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Molecular Sieves

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Barry Jones

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Sep 9, 1998, 3:00:00 AM9/9/98
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Can someone tell me the correct way to use Molecular Sieves to remove
H2O from small quantities of solvent (dueterated)? Is it necessary to
heat the sieves in a vacuum oven before using?

--
Paul J. Franklin (moderator)
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Uncle Al

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Sep 11, 1998, 3:00:00 AM9/11/98
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Barry Jones wrote:
>
> Can someone tell me the correct way to use Molecular Sieves to remove
> H2O from small quantities of solvent (dueterated)? Is it necessary to
> heat the sieves in a vacuum oven before using?

Removing water is not your only worry. H-D exchange is in there too.
Molecular sieves are acidic.

"Activated" sieves as received are pretty good. I'd heat them to 200 C
overnight under hard dynamic vacuum and break to dry argon, just in
case. Sieve dust won't help your NMR. Filter the dried solvent through
a dried (200 C) glass wool plug pushed into a dried Dispo-pipette.
Don't contaminate with finger oil when you roll the glass wool.

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Hans Moessler

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Sep 11, 1998, 3:00:00 AM9/11/98
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Hello,

Barry Jones wrote:
> Can someone tell me the correct way to use Molecular Sieves to remove
> H2O from small quantities of solvent (dueterated)? Is it necessary to
> heat the sieves in a vacuum oven before using?

Yes, it is absolutely necessary to heat molecular sieve (> 200 °C, <1
mbar, >2 days) before use, since it can adsorb moisture from air. Before
that, You must remove organic remains by washing the sieve in water.

Bye Hans

Bill Walker

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Sep 11, 1998, 3:00:00 AM9/11/98
to
The best way to activate the sieves is to heat them under vacuum with a
burner for a couple of hours.
Since there's only a small amount of water in most of our solvents, I've
found it satisfactory to just keep an evaporating dish full of sieves in the
oven, and add them as necessary. It's also a lot faster and more
convenient.

I've only tried this with methanol, but other solvents may require more
highly activated sieves to acheive the desired effect.

Regards,

Bill

Barry Jones wrote:

> Can someone tell me the correct way to use Molecular Sieves to remove
> H2O from small quantities of solvent (dueterated)? Is it necessary to
> heat the sieves in a vacuum oven before using?

Morten Bang Norgaard

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Sep 11, 1998, 3:00:00 AM9/11/98
to
Barry Jones wrote:
>
> Can someone tell me the correct way to use Molecular Sieves to remove
> H2O from small quantities of solvent (dueterated)? Is it necessary to
> heat the sieves in a vacuum oven before using?

Depends on how they're stored. If you just found them in a pot standing
around, I'd go for the heating part. It will do without the vacuum (but
it makes it easier to get rid of more of the water), but an ordinary
oven, 200 - 250 degrees C overnight, should do the job satisfactory.

Morten

David Michaud

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Sep 11, 1998, 3:00:00 AM9/11/98
to
It is absolutely necessary to heat molecular sieves before using them. The
easiest way is to put them in a wide glass vessel and heat it a few minutes
into a domestic microwave oven.

Barry Jones wrote:

> Can someone tell me the correct way to use Molecular Sieves to remove
> H2O from small quantities of solvent (dueterated)? Is it necessary to
> heat the sieves in a vacuum oven before using?

Paul Blackburn

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Sep 12, 1998, 3:00:00 AM9/12/98
to
Yes, you need to activate the sieves before use by drying them. In our lab
we dry ours in a vacuum oven heated to 140 degrees C. I haven't any
experience of using them for dueterated solvent.

Paul B.

Jonas Nilsson

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Sep 12, 1998, 3:00:00 AM9/12/98
to
Barry Jones wrote:

> Can someone tell me the correct way to use Molecular Sieves to remove
> H2O from small quantities of solvent (dueterated)? Is it necessary to
> heat the sieves in a vacuum oven before using?

You should heat them to >170 deg. centigrade for several hours (overnight) in
an ordinary oven. Then let them cool in vacuum.
/jN

David Hemmings

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Sep 12, 1998, 3:00:00 AM9/12/98
to
Yeah, I tend to leave a beaker full in an oven all the time ca. 140C
(activates sieves), when you need some put required sieves in a dried
container, and let cool in a dessicator. Put the sieves into your
deuterated solvent. Don't put hot sieves in solvent (unless you want
to boil it off). Remember to seal carefully under inert gas, otherwise
you've wasted your time esp. if DMSO.

I think Perrin and Armarego handle this in more detail in their book.

HTH
DH

Barry Jones <B...@BI7018.4532> wrote in article
<6t6ldl$k...@panther.Gsu.EDU>...


>
>
> Can someone tell me the correct way to use Molecular Sieves to
remove
> H2O from small quantities of solvent (dueterated)? Is it necessary
to
> heat the sieves in a vacuum oven before using?

--

Jim McGill

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Sep 12, 1998, 3:00:00 AM9/12/98
to
Vacuum drying of molecular sieves, to my knowledge, is necessary in order to
activate them. A vacuum oven is not necessary, though. Simply flame drying
them under vacuum in a round-bottomed flask on the vacuum manifold seems to
work effectively.


> .....correct way to use Molecular Sieves to remove
>H2O .........Is it necessary to heat the sieves in a vacuum oven before

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