Animated Solution for Chemistry - Organic Chemistry: Which of the following reaction is an example of ammonolysis?

Ammonolysis

When you encounter a term like ammonolysis in organic chemistry, the best approach is to break it down into its roots. The word is a combination of "ammono," referring to the ammonia molecule ($\mathrm{N}{\mathrm{H}}_3$), and "lysis," which means cleavage or breaking.

Therefore, ammonolysis is a reaction where an ammonia molecule acts as a nucleophile to cleave a specific bond—most commonly, a carbon-halogen ($\mathrm{C}-\mathrm{X}$) bond in an alkyl or benzyl halide.

Let's evaluate each given reaction to see which one fits our definition perfectly.

Option A: Acylation In this reaction, benzoyl chloride reacts with aniline. The amine acts as a nucleophile, attacking the carbonyl carbon and displacing the chloride ion. This is a classic acylation reaction (specifically, the Schotten-Baumann reaction). Since ammonia is not involved, this is not ammonolysis.

Option B: Reduction Here, benzyl cyanide is treated with a reducing agent to form 2-phenylethanamine. This is a straightforward reduction of a nitrile group to a primary amine. No bonds are being cleaved by ammonia.

Option C: Acid-Base Neutralization Aniline is a base, and hydrochloric acid is an acid. When they react, they undergo a simple acid-base neutralization to form anilinium chloride, a salt. There is no cleavage of a carbon-halogen bond here.

Ammonolysis in Action

Option D: The Correct Answer This reaction features benzyl chloride reacting with ammonia. Let's dive into the mechanism to see exactly why this is our winner.

The nitrogen atom in the ammonia molecule possesses a lone pair of electrons, making it an excellent nucleophile. It seeks out the slightly positive (electrophilic) benzylic carbon atom.

As the ammonia molecule attacks the benzylic carbon, the carbon-chlorine bond begins to break simultaneously. This is a classic ${\mathrm{S}}_{\mathrm{N}}2$ (Substitution Nucleophilic Bimolecular) mechanism. The chloride ion ($\mathrm{C}{\mathrm{l}}^{-}$) acts as the leaving group.

The initial attack forms a protonated amine intermediate (${\mathrm{C}}_6{\mathrm{H}}_5\mathrm{C}{\mathrm{H}}_2\stackrel{+}{\mathrm{N}}{\mathrm{H}}_3$). To regain neutrality, this intermediate quickly loses a proton to another ammonia molecule (or the chloride ion), yielding the final product: benzylamine (${\mathrm{C}}_6{\mathrm{H}}_5\mathrm{C}{\mathrm{H}}_2\mathrm{N}{\mathrm{H}}_2$).

Because the ammonia molecule was directly responsible for the cleavage of the carbon-halogen bond, this reaction is the perfect textbook example of ammonolysis.