Checked by Robert E. Ireland and Robert Czarny.
1. Procedure
A
200-ml., three-necked flask equipped with a reflux condenser, a thermometer, a glass stopper, and a magnetic stirring bar is charged with
13.4 g. (0.101 mole) of durene (Note
1),
4.56 g. (0.0215 mole) of periodic acid dihydrate, and
10.2 g. (0.0402 mole) of iodine. A solution of
3 ml. of concentrated sulfuric acid and 20 ml. of water in
100 ml. of glacial acetic acid is added to this mixture. The resulting purple solution is heated at 65–70° with stirring for approximately 1 hour until the color of
iodine disappears. The reaction mixture is diluted with approximately 250 ml. of water, and the white-yellow solid that separates (Note
2) is collected on a
Büchner funnel and washed three times with 100-ml. portions of water. The product is dissolved in a minimum amount of boiling
acetone (about 125 ml. is required); the solution is cooled to room temperature and subsequently stored overnight in a refrigerator. The product is collected by rapid filtration through a Büchner funnel, yielding
20.8–22.6 g. (
80–87%) of
iododurene as colorless, fine needles, m.p.
78–80°.
2. Notes
1.
Durene (m.p.
79–80°), prepared according to the procedure in
Org. Synth., Coll. Vol. 2, 248 (1943), was used by the submitter. Commercially available
durene, which melted at
79–80° after purification by the
Org. Synth. procedure above, was used by the checkers.
2. Some crystals of
iododurene that have formed during the heating period tend to take on a purple coloration because of occluded
iodine. This impurity is readily removed by the recrystallization procedure.
3. Discussion
The present procedure is the most convenient method for the direct, high-yield preparation of mono-, di-, or triîodo derivatives from various polyalkylbenzenes and their derivatives. It is also applicable to some moderately activated heteroaromatic systems. However, the reaction fails with compounds bearing strongly deactivating substituent groups. Shorter reaction times and higher degree of product purity are assured by the use of
periodic acid as an oxidizing agent. A feature of the reagent is that
iodine is oxidized by
periodic acid and
periodic acid is reduced by
iodine, both forming an active iodinating species which reacts with an aromatic compound, eventually leading to the formation of only the desired iodination product and water. A brief review of the
iodine/
periodic acid reagent has recently appeared.
2 The preparation of tetraiodo and more highly iodinated derivatives of alkylbenzenes by this procedure is difficult, and the Jacobsen reaction for the disproportionation of diîodo compounds by the action of
sulfuric acid is preferred.
3 Polyiodo derivatives are useful for the characterization of polyalkylbenzenes and their derivatives, liquids available only in a small quantities, since the introduction of
iodine atoms increases the molecular weight and converts a liquid hydrocarbon into a highly crystalline solid with a moderate melting range.
4 Table I illustrates the iodoarenes prepared from the corresponding arenes by conditions similar to that described herein.
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