A
100-mL, two-necked, round-bottomed flask is equipped with a magnetic stirrer, pressure-equalizing dropping funnel, and a
1.2- × 24-cm vacuum-jacketed Vigreux column that is connected to a
condenser,
vacuum-take-off adapter, and
fraction collector with three receiving flasks (Note
1). The vacuum-take-off adapter is attached to a
calcium chloride drying tube which is connected to a
water aspirator, and the flask is charged with
35.2 g (28.6 mL, 0.40 mol) of pyruvic acid (Note
2). The
pyruvic acid is stirred at room temperature as
46.4 g (36.1 mL, 0.40 mol) of α,α-dichloromethyl methyl ether (Note
3) is added slowly over 30 min. Evolution of
hydrogen chloride begins after a few minutes. When the addition is complete, the
dropping funnel is removed and replaced by a
glass stopper. The solution is stirred and heated at 50°C in an
oil bath for 30 min (Note
4) while a few drops of
methyl formate are collected as the first fraction (Note
5). The condenser is then cooled to −30°C (Note
6) and the receiving flasks are cooled to −50°C with chilled
acetone. The aspirator is turned on and the pressure is adjusted to 190 mm. With the oil bath at 50°C, a second fraction, bp 25–35°C (190 mm), is collected. As soon as the head temperature begins to drop, the pressure is reduced to 120 mm and the temperature of the oil bath is raised slowly to 75°C. A third fraction, bp
35–40°C (120 mm), consisting mainly of
pyruvoyl chloride is collected (Note
7) and (Note
8). The second and third fractions are combined to give 33–41 g of a mixture of
pyruvoyl chloride and
methyl formate, which is redistilled through a 1.4- by 18-cm vacuum-jacketed Vigreux column (Note
1). The condenser and the receiving flasks are cooled to −5°C with chilled
acetone. The first fraction, weighing
2.3–11.4 g and consisting mainly of
methyl formate, is collected at
25–30°C (190 mm) with an oil bath temperature of 60°C. When the pressure is reduced to 120 mm and the oil bath is maintained at 60°C,
18.6–21.2 g (
44–50%) of
pyruvoyl chloride, bp
43–45°C (120 mm), distills into the
receiver as a light yellow liquid,
nD20 1.4165 (Note
9) and (Note
10).