Preparation of Amines — Gabriel, Hoffmann, reduction
Nitrogen Compounds
8
JEE Qs
8%
Hard
75
min
Master the reagents, conditions, product carbon count, and limitations for each amine preparation method, especially for Gabriel and Hoffmann reactions.
🧮 Key Formulas
✅ Key Points for JEE
- 1Gabriel Phthalimide Synthesis exclusively yields primary amines (R-NH2), and it is not suitable for preparing aromatic primary amines directly from aryl halides due to their poor SN2 reactivity.
- 2Hoffmann Bromamide Degradation converts primary amides (R-CONH2) into primary amines (R-NH2) containing one carbon atom less than the starting amide, proceeding via an isocyanate intermediate and a rearrangement step.
- 3Reduction of nitro compounds (R-NO2) is a versatile method to prepare primary amines (R-NH2) using various reducing agents like Sn/HCl, Fe/HCl, or catalytic hydrogenation (H2/Pd/Pt/Ni).
- 4Nitriles (R-C≡N) can be reduced to primary amines (R-CH2-NH2) with the same number of carbon atoms using strong reducing agents like LiAlH4 or by catalytic hydrogenation.
- 5Primary amides (R-CONH2) can be reduced to primary amines (R-CH2-NH2) with the same number of carbon atoms using Lithium Aluminium Hydride (LiAlH4); similarly, secondary and tertiary amides yield secondary and tertiary amines, respectively.
⚠️ Common Mistakes
- ✕Attempting to synthesize aromatic primary amines (e.g., aniline) directly using Gabriel phthalimide synthesis, which fails due to inertness of aryl halides to SN2 reaction.
- ✕Incorrectly predicting the carbon count in Hoffmann bromamide degradation products, forgetting that the amine formed will always have one less carbon atom than the starting amide.
- ✕Confusing the specific reducing agents required for different functional groups or not knowing their limitations (e.g., using a mild reducing agent for a functional group that requires a strong one).
- ✕Misunderstanding that while Gabriel and Hoffmann reactions are specific for primary amines, LiAlH4 reduction of amides can yield primary, secondary, or tertiary amines depending on the substitution on the amide nitrogen.
📝 Practice Questions
See allQ56.Given below are two statements : Consider the following reaction (1) Both Statement I and Statement II are false (2) Statement I is true but Statement II is false (3) Statement I is false but Statement II is true (4) Both Statement I and Statement II are true
Q56.Identify correct statements : (A) Primary amines do not give diazonium salts when treated with NaNO2 in acidic condition. (B) Aliphatic and aromatic primary amines on heating with CHCl3 and ethanolic KOH form 2025 (28 Jan Shift 2) JEE Main Previous Year Paper carbylamines. (C) Secondary and tertiary amines also give carbylamine test. (D) Benzenesulfonyl chloride is known as Hinsberg's reagent. (E) Tertiary amines reacts with benzenesulfonyl chloride very easily. Choose the correct answer from the options given below : (1) (A) and (B) only (2) (D) and (E) only (3) (B) and (D) only (4) (B) and (C) only
Q68.Match the Compounds (List - I) with the appropriate Catalyst/Reagents (List - II) for their reduction into corresponding amines. Choose the correct answer from the options given below : (1) (A)-(II), (B)-(I), (C)-(III), (D)-(IV) (2) (A)-(III), (B)-(II), (C)-(IV), (D)-(I) (3) (A)-(II), (B)-(IV), (C)-(III), (D)-(I) (4) (A)-(III), (B)-(IV), (C)-(II), (D)-(I)
Q58.The correct set of ions (aqueous solution) with same colour from the following is: 2025 (23 Jan Shift 1) JEE Main Previous Year Paper (1) Sc3+, Ti3+, Cr2+ (2) V2+, Cr3+, Mn3+ (3) Ti4+, V4+, Mn2+ (4) Zn2+, V3+, Fe3+
Q66. For reaction The correct order of set of reagents for the above conversion is : (1) Br2 ∣FeBr3, H2O(Δ), NaOH (2) H2SO4, Ac2O, Br2, H2O(Δ), NaOH (3) Ac2O, Br2, H2O(Δ), NaOH (4) Ac2O, H2SO4, Br2, NaOH
Q55.Total number of nucleophiles from the following is : ⊖ NH3, PhSH, (H3C)2 S, H2C = CH2, O H, H3O⊕, (CH3)2CO, ⇌NCH3 (1) 7 (2) 4 (3) 6 (4) 5
NCERT Chapters
- Class 12 Chemistry Ch 13: Amines