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Topic: how to work up when using DMF as solvent without product missing? help  (Read 25911 times)

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Offline zhangh

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I am currently preparing azide by substituting bromide with DMF as solvent. after the complection of reaction,  pour water into the mixture and extraction with DCE, drying, concentrated in vacuo, but  concentrated crude  still contain so much DMF , it's terrible, azide compound is explosive and not allowed high temperature to concentrated.


how to work up when using DMF as solvent?
 

thanks a lot

Offline HP

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Re: how to work up when using DMF as solvent without product missing? help
« Reply #1 on: August 19, 2006, 05:52:58 AM »
I am thinking about possible process of molecular destilation realized with high vacuum and thin layer of your solvent/product mixture. In such conditions DMF will evaporate at low temperature and the only problem could be if your azide easily sublimate, but then it's also possible to isolate it pure of solvent..
xpp

Offline HP

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Re: how to work up when using DMF as solvent without product missing? help
« Reply #2 on: August 19, 2006, 05:59:49 AM »
Also think about lyophilization (Freeze-Drying) :)
xpp

Offline sjb

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Re: how to work up when using DMF as solvent without product missing? help
« Reply #3 on: August 19, 2006, 07:41:26 AM »
I am currently preparing azide by substituting bromide with DMF as solvent. after the complection of reaction,  pour water into the mixture and extraction with DCE, drying, concentrated in vacuo, but  concentrated crude  still contain so much DMF , it's terrible, azide compound is explosive and not allowed high temperature to concentrated.


how to work up when using DMF as solvent?
 

thanks a lot

Something I've done in the past is use saturated LiCl(aq). This forms a complex with the DMF (I think, can't find a reference to hand) that then allows most of it to fall into an aqueous layer and then extract product using ethyl acetate or similar. Of course, it depends on how soluble your product is in the relative phases as to whether this is of any use.

S

Offline edwin

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Re: how to work up when using DMF as solvent without product missing? help
« Reply #4 on: August 19, 2006, 10:32:19 AM »
In theory, the best solvent for the substitution reaction of azide to bromide is non-proton polar solvent, such as DMF. But in your case, the boiling point of DMF is too high to be removed absolutely. So I think you could change your reaction solvent, using other polar solvent, such as acetone. In this case, you could add some KI as catalyst.

Offline russellm72

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Re: how to work up when using DMF as solvent without product missing? help
« Reply #5 on: August 19, 2006, 11:17:48 AM »
Ok easy.

When you add water can you perhaps use ether for the extraction instead? DMF is less soluble in ether than DCM when water is present i.e. from a aqueous solution. Anyway no problem if it can't be taekn into ether. One thing i do often is azeotrophic distillation. A week or so ago I had to remove about 30 ml of DMF which had previously been removed under high vacuum which takes too long. So I added toluene and spun down again just using the water pump does not need to be heated. Do this a few times and you'll notice your residue going down each time as you evaporate off the toluene. Xylene is better but I just use toluene to good effect. The last traces could be removed by high vacuum or passing down a pad of silica however this depends on your compound.

Another way, once your compound is in DCM (preferably ether as you can just run off the aqueous layer each time) wash with several portions of brine.

Great solvent but you just need a few tricks of the trade to remove :)

Even easier as mentioned previously you could opt for another solvent.

R.

Offline movies

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Re: how to work up when using DMF as solvent without product missing? help
« Reply #6 on: August 20, 2006, 07:51:14 PM »
I've been using DMF lately and have had great luck diluting my reaction mixture with ethyl acetate and then washing with water about 6 times.  I never see any DMF!

Offline HP

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Re: how to work up when using DMF as solvent without product missing? help
« Reply #7 on: August 21, 2006, 12:29:19 PM »
Nice sugestion movies! I am some qurious how it's explained  ??? Washing with water - what disolved at it - DMF or the azide product? Ethylacetate is slightly soluble in water i know but DMF is quite better soluble i think.
xpp

Offline movies

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Re: how to work up when using DMF as solvent without product missing? help
« Reply #8 on: August 21, 2006, 12:52:12 PM »
The idea is that your organic product will be very soluble in EtOAc, but hardly soluble at all in water.  DMF is miscible with water, and probably also with EtOAc.  By washing the organic (EtOAc) layer with water a few times, you can extract out the DMF from the organic layer selectively.  It's the same principle as when you extract your product from an aqueous phase, just in reverse.

Offline HP

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Re: how to work up when using DMF as solvent without product missing? help
« Reply #9 on: August 21, 2006, 01:00:26 PM »
Reverse water extraction i see ;) Cool working!
xpp

Offline evie

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Re: how to work up when using DMF as solvent without product missing? help
« Reply #10 on: September 25, 2006, 07:08:03 AM »
Ok easy.

When you add water can you perhaps use ether for the extraction instead? DMF is less soluble in ether than DCM when water is present i.e. from a aqueous solution. Anyway no problem if it can't be taekn into ether. One thing i do often is azeotrophic distillation. A week or so ago I had to remove about 30 ml of DMF which had previously been removed under high vacuum which takes too long. So I added toluene and spun down again just using the water pump does not need to be heated. Do this a few times and you'll notice your residue going down each time as you evaporate off the toluene. Xylene is better but I just use toluene to good effect. The last traces could be removed by high vacuum or passing down a pad of silica however this depends on your compound.

Another way, once your compound is in DCM (preferably ether as you can just run off the aqueous layer each time) wash with several portions of brine.

Great solvent but you just need a few tricks of the trade to remove :)

Even easier as mentioned previously you could opt for another solvent.

R.

Hi, do u mind explaining what u mean by "passing down a pad of silica". based on my experience, after columning thru silica, traces of dmf may still be found in pdt. so i am confused. thanks

firefox

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Re: how to work up when using DMF as solvent without product missing? help
« Reply #11 on: September 27, 2006, 12:10:50 AM »
I have done some synthesis about the azides (sulfonyl azides),we just get the products througt distillion in low pressure

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