2003 AIPMT AminesProtection of Amino Group and Bromination Hard Question 57 of 61 in Amines

The final product C, obtained in this reaction, would be :

The final product C, obtained in this reaction, would be :
A -
B -
C -
D -

The answer is C.

Solution

Step 1 (A): acetic anhydride acetylates the $-NH_2$ group of p-toluidine, giving p-methylacetanilide, $p-CH_3C_6H_4NHCOCH_3$. This protects the amino group and reduces its strong activating effect, so that only monobromination occurs.
Step 2 (B): bromine in acetic acid substitutes on the ring. The $-NHCOCH_3$ group is ortho/para directing; the para position is occupied by $CH_3$, so Br enters ortho to $-NHCOCH_3$, giving 2-bromo-4-methylacetanilide.
Step 3 (C): acid hydrolysis removes the acetyl group and frees the amino group:
$2-Br-4-CH_3C_6H_3NHCOCH_3 + H_2O \xrightarrow{H^+} 2-Br-4-CH_3C_6H_3NH_2 + CH_3COOH$
So C is 2-bromo-4-methylaniline: $NH_2$ on the ring, Br ortho to it and $CH_3$ para to it. (B, the acetamide, is the intermediate before hydrolysis.)

Concept Acetylation to control bromination of aniline

Amines in past papers

61 questions from this chapter have appeared across 27 exam years.