B.
dl-Valine. To
2 l. of technical ammonium hydroxide (sp. gr. 0.90) in a 3-l. round-bottomed flask is added
330 g. (1.82 moles) of α-bromoisovaleric acid. A stopper is wired in and the flask allowed to stand at room temperature for a week. The contents from three such amination flasks are combined in a
12-l. flask, and the
ammonia is removed by heating on the
steam cone overnight. The solution is then concentrated to a thin paste (about 800 ml.) by means of a
water pump (Note
4). The solid material is collected on a filter and, when dry, amounts to 470 g. This is recrystallized by dissolving in 2.4 l. of water heated to 95° on a steam cone, treating with
10 g. of Norit for 30 minutes, filtering hot, adding an equal volume of
95% ethanol, and cooling overnight in the
icebox. The
valine is collected on a filter and washed with
150 ml. of cold absolute ethanol. The yield is
200–235 g. A second crop is obtained by evaporating the filtrate from the recrystallization on the water pump until crystals form, adding an equal volume of
95% ethanol, and cooling as before. The amino acid obtained in this way amounts to
34 g.
The second filtrate from the recrystallization together with the filtrate from the original concentration is evaporated to dryness and extracted with
500 ml. of glacial acetic acid on a steam cone. The inorganic salts are filtered and the
acetic acid is removed by distillation under reduced pressure. One liter of water is added, and it, too, is removed by distillation under reduced pressure. This operation is repeated. These three distillations require 1 day. The residue is dissolved in the minimum amount of hot water (about 300 ml.). The solution is then treated with
Norit as before and filtered hot, and an equal volume of
95% ethanol is added. The yield on cooling overnight in the icebox is
34 g. An additional
8 g. can be obtained from the mother liquor by concentration and addition of
ethanol as was done with the original mother liquor. The total yield of
valine is
300–311 g. (
47–48%), which decomposes at 280–282° in a sealed capillary (Note
5) and (Note
6).