In a
1-l. three-necked flask provided with a
Hershberg stirrer are mixed 300 ml. of water,
25 ml. of concentrated hydrochloric acid (Note
1), and
100 g. of 2,3-dihydropyran (p. 276). The mixture is stirred until the solution has become homogeneous and then for an additional 20 minutes (Note
2). After the addition of a few drops of
phenolphthalein indicator to the mixture, the acid is neutralized with
20% sodium hydroxide; enough alkali is added so that a faint pink color just persists.
The solution is then transferred to a
continuous extractor and extracted with
ether for about 16 hours. The
ether extract is added in convenient portions to a
250-ml. modified Claisen flask fitted with a condenser and a suitable
fraction-cutter for distillation under reduced pressure. The
ether is removed by distillation under the diminished pressure of a
water pump, and the residue is then distilled at about 10 mm. pressure. After a small fore-run which weighs 2–5 g., the product distils as a clear, colorless, viscous oil at
62–66°/9–10 mm.;
n25D 1.4513. The yield is
90–95 g. (
74–79%) (Note
3) and (Note
4).