Sciencemadness Discussion Board

anyone have experience forming grignards from chlorobenzene

draculic acid69 - 12-8-2018 at 23:12

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.

DavidJR - 13-8-2018 at 02:33

I would be interested in any info about this since chlorobenzene is a lot cheaper than bromobenzene.

CuReUS - 13-8-2018 at 03:27

Quote: Originally posted by draculic acid69  
...if there are any tips or tricks to forming phenylmagnesium chloride. 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

clearly_not_atara - 13-8-2018 at 05:23

Transfer metallation, via e.g. isopropyl bromide, is a good possibility here.

kmno4 - 13-8-2018 at 14:04

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).

CharlieA - 13-8-2018 at 15:56

Aren't PhCl (C6H5CH2Cl) and chlorobenzene (C6H5Cl) two different animals?

Sigmatropic - 13-8-2018 at 21:39

PhCl is chlorobenzene. BnCl is benzyl chloride. They are wildly different, yes.

mackolol - 14-8-2018 at 07:52

Maybe try in dioxane it's cheap as dirt and since it's cyclic same as thf it would work well.

draculic acid69 - 15-8-2018 at 03:00

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]

CharlieA - 15-8-2018 at 17:09

Quote: Originally posted by Sigmatropic  
PhCl is chlorobenzene. BnCl is benzyl chloride. They are wildly different, yes.

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.:)

kmno4 - 15-8-2018 at 21:16

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?

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.

draculic acid69 - 15-8-2018 at 22:04

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/ 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.

zed - 17-8-2018 at 15:24

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.

draculic acid69 - 17-8-2018 at 21:10

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.

S.C. Wack - 18-8-2018 at 06:15

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]

wildfyr - 18-8-2018 at 10:44

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]

S.C. Wack - 18-8-2018 at 13:14

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.

JJay - 18-8-2018 at 14:26

I've read about people using ultrasonic cleaners to initiate difficult Grignards, but I've never tried it.

AvBaeyer - 19-8-2018 at 18:24

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.


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.


[Edited on 20-8-2018 by AvBaeyer]

draculic acid69 - 20-8-2018 at 18:26

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.

Tsjerk - 21-8-2018 at 03:20

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.

[Edited on 21-8-2018 by Tsjerk]

AvBaeyer - 21-8-2018 at 13:52


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.


S.C. Wack - 21-8-2018 at 15:20

There's really no reason why the flask can't be left to reflux for a few days with the'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.