Friedel-Crafts catalysis

The functionalisation of aromatic rings is vitally important to all areas of organic chemistry, and the most popular way of doing this is via electro- 

Friedel-Crafts catalysis is a powerful method for effecting electrophilic aromatic substitution one broad definition of the Friedel-Crafts reaction is that given by George Olah [21]. 

An additional problem is that in many cases the products of the reaction are Lewis bases which can complex with the Lewis acid centres in such a way as to render the acid inert. This is particularly true for acyla- 

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The Irihalides of A1 form a large number of addition compounds or complexes and these have been extensively studied because of their importance in understanding the nature of Friedel-Crafts catalysis. The adducts vary enormously in stability from weak interactions to very stable complexes, and they also vary widely in their mode of bonding, structure and... 

Zinc chloride was used as a catalyst in the Friedel Crafts benzylation of benzenes in the presence of polar solvents, such as primary alcohols, ketones, and water.639 Friedel-Crafts catalysis has also been carried out using a supported zinc chloride reagent. Mesoporous silicas with zinc chloride incorporated have been synthesized with a high level of available catalyst. Variation in reaction conditions and relation of catalytic activity to pore size and volume were studied.640 Other supported catalytic systems include a zinc bromide catalyst that is fast, efficient, selective, and reusable in the /wa-bromination of aromatic substrates.641... 

Rearrangement can also occur after the initial alkylation. The reaction of 2-chloro-2-methylbutane with benzene under Friedel-Crafts conditions is an example of this behavior.30 With relatively mild Friedel-Crafts catalysis such as BF3 or FeCl3, the main... 

The polymerization of tetrahydrofuran is a small and perhaps relatively simple part of the general field of polymerization of cyclic ethers by Friedel Crafts catalysis. The existence of such catalysis has of course been known for a long time (10) but it is only in recent years that the complexity of the reactions has been recognized and an effort made to study them. It is now apparent that the reactions are not only highly complex but vary considerably with the particular catalyst or monomer employed so a good deal of careful research will be required to clarify them. 

The study of cocatalysis in cationic polymerizations is extremely complicated by the fact that Lewis acids can participate in a variety of ill defined reactions (91). Satchell (91, 92) regards the hydrogen exchange reaction between Bronsted acids and aromatics catalyzed by Lewis acids as a prototype for Friedel-Crafts catalysis. He postulates that cocatalytic efficiency is determined by the stability of the complex anion B -f HX + SnCl4 - BH SnCl4Xe. A simple enhancement of conventional acidity by B + HX -> BH Xe as proposed by Plesch (93) and Russel (94) is considered to be unimportant. The stability of the complex and its catalytic activity are determined by the electron density... 

Acybaion. These anhydrides are powerful acylating agents. Thus nonactivated arenes such as benzene arc readily acylatcd without addition of Friedel Crafts catalysis ... 

This chapter presents an alternative to classical Friedel-Crafts catalysis using heterogeneous catalysts such as zeolites, as we believe them to be the ultimate catalyst for the future production of aromatic ketones. After a short introduction to the literature, we focus on catalyst and process issues for different reactions. 

To avoid nuclear chlorination due to Friedel-Crafts catalysis by iron contaminants, benzyl chloride production is carried out in vessels made from pure nickel, or in enamel or borosilicate glass apparatus. The chain reaction takes place with photochemically-produced chlorine radicals, using mercury arc lamps the reaction temperature ranges from 80 to 160 °C. The process is carried out with a chlorine deficiency, so that a high yield of benzyl chloride is achieved with low conversion. The reaction mixture is separated by distillation. 

In the presence of acidic media, organic molecules can undergo a wide range of transformations. The specific case of electrophilic aromatic substitution catalysed by acids, i.e. Friedel-Crafts catalysis, will be discussed at length in a later section. However, the diversity of industrial reactions... 

Palladium chloride dimerizes ethylene at 20-70°C and 1—40 atm to yield butenes vvith 90% selectivity [245]. It has been suggested that this compound initiates the dimerization in the presence of hydrogen chloride by a mechanism analogous to that of Friedel-Crafts catalysis ... 

Gal et al prepared ferrocene-containing polymers by modification of chlorinated PVC and other halogenated polymers using Friedel-Crafts catalysis (reaction 16). Soluble polymers of up to 62% ferrocene content were obtained however, in most cases the substitution is accompanied by dehydrohalogenation. 

Position of infrared band in xanthone complex Basis for ranking Heat evolved on association with oxygenated organic compounds Acylation rates Friedel-Crafts catalysis ... 

Addition compounds of anhydrides and acyl halides have been known for many years (277) and it is surely through their basic interactions with Lewis acids that Friedel-Craft catalysis occurs. 

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