Gabriel's synthesis is used frequency for the preparation of which of the following?

Gabriel's phthalimide synthesis is used to prepare pure primary ($1°$) amines. Phthalimide is treated with KOH to form potassium phthalimide, which reacts with a primary alkyl halide via $S_N2$, followed by hydrolysis (or hydrazinolysis) to release the primary amine. This method avoids over-alkylation (formation of $2°$ and $3°$ amines) that occurs when $NH_3$ reacts directly with alkyl halides.