IODOXYBENZENE

Caution! Reactions and subsequent operations involving peracids and peroxy compounds should be run behind a safety shield. For relatively fast reactions, the rate of addition of the peroxy compound should be slow enough so that it reacts rapidly and no significant unreacted excess is allowed to build up. The reaction mixture should be stirred efficiently while the peroxy compound is being added, and cooling should generally be provided since many reactions of peroxy compounds are exothermic. New or unfamiliar reactions, particularly those run at elevated temperatures, should be run first on a small scale. Reaction products should never be recovered from the final reaction mixture by distillation until all residual active oxygen compounds (including unreacted peroxy compounds) have been destroyed. Decomposition of active oxygen compounds may be accomplished by the procedure described in Korach, M.; Nielsen, D. R.; Rideout, W. H. Org. Synth. 1962, 42, 50 (Org. Synth. 1973, Coll. Vol. 5, 414). [Note added January 2011].

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

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.

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

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.

References and Notes

Department of Chemistry, Brooklyn College of the City University of New York, Brooklyn, New York.
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