Question

Write the reaction involved in Friedel-Crafts acylation of anisole.

Hint:

Para-substituted products are almost always the major products in electrophilic substitution of bulky or activated rings due to steric reasons.

Answer 1

Step 1: Conceptual Overview:
Friedel-Crafts acylation is a method to introduce an acyl group (\( RCO- \)) into a benzene ring. This reaction typically uses an acid chloride and a Lewis acid catalyst to achieve the substitution.
Step 2: Detailed Explanation:
Anisole (\( C_6H_5OCH_3 \)) is an activated aromatic ether, and the methoxy group (\( -OCH_3 \)) is an electron-donating group that makes the benzene ring more reactive towards electrophilic aromatic substitution. The methoxy group is also ortho-para directing, meaning it facilitates substitution at the ortho and para positions on the benzene ring.
When anisole reacts with acetyl chloride (\( CH_3COCl \)) in the presence of anhydrous aluminum chloride (\( AlCl_3 \)), an electrophilic aromatic substitution occurs, forming a mixture of ortho and para products. However, the para-isomer, 4-Methoxyacetophenone, is the major product because it experiences less steric hindrance compared to the ortho-isomer.
The chemical equation for this reaction is as follows:
\[ C_6H_5OCH_3 + CH_3COCl \xrightarrow{\text{anh. } AlCl_3} \text{p-}CH_3OC_6H_4COCH_3 + HCl \]
Step 3: Final Conclusion:
The major product of the Friedel-Crafts acylation of anisole with acetyl chloride is 4-Methoxyacetophenone.