The general procedure for the synthesis of 3-piperidinamine hydrochloride from piperidine-3-carbohydrazide was as follows: 36 g (250 mmol) of racemic piperidine carbohydrazide was added to 125 g of water under ice/salt bath cooling conditions, followed by the addition of 45 mL (500 mmol) of concentrated hydrochloric acid. Keeping the reaction temperature at 0 °C, 25.1 g of isoamyl nitrite (300 mmol) was slowly added over 30 min and stirring was continued at the same temperature for 30 min. The reaction was monitored by HPLC to confirm the complete conversion of piperidine carbohydrazide to the target azide and no starting material remained. The reaction mixture was poured dropwise into 500 mL of water preheated to 80 °C over 10 min and subsequently boiled for 60 min. Upon completion of the reaction, the solution was cooled to room temperature, 40 mL of concentrated hydrochloric acid was added and the solution was concentrated to a viscous state. The solution was again concentrated by adding 100 mL of water, followed by the addition of 100 mL of isopropanol and repeating the concentration process. The residue was dissolved in 50 mL of hot methanol and 100 g of acetone was added dropwise to the cooled methanol solution under vigorous stirring to induce precipitation of 3-aminopiperidine dihydrochloride (40 g of wet product). The product was dried with two portions (50 mL each) of isopropanol by azeotropic distillation under reduced pressure. The dried product was suspended in hot methanol and stirred overnight at room temperature. Subsequently, the suspension was diluted with 70 g of acetone and the solid product was separated by filtration. Finally 33.2 g (192 mmol, 77% yield) of 3-aminopiperidine dihydrochloride was obtained as a white powder. The product had a chemical purity of 98.7% by HPLC and a water content of 0.046% by Karl Fischer titration.
