Organic Syntheses, CV 5, 665
IODOXYBENZENE
[Benzene, iodoxy-]
Submitted by J. G. Sharefkin and H. Saltzman1.
Checked by E. J. Corey and C. P. Lillya.
1. Procedure
Caution! Avoid inhaling the vapor of peracetic acid or allowing the liquid to come into contact with the skin. The reaction is best carried out in a hood (Note 1). Iodoxybenzene explodes if heated to 230°.
A 500-ml. three-necked flask fitted with reflux condenser, stirrer, and dropping funnel and containing 20.4 g. (0.10 mole) of iodobenzene2 is immersed in an oil bath maintained at 35°. Seventy-five grams (65 ml., 0.50 mole) of commercial 40% peracetic acid (Note 1) is added with vigorous stirring over a 30-minute period. Solid may begin to form before all the peracetic acid has been added, but, although this may slow down the stirring, it does not decrease the yield or cause a rise in temperature.
After all the peracetic acid has been added, the reaction mixture is diluted with 80 ml. of water and heated from 35° to 100° over a 20-minute period (Note 2). It is then kept at 100° for 45 minutes. The flask is cooled to 0–5° in an ice bath, and the solid iodoxybenzene is collected on a Büchner funnel and air-dried with suction for 1 hour. Additional material is obtained by concentrating the filtrate to one-fourth of its volume (Caution! (Note 3)). The two crops of crude iodoxybenzene are combined and dried overnight in a desiccator; weight 19.6–20.5 g.; m.p. 230° (Caution! Explodes!). Iodometric titration3 shows the purity to be about 94% (Note 4).
Purification of the crude iodoxybenzene is effected by grinding it to a powder in a mortar, macerating it with 70 ml. of chloroform, and separating the solid by filtration. The chloroform extraction is repeated and the solid is dried; weight 17–19 g. (72–80%); purity 99.0–99.9% by iodometric titration.3
2. Notes
1. For a source and the specifications of 40% peracetic acid and precautions in handling it, see Note 3 and Note1 under the preparation of iodosobenzene diacetate, p. 661.
2. If the temperature of the bath is not raised slowly, foaming is difficult to control. Although the gradual rise in temperature causes considerable foaming, the reaction mixture remains within the flask.
3. The filtrate must not be evaporated to dryness because iodoxybenzene explodes when heated.
4. The major by-products in this reaction are iodobenzene and iodosobenzene diacetate. An excess of 20 ml. of peracetic acid over the 65 ml. recommended results in an increase in the amount of iodobenzene. Both impurities are removed from the product by washing with chloroform.
3. Discussion
Iodoxybenzene has been prepared by the disproportionation of iodosobenzene,4,5,6 by oxidation of iodosobenzene with hypochlorous acid or bleaching powder,7 and by oxidation of iodobenzene with hypochlorous acid or with sodium hydroxide and bromine.8 Other oxidizing agents used with iodobenzene include air,3 chlorine in pyridine,9 Caro's acid,10,11 concentrated chloric acid,12 and peracetic acid solution.13 Hypochlorite oxidation of iodobenzene dichloride has also been employed.14
4. Merits of the Preparation
This one-step method of preparing iodoxybenzene is preferable to earlier methods because it is simpler and the yield is substantially higher. The procedure seems general for iodoxyarenes, at least those with electron-releasing substituents, for the submitters have used it to obtain good yields of o-, m- and p-iodoxytoluene, 2- and 4-iodoxy-m-xylene, 2-iodoxy-p-xylene, o-iodoxyphenetole, 4-iodoxybiphenyl, and o-iodoxybenzoic acid.
Iodoxyarenes are useful in the preparation of iodonium salts, Ar2I+X.15
References and Notes
  1. Department of Chemistry, Brooklyn College of the City University of New York, Brooklyn, New York.
  2. H. J. Lucas and E. R. Kennedy, Org. Syntheses, Coll. Vol. 2, 351 (1943).
  3. C. Willgerodt, Ber., 25, 3500 (1892); 26, 358 (1893).
  4. C. Willgerodt, Ber., 26, 1307, 1806 (1893).
  5. P. Askenasy and V. Meyer, Ber., 26, 1356 (1893).
  6. H. J. Lucas and E. R. Kennedy, Org. Syntheses, Coll. Vol. 3, 485 (1955).
  7. C. Willgerodt, Ber., 29, 1568 (1896).
  8. C. Willgerodt, Ber., 29, 1571 (1896).
  9. G. Ortoleva, Chem. Zentr., 1900, 723.
  10. E. Bamberger and A. Hill, Ber., 33, 534 (1900).
  11. I. Masson, E. Race, and F. E. Pounder, J. Chem. Soc., 1678 (1935).
  12. R. L. Datta and J. K. Choudhury, J. Am. Chem. Soc., 38, 1085 (1916).
  13. B. A. Arbusov, J. Prakt. Chem., 131, 357 (1931).
  14. M. W. Formo and J. R. Johnson, Org. Syntheses, Coll. Vol. 3, 486 (1955).
  15. C. Hartman and V. Meyer, Ber., 27, 504 (1894).

Appendix
Compounds Referenced (Chemical Abstracts Registry Number)

o-, m- and p-iodoxytoluene

sodium hydroxide (1310-73-2)

chloroform (67-66-3)

bromine (7726-95-6)

pyridine (110-86-1)

chlorine (7782-50-5)

chloric acid (7790-93-4)

hypochlorous acid (7790-92-3)

Iodobenzene (591-50-4)

iodobenzene dichloride (2401-21-0)

peracetic acid (79-21-0)

Iodonium

Iodosobenzene (536-80-1)

Iodoxybenzene, Benzene, iodoxy- (696-33-3)

Iodosobenzene diacetate (3240-34-4)

4-iodoxybiphenyl

4-iodoxy-m-xylene

2-iodoxy-p-xylene

o-iodoxyphenetole

o-iodoxybenzoic acid