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A. Malonyl dichloride. In a 250-ml. Erlenmeyer flask (Note 1) fitted by a ground-glass joint to a
reflux condenser capped with a calcium chloride drying tube are placed 52 g. (0.5 mole) of finely
powered, dry malonic acid (Note 2) and 120 ml. (about 1.65 mole) of thionyl chloride (Note 3). The
flask is warmed for 3 days in a heating bath kept at 45–50° (Note 4). During this period the mixture,
which is agitated occasionally by gentle swirling, gradually darkens to a deep brownish red or
sometimes a blue color. Finally the mixture is heated at 60° for 5–6 hours. After cooling, it is transferred
to a 125-ml. modified Claisen flask and distilled at reduced pressure (water aspirator). A calcium
chloride guard tube is inserted between the vacuum line and the apparatus, and the flask is heated with a
bath rather than a free flame. After a small fore-run of thionyl chloride, the malonyl chloride distils at
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58–60°/28 mm. The pale yellow product amounts to 50.5–60 g. (72–85% yield),
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