Sciencemadness Discussion Board - Best Ether for Grignard?

Best Ether for Grignard?

kclo4 - 8-9-2008 at 17:39

All right I really want to perform a Grignard reaction. I however don't have a cheap source of an ether for the Grignard.
I will have to make it.
Considering I only have a 200mm Liebig condenser, and hose water, I don't know if I can condense Diethyl Ether very effectively. However, I beleive I could condense Diisopropyl Ether more effectively.
Diisopropyl ether has a boiling point of 69 °C which is almost twice that of Diethyl Ether, which has a boiling point of 34.6 °C

I was planning on making this, but after doing more research, and having a friend of mine mention that Diisopropyl Ether forms peroxides really easily, and might be one of the worsts It made be have a second thoughts on using it.

THF - Hard to get, Expensive, etc.

I would like to not have to use the ether Immediately after it is produced and dried, and then get rid of the ether right after its use. I get the feeling it will take a few tries for me to get the Grignard to work and I don't want to waist much time on making the solvent.

Could I have some In put on what I should do for my ether problem or am I just SOL?

[Edited on 8-9-2008 by kclo4]

Sandmeyer - 8-9-2008 at 17:50

To make own ether to run a Grignard sounds really hardcore, I wouldn't do this since diethylether is OTC and dirt-cheap. Anyways, if you really have to make it and can't get it dry, you can run Grignard in wet ether under ultrasonic conditions. A ultrasound bath can be easily obtained and is not that expensive second-hand.

This might be of interest: http://www.erowid.org/archive/rhodium/chemistry/grignard.wet...

[Edited on 9-9-2008 by Sandmeyer]

Magpie - 8-9-2008 at 17:59

I make my own ether using a 200 mm West condenser (like a Liebig) and ice water cooling for cooling water. I don't make it very often and only in small quantities so I don't have to store it.

I dried it with 3A molecular sieves and it worked perfectly for a Grignard.

[Edited on 8-9-2008 by Magpie]

kclo4 - 8-9-2008 at 18:09

Well, I know Diethyl Ether can be obtained as a.. solvent of some sort at walmart, etc. but I have heard it is mixed with other things making it have wierd boiling points, etc so figured I'd just not mess with it.
Plus, Once I make the Ether I think I could dry it fairly easily by putting it in a dried bottle with MgO. Perhaps not though?

Sauron said in this thread http://www.sciencemadness.org/talk/viewthread.php?tid=10380&...

"Diethyl ether is not the worst peroxide former. THF is worse, dioxane is worse. Di-isopropyl ether is perhaps the worst. "

But Nicodem a post above Sauron said:
"I have regularly used bottles of diisopropyl ether old about 25 years and never even considered any peroxides. "

and from Wikipedia it says "Diisopropyl ether tends to form explosive peroxides upon standing in air for long periods (years). " but doesn't really give a source.

So.. it all seemed rather confusing.
Do you have any sources that say it is safer then others, etc?
Thank you for your input

I really just want to make Diphenylmethanol via grignard. It is also known as benzhydrol I beleive.
I think I might be able to produce it by decarboxylation of Benzillic acid. This seems like a last resort if I can't get the Grignard to work since I would have to go all the way from toluene and TCCA to Benzilic acid.

smuv - 8-9-2008 at 18:21

how do you propose to make isopropyl ether? Dehydration of isopropanol? This will lead to the formation of only propylene.

Also I dont know how Diisopropyl ether works as a Grignard solvent; it is more sterically hindered than THF or Ethyl ether; I think this may affect how the RMgX is solvated...I am not sure how this would effect reactivity. I know that once a Grignard reagent is made in ethyl ether one can add the carbonyl compound dissolved in MTBE to bring about the Grignard reaction. Although IIRC Grignards form with dificulty in MTBE (if at all). So a sterically hindered ether might be no good to actually synthesize the Grignard reagent in.

To make 500-750mL of ether (minus prep time workup and redistillation) via the dehydration of ethanol with sulfuric acid will take you about 3h (in a 1L flask) and the workup and re distillation will take longer. Dont rush the addition of ethanol to sulfuric acid, the ethanol just passes over unconverted (I rushed a run and got shitty yields). I used to distill ether from starting fluid; but the volumes you need to work with to get a good quantity of ether are annoying. Also even if not listed in the MSDS's there are often other things in starting fluid (hydrocarbon gasses such as propane other ethers such as dimethyl ether and methyl ethyl ether) which are hard to seperate from the ether.

About the condenser it is easy to improvise a Liebeg from two concentric copper pipes with pennies as endcaps. The condensers are pretty effecient (more so than glass IMO).

I think I have read somewhere that Grignard reagents can be prepared in dry starting fluid without any purification whatsoever. But this is just a vague recollection.

[Edited on 9-8-2008 by smuv]

kclo4 - 8-9-2008 at 18:38

I see... Dang.
Are you sure it will only produce Propylene? That seems a bit wierd to me. Why would it skip producing the ether and go straight to the Proplyne? I swear I read that Isopropyl Ether was produced via Dehydration.
I was worried Diisopropyl Ether would not work so well for a Grignard, but from all the things I read there didn't seem to be anything that suggested that it wouldn't. How can you tell that it is more sterically hindered then THF? I thought THF would be more so then Isopropyl Ether.. but I know very little about steric effects, I'll put that on my "to research" list

Sandmeyer - 8-9-2008 at 18:41

Quote:

Originally posted by kclo4
So.. it all seemed rather confusing.
Do you have any sources that say it is safer then others, etc?
Thank you for your input

Both THF and diethylether are primary ethers, yet THF forms peroxides much faster, I think since the carbon attached to the oxygen (where radical is initially formed) is more exposed due to the locked, cyclic nature of THF. I would guess that diisopropyl ether bearing two methyl groups on that carbon forms peroxides even slower than diethylether since that carbon is even more hindered, but I'm not sure, there surely is a paper that discusses the kinetics in detail. For practical purposes I never care about peroxide formation when working with ethers. This is only a problem in industrial applications when using multi ton quantities of ether. If you want to be sure to avoid peroxide formation use methyl tert-butyl ether.

kclo4 - 8-9-2008 at 18:49

According to Wikipedia (not the best source I know, but heh) - "Being an ether, MTBE is a Lewis base. However, unlike other ethers such as diethyl ether or THF, it does not coordinate well enough with magnesium to be used for making Grignard reagents. "

Hmm.. Is there a way I can determine if Diisopropyl Ether works for Grignard? I can't really find any reference to it.

Edit: An ultrasonic humidifier might be able to set it off... just an idea

[Edited on 8-9-2008 by kclo4]

Sandmeyer - 8-9-2008 at 19:04

Sorry for misinforming you, I didn't consider possible coordination problems.

Well, in that case you can use one of the glymes to solve your problems, check out: http://www.glymes.com/

bfesser - 8-9-2008 at 19:09

Just a thought, but wouldn't a low boiling ether be desirable for most Grignard reactions? Because the reactions are exothermic, you can have a lower temp limit for the reaction by reflux. That way you won't get problems with runaway reactions, right? Just a safety feature in case an ice bath isn't enough. Any thoughts? Am I absolutely wrong/nuts?

kclo4 - 8-9-2008 at 19:28

No that is also another problem, but I wasn't planning on getting a run away since I wasn't going to add all of my chlorobenzene at one time. Also with good cooling, and the reaction won't be very big.
I figured I'd add it in bits after the reaction had started via a syringe.

http://www.youtube.com/watch?v=ni8fzSLCd1I This is a pretty cool video.

The more I think about it, the better Diethyl Ether sounds, but I still don't like peroxides, which a few respectable people on the board seem to be very afraid of.

Klute - 8-9-2008 at 21:46

As long as you haev a little bisulfite or FeSO4 at hand, it's not aproblem.. regularily test with starch/iodide paper, and as long as you don't distill it to dryness without treating it, you willl be ok...

BTW don't confuse benzylic and benzoic acid: Benzylic acid cannot be made by simple oxidation of toluene!

kclo4 - 9-9-2008 at 13:32

I should have been more descriptive.
I meant to take toluene chlorinate it with TCCA/HCl to Benzyl Chlorde react that with Hexamine and HCl to make Benzaldehyde, use a thiamine catalyst to cause benzaldehyde to dimerize forming benzoin, which would then be oxidized to form benzil. Then do a benzillic rearrangement forming benzillic acid. Which so I have heard, has been decarboxylated into diphenylmethanol and some other things as well. - This is why the grignard reaction is better.

Yeah, I guess I'll just use Diethyl Ether. Seems to be the best. Thanks for all the input and suggestions

I am still curious as to why propylene is produced via IPA and hot concentrated sulfuric acid and not DIPE. Seems odd since DIPE is a secondary Ether and I thought those could be produced with H2SO4.

[Edited on 9-9-2008 by kclo4]

Klute - 9-9-2008 at 14:37

Steric hindrance I suppose, the carbocation will prefer reacting intra-molecularily than with another alcohol...

kclo4 - 9-9-2008 at 15:06

Oh haha ok that makes sense to me thanks

rrkss - 10-6-2010 at 10:15

I made ether and dried it in preparation for a grignard but some other obligation came up that makes it impossible to run the reaction.

Will the reducing nature of the grignard reaction destroy any peroxides that might form in my unstabilized ether if I store it for a week making it safe for me to run the reaction and do the workup/distillation?

zed - 10-6-2010 at 15:30

Depends on how long that week becomes. And, on how much air is in the vessel you are storing the ether in, and the temperature it is stored at.

Might be better to get in the habit of stabilizing your ether. That way, when a two day break..........Stretches out into an interval of two years, the ether remains safe.

The Grignard reaction itself would probably destroy any peroxides present. It is the handling of the ether before it is reacted that presents the problem. Even opening an old half-emptied can of di-isopropyl is considered perilous.

In the world of chemistry, there are so many potential perils, that it really pays to tie-up loose ends. That way, if you are really lucky, you can live a long, healthy, un-maimed life.

[Edited on 10-6-2010 by zed]

entropy51 - 10-6-2010 at 17:02

Quote: Originally posted by zed

Even opening an old half-emptied can of di-isopropyl is considered perilous.

What does isopropyl ether have to do with Grignards? Must every thread go off on a tangent around here?

Sedit - 10-6-2010 at 17:13

Because the OP asked about using Isopropyl Ether for the Grignard and thats one of the main topics this entire thread is about is whether or not Isopropylether is good for a grignard.

entropy51 - 10-6-2010 at 17:18

The original post was two years ago, for gosh sakes. The current post by rrkss is not about isopropyl. rrkss has better sense than that. Only a moron would use isopropyl ether for a Grignard.

rrkss - 10-6-2010 at 20:23

Its ethyl ether and I am waiting 4 days before I do the reaction. Don't want to stabilize it because then I would have to go through the whole drying/purification process to remove the ethanol stabilizer before I do the grignard. The bottle has about a cm air gap above it tried to minimize the amount of air but ran out of ether due to evaporation from the drying and purification procedures.

Was planning on running the reaction but got called to a meeting out of the blue and my next free day is monday.

[Edited on 6-11-10 by rrkss]

zed - 11-6-2010 at 04:31

Hmmmm. Then a feller would really have to be a moron to use anisole for a Grignard.

As it turns out, occasionally, an odd Ether will do the trick, while a Grignard run using the more common Diethyl Ether will fail to produce the desired product.

Sometimes, steric hindrance is a Good thing. At other times, the higher reaction temperatures, allowed by using an alternate Ether, might be desirable.

At any rate, storing unstabilized Ethyl Ether, for a few days, in a dark place, probably won't allow much peroxide formation.

http://yarchive.net/explosives/ether_peroxides.html

Of some interest, might be Sigma Aldrich's practice of stabilizing Ethers via the use of very small amounts of BHT. Used to be able to buy BHT cheap at the health food store, may still be able to. Since the Grignard is a pretty robust reaction (once you get it going) I can't imagine a little BHT would quench it.

http://www.sigmaaldrich.com/chemistry/solvents/learning-cent...

Aldrich provides some good information on what safe storage times might be for opened chemical containers.

http://www.sigmaaldrich.com/chemistry/solvents/learning-cent...

[Edited on 11-6-2010 by zed]

entropy51 - 11-6-2010 at 05:44

Quote: Originally posted by zed

At any rate, storing unstabilized Ethyl Ether, for a few days, in a dark place, probably won't allow much peroxide formation.

I absolutely agree. The problem with any ether that has not been aged for decades is distilling to dryness. Don't distill ether to dryness no matter how recently purified, stabilized or whatever.

Detectable peroxides form almost immediately in unstabilized ether, but that doesn't make it the equivalent of trinitroglycerine..

Lots of other stuff forms peroxides and no one ever even thinks about the danger, if they even know of it.

Just don't distill anything, ever, close to dryness.

mnick12 - 11-6-2010 at 13:46

Doesnt the ether depend upon the grignard you are going to prepare? I personally have never made a grignard but my one of my chem books mentions different ethers for different grignards. For example they use diethyl ether for making methylmagnesium iodide, and THF for vinylmagnesium chloride. But the most common one mentioned was diethyl ether. I think you can use 1,4-dioxane which may be nice because of its higher bp, but it is harder to dry I think.

If anyone more educated on the subject would like to clear that up, it would be greatly appreciated.

zed - 11-6-2010 at 14:18

It was clear as mud but it covered the ground
And the confusion made the brain go 'round.
I went and ask a good friend of mine,
Known to the world as Albert Einstein.
He said "Son, from the beginning of time and creativity
There existed the force of relativity
Pi r square and a minus ten means a routine only when
The solar system in one light year
Make the Hayden planetarium disappear
So if Mt Everest doesn't move
I am positive that it will prove.........

Is this a request for some overall theory of what ether to use, and when? The answer is.....use the one that works best! Theory may not be able to help you here. Such things are determined experimentally. Hopefully, by somebody else's experiments. Actually crafting experiments is hard work, often rewarded by failure.

Results trump theory. Once you get some positive results, you then craft a theory as to why your Grignard experiment works with one ether, and not another.

This link will take you to a degenerate hippie website, where there is an interesting discussion of using anisole as a Grignard solvent. Note the haziness, as to EXACTLY why one thing works and another doesn't.

http://www.erowid.org/archive/rhodium/chemistry/dmt.indole.g...

[Edited on 11-6-2010 by zed]

rrkss - 11-6-2010 at 14:20

Iodine is a better leaving group than chlorine so you need a higher boiling point to allow more heat to force the reaction. This is why THF is used instead of EtOEt.

For ethyl magnesium bromide I intend to use ethyl ether. I will test for peroxides before I use the ether and if the number is too high, will have to use FeSO4 otherwise I intend to use the reducing nature of the grignard reaction to destroy any peroxide present.

DJF90 - 11-6-2010 at 14:46

Nope. The formation of a Grignard reagent is a radical reaction ("oxidative insertion") and so it's nothing to do with "this is a better leaving group than that". The C-I bond is weaker than the C-Cl bond, but not by much (228kJmol^-1 vs 346kJmol^-1 respectively), and so an iodide will form a grignard reagent faster than a chloride, given similar conditions.

The difference in the given case is that the chloride is also a *vinyl* halide, which are more difficult to form the grignard reagent from (apparently they have long been considered unreactive towards magnesium), and hence the higher boiling solvent is necessary. I also suspect a more active magnesium is used (Riecke magnesium for example).

1,4-dioxane is added to alkyl magnesium halides in order to shift the Schlenk equilibrium, forming the dialkyl magnesium compound and magnesium dihalide, which is complexed to the 1,4-dioxane and precipitates.

rrkss - 11-6-2010 at 15:32

Very interesting. Thanks for sharing!

Quote: Originally posted by DJF90

Nope. The formation of a Grignard reagent is a radical reaction ("oxidative insertion") and so it's nothing to do with "this is a better leaving group than that". The C-I bond is weaker than the C-Cl bond, but not by much (228kJmol^-1 vs 346kJmol^-1 respectively), and so an iodide will form a grignard reagent faster than a chloride, given similar conditions.

The difference in the given case is that the chloride is also a *vinyl* halide, which are more difficult to form the grignard reagent from (apparently they have long been considered unreactive towards magnesium), and hence the higher boiling solvent is necessary. I also suspect a more active magnesium is used (Riecke magnesium for example).

1,4-dioxane is added to alkyl magnesium halides in order to shift the Schlenk equilibrium, forming the dialkyl magnesium compound and magnesium dihalide, which is complexed to the 1,4-dioxane and precipitates.

rrkss - 14-6-2010 at 11:34

Well unstabilized ether does form peroxides very fast. I have a level of between 0.5 ppm and 1 ppm on my test strip from less than 5 days of storage. Normally stabilized ether tests negative for peroxides after a month of storage for me.

Tests negative on iodine starch, only the highly sensitive test gave me a positive reading.

[Edited on 6-14-10 by rrkss]