In a
1-l. three-necked, round-bottomed flask, fitted with a
liquid-sealed mechanical stirrer and
reflux condenser, are placed
69 g. (0.5 mole) of o-nitroaniline (Org. Syn. Coll. Vol. I, 1941, 388),
40 cc. of a 20 per cent solution of sodium hydroxide, and
200 cc. of 95 per cent ethanol. The mixture is stirred vigorously and heated on a
steam bath until the solution boils gently. The steam is turned off, and
10-g. portions of 130 g. (2 gram atoms) of zinc dust (Note
1) are added frequently enough to keep the solution boiling (Note
2) and (Note
3). After the addition of
zinc dust has been completed the mixture is refluxed with continued stirring for one hour; the color of the solution changes from a deep red to nearly colorless. The hot mixture is filtered by suction, and the
zinc residue is returned to the flask and extracted with two
150-cc. portions of hot alcohol. To the combined filtrates is added
2–3 g. of sodium hydrosulfite, and the solution is concentrated under reduced pressure (using a
water pump), on a steam bath, to a volume of 125–150 cc. After cooling thoroughly in an
ice-salt bath, the faintly yellow crystals are collected, washed once with a small amount of ice water, and dried in a
vacuum desiccator. The yield of crude
o-phenylenediamine melting at
97–100° is
46–50 g. (
85–93 per cent of the theoretical amount). If a purer product is desired, the material is dissolved in 150–175 cc. of hot water containing
1–2 g. of sodium hydrosulfite and treated with decolorizing charcoal. After cooling thoroughly in an ice-salt mixture, the colorless crystals are filtered by suction and washed with 10–15 cc. of ice water. The purified
o-phenylenediamine weighs
40–46 g. (
74–85 per cent of the theoretical amount) and melts at
99–101° (Note
4) and (Note
5).