[keetner]

Hello,

I just need a bit of clarification with the oxidation of grignard reagents...I've tried looking it up but the only place that seems to have the reaction is Wikipedia, but it confuses me quite a bit.

The image from Wikipedia:


1) When the starting products are "broken" into radicals, exactly how do they come together to make the R-O-O-MgX?
2) I also don't understand how the addition of another portion of the Grignard reagent would result in R-O-MgX...
Would the RO and O-MgX be split? And same with the R and MgX? That way I guess the RO and MgX could come together...but I'm not sure if this is correct.
3) To obtain the peroxide and the alcohol - is it just from the simple protonation? I'm assuming a bond between O-H are made, causing the Mg-X to leave...but...I don't understand why it's shown as OH-MG-X + H...

Sorry - my chem is pretty rusty (and atrocious); it's something I've never been too fantastic at. Any help would be greatly appreciated though. I think the main problem is that I don't know how the mechanism works, so trying to understand the oxidation process is probably becoming more confusing than it should be. Speaking of which, if someone could show me how the mechanism works (you don't have to though) it would be appreciated as well.

Thanks again.

[orgopete]

I don't know the single electron transfer reaction at the start.

The cleavage of peroxides (ozonides, disulfides, etc) are all pretty similar. If the reagent is reactive enough or the leaving group is stable enough, then the donor can add electrons directly to one of the oxygen atoms and break the O-O bond. In this case, magnesium is quite a good Lewis acid and can complex first to enable the cleavage.

When Grignard reagents are worked up, one generally adds acid as magnesium hydroxides are quite insoluble. If only water is added, you will get a milky mess difficult to work with. Acid will convert the magnesium hydroxides in to more soluble halides (the usual strategy). I cannot say I know the solubility of mixed magnesium hydroxides so I don't know if they are indeed the product or the scheme is simply being tidy more than correct.

[keetner]

Ah, thanks for the response - it did clarify a few things!

Actually, I think the image on Wikipedia is messed up...so the radical bit (in red) can be ignored. Seems as though they were trying to simplify it, but just made it worse...haha.
I looked at it again, and I think for the most part, the Grignard reagent reacts with the oxygen very much like how it would with carbon dioxide (for example). Then to get the peroxide or alcohol, it looks like it'll follow a propagation...seems logical at least.

Thanks again!