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Topic: Tips from removing DMF from a sample?  (Read 12407 times)

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Offline zuriel

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Tips from removing DMF from a sample?
« on: April 30, 2013, 03:36:48 PM »
Hey everyone I'm wondering if anyone has any tips from removing DMF from a worked up product.
Before I would normally quench the reaction with HCl and wash with lots of water after extracting into EtOAc and it worked well but for some reason this week I'm getting glassy and oily type solids and I know there's still DMF in there. I've tried more water washes all to no avail.

If anyone knows any tricks let me know please :) - I'm trying to avoid a column if it's possible at all lol.

Offline opsomath

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Re: Tips from removing DMF from a sample?
« Reply #1 on: April 30, 2013, 03:55:14 PM »
Are you sure the impurity is DMF?

If you have access to a high vacuum pump, throw it on there for a few hours.

Otherwise, try recrystallizing; hopefully the junk will stay in your solvent.

Offline zuriel

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Re: Tips from removing DMF from a sample?
« Reply #2 on: May 01, 2013, 06:30:53 AM »
Yeah I'm fairly certain, I was using DMF as a solvent for the last stage of a reaction.

I'll try putting it on the high vac line tonight! Thanks opsomath.

Offline Archer

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Re: Tips from removing DMF from a sample?
« Reply #3 on: May 01, 2013, 07:00:43 AM »
If the High Vac doesn't work then this is a last resort method which I have used in the past, add a relatively high boiling solvent which your substance is soluble in, for example butanone, and put it on the rotary evaporator. This should azeotrope some of the DMF off the sample. Repeat this several times and you will remove all of the DMF. Butanone is much easier to remove under high vaccum.

As I said this is not the best method and it is time consuming but it is a tried and tested for the last resort when you need elemental analysis.
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Offline zuriel

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Re: Tips from removing DMF from a sample?
« Reply #4 on: May 01, 2013, 07:31:19 AM »
Thanks Archer, I've taken note of your advice too!
I'll place both samples on high vac and then I'll NMR tomorrow to see what it looks like. :)

Offline salteen

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Re: Tips from removing DMF from a sample?
« Reply #5 on: May 01, 2013, 11:39:30 AM »
Hi zuriel,

I've had this problem before as well.  Usually I can manage to get rid of the DMF by co-evaporating with toluene, but it depends on how good the suction is on your rotovap.

If the high vac doesn't work for you, one thing you can try is an extraction between water and ether. DMF is much less soluble in ether than it is in EtOAc or DCM, so after washing several times the DMF will eventually partition into the aqueous layer.  This has worked for me in the past.

Offline opsomath

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Re: Tips from removing DMF from a sample?
« Reply #6 on: May 01, 2013, 02:34:09 PM »
The primary advantage of the high vac method is that you can put it on there and then go browse the internet do something productive in the meantime.

Offline kriggy

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Re: Tips from removing DMF from a sample?
« Reply #7 on: May 01, 2013, 03:04:51 PM »
The primary advantage of the high vac method is that you can put it on there and then go browse the internet do something productive in the meantime.
Totaly. Like wash all the glass used last week :D

what about freeze drying? Could it work here?

Offline opsomath

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Re: Tips from removing DMF from a sample?
« Reply #8 on: May 01, 2013, 03:12:55 PM »
Quote
DMF is much less soluble in ether than it is in EtOAc or DCM

I thought DMF had a high affinity for DCM, actually, for some reason. Wasn't that how someone blew up their lab awhile back? Like, they tried to get rid of DCM by rotovaping it off with DMF, and it didn't work even though the boiling points are like 100°C different?

Yes. http://pubs.acs.org/doi/abs/10.1021/op8000977

"(R)-1-(6-(Benzyloxy)indazol-1-yl)-2-propanol (1, 1.26 kg, 4.45 mol) was converted to mesylate 2 under standard conditions as indicated.(21) After an aqueous quench and phase separation the organic solution was concentrated on a rotary evaporator of 20-L capacity. The dual receiving flasks were then emptied. DMF (4 L) was added to the residue, and concentration (35 °C bath, 20 Torr) was resumed until no further condensation was observed, the intention being to drive off DCM from the product. The residual solution of 2 was diluted with more DMF (12 L) and transferred to a reaction flask. Sodium azide (580 g, 8.9 mol) was added, and the stirred mixture was heated to 70 °C for 16 h, then cooled to rt and partitioned between diethyl ether and water. The organic extract was concentrated on the evaporator, and the receivers were then emptied.

The next morning it was noted that about 30 mL of a two-phase liquid had collected in the glass crosspiece at the bottom of the condenser assembly. The distilling flask containing azide 3 was disconnected and set aside in a walk-in fume hood, and the PTFE stopcock leading to one of the receivers was then opened to drain the liquid. Within seconds a loud explosion occurred. The plastic-coated condenser and receiving flasks shattered. Larger glass fragments were propelled with sufficient force to break other glassware. A 2′ square perforated metal ceiling vent cover above the evaporator was domed by pressure, while a 4 1/2′ × 8′ × 1/4″ annealed glass window panel located 20′ away was fractured by pressure or impact. Two chemists sustained noncritical lacerations but escaped more serious injury, principally by the proper wearing of safety glasses."

I wish I could get my lab accidents published in OPRD. Guess they don't involve enough exploding rotovaps.

Offline salteen

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Re: Tips from removing DMF from a sample?
« Reply #9 on: May 01, 2013, 03:52:28 PM »
The primary advantage of the high vac method is that you can put it on there and then go browse the internet do something productive in the meantime.

Rofl.  Sometimes I wonder how much Reddit affects my success as a chemist....

Offline willug

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Re: Tips from removing DMF from a sample?
« Reply #10 on: May 01, 2013, 04:25:20 PM »
'Wasn't that how someone blew up their lab awhile back?'  No! It wasn't. That was about accidentally making diazidomethane.






Offline opsomath

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Re: Tips from removing DMF from a sample?
« Reply #11 on: May 01, 2013, 04:33:18 PM »
Quote
No! It wasn't. That was about accidentally making diazidomethane.

Yes...from DCM...that unexpectedly stayed in a DMF solution because of its unusually high affinity for DMF. Right?

Offline willug

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Re: Tips from removing DMF from a sample?
« Reply #12 on: May 01, 2013, 05:48:27 PM »
Sorry! Didn't read the whole comment.  :-[

Offline Adamcp898

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Re: Tips from removing DMF from a sample?
« Reply #13 on: May 02, 2013, 05:40:57 AM »
It should come off on the rot. evap. if the pressure on yours goes to close to 0 mbar. Turn the water bath up to ~70oC and add a *Ignore me, I am impatient* trap between your flask and the rot. evap. itself, under those conditions it should be pulled as far as the *Ignore me, I am impatient* trap at least before condensing. But make sure others don't mind you using the rot. evap. under those elevated conditions and wash it afterwards if for nothing else than to get rid of the smell.

Offline zuriel

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Re: Tips from removing DMF from a sample?
« Reply #14 on: May 02, 2013, 10:57:38 AM »
Thanks for all the suggestions guys. The partitioning between ether and water seems like another easy option but I'm not sure if my compound would be soluble in ether. I'll give it a shot!

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