C.
Cycloundecanone. In a well-ventilated hood a 3-l.; three-necked, round-bottomed flask is fitted with a magnetic stirrer (Note
1), a thermometer, a
reflux condenser protected by a calcium chloride tube, and a
rubber stopper. Concentrated
sulfuric acid (600 ml.) is placed in the flask, stirred slowly, and cooled to 5° with an
ice bath.
Methyl 1-cycloundecenecarboxylate (191–196 g., 0.91–0.92 mole) is added through a
long-stemmed funnel, the rate of stirring is increased until the mixture becomes a homogeneous solution, and
500 ml. of chloroform is added. The resulting mixture is heated to 35° by immersion in a warm water bath. Vigorous stirring is continued while
78 g. (1.2 moles) of sodium azide (Note
8) is added in small portions over a 30–50-minute period, the reaction temperature being maintained at 40 ± 2° by adding ice to the water bath.
Caution! This operation should be performed behind a safety shield. After an additional 10–15 minutes of stirring at 35–40°, the reaction mixture is cooled to 5°, poured onto 1 kg. of ice, and transferred together with 1.5–2 l. of water to a
5-l., three-necked flask set up for steam distillation. The
chloroform is distilled off and saved, and the
cycloundecanone is steam distilled with 3.5–4.0 kg. of steam. The steam distillate is extracted with the recovered
chloroform, then with
500 ml. of ether. After the ethereal extract has been washed with concentrated aqueous
sodium chloride, the organic phases are filtered through anhydrous
sodium sulfate, combined, and concentrated under reduced pressure. Vacuum distillation of the residual oil affords
139–143 g. (
83–85%) of
cycloundecanone as a colorless or pale yellow oil, b.p.
84–85° (2 mm.),
n25D 1.4794–1.4796 (Note
8).