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Org. Synth. 1940, 20, 16
DOI: 10.15227/orgsyn.020.0016
1,2,3-BENZOTRIAZOLE
[1H-Benzotriazole]
Submitted by R. E. Damschroder and W. D. Peterson.
Checked by W. E. Bachmann and W. S. Struve.
1. Procedure
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°.
2. Notes
1. Too efficient cooling and stirring are to be avoided. It is essential that the temperature rise to 80°. Too rapid cooling after this temperature has been reached results in lower yields. With runs one-tenth this size it is advisable to remove the mixture from the cooling bath as soon as the sodium nitrite has been added in order to ensure the rise in temperature.
2. The crude product can be purified by repeated crystallizations from benzene or water. Greater losses accompany this tedious method of purification than a single distillation.
3. The submitters report that runs of double this size can be made with equally good results.
3. Discussion
1,2,3-Benzotriazole has been prepared directly by the action of nitrous acid on o-phenylenediamine1 and by the hydrolysis of an acylated or aroylated benzotriazole which has been previously prepared by the action of nitrous acid on the corresponding mono acylated or aroylated o-phenylenediamine.2,3,4 The above procedure is the direct method and gives better over-all yields than the methods involving several intermediate steps. Most methods described in the literature employ mineral acid. Acetic acid is much more satisfactory.

References and Notes
  1. Ladenburg, Ber., 9, 219 (1876).
  2. Bell and Kenyon, J. Chem. Soc., 1926, 954.
  3. Fieser and Martin, J. Am. Chem. Soc., 57, 1838 (1935).
  4. Charrier and Beretta, Gazz. chim. ital., 51, (Part 2), 267 (1921).

Appendix
Chemical Abstracts Nomenclature (Collective Index Number);
(Registry Number)

acetic acid (64-19-7)

Benzene (71-43-2)

sodium nitrite (7632-00-0)

nitrous acid (7782-77-6)

1,2,3-Benzotriazole,
1H-Benzotriazole,
benzotriazole (95-14-7)

o-Phenylenediamine (95-54-5)