Author Topic: Grignard RXN Tried and Successful, the easy way.  (Read 780 times)

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ADDkid

  • Guest
Grignard RXN Tried and Successful, the easy way.
« on: February 07, 2004, 07:47:00 PM »
Before you start thinking about grignard's rxn you first need to determine what ether you are going to use. Diethyl ether is very explosive, but works very well. See on rhodium how to make ether from H2SO4 and ethanol. Other ethers can be used, and THF is yet another option.  After you have the nice and VERY dry ether you will need some magnesium.  In books it states, "turning", but any scraps may do.  Just roll up the scraps into little nuggets.
   Now you need a flask, pick one that is at least 2 to 2.5 times the ether solvent that will be used.  The last thing you need is a balloon, which you have two choices on. 1. Just a regular balloon, or a helium balloon.  I just used a regular balloon, but a helium balloon maybe better.
   Now take the flask and heat the shit out of it with an open flame to rid the flask of any moisture that maybe present.  Try now to let it cool long enough to put a balloon on it without melting the balloon.  Now let it sit there while you prepare the reagents.  Note: When flaming the flask you should have already put your Mg in it to dry the Mg.
Now take the balloon off the flask and put some ether in it and swirl and dump.  Do at least two times quickly and then put the balloon back on the flask that should contain the third volume of ether that will be used in the rxn.  Now put your alkyhalide and a small crystal of iodine in it and put the balloon on the flask.  Slowly heat and then reflux.
Reflux may differ depending on the Grignards.  If you are tired and don't feel like continuing, then when reflux is finished, stopper and put in the icebox.  Good luck.  Again I have tried this and it does work, and I live in a place where the humidly is about 85-100% year round. ADDkid

hypo

  • Guest
the ether can make a difference
« Reply #1 on: February 08, 2004, 01:11:00 AM »
since the solvated organo-metal-compound is conjugated with ether
molecules, the type of ether can have an effect on the
outcome of the reaction:

Post 482867

(hypo: "4-chloro-butanal??", Novel Discourse)

while this may be rare, better start with the proposed ether.


Kinetic

  • Guest
QFAS:
« Reply #2 on: February 08, 2004, 10:12:00 AM »
ADDkid, I have a few questions:

How did you dry your ether?

When you say 'any scraps [of magnesium] may do', is this from experience? The cleanliness of the metal surface is probably the single most important aspect in the initiation of a Grignard reaction.

What scale did you perform the reaction on? Why did you add all your alkyl halide at once? I try to forget the time I added my ethyl iodide all at once to stirred Mg turnings in ether, as the initiation was rather 'vigorous'.

How does the balloon manage to contain the vapours of such a low boiling liquid, especially as formation of Grignards is exothermic?

What Grignard reagent did you prepare? What synthesis did you use it in?

Thanks :)

moo

  • Guest
Ethers
« Reply #3 on: February 08, 2004, 03:08:00 PM »
Another example of a considerable solvent effect with Grignard reagents:

Post 377691

(moo: "Aldehydes from Grignard reagents with formic acid", Methods Discourse)



amine

  • Guest
Et2O ain't that bad.
« Reply #4 on: March 28, 2004, 08:34:00 PM »
IMO diethyl ether is safe for a gridnard, also the magnesium, its best to use thin strips, clean up nice nicely with steel wool, then cut it up into tiny bits, throw it into some anhydrous ether. :).  I've never had ether go crazy on me.