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Author: Subject: Gringard' Regent
Blind Angel
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[*] posted on 22-2-2003 at 14:19
Gringard' Regent


I heard of this many time but still can't figure out what it is, and for what it's use. My chemistery teacher (high school) told me that it was a Mg compound but didn't want to tell me more since it was dangerous (?) anyone can help me? (Synthesis, How It Work, Description...)



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Blind Angel
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[*] posted on 22-2-2003 at 15:01


o thanx a lot

[Edit] I saw that i didn't had the good spelling

[Edited on 22-2-2003 by Blind Angel]




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[*] posted on 22-2-2003 at 15:48


The Grignard reagent, is an organometallic reagent where magnesium is inserted between an alkyl group and a halogen. The most common one is CH3MgBr.
According to my chemistry book they are made by the reaction of an alkyl halide (CH3Br) with Magnesium in an anhydrous ether solvent.
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[*] posted on 22-2-2003 at 17:58


the alkalimetal causes the carbon bonded to it to increase its electron-density and turns it from normally being an electrophil (because of low electronegativity) into a nucleophil which is able to react via SN2("bimolecular nucleophilic substitution";).

So you have actually a tool for generating a new C-C bond.

....dangerous? - No.

In my mind handling hydrazine, hydrogen flouride or perchloric acid would rather be something to fear....

just seems to be one of these chemistry teachers fearing her pupils could eventually dare more than mixing vinegar and baking soda.....;D

HLR

[Edited on 23-2-2003 by BASF]




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Blind Angel
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[*] posted on 23-2-2003 at 13:17


that can be usefull, are they easy to obtain or they're watched?



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BASF
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[*] posted on 23-2-2003 at 17:15


they are sold in etheric solutions but very often made "in situ", right before use.

Maybe i can serve some further info about it, when i have more time in the course of next week.....




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[*] posted on 23-2-2003 at 18:12


That would be really nice BASF :)



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[*] posted on 28-2-2003 at 13:53
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I like this place.

Anyways, I would read up some more on grignard reagents if you really want to learn.. you'll get more out of it that way.

Grignard's are extremely reactive with anything protic, like water, alcohol, etc. For this reason grignard's are produced in a non-protic solvent like ether or THF. Care must be taken to not allow any moisture to come into the flask. Usually you dry the flask in an oven or flame it out. Magnesium oxidizes in air to produce a coating of Mg(OH) (not sure if that's right) - so you want to grind it up first before using it. A lot of people demand that you use an inert atmosphere like nitrogen. It's a good idea.... but they can be ran in plain ether, as the ether makes somewhat of a protective barrier against air.. just be sure you have a drying tube attached.

Grignard reagents are awesome. They open a whole lot of possibilities for syntheses.
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[*] posted on 28-2-2003 at 14:17
two more thoughts


ether is usually distilled right before preparing the grignard to ensure that it is absolutely anhydrous,

and

watch out for peroxides when playing with ether :D
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[*] posted on 28-2-2003 at 17:15


watch out = never distill the whole Et2O off, always leave some of it in the flask.
So the dissolved ether-peroxides cannot overheat and explode, burst the flask and produce a lot of dangerous shrapnel...




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[*] posted on 15-10-2003 at 11:04
drying stuff


If you can get hold of some molecular sieve (A4 will take water and methanol out, A3 will dry methanol, A4 will dry ether (batch wise)). If you can heat it upto 250-300oC, you can reactivate it. Test, put some on your hand and add one drop of water.
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[*] posted on 15-10-2003 at 19:27


Quote:
Originally posted by Blind Angel
that can be usefull, are they easy to obtain or they're watched?


Gringard reagents are pretty heavily watched due to their use in the syth in PCP. I have a document on them somewhere but I am not sure where, when I find it I'll post it. You should look on rhodium’s page for some more info on them; he had several documents on there preparation IIRC.




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