July 01, 2022, 07:32:28 PM
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Topic: best way to remove dimethylformamide  (Read 52208 times)

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Offline rolnor

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Re: best way to remove dimethylformamide
« Reply #15 on: January 20, 2022, 02:18:39 AM »
You can diltue the reaction with Et2O/Hexane and wash repeatedly with water, then evaporate and then put in freezdryer to remove any traces. Its realy not difficult.

Online Babcock_Hall

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Re: best way to remove dimethylformamide
« Reply #16 on: January 20, 2022, 06:24:44 PM »
We washed our ethyl acetate later twice with 5% LiCl, which increased considerably in volume (suggesting the presence of DMF), then we washed once with brine and dried with magnesium sulfate.  Assuming that the remaining mass is product, we removed nearly all of the DMF.

Offline rolnor

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Re: best way to remove dimethylformamide
« Reply #17 on: January 21, 2022, 07:00:53 AM »
I would wash 5 times to get rid of traces.

Online Babcock_Hall

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Re: best way to remove dimethylformamide
« Reply #18 on: January 21, 2022, 09:52:48 AM »
In the past I have used five washes.  We will purify the crude reaction with silica gel; therefore, I thought we could live with a few traces of DMF.  However, there is a chance that it could interfere with the chromatography.

Offline rolnor

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Re: best way to remove dimethylformamide
« Reply #19 on: January 21, 2022, 02:37:33 PM »
OK, yes, DMF is polar so it usually stops at the baseline.

Online Babcock_Hall

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Re: best way to remove dimethylformamide
« Reply #20 on: June 01, 2022, 10:21:45 AM »
Hello Everyone,

I was synthesizing a couple of compounds at a reaction temperature of 80 °C.  Both are very likely to be water-soluble, and so extracting the DMF into the water phase was not an option.  Elsewhere I read a suggestion to use 3:2 toluene and rotary evaporation.  I had to do this about four times for each crude reaction and use a high temperature bath, but eventually I got rid of the majority of the mass, presumably the DMF.  Possibly with a higher ratio of toluene, I would have needed fewer evaporations.

Online Babcock_Hall

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Re: best way to remove dimethylformamide
« Reply #21 on: June 01, 2022, 09:25:47 PM »
I did a little reading on toluene/DMF binary mixtures, and from what I can gather, there is no azeotrope between the two.  There is an azeotrope between DMF and heptane, but it is mostly heptane; therefore, it is not a highly cost effective way to remove DMF.

Offline rolnor

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Re: best way to remove dimethylformamide
« Reply #22 on: June 01, 2022, 11:51:48 PM »
There is really no question in the post? Do you need other options or are you happy?

Online Babcock_Hall

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Re: best way to remove dimethylformamide
« Reply #23 on: June 02, 2022, 10:29:01 AM »
Hi Rolnor,

Mostly it was a follow-up post.  However now that I think about it, my question is whether the toluene is helping or not.
EDT
https://cool.culturalheritage.org/waac/wn/wn28/wn28-3/wn28-304.pdf
"Azeotropes from A to Z," by Chris Stavroudis.  This is a discussion of azeotropes that might come in handy.

When I discussed using a slightly higher vacuum pump to remove DMF more efficiently with a colleague, he pointed out that the rotary evaporator might be leaky (for lack of a better word), such that the higher vacuum pump was not really helping.
« Last Edit: June 02, 2022, 01:57:58 PM by Babcock_Hall »

Online Babcock_Hall

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Re: best way to remove dimethylformamide
« Reply #24 on: June 03, 2022, 01:15:13 PM »
See the link on this page entitled "Efficient extraction of highly polar solvents (i.e. DMF or DMSO) from reaction mixtures - Contributed by Professor Philip Hultin"

http://chem.chem.rochester.edu/~nvd/magicformulas.html

Haven't tried it myself, but it seems useful. 
http://www.chem.rochester.edu/notvoodoo/pages/reagents.php?page=extraction
This is an updated link. 

In my opening post, I mentioned forming an azeotrope with water.  The composition of the azeotrope is 15-20% DMF, from what I can gather elsewhere.

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