A
1500-cc. flask is fitted with a
two-holed rubber stopper carrying a
glass tube which ends below the middle of the flask. The second hole is fitted with a common
glass stopcock (Note
1). To the flask is added
500 cc. of 6 N aqueous ammonia (sp. gr. about 0.95), and
100 g. (0.55 mole) of p-nitrophenylacetic acid (p. 406) is now slowly introduced, with shaking. The flask is then placed in an
ice bath, and the mixture saturated with
hydrogen sulfide, the temperature being held below 50°.
The stopper is removed from the reaction flask, and the solution of
ammonium p-aminophenylacetate gently boiled under the
hood until nearly all the excess
hydrogen sulfide and
ammonia have escaped. The solution changes from a dark orange-red to a pale yellow. The deposited
sulfur is filtered off by suction, and
40 cc. of glacial acetic acid rapidly stirred into the hot filtrate. The
p-aminophenylacetic acid which crystallizes out weighs
69–70 g., but it is contaminated with a small amount of free
sulfur. On evaporating the mother liquor to a small volume, about 5 g. more can be obtained. The crude material is recrystallized from 4 l. of distilled water,
69–70 g. (
83–84 per cent of the theoretical amount) of a product which melts at
199–200° being thus obtained (Note
2).