B.
2-Fluoroheptanoic acid (Note 2). A
250-ml. two-necked flask is fitted with a thermometer and a condenser that has an outlet tube to carry
oxides of nitrogen to a
gas absorption trap3 or the back of a
hood. It is charged with
17.6 g. (0.100 mole) of 2-fluoroheptyl acetate,
50 ml. of glacial acetic acid, and
60 ml. of 16 N nitric acid. The mixture is heated at 48–50° for 25 hours by means of an electric heating mantle. It is diluted with 500 ml. of water and crushed ice and extracted with one 300-ml. portion and five
100-ml. portions of ether (Note
3). The combined
ether extracts are added carefully to a slurry of
125 g. of sodium bicarbonate in 500 ml. of water in a
2-l. beaker. The aqueous alkaline solution is extracted with two
100-ml. portions of ether, which are discarded. The aqueous solution is neutralized to a pH of approximately 4 with about
300 ml. of 10% hydrochloric acid and is extracted with one
300-ml. portion and five 100-ml. portions of ether. The combined extracts are washed with four 100-ml. portions of water to remove traces of
acetic acid and dried over anhydrous
sodium sulfate. The
ether is removed by distillation, leaving
12–13.5 g. of crude
2-fluoroheptanoic acid that soon solidifies. It is purified by distillation under reduced pressure through a
short Claisen still-head with a short condenser that can be heated by steam, a burner, or a heat lamp when the acid solidifies in it.
2-Fluoroheptanoic acid, b.p.
62–64° (0.15 mm.),
78–80° (0.7 mm.), is obtained as a moist, waxy, pale yellow solid that smells faintly of
acetic acid. After being dried on a porous plate, it is odorless and nearly colorless; weight
11.5–12.5 g. (
78–84%), m.p.
38–39°.