In a
1-l. three-necked flask, equipped with a
thermometer and a
reflux condenser, are placed
60 g. of paraldehyde (0.45 mole, equivalent to 1.35 moles of acetaldehyde) and
100 ml. (1.06 moles) of acetic anhydride. Ice water is circulated through the condenser, and the reaction mixture is protected from atmospheric moisture by a
drying tube containing Drierite. The temperature of the mixture is raised slowly by heating with an electric mantle to 125°, at which point gentle refluxing begins. Then
100 g. (0.62 mole) of diethyl malonate is added in 15-ml. portions at a rate of 1 portion every 30 minutes. During the addition of
diethyl malonate, the temperature gradually drops to about 100°, and the mixture is heated so as to maintain a reflux rate of 30–60 drops per minute. After the addition is complete, the reaction mixture is heated under reflux for 4 hours at the specified rate.
The reflux condenser is replaced by a
Claisen distillation head, and the reaction mixture is distilled until the temperature of the vapor reaches 140°. The residue is transferred to a smaller flask and fractionated through a
30-cm. column packed with glass helices. A low-boiling fraction containing
ethylidene diacetate and
diethyl malonate is collected first, followed by
79–89.5 g. (
68–77%) of
diethyl ethylidenemalonate; b.p.
102–106°/10 mm.;
n25D 1.4394 (Note
1) and (Note
2).