A suspension of
sodium amide (1.10 moles) in
liquid ammonia is prepared in a
1-l. three-necked flask equipped with an
air condenser (Note
1), a
ball-sealed mechanical stirrer, and a
glass stopper. In the preparation of this reagent commercial anhydrous
liquid ammonia (800 ml.) is introduced from a cylinder through an inlet tube. To the stirred
ammonia is added a small piece of
sodium. After the appearance of a blue color a few crystals of
ferric nitrate hydrate (about 0.25 g.) are added, followed by small pieces of freshly cut
sodium until 25.3 g. (1.10 moles) has been added. After the
sodium amide formation is complete (Note
2), the glass stopper is replaced by a
pressure-equalizing dropping funnel containing
60.0 g. (0.600 mole) of 2,4-pentanedione (Note
3) in
40 ml. of anhydrous ether. The top of the addition funnel is fitted with a
nitrogen inlet tube. The reaction flask is immersed at least 3 in. into a
dry ice-acetone bath (Note
4), and simultaneously the slow introduction of dry
nitrogen through the inlet tube is begun. After the reaction mixture is thoroughly cooled (about 20 minutes),
2,4-pentanedione is added intermittently in small portions (Note
4) over 10 minutes. The cooling bath is removed. After 20 minutes the
nitrogen purge is stopped, and
68.5 g. (0.500 mole) of 1-bromobutane (Note
5) in
40 ml. of anhydrous ether is introduced dropwise during 10–20 minutes. The addition funnel is rinsed with a small volume of anhydrous
ether, which is added to the reaction mixture. After 30 minutes
400 ml. of anhydrous ether is added, and the
ammonia is removed by cautious heating on the
steam bath. Crushed ice (200 g.) is added causing a thick slurry to form. Next a mixture of
60 ml. of concentrated hydrochloric acid and 10 g. of crushed ice is added. The reaction mixture is stirred until all solids are dissolved and then is transferred to a
separatory funnel, the flask being washed with a little
ether and dilute
hydrochloric acid. The ethereal layer is separated, and the aqueous layer (Note
6) is further extracted three times with
100-ml. portions of ether. The combined ethereal extracts are dried over anhydrous
magnesium sulfate. After filtration and removal of the solvent the residue is distilled through a
12-in. Vigreux column to give
63.0–63.6 g. (
81–82%) of
2,4-nonanedione, b.p.
100–103° (19 mm.), as a colorless liquid (Note
7).