Question

How would you convert:
i) Ethanoic acid to methanamine? (1)
ii) Aniline to 2,4,6-tribromoaniline? (1)
iii) Aniline to benzene diazonium chloride? (1)
iv) Aniline to phenyl isocyanide? (1)
v) Chlorobenzene to chlorobenzene sulphonic acid? (1)
OR
i) Write four chemical equations for the methods of preparation of aniline. (1+1+1+1)
ii) Write the chemical equation of any one method for the preparation of chlorobenzene. (1)

Hint:

Conversions: use Hofmann degradation (acid→amide→amine, one C less), bromine water for tribromoaniline, cold NaNO2/HCl for diazotisation, CHCl3 + KOH for carbylamine, and fuming H2SO4 for sulphonation. Aniline prep: reduce nitrobenzene (Sn/Fe/HCl or H2/Ni).

Answer 1

Option 1 (Conversions) — reagent-focused explanation:
i) Ethanoic acid → methanamine: The key idea is a one-carbon step-down. Heating ammonium acetate gives acetamide; treating acetamide with bromine in alkali (Hofmann degradation) expels one carbon as carbonate and yields methanamine. Reactions: \(CH_3COOH \xrightarrow{NH_3,\,\Delta} CH_3CONH_2\), then \(CH_3CONH_2 \xrightarrow{Br_2,\,NaOH} CH_3NH_2\).
ii) Aniline → 2,4,6-tribromoaniline: Because the amino group pushes electron density into the ring, bromine water (no catalyst needed) brominates all three activated positions at once: \(C_6H_5NH_2 + 3Br_2 \rightarrow\) 2,4,6-tribromoaniline \(+ 3HBr\).
iii) Aniline → benzene diazonium chloride: Cold nitrous acid, generated in situ from \(NaNO_2\) and dilute \(HCl\), converts the primary aromatic amine to a diazonium salt below 278 K to keep it stable: \(C_6H_5NH_2 \xrightarrow{NaNO_2/HCl,\,273-278\,K} C_6H_5N_2Cl\).
iv) Aniline → phenyl isocyanide: The carbylamine (isocyanide) test; a primary amine with \(CHCl_3\) and alcoholic \(KOH\) gives the foul-smelling isocyanide: \(C_6H_5NH_2 + CHCl_3 + 3KOH \rightarrow C_6H_5NC + 3KCl + 3H_2O\).
v) Chlorobenzene → chlorobenzene sulphonic acid: Electrophilic sulphonation with fuming \(H_2SO_4\) places \(-SO_3H\) chiefly para to the chloro group: \(C_6H_5Cl + H_2SO_4 \rightarrow p\text{-}ClC_6H_4SO_3H + H_2O\).

Option 2 — alternative framing:
i) Four routes to aniline: (a) \(Sn + HCl\) reduction of nitrobenzene; (b) \(Fe + HCl\) reduction of nitrobenzene; (c) \(H_2\) over a Ni/Pd catalyst on nitrobenzene; (d) Hofmann bromamide degradation of benzamide \(C_6H_5CONH_2\). Balanced forms: \(C_6H_5NO_2 + 6[H] \rightarrow C_6H_5NH_2 + 2H_2O\) (routes a-b), \(C_6H_5NO_2 + 3H_2 \rightarrow C_6H_5NH_2 + 2H_2O\) (route c), and \(C_6H_5CONH_2 + Br_2 + 4NaOH \rightarrow C_6H_5NH_2 + 2NaBr + Na_2CO_3 + 2H_2O\) (route d).
ii) Chlorobenzene: Direct halogenation of benzene using a halogen carrier: \[C_6H_6 + Cl_2 \xrightarrow{AlCl_3} C_6H_5Cl + HCl\]