C.
dl-Phenylalanine. The crude bromo acid is divided into four portions and each portion is added to
2 l. of technical ammonium hydroxide (sp. gr. 0.90) in a
3-l. round-bottomed flask. The flask is well shaken, a
rubber stopper is wired in, and the mixture is allowed to stand for a week. The contents of the four amination flasks (Note
5) are then combined in a 12-l. flask,
20 g. of Norit is added, and the flasks are heated on a steam cone overnight. The
ammonia which is evolved is conducted into a
gas-absorption trap or merely led into water by a tube from the flask. The solution is filtered while still hot; on cooling most of the
phenylalanine precipitates. This is filtered, washed with
250 ml. of methanol, and the filtrate evaporated under the pressure of a water pump until more crystals form. The solution is then cooled and an additional crop of
phenylalanine obtained, which is also washed with
methanol. The yield of crude product is
500 g., but it is slightly wet; if it is dried overnight in an
oven at about 80°, it will weigh
460 g. This need not be done, however, as the yield of pure product is the same whether or not the crude product is dried.
The
phenylalanine is recrystallized as follows: the crude product is dissolved in 9 l. of water heated to 95° on a steam cone, treated with
15 g. of Norit, and filtered.
Three liters of alcohol is added and the solution cooled in the ice chest overnight. The yield of pure product amounts to
367 g. An additional
45 g. may be obtained by evaporating the mother liquor under reduced pressure until crystals separate, adding an amount of alcohol equivalent to one-third the volume of the concentrated mother liquor, and cooling. Additional material may be obtained by continuing to work down all mother liquors. The yield,
412 g., is
62.4% based on the
diethyl benzylmalonate. The white crystals decompose at 271–273° (uncor.) in a closed capillary (Note
6).