Iodine-Copper(II) Chloride

I2-CuCl2
(I2)

[7553-56-2]  · I2  · Iodine-Copper(II) Chloride  · (MW 253.80) (CuCl2)

[7447-39-4]  · Cl2Cu  · Iodine-Copper(II) Chloride  · (MW 134.45) (CuCl2.2H2O)

[10125-13-0]  · H4Cl2CuO2  · Iodine-Copper(II) Chloride  · (MW 170.49)

(iodinating agent)

Physical Data: see Iodine and Copper(II) Chloride.

Handling, Storage, and Precautions: see Iodine and Copper(II) Chloride.

Aromatic Iodination.

Iodine-copper(II) chloride is a useful reagent combination for the preparation of aryl iodides from aromatic hydrocarbons.1 Thus, heating mesitylene with I2-CuCl2 at 150 °C gives iodomesitylene in 86% yield (eq 1). The reaction proceeds in moderate to good yields with unsubstituted aromatics and compounds with alkyl, halogen, hydroxy, alkoxy, and dimethylamino substituents. Iodination fails, however, with strongly deactivated ring systems such as methyl benzoate, aniline, thiophene, and pyridine.1 Because of the limitations of the simple I2-CuCl2 iodinating system, alternative procedures have been studied. For example, a mixture of I2-AlCl3-CuCl2 is effective for the preparation of aryl iodides, one advantage being that lower reaction temperatures are required.2 Recently, a very efficient iodinating system has been developed using alumina-supported iodine-copper(II) chloride;3 in the absence of solvent at 40-120 °C, monoiodination of polymethylbenzenes, alkoxy aromatics, and polynuclear aromatic hydrocarbons occurs in high yield. The I2-Al2O3-CuCl2 system exhibits very good selectivity, i.e. alkoxy aromatic substrates are almost exclusively para-iodinated (eq 2).

Iodination of Alkynes.

The liquid-phase halogenation of alkenes with copper(II) chloride is well known and has been studied in some detail.4 The halogenation of alkylphenylalkynes with CuCl2-LiCl and CuCl2-I2 in acetonitrile has also been examined.5 Chloroiodination with CuCl2-I2 proceeds more smoothly than chlorination and affords completely regiospecific and highly stereospecific (E)-chloroiodoalkenes in high yields (eq 3).

a-Iodination of Carboxylic Acids.

Combinations of iodine and copper(II) salts have been used for the introduction of iodine at the a-position of aliphatic straight-chain carboxylic acids.6 While Iodine-Copper(II) Acetate gives a slightly higher yield of iodinated acid than CuCl2-I2, the reaction time with the latter reagent combination is considerably shorter. An Iodine-Copper(I) Chloride-Copper(II) Chloride mixture is also effective for this transformation.

Oxidant in Photochemical Reactions.

Photocyclization of 4,4-dimethoxy-a,a-dimethylstilbene in the presence of air with added CuCl2-I2 gives a significantly higher yield (54%) of the desired phenanthrene derivative than the same reaction performed with iodine alone (0.6%).7

Related Reagents.

Copper(II) Chloride; Iodine; Iodine-Aluminum(III) Chloride-Copper(II) Chloride; Iodine-Copper(II) Acetate; Iodine-Copper(I) Chloride-Copper(II) Chloride; Sodium Iodide-Copper.


1. Baird, W. C., Jr.; Surridge, J. H. JOC 1970, 35, 3436.
2. Sugita, T.; Idei, M.; Ishibashi, Y.; Takegami, Y. CL 1982, 1481.
3. Kodomari, M.; Amanokura, N.; Takeuchi, K.; Yoshitomi, S. BCJ 1992, 65, 306.
4. (a) Castro, C. E.; Gaughan, E. J.; Owsley, D. C. JOC 1965, 30, 587. (b) Arganbright, R. P.; Yates, W. F. JOC 1962, 27, 1205. (c) Koyano, T. BCJ 1970, 43, 1439. (d) Koyano, T. BCJ 1970, 43, 3501.
5. Uemura, S.; Onoe, A.; Okano, M. CC 1975, 925.
6. Horiuchi, C. A.; Satoh, J. Y. CL 1984, 1509.
7. Collins, D. J.; Hobbs, J. J. AJC 1967, 20, 1905.

Nicholas D. P. Cosford

SIBIA, La Jolla, CA, USA



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