Friedel–Crafts reaction: Difference between revisions

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{{Short description|A type of electrophilic aromatic substitution reaction}}
= Friedel–Crafts Reaction =


The '''Friedel–Crafts reaction''' is a set of reactions developed by [[Charles Friedel]] and [[James Crafts]] in 1877 to attach substituents to an [[aromatic ring]]. These reactions are of two main types: the [[Friedel–Crafts alkylation]] and the [[Friedel–Crafts acylation]]. Both reactions proceed via an [[electrophilic aromatic substitution]] mechanism.
The '''Friedel–Crafts reaction''' is a set of reactions developed by [[Charles Friedel]] and [[James Crafts]] in 1877 to attach substituents to an [[aromatic ring]]. These reactions are of two main types: [[Friedel–Crafts alkylation]] and [[Friedel–Crafts acylation]].


==Friedel–Crafts Alkylation==
== Friedel–Crafts Alkylation ==
[[File:Friedel-Crafts_alkylation.png|thumb|right|300px|General mechanism of Friedel–Crafts alkylation]]
The Friedel–Crafts alkylation involves the introduction of an [[alkyl group]] into an aromatic ring. This is typically achieved by reacting an [[aromatic compound]] with an [[alkyl halide]] in the presence of a [[Lewis acid]] catalyst, such as [[aluminum chloride]] (AlCl_). The reaction proceeds through the formation of a carbocation intermediate, which then acts as the electrophile in the substitution reaction.


===Mechanism===
[[File:Friedel-Crafts_Equation_Overview.svg|thumb|right|Overview of Friedel–Crafts reactions]]
1. '''Formation of the Electrophile:''' The alkyl halide reacts with the Lewis acid to form a complex, generating a carbocation.
2. '''Electrophilic Attack:''' The aromatic ring donates a pair of electrons to the carbocation, forming a sigma complex.
3. '''Deprotonation:''' The sigma complex loses a proton to regenerate the aromaticity of the ring, yielding the alkylated aromatic compound.


===Limitations===
The Friedel–Crafts alkylation involves the alkylation of an aromatic ring with an [[alkyl halide]] using a strong [[Lewis acid]] catalyst such as [[aluminum chloride]] (AlCl₃). This reaction is used to introduce an [[alkyl group]] into an aromatic compound.
- '''Carbocation Rearrangement:''' The carbocation intermediate can undergo rearrangement, leading to unexpected products.
- '''Polyalkylation:''' The product can be more reactive than the starting material, leading to multiple alkylations.


==Friedel–Crafts Acylation==
[[File:Benzene_ethylation.svg|thumb|left|Ethylation of benzene]]
[[File:Friedel-Crafts_acylation.png|thumb|left|300px|General mechanism of Friedel–Crafts acylation]]
The Friedel–Crafts acylation involves the introduction of an [[acyl group]] into an aromatic ring. This is typically achieved by reacting an aromatic compound with an [[acyl chloride]] or [[acid anhydride]] in the presence of a Lewis acid catalyst.


===Mechanism===
=== Mechanism ===
1. '''Formation of the Electrophile:''' The acyl chloride reacts with the Lewis acid to form an acylium ion, which is the active electrophile.
2. '''Electrophilic Attack:''' The aromatic ring attacks the acylium ion, forming a sigma complex.
3. '''Deprotonation:''' The sigma complex loses a proton, restoring the aromaticity and yielding the acylated aromatic compound.


===Advantages===
The mechanism of the Friedel–Crafts alkylation involves the formation of a carbocation intermediate. The Lewis acid catalyst helps to generate the carbocation from the alkyl halide, which then attacks the aromatic ring to form the alkylated product.
- '''No Rearrangement:''' The acylium ion does not rearrange, leading to more predictable products.
- '''Single Substitution:''' The carbonyl group deactivates the ring, preventing further substitution.


==Applications==
[[File:Propylene+C6H6.svg|thumb|right|Reaction of propylene with benzene]]
Friedel–Crafts reactions are widely used in the synthesis of [[pharmaceuticals]], [[dyes]], and [[fragrances]]. They are also employed in the production of [[polystyrene]] and other [[polymers]].
 
=== Limitations ===
 
Friedel–Crafts alkylation has several limitations, including [[carbocation rearrangement]], [[polyalkylation]], and the deactivation of the aromatic ring by electron-withdrawing groups.
 
[[File:Friedel-CraftsAlkylationStericProtection.png|thumb|left|Steric protection in Friedel–Crafts alkylation]]
 
== Friedel–Crafts Acylation ==
 
The Friedel–Crafts acylation involves the acylation of an aromatic ring with an [[acyl chloride]] or [[acid anhydride]] in the presence of a Lewis acid catalyst. This reaction introduces an [[acyl group]] into the aromatic compound.
 
[[File:Friedel-Crafts-acylation-overview.png|thumb|right|Overview of Friedel–Crafts acylation]]
 
=== Mechanism ===
 
The mechanism of Friedel–Crafts acylation involves the formation of an acylium ion, which is a more stable electrophile than a carbocation. The acylium ion attacks the aromatic ring to form the acylated product.
 
=== Advantages ===
 
Friedel–Crafts acylation does not suffer from polyacylation because the acyl group is electron-withdrawing, which deactivates the aromatic ring towards further electrophilic substitution.
 
== Applications ==
 
Friedel–Crafts reactions are widely used in the synthesis of [[aromatic ketones]], [[alkylbenzenes]], and other aromatic compounds. They are important in the production of [[pharmaceuticals]], [[fragrances]], and [[polymers]].
 
[[File:Neophyl_chloride_synthesis.svg|thumb|left|Synthesis of neophyl chloride]]
 
== Related Reactions ==
 
Friedel–Crafts reactions are related to other electrophilic aromatic substitution reactions such as [[nitration]], [[sulfonation]], and [[halogenation]].
 
[[File:Friedel-Crafts-Alkylierung_2.svg|thumb|right|Example of Friedel–Crafts alkylation]]
 
== Related Pages ==


==Related pages==
* [[Electrophilic aromatic substitution]]
* [[Electrophilic aromatic substitution]]
* [[Aromaticity]]
* [[Lewis acid]]
* [[Lewis acid]]
* [[Carbocation]]
* [[Carbocation]]
* [[Aromaticity]]
 
[[File:1,3-Diisopropylbenzene_via_transalkylation.svg|thumb|left|Synthesis of 1,3-diisopropylbenzene via transalkylation]]


[[Category:Organic reactions]]
[[Category:Organic reactions]]
[[Category:Aromatic compounds]]
[[Category:Aromatic compounds]]

Latest revision as of 14:18, 21 February 2025

Friedel–Crafts Reaction[edit]

The Friedel–Crafts reaction is a set of reactions developed by Charles Friedel and James Crafts in 1877 to attach substituents to an aromatic ring. These reactions are of two main types: Friedel–Crafts alkylation and Friedel–Crafts acylation.

Friedel–Crafts Alkylation[edit]

Overview of Friedel–Crafts reactions

The Friedel–Crafts alkylation involves the alkylation of an aromatic ring with an alkyl halide using a strong Lewis acid catalyst such as aluminum chloride (AlCl₃). This reaction is used to introduce an alkyl group into an aromatic compound.

Ethylation of benzene

Mechanism[edit]

The mechanism of the Friedel–Crafts alkylation involves the formation of a carbocation intermediate. The Lewis acid catalyst helps to generate the carbocation from the alkyl halide, which then attacks the aromatic ring to form the alkylated product.

Reaction of propylene with benzene

Limitations[edit]

Friedel–Crafts alkylation has several limitations, including carbocation rearrangement, polyalkylation, and the deactivation of the aromatic ring by electron-withdrawing groups.

Steric protection in Friedel–Crafts alkylation

Friedel–Crafts Acylation[edit]

The Friedel–Crafts acylation involves the acylation of an aromatic ring with an acyl chloride or acid anhydride in the presence of a Lewis acid catalyst. This reaction introduces an acyl group into the aromatic compound.

Overview of Friedel–Crafts acylation

Mechanism[edit]

The mechanism of Friedel–Crafts acylation involves the formation of an acylium ion, which is a more stable electrophile than a carbocation. The acylium ion attacks the aromatic ring to form the acylated product.

Advantages[edit]

Friedel–Crafts acylation does not suffer from polyacylation because the acyl group is electron-withdrawing, which deactivates the aromatic ring towards further electrophilic substitution.

Applications[edit]

Friedel–Crafts reactions are widely used in the synthesis of aromatic ketones, alkylbenzenes, and other aromatic compounds. They are important in the production of pharmaceuticals, fragrances, and polymers.

Synthesis of neophyl chloride

Related Reactions[edit]

Friedel–Crafts reactions are related to other electrophilic aromatic substitution reactions such as nitration, sulfonation, and halogenation.

Example of Friedel–Crafts alkylation

Related Pages[edit]

Synthesis of 1,3-diisopropylbenzene via transalkylation
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