with H-Beta [88]. 

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... 

Wang, H., Zou, Y. Modified 3-Zeolite as Catalyst for Fries Rearrangement Reaction. Catal. Lett. 2003, 86,163-167. 

Gas-phase acetylation of phenol using /3-zeolites gives phenyl acetate rapidly, which rearranges (see Fries rearrangement, vide infra) to orffto-hydroxyacetophenone and para-hydroxyacetophenone. The ojp ratio is high under these conditions. ... 

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