To a stirred solution of tert-butyl 4-(2-chlorophenyl)piperazine-1-carboxylate (250 mg, 0.844 mmol) in 1,4-dioxane (2 mL) was added slowly and dropwise a 1,4-dioxane solution (0.9 mL, 3.60 mmol) in 4 N HCl at 0 °C. The reaction mixture was gradually warmed to room temperature and stirred continuously for 4 h (complete consumption of feedstock was confirmed by TLC monitoring). Upon completion of the reaction, the volatile solvent was removed under reduced pressure to give the crude product. The crude product was washed with ether (2 x 20 mL) and dried under high vacuum to yield 1-(2-chlorophenyl)piperazine hydrochloride (165 mg, 84% yield) as a white solid.
