In a
5-l. three-necked flask fitted with a mechanical stirrer (Note
1), a
dropping funnel, and a
thermometer for reading low temperatures is placed
790 ml. (7 moles) of 48% hydrobromic acid. The flask and contents are cooled to 10–20° in an
ice-salt bath, and
150 g. (1.59 moles) of 2-aminopyridine (Note
2) is added over a period of about 10 minutes. While the temperature is kept at 0° or lower,
240 ml. (4.7 moles) of bromine is added dropwise (Note
3). A solution of
275 g. (4 moles) of sodium nitrite in 400 ml. of water is added dropwise over a period of 2 hours, the temperature being carefully maintained at 0° or lower (Note
4). After an additional 30 minutes of stirring, a solution of
600 g. (15 moles) of sodium hydroxide in 600 ml. of water is added at such a rate that the temperature does not rise above 20–25° (Note
5). The nearly colorless reaction mixture is extracted with four
250-ml. portions of ether (Note
6). The extract is dried for 1 hour over
100 g. of solid potassium hydroxide and is then distilled through a
Vigreux column 15 cm. in length.
2-Bromopyridine distils at
74–75°/13 mm., and the yield is
216–230 g. (
86–92%) (Note
7).