rrkss
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Drying Ether for Grignard
Will fresh ethyl ether distilled from Anhydrous CaCl2 (after a treatment with acidified FeSO4 solution to remove peroxides) be sufficiently dry to run
a grignard or do I have to take additional steps like using a molecular sieves to dry it further? I intend to prepare a grignard reagent from ethyl
bromide.
Most of the literature tells me to use ether dried by Sodium/Benzophenone method but I don't have Sodium Metal on hand to do this.
[Edited on 5-12-10 by rrkss]
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JohnWW
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That should do it, if the amount of CaCl2 is sufficient. To find out how much CaCl2 would be needed, assume that the diethyl ether is saturated with
water to begin with (I do not have any figure offhand for the solubility of water in diethyl ether - you will have to find it using Google), and then
calculate the potential amount of water in it, and then the amount of CaCl2 that would be required to remove it all as CaCl2.6H2O.
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entropy51
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Quote: Originally posted by JohnWW  | | That should do it, if the amount of CaCl2 is sufficient. To find out how much CaCl2 would be needed, assume that the diethyl ether is saturated with
water to begin with (I do not have any figure offhand for the solubility of water in diethyl ether - you will have to find it using Google), and then
calculate the potential amount of water in it, and then the amount of CaCl2 that would be required to remove it all as CaCl2.6H2O.
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John, you are so full of it.
rrks, there are multiple threads on this topic. Try searching.
[Edited on 12-5-2010 by entropy51]
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rrkss
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If I could find anything relevant, I would have not bothered to post here. The only topic I found was using ultrasonic to initiate a grignard
something I don't have the tools for. I know once the grignard reagent forms it will chemically destroy any remaining water in the ether. Right now
what I intend to do is distill the ether from CaCl2 to remove the ethanol stabilizer and most of the water from the peroxide destroying step. Then
dry it over molecular sieves and redistill it for use. Hopefully this is enough drying.
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entropy51
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rrkss, the threads are there, they may or may not be helpful. Here's one. There are other methods around, including some that employ magnesium. The details I can't recall at the moment. Refluxing the ether with
NaOH and drying with MgSO4 are two possibilities that have been discussed. Molecular sieves are said to be excellent, but being older than Gatterman,
I've never resorted to such new-fangled tomfoolery.
How dry the ether must be depends on the reactivity of the halide and tricks employed to start the Grignard. A touch of iodine heated in the dry
flask with the Mg before adding the ether will often do wonders. Bromine is said to also work such magic. There are quite a few hints here and there
on the forum. If the Management deleted the bullshit threads, the search engines might be able to find the actual information. Anarchy is not really
conducive to science.
[Edited on 13-5-2010 by entropy51]
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Magpie
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Here's another one:
http://www.sciencemadness.org/talk/viewthread.php?tid=11151#...
[Edited on 13-5-2010 by Magpie]
The single most important condition for a successful synthesis is good mixing - Nicodem
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rrkss
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Thanks for those threads. I like the idea of drying over NaOH seems to me that it would also hydrolyse any peroxides that might form.
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rrkss
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Well, drying with a molecular sieve and CaCl2 only was good enough. My ethyl bromide grignard activated almost immediately without needing any iodine
or anything else to force it to start.
Here is an image of the reaction bubbling away :-)
[Edited on 5-13-10 by rrkss]
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Magpie
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Nice going. 
The single most important condition for a successful synthesis is good mixing - Nicodem
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benzylchloride1
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When I run syntheses involving Grignard Reagents, I distill my ether from engine starting fluid. This ether does not need to be dried any further;
though I allow the ether to sit over 4A molecular sieves just in case. I have always been able to prepare Grignard Reagents from the directly
distilled ether. The yield is always better though when the ether has been throughly dried.
Amateur NMR spectroscopist
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rrkss
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Well I am done with the grignard. It was my first grignard reaction and was very interesting. I started it by adding 1 mL of ethyl bromide to 60 mL
of ether in a 250 mL roundbottom with 13g of magnesium. I calculated a 0.7g excess of magnesium from what I needed.
The reaction took off and was very exothermic forcing me to put the flask in an icebath right away since my condenser was not catching all the boiling
ether. Once things calmed down I added the ethyl bromide dropwise over the next 2 hours. The grignard reagent was a nice dark gray almost purplish
color.
After the grignard was prepared, I added the ethyl acetate dropwise. The ethyl acetate reacting with the grignard was even more exothermic than the
preparation of the grignard and took a ton of work to get the addition rate just right.
Once the reaction was done, I quenched with acid. I added the 2.0 M H2SO4 solution dropwise to the flask. The addition was highly exothermic and
formed a white jellylike precipitate. I soon ran out of room and was forced to transfer this mess into a larger flask and do multiple acid rinses.
Being strapped for time I ended up probably using way to much acid to quench the reaction (500 mL of 2 M H2SO4 solution) but eventually all the
magnesium reacted and the precipitate dissolved. I then transferred my organic layer to a new roundbottom and dried it with anhydrous MgSO4.
I lost about 50 mL of organic layer during the workup. Probably due to ether's slight solubility in water and my hastly workup. Hopefully after
distillation, did not lose too much of my alcohol which supposedly is slightly soluble in water as well. Tommorow when I distill the ether away and
get my product, I will finally know.
Things I learned.
1. Transfer the finished reaction mixture to a different and larger flask before doing the acid quench.
2. Do the quench when you are not strapped for time as it takes much longer than expected.
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eniv62
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Grignard reagent
Hello,
I have been reading many threads on this site and I find it really interesting.
I know this thread is old, but I didn't know where to add my post. This is my first post and I apologize if it is not the appropriate place. I
couldn't find any other thread that treats about this.
I have not tried yet Grignard reactions, and I wonder if it is possible to prepare Methyl Magnesium Bromide. This reagent will be good to make
tert-butanol by making it react with acetone and afterwards with protonated water, at least in theory.
The problem I see is that Methyl Bromide is a gas at ambient temperature, its boiling point temp is 3.56 C. So I was thinking in disolving the gas in
Ether firstly and then inject the solution very slowly to a BF with Ether and Magnesium.
I really will appreciate your opinion.
Thanks
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entropy51
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An ether solution of MeBr will work in a Grignard. If you have a suitable source of dry MeBr you can also let it enter the reaction flask as a gas.
It will dissolve in the ether and react with the Mg, especially if the Grignard is first started by adding a little MeI.
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eniv62
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Thanks for your answer.
I was planning to produce the MeBr by a reaction and dry it later. I understand that Grignards need very dry reagents. I have dried other gases by
passing them through a cylinder full with Calcium Chloride, but for other simple experiments. How can I be sure that my MeBr is dry enough for a
Grignard?
Thanks
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rrkss
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When I ran my grignard, I used a molecular sieve to dry my ether and simply CaCl2 for the alkyl halide. Ethyl Bromide is very hydrophobic and the
CaCl2 was sufficient for my reaction. I personally would reccommend using MeI instead of MeBr simply because it has a higher boiling point and can be
used in the liquid phase at ambient conditions. As a bonus it should even be able to initiate the grignard in relatively wet ether. The MeMgI would
then proceed to destroy any remaining water and bubble off as methane.
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eniv62
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Thank you very much entropy51 and rrkss. I'll try that.
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