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Drying DMF

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Tapio

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Apr 19, 1999, 3:00:00 AM4/19/99
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What is the best way to dry dimethylformamide (DMF)? It is said that
DMF may decompose if dried with calcium hydride, is it really so?

Thanks in advance.

Tapio

--
Paul J. Franklin (moderator - sci.chem.organic.synthesis)
http://chemistry.gsu.edu/post_docs/koen/wnewshp.html
Georgia State University <che...@panther.gsu.edu>
Atlanta, GA

Christina Benedek

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Apr 20, 1999, 3:00:00 AM4/20/99
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Tapio wrote:
>
> What is the best way to dry dimethylformamide (DMF)? It is said that
> DMF may decompose if dried with calcium hydride, is it really so?
>
> Thanks in advance.
>
> Tapio
>

Hi!

I always dry it with CaH2. You have to wrap it up with aluminium paper,
because light causes amine formation. That's the reason why you
shouldn't use "old" dried DMF. - Well, that's my expeience and my
synthesis usually works.

Tina

Wim De Borggraeve

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Apr 20, 1999, 3:00:00 AM4/20/99
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> What is the best way to dry dimethylformamide (DMF)? It is said that
> DMF may decompose if dried with calcium hydride, is it really so?

according to "Purification of Individual Organic Chemicals" (2° ed.,
p.224), DMF decomposes at its normal b.p. to give small amounts of
dimethylamine and CO. The decomposition is catalyzed by acid or base (CaH2,
NaOH, KOH). If these reagents are used as dehydrating agents, they should
not be refluxed with DMF.
Use of CaSO4, MgSO4, silicagel or Linde type 4A molecular sieves is
preferable, followed by distn. under reduced pressure. This is adequate for
normal lab purposes. Larger amounts of water can be eliminated by
azeotropic distn. with benzene (10% (v/v) previously dried over CaH2) at
atmospheric pressure. Water and benzene distill below 80°C. The remaining
liquid is is further dried by adding MgSO4 (previously heated overnight at
300-400°)(25 g/l). After shaking for a day another quantity of MgSO4 is
added and DMF distilled at 15-20mm pressure.

other ref: JACS, 79, 1843 (1953)

--
Wim De Borggraeve, PhD student
KU Leuven, Chemistry Department
Celestijnenlaan 200F
B-3001 Heverlee
Belgium

Mark Wilson

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Apr 20, 1999, 3:00:00 AM4/20/99
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I have dried DMF by letting it stir overnight with CaH2 and then
distilling it under reduced pressure (20-30 mmHg) to prevent
decomposition.

Mark Wilson

In article <7ffcpd$f...@panther.Gsu.EDU>, Tapio <tane...@falli.uku.fi> wrote:

> What is the best way to dry dimethylformamide (DMF)? It is said that
> DMF may decompose if dried with calcium hydride, is it really so?

Bill Walker

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Apr 20, 1999, 3:00:00 AM4/20/99
to
Tapio wrote:

> What is the best way to dry dimethylformamide (DMF)? It is said that
> DMF may decompose if dried with calcium hydride, is it really so?
>

Check out:Perrin, D. D.; Armarego, W. L. F.; Perrin, D. R., Purification
of Laboratory Chemicals, 2nd Ed., Pergamon Press, Oxford, 1980

We just dunk in a whole lotta 4A MS and then vacuum distill it.

Bill

> Thanks in advance.
>
> Tapio

Doc Soc

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Apr 20, 1999, 3:00:00 AM4/20/99
to
In article <7ffcpd$f...@panther.Gsu.EDU>,

Tapio <tane...@falli.uku.fi> wrote:
> What is the best way to dry dimethylformamide (DMF)? It is said that
> DMF may decompose if dried with calcium hydride, is it really so?
>
> Thanks in advance.
>
> Tapio


Yes, DMF has been known to explode in the presence of sodium hydride and
sodium borohydride usually after an induction peroid (and possabily with
calcium hydride). Check out Bretherick "Handbook of Reactive Chemical
Hazards" for detials.

Some of the peptide chemists that I once knew, would distil DMF from 3A
molecular sieves (easier said than done). The best place to look is D. D.
Perrin and W. L. F. Armarego "Purification of Laboratory Chemicals", Peramon,
London, 1985 (or later editions).

--
Regards,

Dave

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maggie...@my-dejanews.com

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Apr 20, 1999, 3:00:00 AM4/20/99
to
In article <7ffcpd$f...@panther.Gsu.EDU>,
Tapio <tane...@falli.uku.fi> wrote:
> What is the best way to dry dimethylformamide (DMF)? It is said that
> DMF may decompose if dried with calcium hydride, is it really so?
>
> Thanks in advance.
>
> Tapio

> According to Perrin and Armarego (Purification of
Laboratory Chemicals,3rd ed.), KOH or calcium hydride decompose DMF in a
matter of hours. The preferred way is to store over calcium
or magnesium sulfate, silica gel or molecular seives type 4A (Linde)
and then distill under reduced pressure (bp 76 deg C/39 mm). There are other
methods but IMHO these ae easy and drying agents can be re-cycled. Good luck.
Eric Leopold

Robert C. Schuit

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Apr 20, 1999, 3:00:00 AM4/20/99
to
In article <7ffcpd$f...@panther.Gsu.EDU>,
Tapio <tane...@falli.uku.fi> wrote:
> What is the best way to dry dimethylformamide (DMF)? It is said that
> DMF may decompose if dried with calcium hydride, is it really so?
>
> Thanks in advance.
>
> Tapio


Dear Tapio,

Your are right it decomposes into small amounts of dimethylamine and CO. The
decompostion is catalysed by acidic or basic material. Using CaSO4, MgSO4,
silica gel or Linde type 4A molecul sieves, followed by distn under reduced
pressure. This procedure is adequate for most laboratory purposes.
(from "Purification of Laboratory Chemicals, 3rd Ed., D.D. Perrin & W.L. F.
Armarego)

Robert C. Schuit
Amsterdam, The Netherlands

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