CBSE Class 12 Chemistry 2023: question 24

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Step-by-step solution

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1. (a) Carbylamine reaction: A primary amine (aliphatic or aromatic) is heated with chloroform and ethanolic KOH. It forms an isocyanide (carbylamine), which has a very foul smell. Secondary and tertiary amines do not give this test.
   $\mathrm{R}-\mathrm{N}{\mathrm{H}}_2+\mathrm{CHC}{\mathrm{l}}_3+3KOH\stackrel{\mathrm{\Delta }}{\to }\mathrm{R}-\mathrm{NC}+3KCl+3{\mathrm{H}}_2\mathrm{O}$

   1 mark

2. (b) Gabriel phthalimide synthesis:

   • Phthalimide is treated with ethanolic KOH to form potassium phthalimide.
   • Heating this salt with an alkyl halide gives N-alkylphthalimide.
   • Alkaline hydrolysis of N-alkylphthalimide gives a pure primary amine and sodium phthalate.

   ${\mathrm{C}}_6{\mathrm{H}}_4(\mathrm{CO}{)}_2\mathrm{NH}\stackrel{\mathrm{KOH}(\mathrm{alc})}{\to }{\mathrm{C}}_6{\mathrm{H}}_4(\mathrm{CO}{)}_2{\mathrm{N}}^{-}{\mathrm{K}}^{+}\stackrel{\mathrm{R}-\mathrm{X}}{\to }{\mathrm{C}}_6{\mathrm{H}}_4(\mathrm{CO}{)}_2\mathrm{N}-\mathrm{R}\stackrel{\mathrm{NaOH}(\mathrm{aq})}{\to }\mathrm{R}-\mathrm{N}{\mathrm{H}}_2+{\mathrm{C}}_6{\mathrm{H}}_4(\mathrm{COONa}{)}_2$

   1 mark

Answer: (a) RNH₂ + CHCl₃ + 3KOH → RNC (foul smell); (b) phthalimide → K-phthalimide → N-alkylphthalimide → RNH₂ (1° amine)

Revise the chapter

• Chapter: Amines (notes, formulas, where marks are lost and every past question)