Org. Synth. 1963, 43, 65
DOI: 10.15227/orgsyn.043.0065
IODOXYBENZENE
[Benzene, iodoxy-]
Submitted by J. G. Sharefkin and H. Saltzman
1.
Checked by E. J. Corey and C. P. Lillya.
1. Procedure
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].
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 titration
3 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, Ar
2I
+X
−.
15
Appendix
Chemical Abstracts Nomenclature (Collective Index Number);
(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
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