Question

explain the mechanism of friedel - Craft's alkylation or acylation of benzene​

Answer 1

Answer:

Friedel-Crafts Alkylation refers to the replacement of an aromatic proton with an alkyl group. This is done through an electrophilic attack on the aromatic ring with the help of a carbocation. The Friedel-Crafts alkylation reaction is a method of generating alkylbenzenes by using alkyl halides as reactants.

Explanation:

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Answer 2

Friedel - Craft's alkylation :

Benzene reacts with an alkyl halide in presence of anhydrous aluminium chlorine to give alkyl benzene.

Friedel - Craft's acylation :

The reaction of benzene with an acyl halide or acid anhydride in presence of Lewis acid as catalyst to give acyl benzene.

$\sf C_6H_6 + CH_3COCl \xrightarrow{anh. AlCl_3} C_6H_5 - CH_3 + HCl$

$\sf C_6H_6 + CH_3COCl \xrightarrow {anh. AlCl_3(\Delta)} C_6H_5 - CH_3 + HCl$

Mechanism :

1st step : Formation of electrophilie

• During alkylation and acylation of benzene the Lewis acid anhy AlCl₃ help to generate electrophilie like R+ or RCO+

$\sf CH_3 - Cl + AlCl_3 \to CH_3 + [AlCl_4]^-$

$\sf CH_3CO - Cl + AlCl_3 \to CH_3CO + [AlCl_4]^-$

2nd step : Formation of Carbonation

• The electrophilie attacks benzene ring to form σ complex which contains as sp³ hybridized carbon. The Carbonation is stabilized by resonance.

[Refer fig - 1 from the attachment ]

3rd step : Removal of proton

• The σ complex loses a proton from so³ carbon to restore aromatic character on attack of [AlCl₄]¯

[Refer fig - 2 from the attachment]