B.
Diethyl β-ketopimelate. In a
250-ml. distillation flask fitted with an inlet tube reaching near the bottom of the flask and a
soda-lime drying tube on the side-arm is placed a solution of
50 g. (0.18 mole) of diethyl α-acetyl-β-ketopimelate in
75 ml. of dry ether. The solution is cooled by placing the flask in an
ice-salt bath, and then a slow stream of
ammonia gas is passed through the inlet tube. The solution becomes turbid during the first few minutes and soon becomes clear again. The gas stream is continued for 45–50 minutes, and the yellow liquid is allowed to stand at room temperature overnight with due protection from atmospheric moisture. Most of the
ether is then removed by passing a stream of dry air through the solution, and the residue is transferred to a
separatory funnel with the aid of
50 ml. of ether. The ethereal solution is washed with three
70-ml. portions of cold 3N hydrochloric acid, each extraction being shaken vigorously for 10 minutes. The ethereal layer is set aside, and the acid washings are extracted twice with
50-ml. portions of ether. The combined ethereal extracts are washed once with water and dried over anhydrous
sodium sulfate. After removal of the
sodium sulfate by filtration, the solvent is removed by heating the solution on a water bath. The residue is transferred to a Claisen flask with a short
Vigreux column, and the fraction boiling at
130–132°/0.5 mm. or
120–121°/0.2 mm. is collected (Note
4) and (Note
5). The yield is
21–25 g. (
50–59%),
nD28 1.4400,
nD31.5 1.4376,
nD36.5 1.4338.