dormouse (Member)
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Author  Topic:   Grignard reactions using "wet" ether 
Rhodium
Administrator   posted 11-03-1999 12:12 PM          
-------------------------------------------------------------------------------- http://rhodium.lycaeum.org/chemistry/wetgrignard.txt 


CHEM GUY
Member   posted 11-04-1999 12:58 PM          
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I don't see an application,... Am I being stupid? Enlighten me.
 
Gaston
Member   posted 11-04-1999 04:11 PM          
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if i remember correctly, grignard rxs are used to put a carbon-chain on a (Mg substituted ?) benzenering. now if *that* is not useful (for an example just look at the logo on top of the page)...
the problem with grignard was that it seems to be very picky about rxn-conditions (esp. humidity). my chem-teacher in school just told me to forget it, and so did i until now.

a simple unfailable grignard is *very cool*


CHEM GUY
Member   posted 11-04-1999 05:09 PM          
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I quote from the first paragraph:
"Students can run Grignard reactions in regular laboratory grade ether and in
equipment that has not been specially dried. The reaction begins within one
minute and the product alcohol is ready for assay in one hour."
Okay, let's reveiw, What is the product? An alcohol. Reveiw over. What use is an alcohol for our purposes? I don't know?

If I'm wrong please correct me,...


Gaston
Member   posted 11-04-1999 06:19 PM          
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allright, i was talking bullshit...
grignard reactions tie together a grignar reagent and an aldehyde forming an alkohol. addition to a benzene-ring just seems to be *the* example...

the grignard reaction will in most cases be an intermediate reaction, you can then reduce away the OH or oxidize it to a ketone, or whatever.

1 nice example i found on altavista: http://main.chem.ohiou.edu/~wathen/chem302/grignard.html  (alter the reagents a bit and get anything you want...)


Rhodium
Administrator   posted 11-04-1999 06:25 PM          
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Forming the grignard reagent of bromobenzodioxole, and reacting it with allylbromide to give safrole is a nice application (See TSII, or my page under psycho chemist).
 
Gaston
Member   posted 11-04-1999 09:29 PM          
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Now i'm confused!
Is the grignard-rxn with aldehydes/ketones to form primary/secondary alcohols just a special case?
Is any rxn with a grignard-reagent called a grignard-rxn?
Does this work: Ar-MgBr + Br-R -> Ar-R + ? or R-MgBr + Br-R' -> R-R' + ?
Together with the ultrasonic setup, this would make grignard the perfect allrounder, wouldn't it?


Gaston
Member   posted 11-04-1999 09:31 PM          
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secondary/tertiary alcohols i meant ofcourse...
 
K.C. Nicolaou
Member   posted 11-05-1999 12:55 AM          
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Three questions.
1. Does anyone know what the selectivity of the bromination of benzodioxole is. i.e. - X% 3-bromo, Y% 4-bromo product.

2. I am not that familiar with ultrasonic cleaning. Is the ultrasound source built into the bath and transmitted through the glassware?

3. What do any of you think would be the effect of running Al/Hg reductive amination with ultrasound?


CHEM GUY
Member   posted 11-05-1999 05:12 PM          
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Okay, someone please formulate a way to use this method of grignard reaction, because I don't understand how usefull it is, and I don't understand how bromobenzodioxole is formed with from this.
Help me I'm stupid...
 
psychokitty
Member   posted 11-05-1999 05:19 PM          
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K.C. Nicolaou: In regard to applying ultrasound to a Al-Hg reductive amination, I would say that the reaction could very well be optimized. Ultrasound works great at activating the surfaces of catalysts and would also be valuable in creating some agitation in what is normally a difficult reaction to perform while magnetically stirring.
--PK


K.C. Nicolaou
Member   posted 11-05-1999 11:55 PM          
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That's kind of what I was thinking. Sticking one of those sonicator probes that biologists use to break up cells in one neck of a three neck flask and proceeding a la Osmium's method would definitely be interesting. Someone I never met has always found mag stirring with 40g Al in a 1L flask to be a pain in the ass. Proper stirring usually is not acheived until quite a bit of the Al has reacted.
 
Rhodium
Administrator   posted 11-06-1999 07:08 PM          
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> Is any rxn with a grignard-reagent called a grignard-rxn?
Yes.

> Does this work: Ar-MgBr + Br-R -> Ar-R + ?

Not exactly, but check out the following for an example of a grignard reaction yielding safrole: http://rhodium.lycaeum.org/chemistry/pc/safrole.html 


Gaston
Member   posted 11-07-1999 03:30 PM          
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Ok, thx for your answer, Rhodium.
Actually it was exactly the article you mention, that confused me. But good old Merck cleared this up for me:
"Traditionally, it is the addition of organomagnesium compounds (=GR) to carbonyl compounds to generate alcohols. A more modern interpretation extends the scope of the reaction to include the addition of GRs to a wide variety of electrophilic substrates"

Well, i'm still amazed by the *theoretically* sheer number of uses. e.g. if you take the second example my Merck gives you get:

Acetonitrile + Benzyl-MgX (made from Benzyl-Br) -> (C2H6)-CH2-C(NMgX)-CH3 (+H20) -> P2P.

Of course in reality this wont work (it would be *too* nice). If at all, one would get (1,1)-dibenzyl-ethanol or shit like that unless working in totally crazy conditions (e.g. X=Cd, or whatever).

Anyway, i still believe that an easily done grignard reaction can be and will prove very valuable...


K.C. Nicolaou
Member   posted 11-07-1999 05:41 PM          
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Why wouldn't that "really" work? Avoiding formation of the dibenzyl alcohol should be relatively easy, as long as you add the grignard very slowly to a large excess of ACN. You just have to tune the rxn conditions such that the addition of Bn-MgBr to Bn-C(NMgBr)CH3 is not competitive with the addition of the grignard to ACN. Unless the second addition is >10000 times faster than the first, in which case I'm wrong. I mean come on, are you trying to tell me that a rxn that give a fucking nitrogen dianion is fast? I doubt it.
 
K.C. Nicolaou
Member   posted 11-07-1999 06:05 PM          
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Err... the double addition product would give the amine after hydrolysis, not the alcohol. Someone should try that, it might work.
 
Gaston
Member   posted 11-07-1999 09:00 PM          
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Of course you're right.
IMO unsubstituded P2P is not very interesting, but OTOH Benzyl-Cl is very cheap...
 
K.C. Nicolaou
Member   posted 11-07-1999 10:50 PM          
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Amen to that. I can think of a bunch of interesting meth synths that I won't ever dream about due to my distaste for the effects of that particular compound.
 
Gaston
Member   posted 11-08-1999 07:23 AM          
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sorry??? p2p is ininteresting to me because so is (unsubstutided) methamphetamine. anyway benzyl-cl is very cheap for doing little experimentations...
 
K.C. Nicolaou
Member   posted 11-08-1999 11:47 AM          
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what??? I just agreed with you. Meth does not interest me. I don't like the way it makes me feel. That's why I would have no reason to dream about p2p chemistry.
 
Gaston
Member   posted 11-08-1999 01:09 PM          
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ehehehe....
communication can be quite complicated sometimes, huh?


Gaston
Member   posted 11-09-1999 08:06 AM          
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THE question regarding safrole synth is: why not use Br-acetone or Br-isopropylamine instead of Br-allyl?
Br-acetone is nasty, but br-isopropylamine? hard to make?


Rhodium
Administrator   posted 11-09-1999 01:40 PM          
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Because the grignard reagent would add at the center carbon instead, yielding a tertiary alcohol. No carbonyl groups allowed in the synth.
 
CHEM GUY
Member   posted 11-13-1999 04:11 PM          
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I answered my question myself,...
The mechanism for this sono-Grignard is as follows:
From "Sonochemistry and Sonoluminesesnce", edited by Lawrence A. Crum, Timothy J Mason, Jacques L. Reisse and Kenneth S. Suslick, 1999, page 282-283,

"
R-[ (C=O)-R' ] + R"MgX --> Ultrasound-->

R-[ (C-OH)-R' ]-R"
"


CHEM GUY
Member   posted 11-29-1999 04:02 PM          
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From "Sonochemistry and Sonoluminesesnce", edited by Lawrence A. Crum, Timothy J Mason, Jacques L. Reisse and Kenneth S. Suslick, 1999, page 283
" R'-X -- (Mg turnings / ether)--> R'-MgX Equation 12

...

The formation of organometallic reagents from organic halides has been of grest interest (Equation 12) especially those factors which influence intiation. A long standing problem associated with Grignard reagent synthesis is that in order to facilitate reaction between the organic halide and the metal in an ether solvent all of the reagents must be dry and the surface of the magnesium must be clean and peroxide free. Such conditions are difficult to achieve and so many methods of initiating the reaction have been devolped most of which rely on adding activating chemical to the reaction mixture. Magnesium activation is rather easy by sonication, even in damp solvents. "


dito
Member   posted 12-08-1999 06:47 AM          
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Have anyone of you looked up what a ultrasound bath costs?
I have seen one used for cleaning and it was quite pricy, 1400 dollars and that is much!
Has anyone seen another price?
 
Rhodium
Administrator   posted 12-08-1999 10:02 AM          
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The cheapest ones (capacity 1 liter) go for around $500, afaik. Perhaps you could buy a used one cheaper.
 
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