General procedure for the synthesis of 2-phenylpiperazine from 3-oxo-2-phenylpiperazine: 2-oxo-3-phenylpiperazine (1.76 g, 10 mmol) was dissolved in 30 mL of anhydrous THF and added slowly and dropwise to 20 mL (20 mmol) of a THF solution of 1M LiAlH4. The reaction mixture was stirred at room temperature for 24 hours. Upon completion of the reaction, water and 20% NaOH solution were carefully added to quench the excess LiAlH4. Subsequently, the reaction mixture was filtered and the filter cake was re-extracted with ethyl acetate. The organic filtrate and extract were combined, dried with MgSO4, filtered and concentrated under reduced pressure to give a light yellow solid. The crude product was further purified by silica gel column chromatography (eluent: CHCl3:MeOH:NH4OH = 9:1:0.1) to afford 2-phenylpiperazine (960 mg, 6 mmol, 60% yield) as a colorless solid. The product was characterized by 1H NMR (CDCl3): δ 2.69 (1H, t, J = 11.3 Hz), 2.85-3.10 (7H, m), 3.76 (1H, br d, J = 8.9 Hz), 7.21-7.38 (5H, m). Melting point determination (capillary method): 79-81°C.
