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Org. Synth. 1939, 19, 81
DOI: 10.15227/orgsyn.019.0081
1,2,3-TRIIODO-5-NITROBENZENE
[Benzene, 1,2,3-triiodo-5-nitro-]
Submitted by R. B. Sandin and T. L. Cairns.
Checked by Frank C. Whitmore and L. H. Sutherland.
1. Procedure
Fifty grams (0.13 mole) of 2,6-diiodo-4-nitroaniline (p. 196) is dissolved in 200 cc. of concentrated sulfuric acid (sp. gr. 1.84) in a 1-l. two-or three-necked flask provided with a mechanical stirrer. The solution is cooled to 5° in an ice-salt mixture, and to it is added with stirring a mixture of 100 cc. of concentrated sulfuric acid and 12 g. (0.17 mole) of sodium nitrite, also cooled to 5° (Note 1). To liberate nitrous acid from the nitrosylsulfuric acid, there is then added slowly from a separatory funnel, with rapid stirring, 200 cc. of 85 per cent phosphoric acid (151 cc. of u.s.p. phosphoric acid diluted to 200 cc.). During the addition the temperature is kept below 10°. The mixture is removed from the ice-salt bath and stirred until diazotization is complete (one to two hours) (Note 2). At the end of this time the solution is poured, with stirring, into 2 l. of a mixture of cracked ice and water in a 4-l. beaker. To destroy excess nitrous acid about 15 g. of urea is added in small portions, with stirring, as long as gas is produced. The mixture is filtered if it is not clear and is then treated gradually with a solution of 30 g. (0.18 mole) of potassium iodide in 200 cc. of water. To complete the reaction the mixture is heated until no more gas is evolved. Any free iodine is removed by sodium bisulfite, and the mixture is then filtered on a Büchner funnel, washed free from sulfuric acid and inorganic salts, pressed, and sucked as dry as possible. The product is then air dried to constant weight. The yield of light brown, crude material, m.p. 160–162°, is 60–61 g. (94–95 per cent of the theoretical amount). The pure product can be obtained by dissolving the crude material in 200 cc. of boiling benzene, filtering, and cooling the filtrate to 10°. The yield of yellow crystals melting at 161–162° is 40–42 g. (65–70 per cent recovery) (Note 3).
2. Notes
1. The sodium nitrite must be finely powdered and added slowly with vigorous stirring to the sulfuric acid, which is kept at 5° in an ice-salt mixture. The evolution of oxides of nitrogen during the addition of the nitrite must be avoided.
2. During this time the temperature of the mixture gradually rises to that of the room. When diazotization is complete a drop of the mixture will form a clear yellow solution if added to 10 cc. of cold water.
3. It has been reported that the procedure of Hodgson and Walker1 is preferable to that described above, and that crude triiodonitrobenzene is best purified by crystallization from cellosolve. [Carl Niemann and C. E. Redemann, private communication, and J. Am. Chem. Soc. 63, 1550 (1941).]
3. Discussion
1,2,3-Triiodo-5-nitrobenzene has been prepared by the diazotization of 2,6-diiodo-4-nitroaniline (without the use of phosphoric acid) and subsequent treatment with potassium iodide.1 The present procedure is an example of a general method developed by Schoutissen2 for diazotization of weakly basic amines, such as the 2,6-dihalogen derivatives of p-nitroaniline.

References and Notes
  1. Willgerodt and Arnold, Ber. 34, 3343 (1901); Kalb, Schweizer, Zellner, and Berthold, ibid. 59, 1866 (1926); Harington and Barger, Biochem. J. 21, 175 (1927); Hodgson and Walker, J. Chem. Soc. 1933, 1620.
  2. Schoutissen, J. Am. Chem. Soc. 55, 4531 (1933).

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

oxides of nitrogen

2,6-dihalogen derivatives of p-nitroaniline

sulfuric acid (7664-93-9)

Benzene (71-43-2)

potassium iodide (7681-11-0)

sodium nitrite (7632-00-0)

nitrous acid (7782-77-6)

sodium bisulfite (7631-90-5)

iodine (7553-56-2)

phosphoric acid (7664-38-2)

cellosolve (107-21-1)

urea (57-13-6)

nitrosylsulfuric acid (7782-78-7)

2,6-Diiodo-4-nitroaniline (5398-27-6)

1,2,3-TRIIODO-5-NITROBENZENE,
Benzene, 1,2,3-triiodo-5-nitro- (53663-23-3)

triiodonitrobenzene