350 parts by weight of the potassium salt of 2-phenyl-2-(βdiethylaminoethyl)-pentane-1,5-diacid mononitrile are dissolved with heating in 700 parts by volume of glacial acetic acid, 850 parts by volume of acetic anhydride are added, and then 250 parts by volume of concentrated sulfuric acid introduced portionwise. The temperature of the reaction mixture in this operation rises to 120-130°C. When the reaction subsides, the whole is finally maintained for a further 15 min on the boiling water bath. The solvent is removed on the water bath under reduced pressure, the residue poured onto ice and caustic soda solution, and the whole extracted with chloroform. The chloroform solution washed with water, dried over potassium carbonate and the solvent evaporated. The crystalline residue, consisting of 3-phenyl-3-(βdiethylaminoethyl)-2,6-dioxopiperidine. After recrystallization from a mixture of ethyl acetate and ligroin, melts at 118-120°C.
The hydrochloride (produced by dissolving the base in ethyl acetate and adding an equivalent quantity of hydrochloric acid gas dissolved in ethylacetate) melts, after recrystallization from a mixture of methyl alcohol and ethyl acetate, at 168-172°C.
