Chloroiodomethane-Zinc/Copper Couple

ClCH2I-Zn(Cu)
(ClCH2I)

[593-71-5]  · CH2ClI  · Chloroiodomethane-Zinc/Copper Couple  · (MW 176.38) (Zn(Cu))

[12019-27-1]  · Zn  · Chloroiodomethane-Zinc/Copper Couple  · (MW 65.39)

(used in the preparation of cyclopropanes1, and alkenes from aldehydes2)

Physical Data: ClCH2I: bp 108-109 °C; d 2.422 g cm-3. Zn(Cu): mp >400 °C; d ca. 7.14 g cm-3.

Solubility: ClCH2I: sol organic solvents; insol H2O. Zn(Cu): insol organic solvents and H2O.

Form Supplied in: ClCH2I: colorless to brown liquid. Zn(Cu): reddish-brown or dark gray powder; often prepared directly before use.

Preparative Method: see Zinc/Copper Couple.

Purification: chloroiodomethane can be purified by distillation.

Handling, Storage, and Precautions: chloroiodomethane is light sensitive and should be stored in the dark. It can be stabilized with copper wire. Zinc-copper couple deteriorates in moist air and should be stored under nitrogen. Very active zinc-copper couple is oxygen sensitive. It evolves hydrogen on contact with strong aqueous acids.

Chloroiodomethane reacts with zinc-copper couple to give chloromethylzinc iodide that will rearrange to iodomethylzinc chloride in ethereal solvents (eq 1).3 The Schlenk equilibria favors the bis(halomethyl)zinc-ZnX2, so the active species in solution are bis(chloromethyl)zinc-ZnI2 (1), or bis(iodomethyl)zinc-ZnCl2 (2). Except for the identity of the zinc salt, (2) is the same product formed from zinc-copper couple and diiodomethane, and its reactions parallel those of the Simmons-Smith reagent.4

Chloroiodomethane and zinc-copper couple cyclopropanate alkenes and convert aldehydes to terminal alkenes (eq 2).2 Chloroiodomethane works better than the other dihalomethanes, giving styrene in 80% yield compared to 72% with Diiodomethane

Chloroiodomethane and zinc-copper couple have not been used widely for cyclopropanation, but chloroiodomethane and diethylzinc have been used to generate ClCH2ZnEt. This reagent was first prepared by Miyano1 for cyclopropanations, and was reported to be superior to the Furukawa5 reagent generated from diiodomethane and diethylzinc. Denmark found that cis-cyclodecene cyclopropanated in 94% (GC yield) using chloroiodomethane compared to 12% (GC yield) using diiodomethane under the same conditions (eq 3).6 Miyano found that oxygen accelerated these reactions and proposed a radical mechanism for the formation of the chloromethylzinc intermediate, but Denmark found that the reagent prepared in 1,2-dichloroethane gave comparable results without oxygen.

Related Reagents.

Diethylzinc; Diiodomethane; Zinc/Copper Couple.


1. (a) Miyano, S.; Hashimoto, H. BCJ 1973, 46, 892. (b) Miyano, S.; Izumi, Y.; Fujii, H.; Hashimoto, H. S 1977, 700.
2. Miyano, S.; Hida, M.; Hashimoto, H. JMC 1968, 12, 263.
3. (a) Blanchard, E. P.; Simmons, H. E. JACS 1964, 86, 1337. (b) Wittig, G.; Schwarzenbach, K. LA 1961, 650, 1. (c) Denmark, S. E.; Edwards, J. P.; Wilson, S. R. JACS 1992, 114, 2592.
4. Simmons, H. E.; Cairns, T. L.; Vladuchick, S. A.; Hoiness, C. M. OR 1973, 20, 1.
5. Furukawa, J.; Kawabata, N.; Nishimura, J. T 1968, 24, 53.
6. Denmark, S. E.; Edwards, J. P. JOC 1991, 56, 6974.

Scott D. Rychnovsky & Jay P. Powers

University of Minnesota, Minneapolis, MN, USA



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