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Org. Synth. 1933, 13, 36
DOI: 10.15227/orgsyn.013.0036
2,4-DINITROPHENYLHYDRAZINE
[Hydrazine, (2,4-dinitrophenyl)-]
Submitted by C. F. H. Allen
Checked by Reynold C. Fuson and Mark W. Farlow.
1. Procedure
Thirty-five grams (0.27 mole) of hydrazine sulfate (Org. Syn. Coll. Vol. I, 1941, 309) is suspended in 125 cc. of hot water in a 400-cc. beaker and stirred by hand during the addition of 85 g. (0.87 mole) of potassium acetate (Note 1). The mixture is boiled five minutes and then cooled to about 70°; 75 cc. of alcohol is added, and the solid is filtered with suction and washed with 75 cc. of hot alcohol. The filtered hydrazine solution is saved for the next step.
In a 1-l. flask fitted with a stirrer and reflux condenser, 50.5 g. (0.25 mole) of technical 2,4-dinitrochlorobenzene is dissolved in 250 cc. of alcohol; the hydrazine solution is added, and the mixture is refluxed with stirring for an hour. Most of the product separates during the first ten minutes (Note 2); it is cooled well, filtered, and washed, once with 50 cc. of warm alcohol (60°) to remove unchanged halide and then with 50 cc. of hot water. The solid weighs 30 g. and melts at 190–192° with evolution of gas (Note 3); it is pure enough for most purposes. By distilling half the alcohol from the filtrate a less pure second crop is obtained; this is recrystallized from n-butyl alcohol (30 cc. per g.) (Note 4). The total yield is 40–42 g. (81–85 per cent of the theoretical amount) (Note 5)(Note 10).
2. Notes
1. An equivalent amount of sodium acetate may be substituted for the potassium acetate.
2. Considerable heat is evolved during the separation.
3. The melting point is not sharp; in the capillary tube the sample shrinks about 10° below the melting point.
4. For recrystallization, n-butyl alcohol is the best solvent in spite of the large amount required, but tetralin, pyridine, or dioxane (10 cc. per g.) may be used where large quantities are involved. Fortunately, most of the material as prepared does not need further purification.
5. Complete evaporation of the filtrate yields a gummy residue; the amount of dinitrochlorobenzene present is too small to justify recovery.
6. By substituting 10 g. of sodium hydroxide for every 35 g. of potassium acetate and boiling for five minutes without filtering the salt, a 70 per cent yield of dinitrophenylhydrazine results; the quality is not quite so good as that obtained by the use of potassium acetate.
7. A slightly higher yield is obtained by starting with hydrazine hydrate.
8. 2,4-Dinitrophenylhydrazine is used in qualitative organic analysis for preparing solid derivatives of carbonyl compounds.1, 2
9. By this procedure 2,6-dinitrophenylhydrazine can be prepared from 2,6-dinitrochlorobenzene; picryl chloride gives 2,4,6-trinitrophenylhydrazine.
10. These directions have been used equally successfully with twice, and with five times, the amounts specified.
3. Discussion
2,4-Dinitrophenylhydrazine has been prepared from hydrazine hydrate and 2,4-dinitrochlorobenzene3, 2 or 2,4-dinitrobromobenzene,4 and from the same halogen compounds and hydrazine acetate.1

References and Notes
  1. Allen, J. Am. Chem. Soc. 52, 2955 (1930).
  2. Brady and Elsmie, Analyst 51, 77 (1926); Brady, J. Chem. Sec. 1931, 757.
  3. Purgotti, Gazz. chim. ital. 24 (I) 555 (1894).
  4. Curtius and Dedichen, J. prakt. chem. (2) 50, 258 (1894).

Appendix
Chemical Abstracts Nomenclature (Collective Index Number);
(Registry Number)

alcohol (64-17-5)

sodium acetate (127-09-3)

sodium hydroxide (1310-73-2)

n-butyl alcohol (71-36-3)

pyridine (110-86-1)

hydrazine hydrate (7803-57-8)

2,4-dinitrochlorobenzene (97-00-7)

dinitrochlorobenzene

2,4-Dinitrophenylhydrazine,
Hydrazine, (2,4-dinitrophenyl)- (119-26-6)

Hydrazine sulfate (10034-93-2)

Tetralin (119-64-2)

dioxane (5703-46-8)

potassium acetate (127-08-2)

dinitrophenylhydrazine

2,6-dinitrophenylhydrazine

2,6-dinitrochlorobenzene (606-21-3)

picryl chloride (88-88-0)

2,4,6-trinitrophenylhydrazine (653-49-6)

2,4-dinitrobromobenzene (584-48-5)

hydrazine acetate (7335-65-1)