A dry
1-l. three-necked round-bottomed flask is fitted in the center neck with a sweep-blade stirrer whose shaft passes through an airtight bearing (Note
1). One side neck is fitted with a
condenser topped by a soda-lime drying tube, and the other is fitted with a
solid stopper. In the flask are placed
75 ml. of piperidine (Note
2) and
15.6 g. (0.4 mole) of sodium amide (Note
3), and the mixture is heated at reflux (Note
4) for 15 minutes with good stirring. The mixture is cooled just below reflux temperature, and
46 g. (0.2 mole) of sodium β-naphthalenesulfonate (Note
5) is added, followed by an additional
75 ml. of piperidine. The mixture is then heated at reflux for 12 hours with stirring.
To the cooled reaction mixture, 200 ml. of water is added carefully with stirring.
Potassium carbonate is added with continued stirring until the water layer is saturated; the mixture is now transferred to a
separatory funnel and extracted three times with
60-ml. portions of ether. The combined
ether extracts are dried over
solid sodium hydroxide and are then transferred to a
simple distillation apparatus. Distillation is commenced with a
steam bath as source of heat; when most of the
ether has been removed, the steam bath is replaced by a flame. Distillation is continued until most of the
piperidine (b.p.
106°) has been removed. The cooled residue in the distillation flask is recrystallized from
petroleum ether (boiling range 30–60°) with the use of charcoal. There is obtained
30.0 g. (
71%) of
N-β-naphthylpiperidine as tan crystals, m.p.
52–56°. An additional recrystallization from the same solvent gives crystals, m.p.
56–58°, with about 10% loss in weight (Note
6).