Ammonolysis of alkyl halidesऐल्किल हैलाइडों का अमोनी-अपघटनAmmonolysis of alkyl halides

Class 12 Chemistry · Chapter 9 · interactive diagram

Parts and what they mean

• R–X + NH₃ → R–N⁺H₃X⁻ (R–X + NH₃ → R–N⁺H₃X⁻) — The C–X bond is cleaved by the NH₃ molecule (ammonolysis), carried out with ethanolic NH₃ in a sealed tube at 373 K.
• Substituted ammonium salt (प्रतिस्थापित अमोनियम लवण) — The amine first appears as its salt R–N⁺H₃X⁻.
• Primary amine (प्राथमिक ऐमीन) — Major product when a large excess of NH₃ is used.
• Secondary amine (द्वितीयक ऐमीन) — Formed when R–NH₂ attacks another R–X.
• Tertiary amine (तृतीयक ऐमीन) — Formed from the 2° amine + R–X.
• Quaternary ammonium salt (चतुष्क अमोनियम लवण) — Final product; N has four C groups and no lone pair, so no further alkylation.
• + R–X (further alkylation) (+ R–X (आगे ऐल्किलन)) — This is the disadvantage of ammonolysis: a mixture of 1°, 2°, 3° amines and the quaternary salt.
• Freeing the amine with a strong base (प्रबल क्षारक से ऐमीन मुक्त करना) — The salt treated with a strong base (NaOH) gives the free amine.
• Large excess of ammonia (अमोनिया का बहुत आधिक्य) — Most R–X molecules then meet NH₃ rather than R–NH₂, so 1° amine dominates.
• Order of reactivity RI > RBr > RCl (अभिक्रियाशीलता क्रम RI > RBr > RCl) — The weaker C–I bond breaks most easily.

Steps

1. NH₃ attacks R–X (nucleophilic substitution) → primary amine (as its salt).
2. The 1° amine is also a nucleophile: + R–X → 2° amine.
3. 2° amine + R–X → 3° amine.
4. 3° amine + R–X → quaternary ammonium salt. Result: a mixture.

Original diagram drawn by Simple Learning Hub, based on the NCERT textbook. Report a mistake