Organic Syntheses, CV 4, 633
METHYLGLYOXAL-ω-PHENYLHYDRAZONE
Submitted by George A. Reynolds and J. A. VanAllan
1.
Checked by T. L. Cairns and C. T. Handy.
1. Procedure
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 (Note
1). 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 (Note
2). 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 (Note
3). 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 (Note
4). 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%) (Note
5) and (Note
6); m.p.
148–150°.
2. Notes
2. The test is made by diluting the test drop on a
watch glass with about 1 ml. of water and then placing a drop of this solution on the starch-iodide paper.
3. The solution is neutralized slowly in order to keep it cold so that the
acetoacetic acid will not be decomposed.
4. The reaction proceeds much more rapidly in basic solution.
5. An additional
4–6 g. of product separates slowly from the filtrate.
6. This general procedure is effective for the preparation of many types of phenylhydrazones. For example, a substituted diazo compound can be employed.
2 Alkylated acetoacetic esters
3 and
ethyl benzoylacetate4 may be used. For the higher homologs, the α-formyl derivatives of ketones may be used in place of
ethyl acetoacetate.
5,6 Ethyl pyridylacetates may also be substituted for
ethyl acetoacetate.
7 The products in these cases are the phenylhydrazones of 2-acylpyridines.
3. Discussion
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