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Topic: Grignard Reagent Formation  (Read 9576 times)

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megs

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Grignard Reagent Formation
« on: October 03, 2004, 10:39:59 PM »
Hi,

I'm studying Grignard Reagent formation in my Ochem2 class.  The book is very vague on the mechanism of the synthesis of the Grignard Reagent.

I understand that the process goes like: RX + Mg --> RMgX

But I am interested in learing how the electrons flow, as the book does mention it is a two step process, but does not mention how the Mg combines (i.e. first with the R and then the X?)

 

Thanks!

Demotivator

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Re:Grignard Reagent Formation
« Reply #1 on: October 03, 2004, 11:10:05 PM »
The C-X bond is polarized with partial positive charge on C. Metallic Mg is an electron donor and bonds to the electrophilic C, displacing the X. Now the C gets a partial neg charge and Mg positive. The X- is left to bond with Mg.
However, exactly what the intermediate looks like (a triangle of bonds?) is not well understood.
« Last Edit: October 03, 2004, 11:20:49 PM by Demotivator »

Offline movies

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Re:Grignard Reagent Formation
« Reply #2 on: October 04, 2004, 01:30:13 AM »
Another posibility is that the oxidative insertion occurs through a radical process.  If this is the case, then the mechanism is almost exactly like Demotivator described, but instead think of the R-X bond as being cleaved homolytically (into two radicals) and then the Mg donates one electron to each species (R and X) to give Mg2+ along with R- and Br-.

At any rate, I don't think anyone really knows how oxidative insertion works for sure.

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Re:Grignard Reagent Formation
« Reply #3 on: October 04, 2004, 05:26:44 PM »
Remember you are taking an organic chem class not an inorganic class. Mg enters the bond through a oxidative insertion as movies said. If you want to learn more about it, or learn that the mechanism for it is still poorly understood take an inorganic class next.
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bronzezt

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Re:Grignard Reagent Formation
« Reply #4 on: October 22, 2004, 12:37:22 PM »
you can read the attach ,it will be useful to you

Rotwang

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Re:Grignard Reagent Formation
« Reply #5 on: November 01, 2004, 11:03:25 AM »
I hope this will help you (short and clear, only mechanistic view)  ;)

« Last Edit: November 01, 2004, 11:09:23 AM by Rotwang »

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