[624-70-4]  · C2H4ClI  · 1-Chloro-2-iodoethane  · (MW 190.42)

(iodinating reagent for organometallic compounds1,2 and carbanions;3 alkylating agent4)

Alternate Names: ethylene iodochloride; ethylene chloroiodide.

Physical Data: bp 38-40 °C/18 mmHg, 55-57 °C/37 mmHg, 140 °C/760 mmHg;5 nD25 1.5636; d 2.12 g cm-3.

Solubility: sol all common organic solvents; insol H2O.

Analysis of Reagent Purity: VPC Rt 5.1 min (relative to air) on a 2 m × 6 mm 20% diethylene glycol succinate column at 125 °C;6 NMR d 3.7-3.4 (m, A2B2, CH2I), d 3.6-3.2 (m, A2B2, CH2Cl).6

Preparative Methods: prepared in 76% yield by bubbling Ethylene gas into a CH2Cl2 solution of freshly redistilled Iodine Monochloride maintained at 30 °C by ice-cooling until the temperature begins to fall.7 Other methods of preparation include reaction of ethylene, Copper(II) Chloride, and Iodine at 75-85 °C in a pressure reactor;6 reaction of excess 1,2-dichloroethane with Sodium Iodide in acetone8 or with Aluminum Iodide in CS2;9 and by reaction of 2-iodoethanol with Thionyl Chloride.10

Purification: material that is exposed to light and air develops a slight rose-colored tint due to the formation of I2. It is usually suitable for use unless the color is very pronounced. The compound is purified by washing with aq thiosulfate and redistillation at reduced pressure.7

Handling, Storage, and Precautions: 1-chloro-2-iodoethane is a dialkylating agent and should be used only in an effective fume hood. Avoid inhalation of the vapor and contact of the liquid with the skin. The compound is light sensitive and should be stored refrigerated in the dark.

Iodinating Reagent.

1-Chloro-2-iodoethane is a selective reagent for the introduction of iodine atoms into organic molecules via carbanions or other organometallic species. It is only mildly electrophilic and can be used in the presence of many sensitive functional groups. The byproducts of the iodination reaction are ethylene and a metal chloride. In the syntheses of the hydroquinoid fungal antibiotics Frustulosin2 and Aurocitrin1 the dimethoxyiodo vinyl ether was a crucial intermediate. It was readily prepared from an aryllithium which was available by direct metallation (eq 1).

In their study of planar cyclooctatetraene analogs, Cracknell and co-workers8 investigated a number of reagents to effect iodination of the metalated biphenylene and found that ethylene iodochloride was superior to both Iodine and Diiodomethane for preparation of the iodobiphenylene (eq 2). Similarly, it was shown to be an effective reagent for synthesis of iodobenzylic chlorides (eq 3).11

One of the principal uses of the reagent is to trap organometallic species as the iodides which can then subsequently be used to regenerate the carbanionic intermediates by halogen-metal exchange. This was shown to be especially effective by Fuchs and co-workers in their cytochalasin model studies where halogen-metal exchange on a-iodo sulfones in the presence of acid anhydrides effected acylation with <1% formation of butyl ketones (eq 4).3

Alkylation Reactions.

1-Chloro-2-iodoethane tends to react by electron transfer mechanisms, which makes it an inefficient alkylating agent even with good nucleophiles. For example, even with Na2S little or no alkylation was observed, and the products were ethylene and halide salts.12 Similarly, treatment of anionic metal carbonyl complexes13 resulted in dimerization (eq 5). With Chloroiodomethane these complexes alkylate normally (eq 6). This is probably a consequence of the weak C-I bond for which the activation energy for homolytic cleavage has been estimated to be as little as 30 kcal mol-1.14

However, with extremely powerful nucleophiles, or nucleophilic atoms which are not easily oxidized, the reagent will function as a normal alkylating agent. Carboxylate salts react to form chloroethyl esters, and cyanamino-s-triazine salts are alkylated.15 Collman has used the reagent with highly nucleophilic rhodium complexes to produce organometallic dimers linked by -CH2-CH2- bridges (eq 7).

1. Ronald, R. C.; Lansinger, J. M.; Lillie, T. S.; Wheeler, C. J. JOC 1982, 47, 2541.
2. Ronald, R. C.; Lansinger, J. M. CC 1979, 124.
3. Anderson, M. B.; Lamothe, M.; Fuchs, P. L. TL 1991, 32, 4457.
4. Collman, J. P.; MacLaury, M. R. JACS 1974, 96, 3019.
5. Simpson, M. LA 1863, 127, 372.
6. Baird, Jr., W. C.; Surridge, J. H.; Buza, M. JOC 1971, 36, 2088.
7. Winkle, M. R. Ph.D. Thesis, Washington State Univ., 1981.
8. Cracknell, M. E.; Kabli, R. A.; McOmie, J. F. W.; Perry, D. H. JCS(P1) 1985, 115.
9. Arniaz, F. J.; Bustillo J. M. An. Quim. Ser. C 1986, 82, 270 (CA 1989, 107, 197 464m).
10. Danen, W. C.; Winter, R. L. JACS 1971, 93, 716.
11. Nevill, C. R., Jr.; Fuchs, P. L. SC 1990, 20, 761.
12. Delepine, M.; Ville, L. BSF 1920, 27, 678.
13. King, R. B.; Braitsch, D. M. JOM 1973, 54, 9.
14. Butler, E. T.; Mandel, E.; Polanyi, M. Trans. Faraday Soc. 1945, 41, 298.
15. Amazaspyan, G. S.; Ambartsumyan, E. N.; Dovlatyan, V. V. Arm. Khim Zh. 1990, 43, 668 (CA 1991, 115, 8736h).

Rob Ronald

Washington State University, Pullman, WA, USA

Copyright 1995-2000 by John Wiley & Sons, Ltd. All rights reserved.