Why does aniline fail to undergo Friedel-Crafts alkylation or acylation reactions when treated with alkyl or acyl halides in the presence of anhydrous aluminum chloride (AlCl3)?

Answer and explanation

Correct answer: C. Aniline forms a Lewis adduct with AlCl3 that places positive charge on N and deactivates the ring

  1. Step 1: Aniline possesses an unshared lone pair of electrons on its nitrogen atom, functioning as an active Lewis base.
  2. Step 2: Anhydrous aluminum chloride () is a potent Lewis acid possessing an incomplete octet.
  3. Step 3: Instead of acting as a catalyst to generate electrophilic carbocations from alkyl halides, reacts immediately with aniline in a Lewis acid-base neutralization to form a complex adduct: .
  4. Step 4: The resulting positive charge on nitrogen exerts a powerful deactivating effect on the benzene ring, completely shutting down electrophilic aromatic substitution.
Answer
Aniline is a Lewis base that coordinates with the Lewis acid catalyst AlCl3 to form an adduct salt, imparting a strong positive charge to nitrogen that heavily deactivates the aromatic ring
Why not the others: 'Aniline completely oxidizes AlCl3...' is false because cannot be reduced by aniline; 'The benzene ring in aniline is too electron-deficient...' is false because free aniline is highly electron-rich; 'Friedel-Crafts occurs only on saturated heterocyclic amines...' is the opposite of reality.

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