Question

Write a short note on Gabriel’s phthalimide synthesis. Why is Gabriel’s phthalimide synthesis preferred for synthesizing the primary amines?

Hint:

Always remember: Gabriel’s synthesis cannot be used for preparing aryl amines due to the inert nature of aryl halides towards nucleophilic substitution.

Answer 1

Step 1: Gabriel’s Phthalimide Synthesis.
Gabriel’s phthalimide synthesis is a method for preparing primary amines from phthalimide. The reaction involves: 1. Phthalimide is treated with alcoholic KOH to form potassium phthalimide (nucleophile).
2. Potassium phthalimide undergoes nucleophilic substitution with alkyl halide (\(R{-}X\)) to form N-alkylphthalimide.
3. Hydrolysis of N-alkylphthalimide gives a primary amine. \[ \text{Phthalimide} \xrightarrow{KOH} \text{Potassium phthalimide} \xrightarrow{R{-}X} N\text{-alkylphthalimide} \xrightarrow{Hydrolysis} R{-}NH_2 \] Step 2: Why preferred for primary amines.
Gabriel’s synthesis gives only primary amines and avoids the formation of secondary and tertiary amines, which are formed in other methods like ammonolysis of alkyl halides. Hence, it is highly selective. Conclusion:
Gabriel’s phthalimide synthesis is a reliable method to obtain pure primary amines.