Zeolites toluene, acylation

The same effect is found for toluene acylation over BEA zeolite with derivatives of isobutyric acid isobutyric anhydride presents a higher initial activity compared with isobutyric chloride.[6]... 

Klisakova, J., Cerveny, L. and Cejka, J. On the role of zeolite structure and acidity in toluene acylation with isobutyric acid derivatives, Appl. Catal., A, 2004, 272, 79-86. 

A number of protic acids have been used to catalyze acylation reactions. It is assumed that the reactions involve the generation of acylium ions. Polymeric reagents such as Nafion-H have been used for example 2-fluorobenzoyl chloride and toluene give the benzophenone derivatives with an ortho.para ratio of 4 81. ° A zeolite-catalyzed acylation (equation 6) has been reported to afford 4-dodecenoyltol-uene in 96% yield but the yields are low with short chain carboxylic acids. Early examples of the use of trifluoroacetic and perchloric acids reported good yields of products. Some more recent examples are shown in equations (7) to (9). Phosphoric and polyphosphoric acids have been used together with carboxylic acids (equation 10),anhydrides and acylureas (equation 11). °... 

Among the wide variety of organic reactions in which zeolites have been employed as catalysts, may be emphasized the transformations of aromatic hydrocarbons of importance in petrochemistry, and in the synthesis of intermediates for pharmaceutical or fragrance products.5 In particular, Friede 1-Crafts acylation and alkylation over zeolites have been widely used for the synthesis of fine chemicals.6 Insights into the mechanism of aromatic acylation over zeolites have been disclosed.7 The production of ethylbenzene from benzene and ethylene, catalyzed by HZSM-5 zeolite and developed by the Mobil-Badger Company, was the first commercialized industrial process for aromatic alkylation over zeolites.8 Other typical examples of zeolite-mediated Friedel-Crafts reactions are the regioselective formation of p-xylene by alkylation of toluene with methanol over HZSM-5,9 or the regioselective p-acylation of toluene with acetic anhydride over HBEA zeolites.10 In both transformations, the p-isomers are obtained in nearly quantitative yield. 

Reaction conditions ( )-1-Phenylethanol (0.122g, 1 mmol), acyl donors (1.5 mmol), zeolite beta with Si/AI = 150 (50mg), Novozym 435 (30 mg) and toluene (5 ml) at 60 °C. 

Using acyl nitrates as nitrating agents (compare with Section 4.5.4.2) and zeolite H-ZSM-11 treated with tributylamine, Nagy et al. (1991, 1994) were able to nitrate toluene with an even more impressive percentage of the isomers obtained—ortho 2-3%, meta 1-2%, and para 95-98%. 

Numerous acylations mediated by zeolite materials were described since 1986, when the first results were reported.76 The acylation of toluene and p-xylene with C2—C20 alkanoic acids over Ce-exchanged NaY at 150°C in a batch reactor was reported. Shape selectivity was observed maximum activity was found for Ci2 and C 4 acids. Other studies showed that Br0nsted acid centers are involved in acylation77 and an electrophilic mechanism is operative.78 A comprehensive review2 of the subject is available and, therefore, only the more recent results are discussed here. 

As reported in the literature, the acylation of aromatic hydrocarbons can be carried out by using zeolites as catalysts and carboxylic acids or acyl chlorides as acylating agents. Thus toluene can be acylated by carboxylic acids in the liquid phase in the presence of cation exchanged Y-zeolites (ref. 1). The acylation of phenol or phenol derivatives is also reported. The acylation of anisole by carboxylic acids and acyl chlorides was obtained in the presence of various zeolites in the liquid phase (ref. 2). The acylation of phenol by acetic acid was also carried out with silicalite (ref. 3) or HZSM5 (ref. 4). The para isomer has been generally favoured except in the latter case in which ortho-hydroxyacetophenone was obtained preferentially. One possible explanation for the high ortho-selectivity in the case of the acylation of phenol by acetic acid is that phenylacetate could be an intermediate from which ortho-hydroxyacetophenone would be formed intramolecularly. 

Our pioneering work in 1986[1] has shown that acid zeolites are efficient catalysts in the Friedel-Crafts acylation of toluene and xylene with carboxylic acids and constitutes a breakthrough in environmentally friendly fine chemistry replacing the conventional AICI3 method by a heterogeneous catalysts. Since this initial study, a tremendous amount of work has been performed in this area[2] and particularly, in recent years, the acetylation reaction, which is a field of research with large potential for the production of fine chemicals, has been intensively investigated. 

Chiche, B., Finiels, A., Gauthier, C., Geneste, P., Graille, J. and Pioch, D. Friedel-Crafts acylation of toluene and /7-xylene with carboxylic acids catalyzed by zeolites. J. Org. Chem., 1986, 51, 2128-2130. 

Norrish Type I cleavage of benzylketones occurs very readily to yield benzyl and acyl radicals. In competition with other processes, these can couple by attack of the acyl radical upon the aromatic nucleus of the benzyl radical to give as a product an acyl toluene derivative. Turro has examined the photochemical properties of the 2-phenylalkanones (326) in solution and complexed with cyclodextrins. In solution the major fate of the Type I biradicals formed is intr2unolecular recombination by attack of the acyl radical at the para position of the benzyl radical to generate (327). However, complexatlon of (326) within the cyclodextrin cavity inhibits formation of (327) and promotes disproportionation of the blradicals to give (328). Turro has also examined the photochemistry of dlbenzylketone Included in zeolites.Recombination of the Type I radicals in this case can produce a mixture of (2-methyl-phenyl) benzylketone and (4-methylphenyl)benzylketone decarbonylation of the acyl radical competes and leads to the isolation of 1,2-dlphenylethane. It is found that the relative yields of the products... 

Pioneering and extensive work in this field was realized in 1985 [8] by use of exchanged Ce Y-zeolite as the catalyst for the Friedel-Crafts acylation of toluene (Eq. 3) and xylene with carboxylic acids. Different aspects of this initial work are of interest. Firstly, it shows that the mild acidity of zeolites is sufficient to effect the reaction, and, secondly, it shows that this reaction can be conducted with carboxylic acids and not the corresponding acid chlorides. Only the more lipophilic acids were found reactive whereas no acetylation occurs with acetic acid. The reaction with toluene (Table 1) is extremely para selective and more selective than a conventional aluminum chloride homogeneous process. The different reactivities reported in this paper are essentially because of differences between preferential adsorption of the substrates on the catalyst and not their intrinsic activity. 

Table 1. Acylation of toluene with different acids over Ce -exchanged Y zeolite (150 °C, 48 h).

If the acylation of toluene with acetic acid depicted above [8] failed, use of the more active acyl chlorides instead of acids and La-exchanged Y-zeolite leads to the para-acylated product [20],... 

In terms of reactivity benzoylation seems to be a much easier reaction. By use of zeolites, benzoylation of toluene [23], xylene [24], and benzene [25] have been described under mild conditions (80-140 °C). It is probable that benzoylation is favored because of the greater affinity of the acylating agent for the heterogeneous catalyst. Interesting results have been found for acylation of benzene with phthalic anhydride to form anthraquinone (Eq. 11) [26]. When the H/0 cata-... 

In a series of valuable studies, the activity of various cation-exchanged Y zeolites in the acylation of toluene and xylenes with aliphatic carboxylic acids was investigated In a model reaction between toluene and octanoic acid, the activity of rare earth-, transition metal-, and alkaline earth-cation-exchanged Y zeolites was considered. CeY zeolite exhibits the highest activity (3 yield = 75%) in the para-acylation (Scheme 4.3) in agreement with the results published in an early study qj., contrary, unmodified Y zeolite shows a lower activity (3 yield < 40%), and transition metal and alkaline-earth-exchanged Y are nearly inactive. 

Figure 4.2 Dependence of the degree of sodium ion exchanged by cerium ion on the activity of Y zeolite in the acylation of toluene by octanoic acid at 200°C.

Several BEA zeolites have been tested as catalysts for the liquid-phase acylation of toluene with AAN (Table 4.7). [S]-Named zeolites are hydro-thermally prepared using amorphous silica as the silicon source, whereas [T]-named zeolites are prepared by using tetraethylorthosilicate (TEOS) as the silicon source with different SAR. The acylation process represents a very selective route to 4-methylacetophenone 18 small amounts of ortho- and mete-methylacetophenone 19 and 20 are produced in less than 2% of the total yield of the acetylated products. For the [S]-type BEA zeolites, the acidity values are in good agreement with the catalytic activity, following the order [S]-BEA(32) > [S]-BEA(26) > [S]-BEA(54) [S]-BEA(76). In the [T]-BEA series, the catalytic activity decreases when the SAR increases, regardless of the increase of hydrophobicity. The conclusion is that low SAR lead to better yields in acetophenones (APs). However, the poisoning... 

The vapor-phase acylation of aromafic hydrocarbons wifh acyl chlorides over differenf zeolifes was invesfigafed. Comparing fhe acetylation of toluene with AC over ZSM-5, MOR, and REY zeolites, ZSM-5 was the best catalyst affording para-methylacefophenone with 60% conversion of... 

The process can be carried out with aromatic substrates such as benzene, toluene, and isopropylbenzene and different acylating agents (56%-99% conversion). Zeolite ZSM-5 fails to give any producf with other substrates such as xylenes, mesitylene, and N,N-dimethylaniline. 

More interestingly, carboxylic acids can be employed in the acylation of aromatic compounds. The acylation of toluene and anisole with C2-C42 aliphatic carboxylic acids can be carried out with CsPW, affording the corresponding products in 41%-71% yield. These solid acids are superior in activity to the conventional acid catalysts such as sulfuric acid and zeolites, and can be reused after a simple workup, albeit with reduced activity. 

Botella, R, Corma, A., Lopez-Nieto, J. M., Valencia, S., and Jacquot, R. 2000. Acylation of toluene with acetic anhydride over Beta zeolites influence of reaction conditions and physicochemical properties of the catalyst. /. Catal. 195 161-168. 

Sheemol, V. N., Tyagi, B., and Jasra, R. V. 2004. Acylation of toluene using rare earth cation exchanged zeolite (3 as solid acid catalyst. J. Mol. Catal. A Chem. 215 201-208. 

Gauthier et al. (1989) studied the activity of various cation-exchanged Y-type zeolites in the acylation of toluene with octanoic acid, obtaining selectivities to the para isomer of 94% at 75% yield of acylated product. The most efficient catalysts were rare-earth-exchanged zeolites (70% exchange), the following order of activity being observed Cr3+, Zr4+ < M2+, Cu2+, Co2+ <11 < Pr3+, La3+, Gd3+, Yb3+, Ce3+. 

In contrast to anisole, the acylation of toluene with HPA is far less efficient than that with H-Beta. These results can be explained by the well-known strong affinity of bulk HPA towards polar oxygenates, which would lead to the preferential adsorption of acetic anhydride on HPA, blocking access for toluene to the catalyst surface. It appears that the hydrophobic zeolites with high Si/Al ratios less strongly differentiate the adsorption than the hydrophilic HPA and, therefore, are more suitable catalysts for the acylation of nonpolar aromatics like toluene. 

Cs" salts catalyse the acylation of toluene, p-xylene and m-xylene with crotonic acid. Some alkylation of aromatic compounds with crotonic acid also takes place. Heteropoly acid was found to be more active than zeolites HY and H-Beta in the acylation. 

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