What is the exact reaction mechanism of the reaction of Grignard reagent with ammonia?

$$\ce{RMgX + NH_3 -> RH + MgNH3X}$$

[I found the above equation from a book, and I am not completely sure that that reaction actually happens]

  • $\begingroup$ Why do you think the reaction might not be taking place? $\endgroup$ – Eashaan Godbole Nov 11 '16 at 8:32
  • $\begingroup$ @EashaanGodbole Because I took it from an unreliable book. $\endgroup$ – Shoubhik Raj Maiti Nov 13 '16 at 15:03
  • $\begingroup$ Oh...what I meant to ask was what you think is the chemical/physical reason why such an interaction doesn't take place. $\endgroup$ – Eashaan Godbole Nov 13 '16 at 15:34

Your reaction isn't balanced. It should read:

$$\ce{RMgX +NH3 -> RH +MgNH2X}$$

This is a simple proton transfer. $\ce{MgX+}$ is a spectator ion, so the reaction equation could also be written: $$\ce{R- +NH3 -> RH +NH2-}$$

When the carbanion collides with an ammonia hydrogen, the hydrogen is transferred between the two species. The result is a newly formed carbon to hydrogen bond and an amide anion. Carbanions are several orders of magnitude more basic than amide ions, so the reaction definitely occurs, and will essentially go to completion.

  • $\begingroup$ Well, it shouldn't be written like that. Grignard compounds don't generate free carbanions. $\endgroup$ – Mithoron Nov 11 '16 at 12:32
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    $\begingroup$ I'd be hesitant to say that $\ce{MgX+}$ is a spectator ion. It is effectively that way, but the M-C bond is actually pretty covalent. $\endgroup$ – orthocresol Nov 11 '16 at 14:57
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    $\begingroup$ My point wasn't to imply that it doesn't participate in the reaction or that it isn't closely coordinated to the anions in solution, simply that it exists in the same form on both sides of the equation (though it is much more closely coordinated to one species on one side than the other). $\endgroup$ – ringo Nov 11 '16 at 16:37

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