NCERT · Class 12 · Chemistry · AminesWrite comprehensive chemical notes on the following name reactions related to the preparation and properties of amines, including balanced chemical equations for each: Gabriel Phthalimide Synthesis Hofmann Bromamide Degradation Reaction Carbylamine Test

Important Name Reactions in Amines

1. Gabriel Phthalimide Synthesis\nGabriel synthesis is used for the preparation of pure primary aliphatic amines. Phthalimide on treatment with ethanolic potassium hydroxide forms potassium phthalimide. This potassium salt is further heated with a suitable alkyl halide to give $N$-alkylphthalimide, which on subsequent alkaline hydrolysis with sodium hydroxide yields the corresponding primary aliphatic amine along with phthalic acid.

• Equation: $$\text{C}_6\text{H}_4(\text{CO})_2\text{NH} + \text{KOH} \rightarrow \text{C}_6\text{H}_4(\text{CO})_2\text{N}^-\text{K}^+ + \text{H}_2\text{O}$$ $$\text{C}_6\text{H}_4(\text{CO})_2\text{N}^-\text{K}^+ + \text{R-X} \rightarrow \text{C}_6\text{H}_4(\text{CO})_2\text{N-R} + \text{KX}$$ $$\text{C}_6\text{H}_4(\text{CO})_2\text{N-R} + 2\text{NaOH} \rightarrow \text{C}_6\text{H}_4(\text{COONa})_2 + \text{R-NH}_2$$
• Limitation: Aromatic primary amines cannot be prepared by this method because aryl halides do not undergo nucleophilic substitution with the anion formed by phthalimide.

2. Hofmann Bromamide Degradation Reaction\nThis is a method used for the step-down degradation of amides to prepare primary amines with one carbon atom less than the parent amide. When an amide is treated with bromine and an aqueous or ethanolic solution of sodium hydroxide, it undergoes degradation to yield a primary amine with the elimination of sodium carbonate and sodium bromide.

• Equation: $$\text{R-CONH}_2 + \text{Br}_2 + 4\text{NaOH} \rightarrow \text{R-NH}_2 + \text{Na}_2\text{CO}_3 + 2\text{NaBr} + 2\text{H}_2\text{O}$$
• Significance: This reaction is extremely useful for chain-shortening synthesis and ascending/descending carbon series in organic chemistry.

3. Carbylamine Test (Isocyanide Test)\nPrimary amines (both aliphatic and aromatic) when heated with chloroform and alcoholic potassium hydroxide form isocyanides (carbylamines), which possess an extremely foul, obnoxious, and offensive odor. Secondary and tertiary amines do not give this test.

• Equation: $$\text{R-NH}_2 + \text{CHCl}_3 + 3\text{KOH} \xrightarrow{\Delta} \text{R-NC} + 3\text{KCl} + 3\text{H}_2\text{O}$$
• Significance: This reaction serves as a specific, highly sensitive chemical test for the detection and identification of primary amines.