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draculic acid69
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anyone have experience forming grignards from chlorobenzene
Just read clorobenzene has difficulty forming a grignard reagent in et2o if it forms at all.apparently it works in thf but this is hard to get for me
and I was under the assumption that clorobenzene just takes longer to initiate but it would still happen in et2o.does anyone have any experience with
clorobenzene in ether or thf ? Would like to know if et2o is a no go and thf is a must or if there are any tips or tricks to forming phenylmagnesium
chloride.
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DavidJR
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I would be interested in any info about this since chlorobenzene is a lot cheaper than bromobenzene.
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CuReUS
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https://patents.google.com/patent/US6117372-The authors use THF for their method but you can try using ether.But first try the previously known
methods to activate Mg which the authors have compiled in para 4
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clearly_not_atara
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Transfer metallation, via e.g. isopropyl bromide, is a good possibility here.
[Edited on 04-20-1969 by clearly_not_atara]
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kmno4
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Reaction of PhCl with Mg in THF goes rather smoothly, if initiated by iodine crystal. If reagents are not very anhydrous, initiation should be
repeated (with preheating).
One must remember that THF is not Et2O and some reactions giving very good yields in the latter ether, may give <10% yields in THF.
Example is reaction with benzaldehyde: at least 80% in Et2O (from PhBr), about a half of it in THF (and a lot of useless oil as by-product).
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CharlieA
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Aren't PhCl (C6H5CH2Cl) and chlorobenzene (C6H5Cl) two different animals?
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Sigmatropic
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PhCl is chlorobenzene. BnCl is benzyl chloride. They are wildly different, yes.
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mackolol
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Maybe try in dioxane it's cheap as dirt and since it's cyclic same as thf it would work well.
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draculic acid69
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Mackelol Are you suggesting forming the grignard in dioxane instead of thf or et2o?
Kmno4 would it be ideal to form the clorobenzene grignard in thf and once all has formed nicely distill off most of the thf and replace with
ether?would this avoid the low yield with thf problem your talking about?
Also wanna know if the halogen difference is a yield killer for example does clorobenzene and bromo/iodobenzene give different yields for the same
rxn's ?
[Edited on 15-8-2018 by draculic acid69]
[Edited on 15-8-2018 by draculic acid69]
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CharlieA
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my bad! I didn't know PhCl is chlorobenzene; I thought PhCl was BnCl. I always did have trouble with nomenclature. Thanks for setting me straight.
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kmno4
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Quote: Originally posted by draculic acid69  |
would it be ideal to form the clorobenzene grignard in thf and once all has formed nicely distill off most of the thf and replace with ether?would
this avoid the low yield with thf problem your talking about?
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This procedure is sometimes used if reaction in ether solvent goes slowly or with low yield, but with toluene or other hydrocarbon as dilutent. Of
course it makes additional labour, possibly your reaction in same THF would go quite nicely.
P.S. 1,4 dioxane does not work as replacement for Et2O/THF.. etc.
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draculic acid69
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I just need something clarified once the grignard is formed then toluene/xylene added then the ether or thf can be distilled off and proceeds with
rxn or is the grignard reagent left in its ether and everything else is solvated with xylene/toluene.is this where mackolol suggests dioxane?
KMNO4 I'm thinking about the grignard of 1,4 & 1,2diclorobenzene to clorobenzene and benzene initially do you know how these go in thf? Good,
bad, or am I going to have to experiment to find out? If nobody knowsthen I'll try it and report back but that will be a while.
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zed
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Guys in my neighborhood never did it that way. Bromobenzene forms a Grignard reagent relatively easily; Chlorobenzene.... Not so much. If there is
any way, use Bromobenzene.
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draculic acid69
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Clorobenzene is what I want to know about. Of course bromobenzene would be Ideal for synthesis but right now just curious about clorobenzenes
behaviour and possibilities.
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S.C. Wack
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Gilman said it's possible with ether or no solvent...he has no YT or IG so I guess it never happened.
Chlorobenzene and alkali metal powders can do some things PhMgX does...possible indirect use of Mg there.
[Edited on 18-8-2018 by S.C. Wack]
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wildfyr
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Doesn't some catalytic iodine help get some of these slower grignard formations going? As kmo4 said (man, using a reagent as a username is a funky
choice on this forum)
[Edited on 18-8-2018 by wildfyr]
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S.C. Wack
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Gilman indicated the smallest amount of iodine took a month of refluxing and standing and experiments with more started something within 5 8-hour
days, with another 4 to finish.
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JJay
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I've read about people using ultrasonic cleaners to initiate difficult Grignards, but I've never tried it.
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AvBaeyer
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Doesn't a bit of common sense and basic organic chemistry knowledge suggest that if a Grignard reaction occured easily with chlorobenzene it might ,
just might, be easily found by a simple search? All else is speculation.
AvB
Edit: Chlorobenzene will react with very highly activated magnesium such as Rieke magnesium. A Google search will give several references. However,
the preparation and use of these types of magnesium require specialized equipment and skills. Otherwise chlorobenzene is unreactive in any practical
sense.
End of discussion.
AvB
[Edited on 20-8-2018 by AvBaeyer]
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draculic acid69
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Yep that's what I found when i searched for clorobenzene too.didn't find that much else that was useful to me.don't have reike magnesium or
specialised equipment or skills which is why I made this post.if your not going to contribute in a helpful manner just keep quiet.saying end of
discussion makes you sound like a dick.
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Tsjerk
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AvBaeyer's contribution is quite helpful, chlorobenzene as grignard substrate is researched to death, he even lists your possibilities. Likelihood of
new discoveries because you post the question here is zero to none.
Edit; Although I don't think it is quite that bad, at least it can be done with 80% chlorobenzene.
http://cssp.chemspider.com/article.aspx?id=559
[Edited on 21-8-2018 by Tsjerk]
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AvBaeyer
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Tsjerk,
Interesting find. Note that the reaction is initiated in part with ethyl bromide (an unusual activating agent) which will obviously generate ethyl
Grignard. Based on the reported stoichiometry, there will be about 6% ethyl Grignard in the reaction mixture. What happens to it? Was its reaction
product with benzophenone missed in the work-up? Does the ethyl Grignard play a role as a transmetalation agent/catalyst like isopropyl Grignard often
does (see clearly_not_atara, above)? Overall, this is kind of a strange procedure but very interesting. It would be nice to see this reproduced.
Perhaps now we can end the discussion.
AvB
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S.C. Wack
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There's really no reason why the flask can't be left to reflux for a few days with the iodine...it's not like it's going to run out of control. Water
and oxygen can be kept away with some effort.
But anyways that solventless thing (30-80 mesh Mg, 20-30C above the normal bp, 3 hr, 85%)...the other details such as apparatus probably don't need
duplication if done right...a test tube, extra chlorobenzene in a pipe and caps with teflon tape..should handle it.
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SWIM
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Der Marderosian goes into chlorobenzene grignards a bit in his book Perfunery and Flavoring Synthetics.
In the phenylethyl alcohol chapter he says it was a common industry practice back in the 1930s to do it under pressure with no solvent in an
autoclave.
He also gives references to the activation of the magnesium by treatment with copper hallides but it is not clear if this was actually used in
industry.
They stopped using this route for better non-grignard methods to the alcohol a long time ago but it apparently was once considered the way to go, or
at least a way to go.
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Dr.Bob
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I believe that using an alkyl grignard will react with the aromatic halide and create alkane (which bubbles away) and the aromatic gragnard. I have
used propyl or isopropyl grignard to help initiate slow reactions, and never see any traces of it. But I have heard that chorobenzene is a very
hard one to start, but I have used bromobenzenes and they work OK, even in my hands, which are not great with Grignards. However, I rarely get great
yields from most Grignards, compared to similar reactions with lithium reagents, not really sure why. I think homocoupling (PhBr ----> Ph-Ph)
and other issues seem to be more common with Mg and Cu reagents, as well, the longer reaction times may lead to more water intruding into the
reaction, as I often find ArH after the reaction, no matter how carefully I have tried to drive the Grignard to completion. So I try to avoid
Grignards, except when the Ar-Br is cheap or readily available, which is often is not...
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