Friedel-Crafts reaction Lewis acid

Some common initiators for cationic polymerization reactions are protonic acids, Friedel-Crafts catalysts (Lewis acids), compounds capable of generating cations, or ionizing radiation. 

This type of duality of action is presumably present in other situations, such as the Fries rearrangement (78), the Friedel-Crafts reaction with acid chlorides (65) or acid anhydrides (21), and the catalytic chlorination of nitrobenzene (17). In these reactions it appears that the uncoordinated Lewis acid is the effective catalyst. The same situation is illustrated by recent work on aromatic amination (32, 33) and halogenation (57, 58, 71) and seems to be general feature of Lewis acid-catalyzed electrophilic reactions of aromatic compounds containing suitable donor groups. 

Mayr, H., Striepe, W. Scope and limitations of aliphatic Friedel-Crafts alkylations. Lewis acid catalyzed addition reactions of alkyl chlorides to carbon-carbon double bonds. J. Org. Chem. 1983, 48, 1159-1165. 

Although Friedel-Crafts or Lewis acid catalysts are often used to initiate carbocationic polymerizations and are very important from an industrial viewpoint, very little is known about the active intermediates involved. Such information is important because, in general for ionic polymerization reactions, small changes in the structure of the active center can result in large changes in molecular weight, molecular weight distribution (MWD),... 

The most widely used reactions are those of electrophilic substitution, and under controlled conditions a maximum of three substituting groups, e.g. -NO2 (in the 1,3,5 positions) can be introduced by a nitric acid/sul-phuric acid mixture. Hot cone, sulphuric acid gives sulphonalion whilst halogens and a Lewis acid catalyst allow, e.g., chlorination or brom-ination. Other methods are required for introducing fluorine and iodine atoms. Benzene undergoes the Friedel-Crafts reaction. ... 

Several methods are available to supplement the phenol alkylations described above. Primary alkylphenols can be produced using the more traditional Friedel-Crafts reaction. Thus an -butylphenol can be synthesized direcdy from a butyl haUde, phenol, and mild Lewis acid catalyst. Alternatively, butyryl chloride can be used to acylate phenol producing a butyrophenone. Reduction with hydrazine (a Wolff-Kishner reduction) generates butylphenol. 

The Friedel-Crafts reaction is a very important method for introducing alkyl substituents on an aromatic ring. It involves generation of a carbocation or related electrophilic species. The most common method of generating these electrophiles involves reaction between an alkyl halide and a Lewis acid. The usual Friedel-Crafts catalyst for preparative work is AICI3, but other Lewis acids such as SbFj, TiC, SnCl4, and BF3 can also promote reaction. Alternative routes to alkylating ecies include protonation of alcohols and alkenes. 

A good deal of experimental care is often required to ensure that the product mixture at the end of a Friedel-Crafts reaction is determined by kinetic control. The strong Lewis acid catalysts can catalyze the isomerization of alkylbenzenes, and if isomerization takes place, the product composition is not informative about the position selectivity of electrophilic attack. Isomerization increases the amount of the meta isomer in the case of dialkylbenzenes, because this isomer is thermodynamically the most stable. ... 

Lewis acid catalysts such as aluminum chloride and iron(III) halides also bond to nitrogen to strongly deactivate the ring toward Friedel-Crafts reactions and halogenation. 

The rate-determining step is the electrophilic aromatic substitution as in the closely related Friedel-Crafts reaction. Both reactions have in common that a Lewis acid catalyst is used. For the Blanc reaction zinc chloride is generally employed, and the formation of the electrophilic species can be formulated as follows ... 

This section deals with Bronsted acid and Lewis acid catalyzed reactions, excluding Friedel-Crafts reactions, but including reactions such as nitrations, halogenations, and Claisen rearrangements. Friedel-Crafts reactions are discussed in the subsequent Sections 5.1.2.2 and 5.1.2.3. 

Friedel-Crafts reactions have been studied in detail by Olah [74, 75]. These reactions result in the formation of carbon-carbon bonds and are catalyzed by strong Bronsted or Lewis acids. 

Alkenes can be acylated with an acyl halide and a Lewis acid catalyst in what is essentially a Friedel-Crafts reaction at an aliphatic carbon. ° The product can arise by two paths. The initial attack is by the acyl cation RCO (or by the acyl halide free or complexed see 11-14) at the double bond to give a carbocation ... 

To optimize the alkylation conditions, ferrocene was reacted with allyldimethyl-chlorosilane (2) in the presence of various Lewis acids such as aluminum halides and Group lO metal chlorides. Saturated hydrocarbons and polychloromethanes such as hexane and methylene chloride or chloroform were used as solvents because of the stability of the compounds in the Lewis acid catalyzed Friedel-Crafts reactions. The results obtained from various reaction conditions are summarized in Table IV. 

It turned out that the Friedel-Crafts reaction and the chlorination can be done in the same pot. The vhlorination needs to be chemoselective as reaction on -.he methyl group or next to the carbonyl group could ccur. Lewis acid catalysis Is the answer. 

In 2007, Womack et al. published the conversion of 2-aUcylcinnamyldehydes to 2-aLkylindanones via a catalytic intramolecular Friedel-Crafts reaction. In the presence of 5-10 mol% FeCls different in situ generated ( )-2-alkylcinnamaldehydes-derived dimethyl acetals cyclized to l-methoxy-2-aIkyl-7//-indenes in good to high yields (Scheme 6) [22]. The transformation corresponds to a formal intramolecular Friedel-Crafts acylation which is achieved with catalytic quantities of Lewis acid. This result is in strong contrast to traditional Friedel-Crafts acylations which require stoichiometric amounts of Lewis acid. 

The aluminum trihalides are particularly important Lewis acids in the chemical industry. They promote or catalyze a large variety of reactions. One of the most important applications is the Friedel-Crafts reaction, in which two molecules combine, forming a new C—C bond. For example, aluminum chloride or some other Lewis acid catalyzes the reaction between an acid chloride and benzene to form acetophenone ... 

All acids but especially Lewis acids (particularly aluminium chloride), give rise to dangerous interactions with nitrated derivatives and nitrates (there is not much information about nitrates). Aluminium chloride causes a large number of accidents due to nitrobenzene and sometimes nitromethane when used as a solvent in Friedel-Crafts reactions for which aluminium chloride is the common catalyst. 

A combination of Friedel-Crafts alkylation and reduction can be achieved using InCl3 and chlorodimethylsilane. The Lewis acid presumably promotes both the Friedel-Craft reaction and the subsequent reduction.179... 

Apart from the alkyl halide-Lewis acid combination, two other sources of carbo-cations are often used in Friedel-Crafts reactions. Alcohols can serve as carbocation precursors in strong acids such as sulfuric or phosphoric acid. Alkylation can also be effected by alcohols in combination with BF3 or A1C13.37 Alkenes can serve as alkylating agents when a protic acid, especially H2S04, H3P04, and HF, or a Lewis acid, such as BF3 and A1C13, is used as a catalyst.38... 

Under Lewis-acid-catalyzed conditions, electron-rich arenes can be added to alkenes to generate Friedel-Crafts reaction products. This subject will be discussed in detail in Chapter 7, on aromatic compounds. However, it is interesting to note that direct arylation of styrene with benzene in aqueous CF3CO2H containing H2PtCl6 yielded 30-5% zram-PhCH CHR via the intermediate PhPt(H20)Cl4.157 Hydropheny-lation of olefins can be catalyzed by an Ir(III) complex.158... 

Indium trichloride349-351 is a mild Lewis acid that is effective for various kinds of Lewis-acid-catalyzed reactions such as Diels-Alder reactions (Scheme 85), aldol reactions, and Friedel Crafts reactions. Since indium trichloride is stable in water, several aqueous reactions have been investigated (Scheme 85) indium(III) triflate is also used as a Lewis acid. 

Antimony pentachloride is a reactive Lewis acid that can be used for Friedel-Crafts reactions and some other Lewis-acid-catalyzed reactions. The HF-SbF5 system is known as magic acid, and carbocations are stabilized in this medium.353 By using the HF-SbF5 system, alkylation of acetophenone (a relatively unreactive aromatic compound) has been achieved (Scheme 87). 

Many important reactions involve catalysis by Lewis acids or bases. One of the most important of these is the type of reaction carried out by Charles Friedel and James Crafts. These reactions, known as the Friedel-Crafts reactions, actually involve several types of important processes. One of these is alkylation, which is illustrated by the reaction of benzene with an alkyl halide in the presence of A1C13, a strong Lewis acid. 

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. 

Friedeb Crafts reaction Anisole undergoes Friedel-Crafts reaction, i.e., the all rl and acyl groups are introduced at ortho and para positions by reaction with alkyl halide and acyl halide in the presence of anhydrous alurntnlurn chloride (a Lewis acid) as catalyst. 

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