Question

Write the reaction involved in the following:

Friedel-Crafts acylation of anisole

Hint:

In Friedel-Crafts acylation an acyl group (\(-COR\)) is introduced into an aromatic ring using an acid chloride and anhydrous \(AlCl_3\).

Answer 1

Step 1: Aim of the reaction.
Friedel-Crafts acylation puts an acyl group \((-COR)\) onto an aromatic ring. With anisole \((C_6H_5OCH_3)\), an acetyl group can be added to the ring.

Step 2: Reagents used.
Anisole is treated with an acid chloride such as acetyl chloride \((CH_3COCl)\) in the presence of anhydrous aluminium chloride \((AlCl_3)\), which acts as the Lewis acid catalyst.

Step 3: Generation of the electrophile.
\(AlCl_3\) pulls a chloride from acetyl chloride to make the acylium ion \((CH_3CO^+)\), which is the electrophile that attacks the ring.

Step 4: Directing effect of OCH3.
The methoxy \((-OCH_3)\) group donates electrons and is ortho/para directing. Because the ortho position is crowded near the bulky \(-OCH_3\), the acyl group goes mainly to the para position.

Step 5: Product formed.
The main product is para-methoxyacetophenone (4-methoxyacetophenone).

Step 6: Overall reaction.
\[ C_6H_5OCH_3 + CH_3COCl \xrightarrow{\text{anhyd. } AlCl_3} p\text{-}CH_3O\text{-}C_6H_4\text{-}COCH_3 + HCl \]

Answer: Anisole reacts with acetyl chloride in the presence of anhydrous \(AlCl_3\) to give mainly para-methoxyacetophenone (4-methoxyacetophenone), with HCl as the by-product.