Zinc chloride Friedel-Crafts reaction

Friedel-Crafts reaction of ahyl alcohol with benzene or alkylbenzene yields many kinds of products, in which the reaction species and the product ratio depend on the type of catalyst. Zinc chloride is the most effective catalyst for producing ahyl compounds by this reaction (32). 

Further dechlorination may occur with the formation of substituted diphenyhnethanes. If enough aluminum metal is present, the Friedel-Crafts reactions involved may generate considerable heat and smoke and substantial amounts of hydrogen chloride, which reacts with more aluminum metal, rapidly forming AlCl. The addition of an epoxide inhibits the initiation of this reaction by consuming HCl. Alkali, alkaline-earth, magnesium, and zinc metals also present a potential reactivity hazard with chlorinated solvents such as methylene chloride. 

The synthesis of deoxybenzoin from phenacetyl chloride and benzene by the Friedel-Crafts reaction has been described. For symmetrically substituted deoxybenzoins, direct reduction of the readily accessible benzoin is a more convenient method. Reduction of benzoin by zinc dust and acetic acid, and by hydrochloric acid and granulated tin or amalgamated powdered tin has been reported. The present method is based on a publication of the authors. ... 

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 ... 

Zinc chloride exchanged clay catalysts have been reported to be highly active for the Friedel-Crafts alkylation and acylation reactions these are commercially sold by Contract Catalysts under the name Envirocats. These are montmorillonite catalysts modified by ZnCU and FeCli. Some of the reported examples of Friedel-Crafts reactions are given below there are claims that some of the processes are commercially practised. 

There are a number of variations of the Friedel-Crafts reactions that are useful in synthesis. The introduction of chloromethyl substituents is brought about by reaction with formaldehyde in concentrated hydrochloric acid and halide salts, especially zinc chloride.62 The reaction proceeds with benzene and activated derivatives. The reactive electrophile is probably the chloromethylium ion. 

FRIEDEL-CRAFTS REACTION. Aluminum chloride anhydrous, introduced by Friedcl and Crafts, is used as reagent, generally in CS solution to avoid rise in temperature, for the preparation of (I) aryl-alkyl hydrocarbons, (2) di- and triphenylmethane and derivatives, and (3) aryl-alkyl and diaryl ketones, Other chlorides, such as those of zinc, irun(lll), and liniiV), are often effective in certain cases. 

The action of zinc in this case resembles that of anhydrous aluminium chloride in the Friedel-Crafts reaction. Phthalyl chloride here reacts in the s- form (cf. Reaction XX. (6) (vi.)). Both forms have been prepared (A., 392, 245 M., 40, 81). The s- form melts at 15°—16°, the as-at 88°—89°, while both boil at 275° at 720 mms. The s- form is converted into the as- by the action of aluminium chloride, while the reverse change is effected by the action of heat or of hydrogen chloride. (B., 55, 1305.)... 

In practice, zinc chloride was used as the Lewis acid to catalyze the Friedel-Crafts reaction (64% yield). Oxidation of the methyl groups occurs preferentially because the fert-butyl group has no benzylic hydrogens. 

Friedel-Crafts reaction of phthalic anhydride with benzene in the presence of aluminium chloride followed by cyclization under acidic conditions gives anthra-9,10-quinone (Scheme 12.10). Distillation over zinc dust gives anthracene. 

The addition of a chloromethyl ether to olefinic linkages takes place under conditions similar to the Friedel-Crafts reaction and leads to y-chloro ethers. Substitution of zinc chloride for mercuric chloride as catalyst has improved the yields. Allyl chloride and chloromethyl ether react to give a high yield of l-methoxy-3,4-dichlorobutane (98%). ... 

Because of the extensive amount of waste generated in traditional Friedel-Crafts reactions, it is not surprising that this reaction has been studied in RTIL. Early examples included the use of catalytic chloroaluminate ionic liquids. However, the moisture sensitivity of such systems was a drawback. Therefore, water-stable rare-earth Lewis acids, such as Sc(CF3S03)3, have come to be used for these reactions.The same Lewis acid has also been used to catalyse Diels-Alder reactions in RTILs.Interestingly, in this example, the RTIL not only provided a means for recycling the catalyst but also accelerated the rate and improved selectivity. It has also been demonstrated that a moisture stable, Lewis acidic, catalytic ionic liquid could be prepared from choline chloride and zinc dichloride, and that this was an excellent medium for the Diels-Alder reaction. Yields of 90% or more were achieved in reaction times of between 8 min and 5h for a range of dienes and dienophiles. 

It may be synthesized also from benzal chloride and benzene by the Friedel-Craft reaction, or from benzaldehyde and benzene by heating with anhydrous zinc chloride to 2 o°-2jo°. 

Preparation from Phthalic Acid.—In discussing phthalic acid (p. 691) we spoke of the fact that phthalic anhydride or phthalyl chloride with phenol yields phenolphthalein. The reaction takes place in the presence of anhydrous zinc chloride as a dehydrating agent or in the presence of aluminium chloride (Friedel-Craft). Phthalyl chloride being the unsymmetrical compound (p. 692), the two reactions are represented as follows ... 

Surprisingly simple Friedel-Crafts reactions introduce ferrocene units into amphiphiles. For example, 11-bromo-undecanoyl chloride can be added directly to ferrocene in dichloromethane with aluminium chloride as a catalyst. The corresponding (11-bromo-undecanoyl) ferrocene can be isolated via simple recrystallization, and the ketone removed by amalgamated zinc (does not remove the bromide). The bromide can finally be substituted by alcohols and amines to yield ethers and ammonium salts (Scheme 2.13). 

The most important side-chain conversion involves reduction of ketones either by amalgamated zinc and HCl (Clemmensen reduction) or by hydrazine and strong base Wolff-Kishner reduction). This method is important because the necessary ketones are readily available through a modification of the Friedel-Crafts reaction that involves acid chlorides (see Sec. 19.6). Unlike alkylation by the Friedel-Crafts reaction, this method does not involve rearrangement. 

Halomethylation of arenes. Arenes, under catalysis with stannic chloride or zinc bromide, undergo a Friedel-Crafts reaction with these reagents to give halomethylarenes. 

Acridines are an important structural feature of many natural products and medicinally important compounds. They can be produced in a straightforward manner by a Friedel-Crafts reaction, the Bernthsen acridine synthesis, 1 9 which couples diaryl amines (such as diphenylamine) with a carboxylic acid (such as benzoic acid) in the presence of a Lewis acid (zinc chloride, ZnCl2, is a typical reagent). Heating to 260°C (10 h) gave a 48% yield of acridine 317.1 9 ... 

In place of the aluminium chloride used in the Friedel-Crafts reaction, it has been found that some of the chemical changes may be accelerated by the addition of other catalysts to the reaction mixtures. Anhydrous zinc chloride has been used to some extent in this w ay. The following reactions are a partial list of such changes. The part played by the zinc chloride, in the formation of the probable complex intermediate compounds and the equilibria of the latter with various sets of products, is omitted and only the main reactions or changes are shown just as in the Friedel-Crafts reaction. 

It is evident that zinc chloride is almost as universal a catalyst for such reactions as aluminium chloride, and undoubtedly it would be found experimentally that in many of the Friedel-Crafts reactions zinc chloride would answer as well as aluminium chloride. 

Other Catalysts used in Friedel-Crafts Reaction. In addition to aluminium chloride there are a number of other catalysts that are used frequently, such as Ferric chloride [FeClg] Boron trifluoride [BFg] Zinc chloride [ZnCl2] etc. 

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