In a
1-l. beaker are placed
108 g. (1 mole) of o-phenylenediamine,
120 g. (115 ml., 2 moles) of glacial acetic acid, and 300 ml. of water. By warming the mixture slightly a clear solution is obtained. The beaker is placed in ice water, and the contents are cooled to 5°. As soon as this temperature is reached, a cold solution of
75 g. (1.09 moles) of sodium nitrite in 120 ml. of water is added all at once, the mixture being stirred with a
glass rod or by a
slow mechanical stirrer. The reaction mixture turns dark green, and the temperature rises rapidly to 70–80° (Note
1). The color of the solution changes to a clear orange-red. The beaker is now removed from the
cooling bath, and the contents are allowed to stand for 1 hour; as the solution cools, the
benzotriazole separates as an oil. The beaker is then packed in ice, and the mixture is stirred until it sets to a solid mass. After being kept cold for 3 hours, the solid is collected on a
Büchner funnel, washed with 200 ml. of ice water, and sucked as dry as possible under a
rubber dam. The tan-colored product, after drying at 45–50° overnight, weighs
110–116 g.
The crude
benzotriazole is placed in a
200-ml. modified Claisen flask and distilled under reduced pressure (Note
2). The yield of white solid (yellow cast) boiling at
201–204° at 15 mm. or
156–159° at 2 mm. is
92–99 g. The product in the receiver is melted over a luminous flame and poured into
250 ml. of benzene. The clear solution is stirred until crystallization sets in; after being chilled for 2 hours, the product is filtered on a Büchner funnel. The colorless
benzotriazole weighs
90–97 g. (
75–81%) (Note
3) and melts at
96–97°.