Zeolite Friedel-Crafts reaction

In one accident, benzyl bromide had been stored on zeolites. The bottle detonated after eight days because of the overpressure resulting from the formation of large quantities of hydrogen bromide. This accident was put down to the Friedel-Crafts reaction (see on p.256) of benzyl bromide, itself catalysed by zeolites. This is an identical behaviour to the one described with benzyl alcohol on p.256. 

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. 

We have recently shown that metal-exchanged zeolites give rise to carbocationic reactions, through the interactions with alkylhalides (metal cation acts as Lewis acid sites, coordinating with the alkylhalide to form a metal-halide species and an alkyl-aluminumsilyl oxonium ion bonded to the zeolite structure, which acts as an adsorbed carbocation (scheme 2). We were able to show that they can catalyze Friedel-Crafts reactions (9) and isobutane/2-butene alkylation (70), with a superior performance than a protic zeolite catalyst. 

At higher temperatures, C—H and C—C bonds may be similarly broken. Thus, zeolite catalysts may be used for (i) alkylation of aromatic hydrocarbons (cf. the Friedel-Crafts reactions with AICI3 as the Lewis acid catalyst), (ii) cracking of hydrocarbons (i.e., loss of H2), and (Hi) isomerization of alkenes, alkanes, and alkyl aromatics. 

In addition to large-scale industrial applications, solid acids, such as amorphous silica-alumina, zeolites, heteropoly acids, and sulfated zirconia, are also versatile catalysts in various hydrocarbon transformations. Zeolites are useful catalysts in fine-chemical production (Friedel-Crafts reactions, heterosubstitution).165-168 Heteropoly compounds have already found industrial application in Japan, for example, in the manufacture of butanols through the hydration of butenes.169 These are water tolerant, versatile solid-phase catalysts and may be used in both acidic and oxidation processes, and operate as bifunctional catalysts in combination with noble metals.158,170-174 Sulfated zirconia and its modified versions are promising candidates for industrial processes if the problem of deactivation/reactivation is solved.175-178... 

Method 1 is known as the method of incipient wetness, because the ionic liquid is added to the support until the mixture starts to lose the appearance of an dry powder. This is the most simple of the presented methods, allowing the immobilisation of high amounts of chloroaluminate liquids on any given silica support. Unfortunately, during the immobilisation step HC1 is created which leads to a decomposition of zeolites and MCM 41 type supports. This problem could be overcome by a modification of the immobilisation method. The supported ILs synthesised this way show a high catalytic activity in Friedel-Crafts reactions. 

Friedel-Crafts reactions what possible technology might replace the old stoicheiometric Lewis acid route The use of acido/basic (particularly zeolites) materials to catalyse this reaction will be discussed as well as the industrial aspects such as recycling, regeneration, and process simplification. 

Benzoylation. The regioselective Friedel-Crafts reaction of activated arenes with a,a,a-trichlorotoluene in refluxing 1,2-dichloroethane (53-97% yield) is catalyzed by HZSM-5 zeolite. 

Friedel-Crafts reactions Replacement of stoichiometric quantities of Lewis acids (AICI3, FeCls, BF3, ZnCh, TiClJ or Bronsted acids (F13P04, HF) by heterogeneous catalysts (zeolites, ion exchangers, heteropolyacids, etc.). 

Alkylation by zeolites made a major entry in the field of industrial catalysis through the highly acclaimed Mobil-Badger process for ethylbenzene (Csicsery, 1984, Hoelderich et al., 1988 Hoelderich and Van Bekkum, 1991) by replacing the toxic, eco-unfriendly, corrosive Friedel-Crafts reaction. A modified version developed by the National Chemical Laboratory (the Albene process), using a similar class of catalysts known as Encilites, is particularly suited to alkylation by ethyl alcohol of any concentration down to 30% (Bhowmik and Ratnasamy, 1991). 

Direct C-acylation of imidazole and pyrazoles in Friedel-Crafts reactions were previously unknown and it was predicted that this is not possible at all. It was previously necessary to rely on other more expensive methods of preparation. This direct acylation in the gas phase has been made possible by zeolite catalysts [15]. For example, if a mixture of 2-methylimidazole and acetic acid or acetic anhydride is reacted at 400 °C over a pentasil zeolite, the result is a conversion of 63 % and a selectivity of 85 % for 2-methyl-4-acetylimidazole. 

When in catalysis with functionaKzed molecules unfavorable sorption ratios in the intracrystalline space occur, significant reduction of turnovers is encountered [86]. Therefore, zeolite-catalyzed conversion of reactants with strongly different polarity, remains a challenge [86], though this phenomenon is less of a problem in the gas phase [87]. A number of observations in oxidations with H2O2 over TS-1 have been rationalized in this way [88]. Benign effects on Friedel-Crafts reactions by zeolites in supercritical CO2 [89] are not unexpected as its density is between that of liquid and vapor phase. 

Hydroperoxidative synthesis 4 (Figure 12.4, middle) accounts for approximately 2.5 x 10 kg of hydroquinone production per year. p-Diisopropylbenzene is synthesized by zeolite-catalyzed Friedel-Crafts reaction of benzene or cumene with propylene or isopropanol. Air oxidation of p-diisopropyl-benzene proceeds at 90-100°C in an aqueous NaOH solution containing organic bases along with cobalt... 

In the first stage, a Friedel-Crafts reaction is commonly carried out by treating benzene with ethylene in the liquid phase at 90-100°C at slightly above atmospheric pressure. The catalyst is aluminium chloride (with ethyl chloride as catalyst promoter). A molar excess of benzene is used to reduce the formation of polyethylbenzenes the molar ratio of reactants is generally about 1 0.6. The reactants are fed continuously into the bottom of a reactor whilst crude product is removed from near the top. The product is cooled and allowed to separate into two layers the lower layer, which consists of an aluminium chloride-hydrocarbon complex, is removed and returned to the reactor. The remaining ethylbenzene is then separated by distillation from polyethylbenzenes and benzene, which are recycled (since dealkylation also occurs under the reaction conditions). In newer plants, ethylbenzene is produced in a gas phase process. An excess of benzene is treated with ethylene at about 420°C and 1.2-2 MPa (12-20 atmospheres) in the presence of a zeolite catalyst. 

Friedel-Crafts acylation is widely used for the production of aromatic ketones applied as intermediates in both fine chemicals and pharmaceutical industries. The reaction is carried out by using conventional homogenous catalysts, which represents significant technical and environmental problems. The present work reports the results obtained in the Friedel-Crafts acylation of aromatic substrates (anisole and 2-methoxynaphthalene) catalyzed by Beta zeolite obtained by crystallization of silanized seeds. This material exhibits hierarchical porosity and enhanced textural properties. For the anisole acylation, the catalytic activity over the conventional Beta zeolite is slightly higher than with the modified Beta material, probably due to the relatively small size of this substrate and the weaker acidity of the last sample. However, the opposite occurred in the acylation of a bulky substrate (2-methoxynaphthalene), with the modified Beta showing a higher conversion. This result is interpreted due to the presence of a hierarchical porosity in this material, which favors the accessibility to the active sites. 

Simple ways to catalyze nitrations and sulfonylations of aromatic compounds are of great interest since these reactions are carried out industrially on large scale. Clays and zeolites with defined pore structures and channels as acidic catalysts have been utilized in nitrations [109] and Friedel-Crafts sulfonylations [110]. 

Hardacre et al. report the Friedel-Crafts benzoylation of anisole with benzoic anhydride to yield 4-methoxybenzophenone with various ILs and zeolite catalysts (USY, HZSM-5, H-beta, and H-mordenite). The rates of reaction were found to be significantly higher using ionic liquids compared with organic solvents.Continuous-flow studies of successful ionic liquid systems indicate that the bulk of the catalysis is due to the formation of an acid via the ion exchange of the cation with the protons of the zeolite as shown in the following reaction. Scheme 8. 

The Friedel-Crafts acylation of aromatic compounds is an important synthesis route to aromatic ketones in the production of fine and specialty chemicals. Industrially this is performed by reaction of an aromatic compound with a carboxylic acid or derivative e.g. acid anhydride in the presence of an acid catalyst. Commonly, either Lewis acids e.g. AICI3, strong mineral acids or solid acids e.g. zeolites, clays are used as catalysts however, in many cases this gives rise to substantial waste and corrosion difficulties. High reaction temperatures are often required which may lead to diminished product yields as a result of byproduct formation. Several studies detail the use of zeolites for this reaction (1). 

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