Re: ORGLIST: preparation of ammonium fluoride

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From: Alexey Gromov (alexey.gromov$##$univie.ac.at)
Date: Tue Sep 16 2008 - 18:58:04 EDT


Lucy,
In your question you are asking about ammonium fluoride (NH4F), but
the paper you sent describes preparation of triethylammonium fluoride
(Et3N*HF). So, what do you really need?
Just in case here is the translated procedure:
Et3N (1.1 mmol) was slowly mixed under cooling with 48% HF (1 mmol).
After staying overnight a formed heavy phase (I think they mean the
bottom phase) was separated, concentrated in vacuum at 40C and
further dried via azeotropic distillation of residual water with
benzene. The resulted syrup (viscous oil) was used as it is. (They use
it for cleavage of TMS-cyanohydrins in THF.)

Please note, that HF is a nasty chemical. Although it is a weak acid,
HF causes formation of bubbles up to long-living abscesses (conc. HCl
or H2SO4 are not dangerous comparatively to relatively diluted HF).
Even 0.03% solution of HF in water irritates skin. Only concentrated
solution of HF causes immediate pain. After contact with more diluted
HF a burn sometimes can appear even after 5-6 days. If you got some HF
on your skin, the first aid is necessary even if you DON'T feel any
pain at the moment. The "first aid" is not just to rinse the skin with
water. For details on what to do exactly in these cases see here:
http://chemknowhow.com/forum/viewtopic.php?t=125

Sounds too cautious, but this is an experience of people who work with
HF on a regular base. A similar information is written in any MSDS,
e.g. here:
http://www.jtbaker.com/msds/englishhtml/h3994.htm

By the way, all fluorides are toxic, but HF is especially toxic,
moreover, it's volatile. So, personally I would never work with it
alone or in the evening.

I don't want to scare you, chemistry is chemistry, and to work with HF
is not a big deal, but taking a special care does make sense. The same
is true e.g. for HCN and HN3 (the latter is much more toxic than
explosive).

Best regards,
Alexey.
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