Solid acids Friedel-Crafts reactions

Solid Lewis acid halide catalysts seem to have advantages in some Friedel-Crafts reactions. ZnCl2 and NiCl2, supported on K10 montmorillonite exhibit high activity and selectivity in benzylation 140... 

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... 

More stable catalysts are obtained by using fluorinated graphite or fluorinated alumina as backbones and Lewis acid halides, such as SbFs, TaFs and NbFs, which have a relatively low vapor pressure. These Lewis acids are attached to the fluorinated solid supports through fluorine bridging. They show high reactivity in Friedel-Crafts reactions including the isomerization of straight chain alkanes such as n-hex-ane. 

Another type of solid superacid is based on perfluorinated resin sulfonic acids, such as the acid form of DuPont s Nafion resin, a copolymer of a perfluorinated epoxide and vinylsulfonic acid, or higher perflu-oroalkanesulfonic acids such as perfluorodecanesulfonic acid, CF3(CF2) 03H. Such solid catalysts were found to be very efficient in alkylation of aromatic hydrocarbons and other Friedel-Crafts reactions. A comprehensive review is available on the application of Nafion-H in organic catalysis. ... 

Intramolecular Friedel-Crafts reaction Worthy of mention is the case of intramolecular Friedel-Crafts-type reaction affording 4(lH)-quinolone derivatives [443]. Thus, after extensive investigations, the authors prepared a solid-supported Meldrum s acid derivative by alkylation of a Merrifield resin with ethyl acetoacetate, decarboxylation, and subsequent ketalization of the resulting supported ketone with malonic acid (638). Treatment with triethyl orthoformate and various arylamines (639) afforded immobilized arylamino-methylene derivatives of Meldrum s acid (640). Upon thermal cyclization, these intermediates afforded 4(lH)-quinolone derivatives with simultaneous release from the resin (641). Highly pure final compounds were obtained in moderate to good yields. The resin was recovered in the form of the precursor of (638), i.e., the ketone (642), and thus could be potentially reused (Scheme 133). 

Recent developments in the design and application of supported reagent catalysts offer considerable potential for clean synthesis. Synergistic effects between the support material and the reagent can lead to unexpectedly high activity. Thus "clayzic" is a potent solid acid catalyst for certain Friedel-Crafts reactions despite the low activity of the individual components. This and other similar clay and silica-based solid acid catalysts have been shown to have many useful applications in liquid phase reactions and some of them have been commercialised as environmentally friendly replacements for conventional acidic reagents. ... 

Izumi, Y., Ogawa, M., and Urabe, K. 1995. Alkali metal salts and ammonium salts of Keggin-type heteropolyacids as solid acid catalysts for liquid-phase Friedel-Crafts reactions. Appl. Catal. A Gen. 132 127-140. 

Friedel-Crafts reactions are commonly performed both at the laboratory and industrial scale by using acid catalysts and acyl chlorides or alcohols as acylating or alkylating agents. The advantages of SCFs for these types of reactions are clear. There is less need for reactive acid catalysts such as AICI3, which are difficult to separate from the reaction mixture and are, on the whole, environmentally unfriendly [45]. Instead, solid acid catalysts can be used efficiently [46, 47]. 

In homogeneous solutions, fluorosulphonic acid combined with antimony pentafluoride is used as a superacid having some useful catalytic properties in organic chemistry. In its protonated form, perfluorosulphonic Nafion powders are used as the catalyst for a variety of organic syntheses. The catalytic power is higher than that of other solid phase superacid catalysts. It enables lower temperatures and pressures to be used and its specificity is higher. Nafion is used as the solid superacid catalyst for the gas phase alkalination of aromatic hydrocarbons and liquid phase esterification or Friedel-Craft reactions ... 

It was also possible to perform the pyrrole 5 Michael addition with a variety of a,p-unsaturated ketones 2 catalyzed by MSSA in the same fashion, affording 2-substituted pyrroles 6 in good yields (Scheme 1.3b). Furthermore, MSSA was used as a solid acid heterogeneous catalyst to synthesize 1,1,3-triindolyl compounds through the tandem Michael addition and Friedel-Craft reaction of a, P-unsaturated aldehydes or ketones and indole (3) (Scheme 1.4). The authors found two protocols of general applicability employing 1 mmol of a,P-unsaturated compound and 4 mmol... 

Strong, solid Bronsted acid catalyst. It has a wide range of applications including alkene alkylations, Beckmann rearrangements and esterification reactions its uses in Friedel-Crafts reactions are described in section 16.5.1. 

There is much in common between catalysts for cationic polymerization and the Friedel-Crafts and its analogous reactions. Although the field of Friedel-Crafts reactions has a long history, exploring new catalysts is still a vital area. The purpose of those studies is primarily to realize acylation and/or reactions of substrates with hetero atoms, such as heterocyclic compounds, using a catal)rtic amount of a Lewis acid. Since a conventional add, such as AICI3, forms the complex with a product and/or a substrate, an equimolar amount of the acid to a substrate is required. Consequently, the main product is often accompanied by significant by-produrts in industrially used Friedel-Crafts processes. Thus, reactions with various Lewis adds and solid adds have been reported recently. 

Of the many methods which have been published so far for the substitution of existing crowns, probably the most straightforward are Friedel-Crafts alkylation or acylation reactions. Cygan, Biernat and Chadzynski have reported the successful di-t-butylation of dibenzo-24-crown-8 using t-butanol as alkylating agent s . The crown was heated at 100° for 4 h in the presence of excess t-butanol and 85% phosphoric acid. The product was obtained as a crystalline (mp 52—74°) solid in 93% yield. The alkylated crowns are presumably a mixture of isomers substituted once in each ring as illustrated in Eq. (3.14). 

Friedel-Crafts alkylations are among the most important reactions in organic synthesis. Solid acid catalysts have advantages in ease of product recovery, reduced waste streams, and reduction in corrosion and toxicity. In the past, people have used (pillared) clays (18), heteropolyacids (19) and zeohtes (20) for Friedel-Craft alkylations, with mixed success. Problems included poor catalyst stabihty and low activity. Benzylation of benzene using benzyl chloride is interesting for the preparation of substitutes of polychlorobenzene in the apphcation of dielectrics. The performance of Si-TUD-1 with different heteroatoms (Fe, Ga, Sn and Ti) was evaluated, and different levels of Fe inside Si-TUD-1 (denoted Fei, Fe2, Fes and Feio) were evaluated (21). The synthesis procedure of these materials was described in detail elsewhere (22). 

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