A
3-l., three-necked flask equipped with a
mechanical stirrer, a
reflux condenser, and an
addition funnel is charged with
112.5 g. (100.0 ml., 0.7492 mole) of triethylene glycol and
600 ml. of tetrahydrofuran (Note
1). Stirring is begun and a
60% potassium hydroxide solution, prepared by dissolving
109 g. (1.65 moles) of 85% potassium hydroxide in 70 ml. water, is added (Note
2). The solution warms slightly. After about 15 minutes of vigorous stirring (the solution begins to develop color and gradually becomes rust brown; (Note
3)), a solution of
140.3 g. (0.7503 mole) of 1,2-bis(2-chloroethoxy)ethane (Note
4) in
100 ml. of tetrahydrofuran is added in a stream. After the addition is complete, the solution is heated at reflux and stirred vigorously for 18–24 hours. The solution is allowed to cool and the bulk of the
tetrahydrofuran is evaporated under reduced pressure (Note
5). The resulting thick, brown slurry is diluted with
500 ml. of dichloromethane and filtered through a glass frit. The salts removed by filtration are washed with more
dichloromethane to remove absorbed crown and the combined organic solution is dried over anhydrous
magnesium sulfate (Note
6), filtered, evaporated to minimum volume (aspirator vacuum), and distilled under high vacuum using a simple distillation head. The distillation should be carried out at the lowest possible pressure; a typical fraction contains
76–87 g. (
38–44%) of crude
18-crown-6 and is collected over
100–167° (0.2 mm.) (Note
7),(Note
8),(Note
9).
To
50 g. of the crude 18-crown-6 in a
250-ml. Erlenmeyer flask is added
100 ml. of acetonitrile. A
magnetic stirring bar is added, and the flask is equipped with a
calcium chloride drying tube. The resulting slurry is heated on a hot plate to effect solution. The solution is stirred vigorously as it is allowed to cool to ambient temperature; fine white crystals of crown-acetonitrile complex are deposited. The flask is allowed to stand in a freezer for 24–48 hours and is finally cooled in a −30° bath to precipitate as much of the complex as possible. The solid is collected by rapid filtration (Note
10) and washed once with a small amount of cold
acetonitrile. The hygroscopic crystals are transferred to a
200-ml., round-bottomed flask equipped with a magnetic stirring bar and a vacuum takeoff. The
acetonitrile is removed from the complex under high vacuum (0.1–0.5 mm.), with gentle heating (

35°), over 2–3 hours. The pure colorless crown (
28–33 g.,
56–66%) (Note
11) crystallizes on standing, m.p.
38–39.5° (Note
12).