Question: Draw a stepwise mechanism for the following reaction.

Acyl chlorides are derivatives of carboxylic acids. They are also called acid chlorides.

Acid chlorides are formed when the hydroxyl group of an acid is replaced with a chloride group.

These compounds are highly reactive to nucleophiles.

The oxygen atom and chlorine atom are electron-withdrawing groups. Therefore, the carbon atom is easily attacked by nucleophiles.

This causes the replacement of chloride with the nucleophile.

Acid chlorides react with amines to form amides.

The reaction mechanism has mainly three steps:

• Amine being a nucleophile, reacts with electrophilic carbon of acid chloride.
• The chloride is removed from the adduct forming a cation
• A nitrogen base removes the proton to form amide and quarternium salt of the base.

The reaction can be carried out using two amine equivalents or one equivalent of amine and pyridine.

In some reactions, the removal of hydrogen precedes the removal of chloride from the adduct.

In the given reaction, benzoyl chloride reacts with hydrazine to form benzamide and pyridinium chloride.

In the first step of the reaction, the nitrogen atom of hydrazine attacks the electrophilic carbon of benzoyl chloride to form an adduct with positively charged nitrogen and negatively charged oxygen.

In the next step, pyridine abstracts hydrogen from the nitrogen atom in the adduct, forming a pyridinium ion.

Chloride is removed from the adduct to form benzamide.

The chloride ion forms pyridinium chloride with the pyridinium ion.

The final products of the reaction are benzamide and pyridinium chloride.

Mechanism of reaction of benzoyl chloride with hydrazine