In a 2-l. three-necked round-bottomed flask, equipped with a thermometer, a dropping funnel, a mechanical stirrer and a gas vent (Note 1), are placed 258 g. (3.74 moles) of sodium nitrite and 250 ml. of water. The contents of the flask are heated and stirred to dissolve the solid. A solution of 258 g. (1 mole) of mucobromic acid (p. 688) in 250 ml. of warm 95% ethanol is placed in the dropping funnel and added dropwise with constant stirring over a period of 70–80 minutes. A mildly exothermic reaction occurs; the solution in the flask becomes deep red, and gas is evolved. During the addition, the temperature is kept at 54 ± 1° by intermittent application of an ice bath to the flask (Note 2). The mixture is stirred for an additional 10 minutes at 54 ± 1°. While being stirred continuously, it is then cooled to 0–5° by application of an ice bath. The fine, yellow precipitate is collected on a previously chilled Büchner funnel.

The slightly moist cake of crude product is transferred to a 1-l. flask and heated to boiling with a mixture of 400 ml. of 95% ethanol and 100 ml. of water. The hot solution is filtered to remove a fine yellow solid, and the clear red filtrate is cooled to 0–5°. The recrystallized product is collected on a Büchner funnel and dried in air at room temperature. The yield is 57–65 g. (36–41%) of pink or tan needles of sodium nitromalonaldehyde monohydrate (Note 3).