Does anyone know why Grignard reagent of CH3I can only be prepared using diethyl ether as a solvent and yields no reaction when developed in THF? Theoretically, I is the most reactive halogen for Grignard reactions, so using THF or diethyl ether should make no difference.

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    $\begingroup$ Can you provide a reference for this? I have never heard of this problem. $\endgroup$
    – bon
    Commented Jun 7, 2016 at 21:21
  • $\begingroup$ It was something my lab teacher said. He tried several times doing the reaction in THF but it didn´t work. $\endgroup$ Commented Jun 9, 2016 at 1:06

1 Answer 1


MeMgI is usually prepared in ether, but it can also be prepared in THF. However, magnesium iodide is sparingly soluble in THF, so RMgI reagent in THF should not be very concentrated, so that no MgI2 precipitate forms.

  • $\begingroup$ It seems like $\ce{MgI2}$ should be equally sparingly soluble in diethyl ether. Do you have a reference for your solubility claim? $\endgroup$
    – Ben Norris
    Commented Jun 8, 2016 at 0:59
  • $\begingroup$ @BenNorris It is repeatedly pointed in Gringnard-related literature that MgI2 is soluble in DEE, but not THF (and similarly for MgCl2 ). I was unable to find trustworthy values on quick googling, though. $\endgroup$
    – permeakra
    Commented Jun 8, 2016 at 7:26

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