B.
4,4-Dimethyl-2-cyclohexen-1-one. A dry,
1-l., three-necked flask is equipped with a
mechanical stirrer, a pressure-equalizing dropping funnel, a nitrogen inlet tube, and an
ice-water cooling bath. The apparatus is flushed with
nitrogen, and a static
nitrogen atmosphere is maintained in the reaction vessel throughout the reaction.
1-(2-Methylpropenyl)pyrrolidine (62.6 g., 0.501 mole) is added to the reaction flask before
42.1 g. (0.601 mole) of methyl vinyl ketone (Note
6) is added, dropwise with stirring and cooling, over 5 minutes. After the resulting mixture has been stirred with cooling for 10 minutes, the ice bath is removed and stirring at room temperature is continued for 4 hours (Note
7). The reaction mixture is again cooled with an ice-water bath, and
250 ml. of 8 M hydrochloric acid is added, dropwise and with stirring (Note
8). After addition is complete, the mixture is stirred with cooling for 10 minutes, then stirred at room temperature for 14 hours (Note
9). The resulting brown reaction mixture is extracted with two
300-ml. portions of diethyl ether. The residual aqueous phase is neutralized by the cautious addition of
150–155 g. of solid sodium hydrogen carbonate and extracted with two
400-ml. portions of ether. The combined ethereal extracts (Note
10) are dried over anhydrous
sodium sulfate and concentrated with a
rotary evaporator. The residual liquid is distilled under reduced pressure, yielding
44.2–53.0 g. (
71–85%) of
4,4-dimethyl-2-cyclohexen-1-one as a colorless liquid, b.p.
73–74° (14 mm.),
n25D 1.4699–1.4726 (Note
11).