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I'm planning on an Iodination reaction of a 2-aminothiazole derivative. Specifically, 2-aminothiazole, with two Boc groups on the amine.

  1. What practical advice do you have for recrystallising NIS? Literature recommends dissolving in hot dioxane and then adding $\ce{CCl4}$ to precipitate out the NIS.

  2. If I do not have access to $\ce{CCl4}$ would $\ce{CHCl3}$ suffice?

  3. Do NIS and NBS (I've previously used NBS for this reaction in $\ce{CHCl3}$) have similar solubilities in $\ce{CHCl3}$?

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  • $\begingroup$ Recrystallization is finicky. Maybe it'll work, maybe it won't. Try just lowering the temperature first. The reference I saw was -20 degrees C. $\endgroup$ – Zhe Jan 22 '17 at 17:26
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Purification of Laboratory Chemicals (a generally accepted reference book for methods of purification of common chemicals) appears to agree with your procedure:

N-Iodosuccinimide [516-12-1] M 225.0, m 200-201 °C. Crystallise it from dioxane/CCl4. It iodinates arenes in triflic acid. [Olah et. al. J. Org. Chem. 1993, 58, 3194, Beilstein 21/9 V 544.]

As you point out, carbon tetrachloride is difficult if not impossible to get hold of now, so the methodology will not work.

The most obvious thing to try would be the method for the purification of NBS, however NIS is not tolerant to recrystallisation from water and from previous attempts doesn't achieve anything.

Depending on what you're doing with the NIS, I've often had success in simply dissolving in solvent and washing with sodium thiosulfate to remove any liberated iodine. Drying and evaporation then gives cleaner, though probably not pure NIS.

Also note that NIS should be stored in the dark at reduced temperatures to prevent decomposition (which is noted by the appearance of an orange/brown decoloration).

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  • $\begingroup$ I've seen this entry before in the book, and I've always wondered why use $\ce{CCl4}$. Surely its only purpose is as a poor solvent for NIS, but which is still good for the main impurity, molecular iodine. If so, then precipitation of pure NIS from a dioxane solution by adding hexane should work just as well. $\endgroup$ – Nicolau Saker Neto Apr 17 '17 at 2:49

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