m-NITROBENZAZIDE

A. m-Nitrobenzoyl chloride. In a 1-l. round-bottomed flask are placed 200 g. (1.2 moles) of crude m-nitrobenzoic acid² and 500 g. (300 ml., 4.2 moles) of thionyl choride (Note 1). The flask is fitted (ground-glass joint) with a reflux condenser carrying a calcium chloride drying tube leading to a gas-absorption trap³ and is heated on a steam bath for 3 hours. The condenser is then set for downward distillation, and as much of the excess thionyl chloride as possible is distilled at the temperature of the steam bath. The residue is transferred to a 250-ml. Claisen flask and distilled at reduced pressure (water pump), b.p. 153–154° /12 mm. (Note 2). The yield is 200–217 g. (90–98%), m.p. 33°.

B. m-Nitrobenzazide. In a 2-l. round-bottomed flask fitted with an efficient mechanical stirrer is placed a solution of 78 g. (1.2 moles) of commercial sodium azide in 500 ml. of water (Note 3). The flask is surrounded by a water bath kept at 20–25°. The stirrer is started, and over a period of about 1 hour a solution of 185.5 g. (1 mole) of m-nitrobenzoyl chloride in 300 ml. of acetone (previously dried over anhydrous potassium carbonate) is added from a dropping funnel. m-Nitrobenzazide separates at once as a white precipitate. Stirring is continued for 30 minutes after the addition is complete; then 500 ml. of water is added and the reaction mixture stirred for an additional 30 minutes. The azide is separated on a suction filter, washed with water, and dried in the air. The yield of crude product, m.p. 68°, is 189 g. (98%) (Note 4). It may be recrystallized from a mixture of equal parts of benzene and ligroin (b.p. 100–140°), when the temperature is kept below 50° (Note 5). The product thus obtained consists of almost colorless crystals, m.p. 68–69° (Note 6), the recovery being 80–90% (Note 7).

1. Eastman Kodak Company white label grade thionyl chloride is satisfactory.

2. Since the product crystallizes readily, water cooling should be applied only at the receiver, not at the side arm.

3. The reaction should preferably be carried out in a hood, as hydrazoic acid may be liberated in small amounts. This compound, which is volatile, is highly toxic, and its inhalation may cause temporary headache and giddiness.

4. This product is sufficiently pure for general reagent use. m-Nitrobenzazide is recommended⁴^,⁵^,⁶^,⁷ as a reagent for the characterization and estimation of aliphatic and aromatic hydroxyl compounds. It reacts to form nicely crystalline m-nitrophenylcarbamic esters,⁵^,⁶^,⁸ in which the nitro group may be titrated with titanous chloride. With amines it forms substituted m-nitrophenylureas.⁹^,¹⁰

5. At higher temperatures a Curtius rearrangement into the isocyanate may occur, nitrogen being liberated. An alternative procedure for recrystallization (preferred by the checkers) consists in dissolving the crude product in a small amount of benzene (if the solution is discolored it may be treated with decolorizing carbon) and adding an equal volume of ligroin. On seeding, the product crystallizes.

6. The melted compound decomposes with liberation of nitrogen.

7. Using the same procedure, p-nitrobenzazide, m.p. 71–72° (Note 6), may be prepared. The yield of crude product is 90%, and of recrystallized product 70%.

References and Notes

Technical University of Denmark, Copenhagen, Denmark.
Org. Syntheses Coll. Vol. 1, 391 (1941).
Org. Syntheses Coll. Vol. 2, 4 (1943).
Veibel, Anal. Chem., 23, 665 (1951).
Sah and Woo, Rec. trav. chim., 58, 1013 (1939).
Veibel and Lillelund, Dansk Tidsskr. Farm., 14, 236 (1940) [C. A., 35, 2444 (1941)].
Veibel, Lillelund, and Wangel, Dansk Tidsskr. Farm., 17, 183 (1943) [C. A., 39, 1608 (1945)].
Hoeke, Rec. trav. chim., 54, 505 (1935).
Sah et al., J. Chinese Chem. Soc., 13, 22 (1946) [C. A., 42, 148 (1948)].
Karrman, Svensk Kem. Tidskr., 60, 61 (1948) [C. A., 42, 5804 (1948)].
Naegeli and Tyabji, Helv. Chim. Acta, 16, 361 (1933).
Barret and Porter, J. Am. Chem. Soc., 63, 3434 (1941).