Q.(i) Convert aniline to fluorobenzene. (1 mark)

Fluorobenzene is made from aniline by diazotisation followed by the Balz-Schiemann reaction; the nitrobenzene sequence demonstrates the step-wise partial reduction of a nitro group (NO2 → NHOH → NO) alongside selective mono-reduction of a dinitro compound.

1. Aniline to fluorobenzene: $C_6H_5NH_2 \xrightarrow{NaNO_2/HCl,\ 0\text{-}5^\circ C} C_6H_5N_2^+Cl^- \xrightarrow{HBF_4} C_6H_5N_2^+BF_4^- \xrightarrow{\Delta} C_6H_5F + N_2\uparrow + BF_3$ This is the Balz-Schiemann reaction: aniline is first diazotised, the diazonium salt is converted to its fluoroborate, and gentle heating (thermal decomposition) releases fluorobenzene, N2 and BF3.
2. Nitrobenzene sequence:

• Nitrobenzene $\xrightarrow{conc.\ HNO_3/conc.\ H_2SO_4,\ 100^\circ C}$ A = m-dinitrobenzene (the NO2 group is meta-directing, so the second nitro group enters meta to the first).
• A $\xrightarrow{NaSH}$ B = m-nitroaniline: NaSH (or ammonium sulphide) is a classical mild/selective reducing agent that reduces only ONE of the two nitro groups of m-dinitrobenzene to an amino group. …