Identify A and B in the following reaction sequence. [figure]
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Answer
(3) [figure]
Solution
[figure]
Conc. HNO3: –Br is o, p-directing ⇒ –NO2 enters C-2, C-4, C-6 ⇒ A = 1-bromo-2,4,6-trinitrobenzene
∵ three –NO2 (–R) at o/p make the C–Br carbon electron-poor ⇒ OH- easily replaces Br (aromatic nucleophilic substitution) ⇒ sodium picrate
(ii) HCl ⇒ B = 2,4,6-trinitrophenol (picric acid)
(1): Br is not lost on nitration ⇒ (1) is wrong
(2), (4): NaOH replaces Br, so B cannot keep Br ⇒ (2), (4) are wrong
(3): A and B exactly as above ⇒ (3) is correct
Answer: (3)