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Home > News & Articles > Friedel Crafts Acylation Reaction: Definition, Examples, Benzene, Mechanism, Applications, and Limitations
Updated on 01st July, 2023 , 4 min read
A Friedel-Crafts reaction is an organic coupling reaction that attaches different substituents to aromatic rings by using an electrophilic aromatic substitution. Electrophilic aromatic substitution occurs in each of these processes.
A Friedel-Crafts reaction is a type of organic coupling reaction that uses an electrophilic aromatic substitution to attach substituents to aromatic rings. The French scientist Charles Friedel and the American chemist James Crafts invented these reactions in 1877. The electrophilic aromatic substitution of an aromatic substance is the Friedel-Crafts reaction. In the Friedel-Crafts reaction, the aromatic molecule undergoes an electrophilic substitution. The hydrogen atom in the benzene is substituted with an electrophile in the presence of a Lewis acid such as anhydrous aluminum chloride. Friedel-Crafts reactions are classified into two types-
As with the F.C. alkylation, the specific Lewis acid in the Friedel-Crafts acylation can vary. Aluminum chloride (AlCl₃)is often used, butFeCl₃and other Lewis acids will also do the job.
Friedel and Crafts discovered Friedel-Crafts acylation, a technique related to Friedel-Crafts alkylation, at the same time (1877). When a Lewis acid is introduced to an acyl halide in the presence of an aromatic ring, an electrophilic aromatic substitution reaction occurs in which the acyl group attaches to the aromatic ring (with HX loss).
The Friedel-Crafts reactions were invented in 1877 by Charles Friedel and James Crafts to attach substituents to aromatic rings. There are two types of Friedel-Crafts reactions: alkylation reactions and acylation processes. Both are accomplished by electrophilic aromatic substitution.
The acylation reaction of Friedel-Crafts is analogous to the alkylation reaction. The sole difference is that, unlike the alkylation process, the Friedel-Crafts acylation reaction results in the creation of a ketone. The Friedel-Crafts acylation procedure is applicable to a wide range of aromatic chemicals. However, if the reactant is alcohol or amine, the oxygen and nitrogen atoms are acylated. The Friedel acylation reaction can be summarized as follows-
The Friedel-Crafts process may be used to acylate a variety of aromatic substances. When an alcohol or an amine is used as the reactant, the oxygen and nitrogen atoms are acylated.
When benzene is treated with an acyl halide in the presence of Lewis acid, it creates acyl benzene. Friedel Craft's acylation reaction is what this is.
The following table gives details about the Friedel Crafts Acylation reaction-
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Friedel Crafts Acylation Reaction |
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|
Named After |
Charles Friedel James Crafts |
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Reaction Type |
Coupling reaction |
|
Reaction |
|
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Aromatic Ring + Alkyl Halide, Alcohol, Alkene, or Alkyne ↓ Coupling Product |
|
|
Conditions |
|
|
Catalyst |
Strong Lewis acid: Zeolite, AlCl3 |
The Friedel-Crafts Acylation reaction mechanism is depicted in the stages below-
The anhydrous aluminum chloride combines with the acyl halide to create the acylium ion. The generated acylium ion is stabilized via resonance.
The aromatic ring is attacked by the acylium ion generated by the interaction of Lewis acid and an acyl halide. An intermediate is generated when it attacks the aromatic ring. Because the carbon-carbon double bond breaks, the aromatic ring loses its aromaticity.
The intermediate complex is deprotonated, which means it loses one proton. The aromatic ring's carbon-carbon double bond is repaired, restoring the ring's aromaticity. The proton produced by deprotonation is used to renew the aluminum chloride catalyst. The Friedel-Crafts Acylation process has the following typical reactivity order:
The following are some of the applications of Friedel Craft's acylation reaction-
The following are some of the limitations of Friedel Craft's acylation reaction-
In the Friedel craft reaction, acylation is favored over alkylation. Because the acyl group is an electron-withdrawing group in acylation, it reduces the electron density, so further electrophilic substitution is prohibited. Because the carbon chain of acyl halide does not rearrange, isomeric ketone compounds cannot be formed. In contrast, in alkylation, the methyl group acts as an electron donor, increasing the electron density and electrophilic reactivity of the substrate. As a result, poly alkylation occurs rather than mono alkylation.
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By - Nikita Parmar 2023-08-25 09:48:44 , 11 min readAns. There are various advantages to Friedel Craft’s acylation over Friedel Craft Alkylation. These benefits include enhanced control over the reaction products and the acylium cation being stabilized by resonance, which eliminates the possibility of rearrangement. The ketones produced can be converted to alkyl groups by Clemmensen reduction.
Ans. In the first stage of the reaction, a carbocation is generated, which undergoes rearrangement (if feasible) to form a more stable carbocation, however, rearrangement of the carbocation is not possible in the presence of weak Lewis acid.
Ans. In 1877, Friedel and Craft discovered that a haloalkane reacts with benzene in the presence of an aluminum halide. Friedel Crafts acylation is preferred over Friedel Crafts alkylation because it contains oxygen with a double bond in addition to R, resulting in a decrease in electron density. However, in Friedel craft alkylation, there is a +I effect that causes the electron density of the benzene to increase.
Ans. An alkyl group can be added to a benzene molecule by an electrophilic aromatic substitution process known as the Friedel-Crafts alkylation reaction. One example is the insertion of a methyl group into a benzene ring. The electron of the benzene ring attacks the electrophile to generate a nonaromatic carbocation.
Ans. An example of an electrophilic substitution reaction is the Friedel-Crafts reaction.
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