Question

Which of the following amines undergoes acylation reaction?

• A. Ethyldimethylamine
• B. N-Methylaniline
• C. N,N-Dimethylmethanamine
• D. N,N-Dimethylaniline

Hint:

Logic Tip: A quick way to identify amine classes from their IUPAC/common names: if the name has "N,N-di...", it is almost certainly a tertiary amine (assuming the main chain also attaches to N). If it has just one "N-alkyl...", it is a secondary amine.

Answer 1

The Correct Option is B

Concept:
Acylation is the process of introducing an acyl group ($R-C=O$) into a molecule. Amines undergo acylation by reacting with acid chlorides, anhydrides, or esters. For this reaction to occur, the amine must have at least one replaceable hydrogen atom attached to the nitrogen. Therefore, only primary ($1^\circ$) and secondary ($2^\circ$) amines undergo acylation, while tertiary ($3^\circ$) amines do not.
Step 1: Classify each of the given amines.
Let's look at the structure and classification of each option:

• (A) Ethyldimethylamine: $CH_3CH_2-N(CH_3)_2$. The nitrogen is attached to three alkyl groups. It is a tertiary ($3^\circ$) amine.
• (B) N-Methylaniline: $C_6H_5-NH-CH_3$. The nitrogen is attached to a phenyl group, a methyl group, and one hydrogen atom. It is a secondary ($2^\circ$) amine.
• (C) N,N-Dimethylmethanamine (Trimethylamine): $(CH_3)_3N$. The nitrogen is attached to three methyl groups. It is a tertiary ($3^\circ$) amine.
• (D) N,N-Dimethylaniline: $C_6H_5-N(CH_3)_2$. The nitrogen is attached to a phenyl group and two methyl groups. It is a tertiary ($3^\circ$) amine.

Step 2: Identify the amine capable of acylation.
Since tertiary amines lack a hydrogen atom on the nitrogen, they cannot form the stable amide product and instead form an unstable salt that rapidly decomposes back to the reactants. N-Methylaniline is the only secondary amine in the list, possessing a reactive $N-H$ bond. Thus, it will successfully undergo acylation to form an N-acyl derivative (an amide).