The primary amine is obtained by reduction of -NO2 group using scrap iron and HCl (in small amounts) because:
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → FeCl2 formed gets hydrolysed to release hydrochloric acid during the reaction.
Nitro compounds are reduced to primary amines by metals in acid, such as Sn/HCl or Fe/HCl. With iron, the reducing hydrogen is produced as iron reacts with HCl:
\( \displaystyle \ce{C6H5NO2 + 3Fe + 6HCl -> C6H5NH2 + 3FeCl2 + 2H2O} \)
The FeCl2 formed is hydrolysed:
\( \displaystyle \ce{FeCl2 + 2H2O -> Fe(OH)2 + 2HCl} \)
Why the other options are incorrect
Option (2) HCl forms nascent hydrogen and FeCl3 which on hydrolysis regenerates HCl during the reaction — Incorrect. Iron reacts with HCl to give FeCl2 (iron(II)), not \( \ce{FeCl3} \).
Option (3) Scrap iron is readily available and can be used for this reaction to avoid its presence and minimize its hazardous environmental effects — Incorrect. Using scrap iron does recycle waste, but it does not explain why only a small amount of HCl is enough; the acid is regenerated by hydrolysis of FeCl2.
Option (4) Other reducing agents are very expensive compared to scrap Fe/HCl — Incorrect. Cost does not explain why a small amount of HCl is enough; the acid is given back as the FeCl2 is hydrolysed: \( \ce{FeCl2 + 2H2O -> Fe(OH)2 + 2HCl} \)
NCERT (2026-27 edition):
Reduction of Nitro Compounds – …
