Methylglyoxal-ω-Phenylhydrazone could be produced through the following synthetic routes.

In a 4-l. beaker equipped with a mechanical stirrer is placed a solution of 35 g. (0.53 mole) of 85% potassium hydroxide in 1120 ml. of water. To the solution is added, with stirring, 65 g. (64 ml., 0.5 mole) of ethyl acetoacetate. The mixture is allowed to stand at room temperature for 24 hours.

Forty-seven grams (48 ml., 0.5 mole) of aniline is dissolved in 200 ml. of aqueous hydrochloric acid (prepared from equal volumes of concentrated acid and water) in a 2-l. beaker. The beaker is equipped with a mechanical stirrer and immersed in an ice-salt bath. After the solution has cooled to ±5°, 36 g. (0.52 mole) of sodium nitrite dissolved in 1 l. of water is added slowly, with stirring, from a separatory funnel. The tip of the stem of the separatory funnel should dip well below the surface of the liquid. The rate of addition is adjusted to maintain the temperature below 10°. A drop of the reaction mixture is tested from time to time with starch-iodide paper. The sodium nitrite solution is added until nitrous acid persists in the solution during a 5-minute interval.

The solution of potassium acetoacetate is cooled to 0°, and 45 ml. of concentrated hydrochloric acid in 150 ml. of ice water is added slowly with stirring. The diazonium salt solution is then added over a period of 20 minutes, and the mixture is made basic by the addition of 82 g. of sodium acetate dissolved in 300 ml. of water. The temperature of the reaction mixture is raised slowly to 50° and maintained at this value for 2 hours; the solid that separates is collected on a filter and dried. The yield of crude product is 72–77 g. (89–95%). Purification can be effected by recrystallization from 200 ml. of toluene. The purified product weights 59–66 g. (73–82%); m.p. 148–150°.