The apparatus (
.htmFig. 15) consists of a
reaction tube, 100 cm. long and 3 cm. in diameter, provided with an inlet tube to which a graduated dropping funnel is connected. The lower end of the reaction tube is fitted with a
Friedrichs condenser and
receiver. A
thermocouple well, concentric with the reaction tube, is passed through the upper end by means of a standard ground-glass joint. The tube is packed with
200 ml. of 4- to 8-mesh alumina (Note
1) held in place by a plug of glass wool supported by indentations in the tube, followed by 100 ml. of marble chips which serve as a vaporizer and preheater for the reactants. The reaction tube is supported in an
electrically heated furnace (Note
2) extending from the inlet tube to the joint connecting the condenser.
Fig. 15.
The reaction tube is heated to 330–340° (Note
3) and is swept out with a stream of
nitrogen gas. A solution of
258 g. (3 mole) of tetrahydropyran (Note
4) and
559 g. (6 mole) of aniline is then placed in the graduated funnel and introduced into the reaction tube at a rate of 90–100 ml. per hour.
The product, which is collected in a
1-l. flask containing
10 g. of sodium chloride, consists of a light-yellow oil and a lower aqueous layer. After the addition of the reactants is complete, a slow stream of
nitrogen is passed through the reaction tube for 20–30 minutes to remove any product adsorbed on the catalyst. The lower aqueous layer is separated and discarded, and the upper organic layer is dried over
sodium hydroxide pellets. The product is fractionated under reduced pressure using a
Whitmore-Lux column2 (Note
5) only to remove the small amount of unchanged
tetrahydropyran and excess
aniline. The column is permitted to drain, and the residue is distilled from an
ordinary Claisen flask
under reduced pressure.
1-Phenylpiperidine is obtained as a colorless or very light-yellow liquid, b.p.
123–126°/12.5 mm.,
133–136°/21 mm.,
nD25 1.5603. The yield is
403–435 g. (
83–90% based on
tetrahydropyran) (Note
6).