A mixture of
200 g. of ethyl hydrazodicarboxylate in
125 ml. of 70% nitric acid is placed in a
1-l., three-necked flask equipped with a
mechanical stirrer,
gas-outlet tube, and thermometer. The flask is cooled in an ice bath, and, when the temperature of the solution reaches 5°,
220 ml. of ice-cold yellow fuming nitric acid (90–95% HNO3, d15 = 1.49–1.50) is added. The reaction mixture is maintained at 0–5° for 2 hours with stirring and is then carefully poured on a stirred mixture of 500 g. of ice, 500 ml. of ice water, and
100 ml. of methylene chloride in a
2-l. beaker placed in a metal pan (Note
4). After the ice melts, the solution is transferred carefully to a
2-l. separatory funnel. The organic (lower) layer is removed, and the acid layer is extracted (Note
5) with three
100-ml. portions of methylene chloride. The combined organic layers are washed twice with 100-ml. portions of ice water and are then stirred mechanically for 10 minutes with 500 ml. of
ice-cold 10% potassium bicarbonate solution. The layers are separated in a
separatory funnel, and the organic layer is finally washed with 100 ml. of ice water and dried quickly with a small portion of anhydrous
magnesium sulfate that is removed by filtration. The solution is dried overnight with a fresh portion of anhydrous
magnesium sulfate.
Caution! The following distillations should be well shielded. The
methylene chloride is removed on a
steam bath under reduced pressure, and the residue is rapidly distilled without fractionation under vacuum (1–5 mm.) from a flask immersed in an
oil bath whose temperature is raised gradually from 75° to 130°. The crude distillate is then fractionally distilled under vacuum through a
short column packed with glass helices, using an oil bath to heat the distillation flask. After a short fore-run, the main fraction is collected at
93–95°/5 mm. There is obtained
138–158 g. (
70–80%) of
ethyl azodicarboxylate which freezes at 6° (Note
6), (Note
7), and (Note
8).