Iodine-Potassium Iodate


[7553-56-2]  · I2  · Iodine-Potassium Iodate  · (MW 253.80) (KIO3)

[7758-05-6]  · IKO3  · Iodine-Potassium Iodate  · (MW 214.00)

(conversion of alkenes to iodohydrins;1 iodination of some aromatic molecules;2 the iodohydrins (or iodoacetates) formed are readily converted to cis-diols3)

Physical Data: KIO3: mp 560 °C; d 3.930 g cm-3. I2: see Iodine.

Solubility: KIO3: sol water: 9.16 g/100 g water at 25 °C and 32.2 g/100 g water at 100 °C.4 In other work, the solubility in water was measured to be: 8.40 g KIO3/100 g water at 25 °C; 13.7 g/100 g at 50 °C; and 24.4 g/100 g at 100 °C.5 It shows some solubility in aqueous dioxane mixtures: 8.472 g/100 g (0% dioxane:100% water); 5.30 g/100 g (10% dioxane); 3.172 g/100 g (20% dioxane); 1.811 g/100 g (30% dioxane); 0.886 g/100 g (40% dioxane); and 0.471 g/100 g (50% dioxane). KIO3 insol pure dioxane and most common organic solvents.

Form Supplied in: the active reagent is generated in situ, as needed. KIO3: colorless monoclinic crystals; commercially available in at least 99.5% purity.

Preparative Method: in reactions with alkenes, the following ratio of reactants is typical: alkene:KIO3:I2, 4:1:2 in acetic acid.3 The iodine and potassium iodate are premixed in acetic acid at ambient temperatures and then treated with the organic substrate and allowed to react at a suitable temperature.

Handling, Storage, and Precautions: the reagent should be prepared in solution, as needed, and used in situ. Potassium iodate is an irritant, particularly of the upper respiratory tract. Ingestion causes headache, nausea and vomiting, dizziness, and gastrointestinal irritation. Avoid ingestion, skin contact, and eye contact. Potassium iodate is a powerful oxidant and should not be stored near combustible materials, near flammable materials, or near powdered metals. Mixing with powdered metals can cause an explosion. It should be stored in a separate and tightly closed container. This combination reagent should be handled in a fume hood.

Addition to Alkenes.

Potassium iodate is a powerful oxidant and Iodine is an electrophilic reagent. When mixed together in acid media, the combined reagent converts alkenes to iodohydrins, which can be converted to cis-diols. Cornforth reacted propene with a mixture of iodine and potassium iodate, in aqueous sulfuric acid, and obtained a 92% yield of 1-iodo-2-propanol, along with 8% of 2-iodo-1-propanol (eq 1).1 When the same reaction is done in acetic acid and aqueous dioxane, a 78% yield of the iodohydrin is obtained.

This fundamental iodohydrin procedure has been modified to produced syn-diols from alkenes. When cyclohexene is treated with I2/KIO3 in acetic acid, the trans-iodohydrin is formed. Subsequent reflux of this product with aqueous acetic acid or with aqueous DMSO produces syn-1,2-cyclohexanediol in 70% yield.1 This same procedure has been applied to 5a-cholest-2-ene to give 2b-acetoxy-3a-iodo-5a-cholestene (eq 2). Refluxing in aqueous acetic acid leads to an 84% yield of 5a-cholestene-2b,3b-diol.1,6 This two-step procedure is a useful alternative to the Woodward-Prévost reaction (see Iodine-Silver Acetate) that produces syn-diols from alkenes. This I2/KIO3 procedure is attractive for this purpose since it does not rely on expensive silver reagents.

Quinones can be converted to iodoquinones with this mixed reagent. When 2-dimethylamino-1,4-benzoquinone is treated with iodine/potassium iodate in a solvent of ether and aqueous sulfuric acid, 2-dimethylamino-3-iodo-1,4-benzoquinone is formed, but in only 22% yield (eq 3).3

1. Cornforth, J. W.; Green, D. T. JCS(C) 1970, 846.
2. Wunderer, H. CB 1972, 105, 3479.
3. Mangoni, L.; Adinolfi, M.; Barone, G.; Parrili, M. TL 1973, 4485.
4. Kirk-Othmer Encyclopedia of Chemical Technology, 3rd ed.; Wiley: New York, 1978; Vol. 13, p 666.
5. Linke, W. F. Solubilities of Inorganic and Metal-Organic Compounds; Van Nostrand: New Jersey 1965; Vol. 2, p 235.
6. Mangoni, L.; Adinolfi, M.; Barone, G.; Parrilli, M. G 1975, 105, 377.

Michael B. Smith

University of Connecticut, Storrs, CT, USA

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