The correct sequence of reagents to carry out the following conversion is:
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → (i) $Conc.HNO_3/Conc.H_2SO_4$ (ii) $Sn/HCl$ (iii) $DIBAL-H$ (iv) $NaNO_2/HCl$ (v) $HBF_4$
Initial compound: Benzonitrile ($-CN$)
Target compound: m-Fluorobenzaldehyde
Step 1: Nitration
$-CN$ is strongly electron-withdrawing and meta directing. Treatment with Conc. $HNO_3$ / Conc. $H_2SO_4$ gives m-nitrobenzonitrile.
Step 2: Reduction
Reduce $-NO_2$ to $-NH_2$ using $Sn/HCl$.
Step 3: Reduction of nitrile to aldehyde
DIBAL-H selectively reduces $-CN$ to $-CHO$.
Gives m-aminobenzaldehyde.
Step 4: Diazotization
Treat $-NH_2$ with $NaNO_2 / HCl$ at low temperature.
Forms diazonium salt.
Step 5: Balz–Schiemann reaction
Treat diazonium salt with $HBF_4$.
Fluorine replaces diazonium group.
Final product: m-Fluorobenzaldehyde.
