Phenyl acetate Fries rearrangement

R2NC1, 91, 92 phenyl acetate, Fries rearrangement of, 475 phenyacetyl halides, acylation by, 173 2-phenylbenzoic acid, cycliacylation, 185 phenyl ethers, alkylation of, 149 —, bromination of, 130 —, hydrogen exchange with, 260 —, rearrangement of, 476 phenyl ethyl mercury, mercuridemercuration of, 359, 360... 

Actually, another method for obtaining hydroxyacetophenones is the rearrangement of phenyl acetate (Fries rearrangement, scheme 1). 

A continuous gas-phase catalytic acetylation of phenol with acetic anhydride to phenyl acetate followed by simultaneous Fries rearrangement to yield ortho- and para-hydroxyacetophenones over a silica-supported heteropoly acid has been described. A complete conversion of phenol to phenyl acetate is achieved at 140°C. Upon increasing the temperature to 200°C, the phenyl acetate formed rearranges into hydroxyacetophenones with 10% yield and 90% selectivity to the para isomer. 

The availability of Nafion on silica has not only lowered the cost of the resin but also has made it versatile (Sun et al., 1997 Harmer et al., 1998). A number of industrially important reactions have been attempted, with considerable success, with these catalysts. Consider the Fries rearrangement of phenyl acetate to p-acetyl phenol (/t-hydroxy acetophenone). This has been accomplished by Hoelderich and co-workers (Heidekum, 1998). In the ca.se of alkylation of benzene with benzyl alcohol, Amberlyst-15 and p-toluene sulphonic acid are ineffective and Nafion on silica works well at 80 °C. 

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. 

If the photo-Fries reaction would occur via a concerted mechanism, the absence of solvent should be of minor importance for the formation of rearranged products. However, conclusive evidence supporting the radical pair mechanism arises from the experiments carried out with phenyl acetate (10) in the vapor phase. The major product in the irradiations of 10 is phenol (13), which accounts for 65% of the photoproducts. Under these conditions, less than 1% of ortho -hydroxyace-tophenone (11) appears to be formed [19,20]. Conversely, when a high cage effect is expected, as in rigid matrixes (i.e., polyethylene), the result is completely different, and phenol is practically absent from the reaction mixtures [29]. In the intermediate situation (liquid solution), both rearranged products and phenol are formed in variable amounts depending on solvent properties. These observations... 

Problem 19.16 Phenyl acetate undergoes the Fries rearrangement with AlCl, to form ortho- and para-hydroxyacetophenone. The ortho isomer is separated from the mixture by its volatility with steam. 

A variety of aromatic esters undergo light-induced rearrangements similar to the Fries rearrangement. Irradiation of 2-hydroxyphenyl acetate (Formula 419) gives o-dihydroxybenzene (Formula 420) (46%), 2,3-dihydroxyacetophenone (Formula 421) (22%) and 3,4-dihydroxy-acetophenone (Formula 422) (18%) (186). Phenyl acetate gives 2-... 

Fries rearrangement—that is, the transformation of phenolic esters to isomeric hydroxyphenyl ketones—is related to Friedel-Crafts acylations.392,393 Olah et al.394 have found a convenient way to perform the Fries rearrangement of a variety of substituted phenolic esters in the presence of Nafion-H in nitrobenzene as solvent [Eq. (5.153)]. A catalytic amount of Nafion-H is satisfactory, and the catalyst can be recycled. In contrast, Nafion-silica nanocomposites, in general, exhibit low activities in the Fries rearrangement of phenyl acetate to yield isomeric hydroxyacetophe-nones.239,395 In a recent study, BF3-H20 was found to be highly efficient under mild conditions (80°C, 1 h) to transform phenolic esters of aliphatic and aromatic carboxylic acids to ketones (71-99% yields).396 In most cases the para-hydroxyphenyl isomers are formed with high (up to 94%) selectivity. 

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.

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...

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...

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]. 

The exact mechanism has still not been completely worked out. " Opinions have been expressed that it is completely intermolecular, ° completely intramolecular, and partially inter- and intramolecular. One way to decide between inter- and intramolecular processes is to run the reaction of the phenolic ester in the presence of another aromatic compound, say, toluene. If some of the toluene is acylated, the reaction must be, at least in part, intermolecular. If the toluene is not acylated, the presumption is that the reaction is intramolecular, though this is not certain, for it may be that the toluene is not attacked because it is less active than the other. A number of such experiments (called crossover experiments) have been carried out sometimes crossover products have been found and sometimes not. As in 11-17, an initial complex (68) is formed between the substrate and the catalyst, so that a catalyst/substrate molar ratio of at least 1 1 is required. In the presence of aluminum chloride, the Fries rearrangement can be induced with micro-wave irradiationSimply heating phenyl acetate with microwave irradiation gives the Fries rearrangement. " The Fries rearrangement has been carried out in ionic melts. 

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. ... 

Nafion-H-silica nanocomposite (13% Nafion-H) catalyzed Fries rearrangement of phenyl acetate at high temperatures gives phenol, ort/zo-acetylphenol, para-acetylphenol and para-acetylphenyl acetate in a ratio of 45 5 24.5 25.5 (equation 69). The rearrangement in the presence of added phenol gives exclusively the para-acetylphenol, showing that the Fries rearrangement under these conditions is intermolecular in nature. ... 

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