Org. Synth. 1960, 40, 34
DOI: 10.15227/orgsyn.040.0034
[Benzene, 1-iodo-2,4-dinitro-]
Submitted by J. F. Bunnett and R. M. Conner1.
Checked by Virgil Boekelheide and James S. Todd.
1. Procedure
Caution! 2,4-Dinitrochlorobenzene causes sever skin irritation to some individuals. Sensitive persons are advised to wear rubber gloves.
To 200 ml. of redistilled technical grade dimethylformamide (Note 1) in a 1-l. round-bottomed flask are added 150 g. (1 mole) of sodium iodide (Note 2) and 40.5 g. (0.2 mole) of 2,4-dinitrochlorobenzene (Note 3). The flask is fitted with a reflux condenser, and the red-brown mixture is refluxed for 15 minutes over a free flame arranged to impinge somewhat off-center (Note 4).
The hot reaction mixture is poured with stirring over about 0.75 l. of crushed ice in a 2-l. beaker. The beaker is filled with water, and the mixture is stirred to dissolve inorganic salts (Note 5). The insoluble red-brown solid is collected on a suction filter. This crude product, even while damp, is transferred to a 2-l. round-bottomed flask, and 500 ml. of a mixture of 75% (375 ml.) of petroleum ether (b.p. 90–100°) and 25% (125 ml.) of benzene is added. The flask is provided with a reflux condenser, and the mixture is heated at reflux for 15 minutes by means of an electric mantle (Note 6). The resulting solution is decanted into a second 2-l. flask, leaving in the first flask some water and a red-brown solid residue. To the slightly cooled liquor in the second flask is added cautiously 7 g. of powdered activated carbon. The carbon is dispersed by swirling, and the mixture is heated for an additional 5 minutes. The mixture is then filtered through a fluted filter into a 1-l. Erlenmeyer flask. This flask is stoppered and chilled to cause crystallization of the product (Note 7).
The product is collected on a suction filter. The yield of air-dried product, as yellow-orange crystals, m.p. 87–89°, is 38–42 g. (65–71%) (Note 8). A purer, lemon-yellow product, m.p. 88.5–90°, is obtained by an additional recrystallization from 1 l. of petroleum ether (b.p. 90–100°) with use of carbon; the yield after this second crystallization is 28–34 g. (48–58%).
2. Notes
1. Dimethylformamide is available from E. I. du Pont de Nemours and Co., Inc., Wilmington, Delaware.
2. Reagent grade sodium iodide was used.
3. Eastman Kodak white label 2,4-dinitrochlorobenzene, which had a light tan color, was used without further purification.
4. The burner should be so arranged that the flame impinges upon the side of the flask in such a way as to dissolve the sodium iodide from the top downward. The flask should be shaken or swirled frequently during the onset of boiling. A small amount of white solid remains undissolved even at reflux.
5. At this point there may be a lumpy, dark-brown material mixed with the orange-brown crude precipitated product. There appears to be no need to break up the lumps.
6. Alternatively, the flask can be heated on an efficient steam bath with swirling until the crude product melts. After an additional 15 minutes of heating, the solution can be decanted as described.
7. The submitters placed the flasks of warm filtrate in the refrigerator for storage overnight or in a freezing cabinet at −20° for at least 1 hour.
8. From a run of five times the scale described, the submitters obtained 219 g. (71%) of an orange-yellow crystalline product, m.p. 88–90°.
3. Discussion
2,4-Dinitroiodobenzene has been prepared by the nitration of o- or p-nitroiodobenzene,2 by treatment of 2,4-dinitrobenzenediazonium sulfate with potassium iodide,3 and by the reaction of sodium iodide with 2,4-dinitrochlorobenzene in refluxing ethylene glycol.4 The present procedure is a modification5 of the last-mentioned one.
This preparation is referenced from:

References and Notes
  1. Department of Chemistry, University of North Carolina, Chapel Hill, North Carolina.
  2. W. Körner, Gazz. Chim. Ital., 4, 323 (1874).
  3. A. L. Beckwith, J. Miller, and G. D. Leahy, J. Chem. Soc., 3556 (1952).
  4. G. M. Bennett and I. H. Vernon, J. Chem. Soc., 1783 (1938).
  5. J. F. Bunnett and R. M. Conner, J. Org. Chem., 23, 305 (1958).

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

petroleum ether

o- or p-nitroiodobenzene

Benzene (71-43-2)

potassium iodide (7681-11-0)

activated carbon (7782-42-5)

ethylene glycol (107-21-1)

sodium iodide (7681-82-5)

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

dimethylformamide (68-12-2)

Benzene, 1-iodo-2,4-dinitro- (709-49-9)

2,4-dinitrobenzenediazonium sulfate