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To remove the protective groups, 40 g (135 mmol) of the tert-butyl 4-(4-ethylpiperazin-1-yl)piperidine-1-carboxylate were initially charged in 200 ml of methanol and 1.8 l of dichloromethane, and 100 ml 5-6 M HCl solution in isopropanol were added. The solution became a suspension, and a slight evolution of gas could be observed. The reaction mixture was stirred at 40° C. (water bath temperature) for one hour and at room temperature over the weekend. For complete deprotection to the desired product, another 50 ml of the 5-6 M HCl solution in isopropanol were added, and the mixture was stirred at 40° C. The dichloromethane was distilled off on a rotary evaporator, and another 200 ml of methanol and 30 ml of the 5-6 M HCl solution in isopropanol were added. After one hour of stirring under reflux, a white suspension formed with strong evolution of gas. Subsequently, a low-viscosity suspension was formed, which was cooled to room temperature. The precipitate was filtered off with suction and washed with methanol and diethyl ether. After drying, 36 g (117 mmol, 87%) of 1-ethyl-4-piperidin-4-ylpiperazine were isolated as chloride salt.

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