Why is the Gabriel phthalimide synthesis specifically restricted to the preparation of primary aliphatic amines and cannot be used to synthesize aniline (primary aromatic amine)?

Answer and explanation

Correct answer: A. Aryl halides resist nucleophilic substitution with phthalimide anion due to partial C-X double bond

  1. Step 1: In Gabriel phthalimide synthesis, phthalimide is deprotonated by ethanolic to generate the nucleophilic phthalimide anion.
  2. Step 2: The anion attacks an alkyl halide in an displacement to form an N-alkylphthalimide, which is then hydrolyzed with aqueous to yield a primary aliphatic amine () and sodium phthalate.
  3. Step 3: To prepare aromatic amines like aniline, one would need to use an aryl halide (, e.g., chlorobenzene).
  4. Step 4: However, aryl halides do not undergo nucleophilic aromatic substitution with phthalimide anion because the lone pair on the halogen is delocalized into the benzene ring, imparting partial double-bond character to the bond and creating electrostatic repulsion from the benzene -electron cloud.
Answer
Aryl halides do not undergo nucleophilic substitution with the phthalimide anion under normal conditions due to partial double-bond character of the C-X bond
Why not the others: 'Aniline is a gas...' is false; aniline is an oily liquid (bp 184°C); 'Phthalimide reacts with aniline to form an insoluble polymer...' does not represent the synthetic bottleneck; 'Potassium phthalimide is insoluble...' is false since reactions are carried out in DMF or ethanol.

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