Iodine Monochloride1

ICl

[7790-99-0]  · ClI  · Iodine Monochloride  · (MW 162.35)

(iodinating reagent for aromatic compounds;2 chloroiodinating reagent for unsaturated compounds;3 cleaves carbon-metal bonds4)

Physical Data: mp 27.2 °C (a-form; black needles, ruby-red by transmitted light); mp 13.9 °C (b-form; black platelets, brownish-red by transmitted light); bp 97 °C (b-form, partial decomposition); d 3.10 g cm-3.

Solubility: sol alcohol, ether, CS2, acetic acid, acetone, pyridine; sol H2O, but hydrolyzes to HCl and IOH.

Form Supplied in: low melting black or brownish-red solid; widely available (usually 97-98% purity).

Handling, Storage, and Precautions: corrosive solid and vapor; readily absorbed through skin and mucous membranes; use in a fume hood and wear gloves and appropriate protective clothing; air-, moisture-, and light-sensitive; should be stored refrigerated (under N2) in a tightly sealed amber bottle. Explodes on contact with potassium metal; mixtures with sodium metal can explode if impacted. Reaction with PCl3 is extremely exothermic.

Iodination of Aromatic Compounds.

As a source of electrophilic iodine, iodine monochloride is an effective reagent for iodination of a wide variety of aromatic compounds,2 including heterocyclic aromatic compounds (eq 1).5 In a related mode of reactivity, uracil bases and protected nucleosides can be iodinated in excellent yield (eq 2).6 See also Iodine-Silver(I) Fluoride and Trifluoroacetyl Hypoiodite for iodination of aromatic compounds.

Chloroiodination of Unsaturated Compounds.3

Formation of vicinal chloroiodoalkanes via iodine monochloride addition to alkenes generally occurs with high anti stereospecificity, implicating the intermediacy of an iodonium ion in the reaction sequence. Unsymmetrical alkenes typically undergo predominantly Markovnikov addition (e.g. reaction of 1-hexene produces a 66:34 mixture of 2-chloro-1-iodohexane and 1-chloro-2-iodohexane in 75% overall yield7). Regioselectivity and stereoselectivity in additions to alkynes are very dependent on the alkyne structure.

Bond Cleavage Reactions.4

Except in the case of C-Fe and C-Co bonds, cleavage of carbon-metal bonds by iodine monochloride specifically produces the organic iodide and the metal chloride. Organosilicon8 (eq 3), organoboron9 (eq 4), and organoaluminum10 (eq 5) bond cleavage reactions are probably of greatest utility to synthetic organic chemists.

Other Applications.

Iodine monochloride can function as a chlorinating agent because of its tendency to disproportionate to molecular iodine and molecular chlorine in nonpolar solvents.11 Oxidation of dioxolanes to esters has been reported to proceed in good to excellent yield.12 Also, a variety of conditions have been reported for the in situ generation of iodine monochloride, including t-Butyl Hypochlorite/Iodine,13 Antimony(V) Chloride/I2,14 and Iodine-Copper(II) Chloride.15


1. McCleland, C. W. In Synthetic Reagents; Pizey, J. S., Ed.; Wiley: New York, 1983; Vol. 5, pp 85-164.
2. (a) See Ref. 1, pp 88-100. (b) For a general review of aromatic iodination, see Merkushev, E. B. S 1988, 923.
3. (a) See Ref. 1, pp 101-120. (b) Schmid, G. H.; Garratt, D. G. In The Chemistry of Doubly-Bonded Functional Groups; Patai, S., Ed.; Wiley: New York, 1977; Part 2, pp 796-799.
4. See Ref. 1, pp 130-143.
5. Surrey, A. R.; Cutler, R. A. JACS 1946, 68, 2570.
6. Robins, M. J.; Barr, P. J.; Giziewicz, J. CJC 1982, 60, 554.
7. Ingold, C. K.; Smith, H. G. JCS 1931, 2742.
8. Hillard, R. L., III; Vollhardt, K. P. C. JACS 1977, 99, 4058.
9. Kabalka, G. W.; Gooch, E. E.; Hsue, H. C. SC 1981, 11, 247.
10. Zweifel, G.; Lewis, W.; On, H. P. JACS 1979, 101, 5101.
11. See Ref. 1, pp 121-129.
12. (a) See Ref. 1, pp 143-147. (b) Mingotaud, A.-F.; Florentin, D.; Marquet, A. SC 1992, 22, 2401.
13. Akhtar, M.; Barton, D. H. R. JACS 1964, 86, 1528.
14. Uemura, S.; Onoe, A.; Okano, M. BCJ 1974, 47, 147.
15. Baird, W. C., Jr.; Surridge, J. H.; Buza, M. JOC 1971, 36, 3324.

Ronald G. Brisbois & Randall A. Wanke

Hamline University, St. Paul, MN, USA



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