Identify the set of reagents (X) in the given reaction sequence
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Fluoroboric acid ($\text{HBF}_4$) is widely used to prepare stable, isolable diazonium fluoroborates.
This salt can either be heated alone to form fluorobenzene (Schiemann reaction) or heated with $\text{NaNO}_2/\text{Cu}$ to form nitrobenzene.
(i) $\text{HBF}_4$ ; (ii) $\text{Conc. }\text{HNO}_3 + \text{H}_2\text{SO}_4$
(i) $\text{HBF}_4$ ; (ii) $\text{NaNO}_2$, $\text{Cu}, \Delta$
(i) $\text{BF}_3$ ; (ii) $\text{NaNO}_2$, $\text{Cu}, \Delta$
(i) $\text{H}_2\text{O}, 283\text{ K}$ ; (ii) $\text{Conc. }\text{HNO}_3$
Show Solution
The Correct Option isB
Solution and Explanation
Step 1: Form the diazonium salt. Aniline with $\text{NaNO}_2$/HCl at low temperature gives benzenediazonium chloride. Step 2: Stabilise it as the fluoroborate salt. Treating the diazonium salt with $\text{HBF}_4$ precipitates the more stable fluoroborate form, the same trick used before a Balz-Schiemann fluorination. Step 3: Swap in a nitro group instead of fluorine. Instead of just heating this salt alone (which would give fluorobenzene), heating it together with $\text{NaNO}_2$ and copper powder replaces the diazonium group with a $-\text{NO}_2$ group, giving nitrobenzene directly. Step 4: State the reagent set. So X is (i) $\text{HBF}_4$, (ii) $\text{NaNO}_2$, Cu, heat. Final answer: Option 2.
