Chapter 9 Solutions — Amines

Exercises

1. 1.
   Write IUPAC names of the following compounds and classify them into primary, secondary and tertiary amines:

   • (i) (CH₃)₂CHNH₂
   • (ii) CH₃(CH₂)₂NH₂
   • (iii) CH₃NHCH(CH₃)₂
   • (iv) (CH₃)₃CNH₂
   • (v) C₆H₅NHCH₃
   • (vi) (CH₃CH₂)₂NCH₃
   • (vii) m-BrC₆H₄NH₂
2. 2.
   Give one chemical test to distinguish between the following pairs of compounds:

   • (i) Methylamine and dimethylamine
   • (ii) Secondary and tertiary amines
   • (iii) Ethylamine and aniline
   • (iv) Aniline and benzylamine
   • (v) Aniline and N-methylaniline.
3. 3.
   Account for the following:

   • (i) pKb of aniline is more than that of methylamine.
   • (ii) Ethylamine is soluble in water whereas aniline is not.
   • (iii) Methylamine in water reacts with ferric chloride to precipitate hydrated ferric oxide.
   • (iv) Although amino group is o- and p-directing in aromatic electrophilic substitution reactions, aniline on nitration gives a substantial amount of m-nitroaniline…
4. 4.
   Arrange the following:

   • (i) In decreasing order of the pKb values: C₂H₅NH₂, C₆H₅NHCH₃, (C₂H₅)₂NH and C₆H₅NH₂.
   • (ii) In increasing order of basic strength: C₆H₅NH₂, C₆H₅N(CH₃)₂, (C₂H₅)₂NH and CH₃NH₂.
   • (iii) In increasing order of basic strength:
   • (a) Aniline, p-nitroaniline and p-toluidine;
   • (b) C₆H₅NH₂, C₆H₅NHCH₃, C₆H₅CH₂NH₂.
   • (iv) In decreasing order of basic strength in gas phase: C₂H₅NH₂…
5. 5.
   How will you convert:

   • (i) Ethanoic acid into methanamine
   • (ii) Hexanenitrile into 1-aminopentane
   • (iii) Methanol to ethanoic acid
   • (iv) Ethanamine into methanamine
   • (v) Ethanoic acid into propanoic acid
   • (vi) Methanamine into ethanamine
   • (vii) Nitromethane into dimethylamine
   • (viii) Propanoic acid into ethanoic acid?
6. 6.
   Describe a method for the identification of primary, secondary and tertiary amines. Also write chemical equations of the reactions involved.
7. 7.
   Write short notes on the following:

   • (i) Carbylamine reaction
   • (ii) Diazotisation
   • (iii) Hofmann's bromamide reaction
   • (iv) Coupling reaction
   • (v) Ammonolysis
   • (vi) Acetylation
   • (vii) Gabriel phthalimide synthesis.
8. 8.
   Accomplish the following conversions:

   • (i) Nitrobenzene to benzoic acid
   • (ii) Benzene to m-bromophenol
   • (iii) Benzoic acid to aniline
   • (iv) Aniline to 2,4,6-tribromofluorobenzene
   • (v) Benzyl chloride to 2-phenylethanamine
   • (vi) Chlorobenzene to p-chloroaniline
   • (vii) Aniline to p-bromoaniline
   • (viii) Benzamide to toluene
   • (ix) Aniline to benzyl alcohol.
9. 9.
   Give the structures of A, B and C in the following reactions:

   • (i) CH₃CH₂I -(NaCN)-> A -(OH⁻, partial hydrolysis)-> B -(NaOH + Br₂)-> C
   • (ii) C₆H₅N₂Cl -(CuCN)-> A -(H₂O/H⁺)-> B -(NH₃)-> C
   • (iii) CH₃CH₂Br -(KCN)-> A -(LiAlH₄)-> B -(HNO₂, 0 C)-> C
   • (iv) C₆H₅NO₂ -(Fe/HCl)-> A -(NaNO₂/HCl, 273 K)-> B -(H₂O/H⁺)-> C
   • (v) CH₃COOH -(NH₃)-> A -(NaOBr)-> B -(NaNO₂/HCl)-> C
   • (vi) C₆H₅NO₂ -(Fe/HCl)-> A -(HNO₂…
10. 10.
    An aromatic compound 'A' on treatment with aqueous ammonia and heating forms compound 'B' which on heating with Br₂ and KOH forms a compound 'C' of molecular formula C₆H₇N. Write the structures and IUPAC names of compounds A, B and C.
11. 11.
    Complete the following reactions:

    • (i) C₆H₅NH₂ + CHCl₃ + alc. KOH ->
    • (ii) C₆H₅N₂Cl + H₃PO₂ + H₂O ->
    • (iii) C₆H₅NH₂ + H₂SO₄ (conc.) ->
    • (iv) C₆H₅N₂Cl + C₂H₅OH ->
    • (v) C₆H₅NH₂ + Br₂(aq) ->
    • (vi) C₆H₅NH₂ + (CH₃CO)₂O ->
    • (vii) C₆H₅N₂Cl -(i) HBF₄
    • (ii) NaNO₂/Cu, heat->
12. 12.
    Why cannot aromatic primary amines be prepared by Gabriel phthalimide synthesis?
13. 13.
    Write the reactions of

    • (i) aromatic and
    • (ii) aliphatic primary amines with nitrous acid.
14. 14.
    Give plausible explanation for each of the following:

    • (i) Why are amines less acidic than alcohols of comparable molecular masses?
    • (ii) Why do primary amines have higher boiling point than tertiary amines?
    • (iii) Why are aliphatic amines stronger bases than aromatic amines?