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Author Topic: Can I use Magnesium Bromide Ethyl Etherate for a Grignard reaction?  (Read 655 times)

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Toneman

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I'm brand new to the forum and chemistry for that matter so I apologize if I've posted my question in the improper place.
I'm working on a project due to forum rules purposes I don't believe I should identify.

I have what I believe is a simple question. I'm following a guide for this project which calls for the preparation of a Grignard reaction by using ethyl magnesium bromide and it goes on to tell how to make it giving the number of grams of magnesium and ethyl bromide and ml of ether that should be used.
 
I've acquired the necessary materials but in the interim happened to acquire an unopened 500g bottle of Magnesium Bromide Ethyl Etherate (Sigma Aldrich brand) in powder form.

My question is can I shortcut the Grignard reaction by using this product in diethyl ether instead of preparing my own magnesium bromide? From what I was able to research it's the same thing (?).

If the answer is yes how would I calculate how much to use since the information I have just tells me how many grams of Mg, ethyl bromide and ml of ether to use?
Any advice would be appreciated.
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sjb

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Re: Can I use Magnesium Bromide Ethyl Etherate for a Grignard reaction?
« Reply #1 on: July 16, 2017, 10:46:33 PM »

This is very unlikely to work for you. Ethyl grignard (what you appear to be wanting to prepare) is 99.99% of the time probably used as a solution as it is pyrophoric.
 
Your bottle of powder is likely to be somewhat similar to CuSO4ยท5H2O or similar, a salt with some "ether of crystallisation".

Can you post the guide you have found, to be sure?

I've also moved this to the organic chemistry forum, FYI

sjb
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clarkstill

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Re: Can I use Magnesium Bromide Ethyl Etherate for a Grignard reaction?
« Reply #2 on: July 17, 2017, 06:05:38 AM »

SJP may have misread what you said - the bottle you have contains MgBr2.Et2O, which is just magnesium bromide with a solvent molecule stuck on. There is no plausible mechanism for using this to generate the grignard that you need, since the formation of a grignard reagent from an alkyl halide occurs by an oxidative addition of Mg(0) - all you have in that pot is Mg(II) so it can't do the necessary oxidative addition.

I'm afraid you'll have to make your Grignard the old fashioned way, but on the plus side they are quite fun to make. If you're having trouble forming the Grignard there are a bunch of ways to make the reaction work better, including mechanical activation of the Mg, and addition of I2 and/or 1,2-DBE.

Hope this helps.
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DrCMS

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Re: Can I use Magnesium Bromide Ethyl Etherate for a Grignard reaction?
« Reply #3 on: July 17, 2017, 10:13:11 PM »

clarkstill - I think it is you that has misread things. 

In his answer sjb said this was a salt with an ether of crystallisation which is correct and just the same as your answer.

Next time before you criticise someone else make sure you are 100% correct before you jump in and always make sure you get their name correct otherwise stay quiet.
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clarkstill

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Re: Can I use Magnesium Bromide Ethyl Etherate for a Grignard reaction?
« Reply #4 on: July 18, 2017, 01:27:11 AM »

Blimey - I wasn't being particularly critical, I just thought SJB's statement of 'ethyl grignard is 99.99% of the time probably used as a solution as it is pyrophoric' gave the impression he thought the sample may have been either solid EtMgX, or a salt formed by partial hydrolysis of the grignard. Clearly he/she knows what they are talking about, I just wanted to give some additional information to the OP.

I hope SJP wasn't offended by me pitching in, I don't think I was disrespectful but apologize if I was. But I fail to see what it has to do with you. Please don't try to unnecessarily escalate what was an entirely respectful exchange between peers.
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DrCMS

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Re: Can I use Magnesium Bromide Ethyl Etherate for a Grignard reaction?
« Reply #5 on: July 18, 2017, 03:18:21 AM »

I got involved because your answer did not really add much to the answer that had been given gave while suggesting it was wrong combined with getting their name wrong.  Something you have done again in reply to me even though I pointed it out to you; you have repeatedly used SJP when the correct user name is sjb.

Go reread his answer again he said it was an inorganic salt with an ether of crystallisation which it is and told the OP they probably needed to prepare the Grignard solution which they do. 

I will post every time I see something I can answer or when something needs correcting.  I care not a jot how you feel about my posting but if it does bother you then simply do not post incorrect info.  In my opinion a respectfully exchange does not start when you point out somebody was wrong when they were right but does involves getting people's names correct. 

With that later in mind I should for consistency have a go at sjb (and you in your 2nd post) for not capitalising Grignard correctly.
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clarkstill

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Re: Can I use Magnesium Bromide Ethyl Etherate for a Grignard reaction?
« Reply #6 on: July 18, 2017, 04:02:53 AM »

Once again apologies to SJB if any offence was taken, it certainly wasn't meant.

I got involved because your answer did not really add much to the answer that had been given

I summarized the mechanism of grignard reagent formation to explain why MgBr2 won't do the trick, and gave three suggestions for helping to initiate slow formation. I regret that this doesn't meet your threshold for pertinent information in a forum post, I promise to try harder ;)
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rolnor

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Re: Can I use Magnesium Bromide Ethyl Etherate for a Grignard reaction?
« Reply #7 on: July 18, 2017, 04:12:38 AM »

It all seems like a storm in a glass of water.
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sjb

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Re: Can I use Magnesium Bromide Ethyl Etherate for a Grignard reaction?
« Reply #8 on: July 18, 2017, 04:25:07 AM »

No offence taken, and apologies for miscapitalising Grignard.

Looking at my post again, it does seem to be missing key things in the middle, which have been provided.

Having said all that, the MgBr2.Et2O may still prove useful - see e.g. http://dx.doi.org/10.1016/0020-1693(94)03928-3 ?
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DrCMS

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Re: Can I use Magnesium Bromide Ethyl Etherate for a Grignard reaction?
« Reply #9 on: July 18, 2017, 04:27:16 AM »

I summarized the mechanism of grignard reagent formation to explain why MgBr2 won't do the trick, and gave three suggestions for helping to initiate slow formation. I regret that this doesn't meet your threshold for pertinent information in a forum post, I promise to try harder ;)

I think given that the OP may be up to no good

I'm brand new to the forum and chemistry for that matter so I apologize if I've posted my question in the improper place.
I'm working on a project due to forum rules purposes I don't believe I should identify.

not trying quite so hard might be even better.
 
I was somewhat harsh in my criticism earlier and I appologise.
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clarkstill

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Re: Can I use Magnesium Bromide Ethyl Etherate for a Grignard reaction?
« Reply #10 on: July 18, 2017, 05:06:25 AM »

Friends again! :)



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Babcock_Hall

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Re: Can I use Magnesium Bromide Ethyl Etherate for a Grignard reaction?
« Reply #11 on: July 18, 2017, 06:07:59 AM »

@OP,  What compound are you trying to make?  What is the CAS registry number or catalog number of the substance from Sigma-Aldrich?
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