A.
6-Chloro-2-hexyne. A
2-l., three-necked, round-bottomed flask is equipped with a
low-temperature condenser (Note
1), a
gas-inlet, and a
magnetic stirrer.
Sodium hydroxide drying tubes are placed to precede the inlet and on the condenser. The system is purged with
nitrogen, and approximately
650 ml. of anhydrous ammonia (Note
2) is condensed. Freshly cut
sodium metal (20.2 g., 0.878 g.-atom) is added to the refluxing
ammonia. After dissolution of the
sodium (about 20 minutes is required),
0.2 g. of iron(III) nitrate is added. Two hours of stirring are allowed for conversion of the deep-blue solution of
sodium in
ammonia to
sodium amide. The reaction mixture is cooled to −73° using an
acetone-dry ice bath and
35.3 g. (50.0 ml., 0.882 mole) of precondensed propyne (Note
3), (Note
4), is added in portions over a 1-minute period through a
glass funnel precooled in dry ice (Note
4). The mixture is stirred, with continued cooling for 15 minutes, and
153.5 g. (0.975 mole) of 1-bromo-3-chloropropane (Note
5) is added from an addition funnel over 20 minutes (Note
6). After 30 minutes of additional stirring,
250 ml. of diethyl ether is added to the flask, the dry
ice bath is removed, and the
ammonia is allowed to evaporate (Note
7). Water (200 ml.) is added to the reaction vessel, and the resulting solution is transferred to a
1-l. separatory funnel. The water layer is removed and extracted once with
100 ml. of ether. The combined
ether extracts are treated with 6
M hydrochloric acid until the aqueous layer is acidic (approximately 20 ml. is required). The
ether layer is separated and dried in three stages over
magnesium sulfate. Removal of the solvent and distillation of the crude product through a
20-cm. Widmer column (Note
8) yields
49.4–56.0 g. of
6-chloro-2-hexyne, b.p.
58–64° (20 mm.), which contained some
1-bromo-3-chloropropane (to be removed in the next step). The corrected yield is
29–31% (Note
9).