Tremblex,Brocades,Italy,1981
400 parts glacial acetic acid are cooled to 10°C to 20°C. Then there are added
first dropwise 300 parts concentrated sulfuric acid followed by portionwise
addition of 50 parts dl-1-benzyl-4-(1,3-dicyano-1-phenylpropyl)-piperidine
hydrochloride at the same temperature. After the addition is complete, the
whole is heated to 125°C in the course of 15 to 20 minutes. This temperature
is then maintained for 10 minutes. After cooling, the reaction mixture is poured into ice, alkalized with NH4OH at a temperature < 20°C and extracted
with chloroform. The chloroform layer is first washed twice with a K2CO3 5%
solution, and then washed twice with water, dried over MgSO4, filtered and
evaporated. The residue is dissolved in a mixture of 320 parts acetone and
600 parts diisopropylether, filtered and HCl gas is introduced into the filtrate.
The solid hydrochloride is filtered off and dried, to yield 43 parts less pure lbenzyl-4-(2.6-dioxo-3-phenyl-3-piperidyl)-piperidine hydrochloride, melting
point 283°C to 294°C.
A sample of 4 parts is recrystallized from a boiling mixture of 80 parts
isopropanol, 40 parts methanol and 500 parts water. The whole is filtered and
after cooling the filtrate overnight at -20°C, 1-benzyl-4-(2,6-dioxo-3phenyl-3-
piperidyl)-piperidine hydrochloride is obtained, melting point 299°C to
301.5°C, as a white amorphous powder.
The dextro-isomer may be separated via the dextro-camphorsulfonate of the
base.
