Potassium Iodide1

KI

[7681-11-0]  · IK  · Potassium Iodide  · (MW 166.00)

(source of iodide ion for nucleophilic displacement reactions;4 -9 cleaves some ethers in the presence of acid;10-12 acts as a mediator in electrochemical oxidations of aldehydes;13 reacts with sulfonyl chlorides to give symmetrical thiosulfonic S-esters;14 with oxidizing agents, iodinates aromatic compounds;15 iodinates organothallium compounds16)

Physical Data: mp 681 °C; bp 1330 °C; d 3.130 g cm-3.

Solubility: very sol cold H2O (127.5 g/100 mL, 6 °C), hot H2O (208.0 g/100 mL, 100 °C); sol alcohol (1.88 g/100 mL, 25 °C), acetone (1.31 g/100 mL, 25 °C); slightly sol ether, ammonia.2

Form Supplied in: white solid (crystalline, granular, or powder); widely available. Drying: can be dried under vacuum over P2O5 at 70-100 °C.3

Handling, Storage, and Precautions: slightly deliquescent in moist air, and upon long exposure to air will turn yellow due to liberation of iodine; storage in a dry or inert atmosphere recommended.

Introduction.

KI is used primarily as a source of iodide in organic synthesis. KI can often be used interchangeably with NaI (see Sodium Iodide and Tetra-n-butylammonium Iodide).

Displacement Reactions.

KI will react with alkyl halides to give alkyl iodides. Alkyl iodides have been prepared from alkyl chlorides and bromides using KI supported on alumina.4 The product iodide may be isolated or may react with a second nucleophile (e.g. Dimethyl Sulfoxide).5 KI/Phosphoric Acid has been used to convert 1,6-hexanediol to 1,6-diiodohexane6 and cyclohexene to cyclohexyl iodide.7 KI reacts with aryl diazonium compounds to give aryl iodides.8 This reaction has been shown to involve radicals, and proceeds faster and in higher yield in the absence of oxygen.9

Ether Cleavage Reactions.

KI in acetic acid or formic acid has been used to cleave aryl methyl ethers in high yield (yields were somewhat higher with KI than with NaI).10 KI/H3PO4 has been used to convert THF to 1,4-diiodobutane.11 KI/Boron Trifluoride Etherate cleaves methyl, allyl, and benzyl ethers and opens cyclic alkyl ethers (including THF and epoxides) to give iodo alcohols.12 Aryl methyl ethers are cleaved slowly by this reagent, allowing for some selectivity.

Electrochemical Oxidations.

KI has been used as a catalytic mediator in the electrochemical oxidation of aldehydes to esters13 and nitriles.13c (NaI and Et4NI may be used in place of KI in these electrochemical oxidations.)

Preparation of Symmetrical Thiosulfonic S-Esters.

KI reacts with sulfonyl chlorides (RSO2Cl) to give thiosulfonic S-esters (RSO2SR).14

Iodination of Aromatic Hydrocarbons.

KI/O2/NO+BF4- in TFA/CH2Cl2 or TFA iodinates aromatic hydrocarbons; however, the reaction fails with electron-deficient aromatics.15 (NaI, n-Bu4NI, and Iodine may be substituted for KI.) KI reacts with arylthallium bis(trifluoroacetate) compounds to give aryl iodides (and thallium triiodide) (eq 1).16 Vinyl iodides have been prepared similarly from vinylthallium bis(trifluoroacetates).16f


1. (a) Kirk-Othmer Encyclopedia of Chemical Technology, 3rd ed.; Wiley: New York, 1983; Vol. 18, p 939. (b) Comprehensive Inorganic Chemistry; Bailar, J. C.; Emeléus, H. J.; Nyholm, S. R.; Trotman-Dickenson, A. F., Eds.; Pergamon: Oxford, 1973; Vol. 1, pp 402-413.
2. CRC Handbook of Chemistry and Physics, 73rd ed.; Lide, D. R., Ed. CRC Press: Boca Raton, FL, 1992.
3. Perrin, D. D.; Armarego, W. L. F.; Perrin, D. R. Purification of Laboratory Chemicals, 2nd ed.; Pergamon: New York, 1980; p 514.
4. Clark, J. H.; Jones, C. W. JCR(S) 1990, 39.
5. Bauer, D. P.; Macomber, R. S. JOC 1975, 40, 1990.
6. Stone, H.; Shechter, H. OSC 1963, 4, 323.
7. Stone, H.; Shechter, H. OSC 1963, 4, 543.
8. (a) Lucas, H. J.; Kennedy, E. R. OSC 1943, 2, 351. (b) Dains, F. B.; Eberly, F. OSC 1943, 2, 355. (c) Sandin, R. B.; Cairns, T. L. OSC 1943, 2, 604.
9. Kumar, R.; Singh, P. R. TL 1972, 613.
10. Mustafa, A.; Sidky, M. M.; Mahran, M. R. LA 1967, 704, 182.
11. Stone, H.; Shechter, H. OSC 1963, 4, 321.
12. Mandal, A. K.; Soni, N. R.; Ratnam, K. R. S 1985, 274.
13. (a) Chiba, T.; Okimoto, M.; Nagai, H.; Takata, Y. BCJ 1982, 55, 335. (b) Shono, T.; Matsumura, Y.; Hayashi, J.; Inoue, K.; Iwasaki, F.; Itoh, T. JOC 1985, 50, 4967. (c) Okimoto, M.; Chiba, T. JOC 1988, 53, 218.
14. Palumbo, G.; Caputo, R. S 1981, 888.
15. Radner, F. JOC 1988, 53, 3548.
16. (a) Taylor, E. C.; Kienzle, F.; McKillop, A. OS 1976, 55, 70. (b) Taylor, E. C.; Kienzle, F.; McKillop, A. OSC 1988, 6, 709. (c) Gilliland, D. L.; Basmadjian, G. P.; Marchand, A. P.; Hinkle, G. H.; Earlywine, A.; Ice, R. D. J. Radioanal. Chem. 1981, 65, 107. (d) Braun, S. L.; Duermeyer, E.; Jacob, K.; Vogt, W. ZN(B) 1983, 38B, 696. (e) Merkushev, E. B.; Gulyaeva, N. E. ZOR 1983, 19, 1120. (f) Srivastava, P. C.; Knapp, F. F., Jr.; Kabalka, G. W.; Kunda, S. A. SC 1985, 15, 355.

James J. Kowalczyk

Eisai Research Institute, Andover, MA, USA



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