A
3-l. three-necked round-bottomed flask is fitted with a
thermometer, a
graduated dropping funnel (Note
1), a
stirrer (Note
2), a
fine capillary tube for introducing
nitrogen near the bottom of the flask, and an
exit tube attached through a manometer to three traps set in series. In the flask are placed
360 ml. of 33% (by volume) propargyl alcohol [112.1 g. (120 ml., 2.0 moles)] (Note
3) and a cooled solution of
135 ml. of sulfuric acid and 200 ml. of water. The flask is cooled in an ice-salt mixture. While the contents of the flask are cooling, the first trap is cooled to about −15° with
acetone and Dry Ice. The last two traps in the series are cooled to −78° with
acetone and Dry Ice (Note
4). The pressure in the system is reduced to 40–60 mm.,
nitrogen is introduced through the capillary, and the mixture is stirred vigorously. A solution of
210 g. of commercial chromium trioxide (2.1 moles) in 400 ml. of water and
135 ml. of sulfuric acid is added dropwise in the course of about 3 hours while maintaining a reaction temperature of 2–10°. After the addition of the
chromium trioxide, the
ice bath is removed, and the flask is permitted to warm to room temperature while the pressure is gradually lowered to 14–20 mm. to remove the last of the aldehyde. The condensates of the three traps are combined (Note
5) and dried over anhydrous
magnesium sulfate. The
propiolaldehyde is distilled through a
16-in. column packed with platinum gauze. The fraction distilling at
54–57° weighs
38–44 g. (
35–41%),
nD25 1.4050 (Note
6) and (Note
7).