Alkyl halides superacidic alkylation with

The conventional resinsulfonic acids such as sulfonated polystyrenes (Dowex-50, Amberlite IR-112, and Permutit Q) are of moderate acidity with limited thermal stability. Therefore, they can be used only to catalyze alkylation of relatively reactive aromatic compounds (like phenol) with alkenes, alcohols, and alkyl halides. Nafion-H, however, has been found to be a suitable superacid catalyst in the 110-190°C temperature range to alkylate benzene with ethylene (vide infra) 16 Furthermore, various solid acid catalysts (ZSM-5, zeolite /3, MCM-22) are applied in industrial ethylbenzene technologies in the vapor phase.177... 

Halonium ions are an important class of onium ions.43 The dialkylchloro, bromo, and iodohalonium ions can be prepared and even isolated as stable salts (i.e., 46), as shown by Olah et al. by reacting an excess of haloalkane with strong Lewis acid halides in solvents of low nucleophilic-ity (eq 14). In superacid solution, dialkylhalonium ions show enhanced alkylating reactivity.44 It is considered that this enhanced reactivity is due to further protolytic (or electrophilic) activation involving the non-bonded... 

Benzylation of toluene with benzyl chloride, which is a typical example of Friedel-Crafts alkylation, is known to be catalyzed by Lewis-type superacids such as A1C13 and BF3. This type of catalyst has been mostly used for the Friedel-Crafts reaction, which is one of the most studied of organic reactions. This reaction was performed over several metal oxides and sulfates, and iron sulfates showed an unexpected effectiveness for the reaction (102-104). The catalytic activities of FeS04 and Fe2(S04)3 for the reaction were examined in detail the activities were remarkably dependent on calcination temperature, the maximum activity being observed with calcination at 700°C (105-107). Catalytic actions analogous to the above case were also observed with other Friedel-Crafts reactions, the benzoyl-ation of toluene with benzoyl chloride (108), the isopropylation of toluene with isopropyl halides (109), and the polycondensation of benzyl chloride UIO). 

Lewis superacid-catalyzed direct alkylation of alkanes is also possible with alkyl cations prepared from alkyl halides and SbFs in sulfuryl chloride fluoride solution. " Typical alkylation reactions are those of propane and butanes by 2-butyl and ZerZ-butyl cations. The ClfU-Sbfs and C2H5F-SbF5 complexes acting as incipient methyl and ethyl cations besides alkylation preferentially cause hydride transfer. Since intermolecular hydride transfer between different carbocations and alkanes are faster than alkylation, a complex mixture of alkylated products is usually formed. A significant amount of 2,3-dimethylbutane was, however, detected when propane was propylated with the 2-propyl cation at low temperature [Eq. (6.36)]. No 2,2-dimethylbutane, the main product of conventional acid-catalyzed alkylation, was detected, which is a clear indication of predominantly nonisomerizing reaction conditions. 

In superacid systems consisting of a composite of a Brpnsted acid and a Lewis acid, the anion interacts chemically with one or more molecules of the latter. Thus, up to 4 equiv of SbF5 has been recommended for conversion of alkyl halides to the corresponding carbocations (38). For those systems, the anion stabilization is accomplished by chemical bonding between the Lewis acid and the anion. The existence of carbocations in such solutions has been demonstrated by various physical methods. 

Primary alkyl halides do react in superacids, but ordinarily the products are 2° or 3° carbocations arising from rearrangements. Nevertheless, there is evidence for the ethyl cation in mixtures of CH3CH2F and SbFs at low temperature in SO2 solution as well as in a H3PW12O40 pseudoliquid phase. There are also indications for formation of the ethyl cation in a reaction of ethene with methane and a HF-TaFs catalyst and in the solvolysis of ethyl tosylate in concentrated H2S04. In addition, a 1° carbocation-brosylate ion pair was proposed as an intermediate in the El... 

Carbon-Carbon Bond Formation. Various types of Bronsted and Lewis acids and superacids may be applied to perform the reaction of alkanes or arenes with different alkylating agents (alkenes, alkynes, alkyl halides, alcohols, ethers, esters). Acid-catalyzed alkylations, particularly alkane-alkene reactions, are of great practical importance in upgrading motor fuels. Acid-catalyzed alkylation produces alkylaromatics for manufacture of plastics (styrenes), detergents, and chemicals. 

The important catalysts applied in this process are Lewis acids (promoted by hydrogen halide) and protic acids (61,77). Hydrogen fluoride and sulfuric acid are the preferred catalysts because they are handled more conveniently and can be reused. Of the reactants, alkanes and cycloalkanes with tertiary carbon atoms are the most reactive in the alkane-alkene reaction. The process may yield alkylates of markedly different product compositions, depending on the reactants, catalysts, and reaction conditions. Superacids may also be used as catalysts with signiflcant and characteristic differences in product distribution (63). 

Monoalkylated Ceo Cation (RCeo )- Derivatized Ceo cations with an alkyl group attached, RCeo, can be generated from the corresponding fullerenols 1,4-RCeoOH (2a-d) in strong acid (Scheme 9.3). Ionization of alcohols and alkyl halides in a superacid, such as magic acid (FSOsH-SbFs), is a well established method, devel-... 

A new type of catalyst, a cobalt carbonyl complex, has been found for low-temperature (viz. 50 °C) homogeneous hydroformylation of alkenes. Nafion-H (a superacidic perfluorinated resin sulphonic acid) impregnated with mercury is recommended as a catalyst for the hydration of alkynes R C=CR (R = H or aryl, R = H, alkyl, or aryl) to form ketones R CH2C0R. Two mild methods for the hydrolysis of vinyl halides to ketones have been described one utilizes Bp3,Et20 and mercury(ii) acetate in acetic acid and the second mercury(ii) acetate in trifluoroacetic acid/ ... 

In 1877, Charles Friedel and James Mason Crafts [30a, b] corporately discovered that treatment of amyl chloride with aluminum strips in benzene led to the formation of amylben-zene. This type of transformation was found to be general for alkyl halides and aromatics under the catalysis of Lewis acid. Along with the discovery of the closely related acylation [30c, d], these two men are best remembered by Friedel-Crafts reaction that bears their names. With various modem modifications that appeared in the Uterature, including enan-tioselective variants [31], Friedel-Crafts alkylation and acylation have already become one of the most powerful C—C bond forming reactions in organic chemistry [32]. These methods are recognized to date as of fundamental importance not only in acadania but also in industry [33]. As shown in Scheme 10.18, some heteroaromatics, instead of the aryl component or alcohol, and alkenes instead of halides can be used as suitable substrates. Also, other common Lewis acids like BFj, TiCl, SnCl, ScfOTOj, etc., and Brpnsted acids snch as HF, H SO, and superacids (e.g., HF SbFj, HS03-SbFj) can also used as catalysts. 

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