A
3-l. three-necked flask, equipped with a Dry Ice condenser (Note
1), a
sealed Hershberg-type stirrer, and an
inlet tube, is set up in a
hood and charged with
108 g. (0.75 mole) of α-naphthol (Note
2). The stirrer is started, and to the rapidly stirred flask contents (Note
3) is added
1 l. of liquid ammonia as rapidly as possible (about 5 minutes). When the
naphthol has gone into solution (about 10 minutes),
20.8 g. (3.0 g. atoms) of lithium metal (Note
4) is added in small pieces and at such a rate as to prevent the
ammonia from refluxing too violently (Note
5). After the addition of the
lithium has been completed (about 45 minutes), the solution is stirred for an additional 20 minutes and is then treated with
170 ml. (3.0 moles) of absolute ethanol which is added dropwise over a period of 30–45 minutes (Note
6). The condenser is removed, stirring is continued, and the
ammonia is evaporated in a stream of air introduced through the inlet tube. The residue is dissolved in 1 l. of water, and, after the solution has been extracted with two
100-ml. portions of ether, it is carefully acidified with concentrated
hydrochloric acid. The product formed is taken into
ether with three 250-ml. extractions, and then the
ether extract is washed with water and dried over anhydrous
sodium sulfate. The
ether is removed by evaporation to yield
106–108 g. (
97–99%) of crude
5,8-dihydro-1-naphthol, m.p.
69–72°. This material is dissolved in
250 ml. of ethyl acetate and hydrogenated with
3.0 g. of 10% palladium on charcoal catalyst (Note
7) at 2–3. atm. pressure in a Parr apparatus until the theoretical amount of
hydrogen has been absorbed (about 45 minutes). The catalyst is removed by filtration, and the solvent is removed by distillation to leave
105–107 g. of an oil which quickly solidifies, m.p.
67–69.5°. Recrystallization from
250 ml. of petroleum ether (b.p.
88–98°) gives
93–97 g. (
84–88%) of almost colorless crystals, m.p.
68–68.5°.