The general procedure for the synthesis of 4-cyanopiperidine hydrochloride from piperidine-4-carboxamide: 11.9 g (75.7 mmol, 99% purity) of dibutylcarboxamide was slowly added to 10 g (75.7 mmol, 97% purity) of piperidine-4-carboxamide dissolved in 50 ml of toluene in a suspension over a period of 5 min at 20 °C. After 5 min, the reaction was started at 20 °C. After 5 min, 18.91 g (158.9 mmol) of thionyl chloride was added dropwise at 20 °C. The dropwise addition took 45 min, during which the reaction temperature was kept constant at 20 °C. The reaction temperature was kept constant at 20 °C. After the dropwise addition, the reaction mixture was stirred at 20 °C for 18 hours. After completion of the reaction, the suspension was filtered and the filter cake was washed with toluene. After drying, 9.63 g of colorless solid product was obtained. The purity of 4-cyanopiperidine hydrochloride was measured to be 99.7% (w/w) by GC analysis of the sample after methanosilylation, and the theoretical yield calculated from this was 86.5%.
