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JJay
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Quote: Originally posted by clearly_not_atara  | What if you dried it starting from a methanolic solution rather than water?
In particular sodium acetates are soluble in methanol, and this solution could be sequentially gassed with NH3 and then CO2, precipitating NaHCO3 in a
sort of Solvay process, and then you remove methanol at much lower temperature to hopefully leave behind NH4OAc. Methanol will even take some water
with it which is nice. |
That's an interesting idea. I'm out of both ammonium hydroxide and acetic acid at the moment... but how would methanol take water with it?
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XeonTheMGPony
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Azeotrops
Methanol has the effect of lowering waters BP, same goes for Isoproponal. So by adding a bit it will allow you to dry a part or chem at reduced temp.
Same concept is used in refrigeration as well in Auto cascades with Argon, or H2 in ammonia absorption systems, it never condenses into the
refrigerant fluid but modifies the vapour pressure allowing it to boil off colder
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JJay
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Methanol doesn't form an azeotrope with water, though....
Drying under vacuum over sodium hydroxide seems to work but is slow. At this rate, it's going to take days to obtain a dry product. I think slight
sublimation may be occurring, but it isn't worrysome, and the ammonium acetate is getting dryer.
I've been taking it off vacuum and stirring it every few hours to expose more wet material and to try to prevent a situation where I have to remove a
cake of solidified material stuck to glass.
[Edited on 2-8-2017 by JJay]
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JJay
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I found that what seemed to work best for drying was pulling a vacuum continuously and ended up getting 69.3 grams of a granular solid that smells
kind of like a combination of acetic acid and ammonia but slightly more like acetic acid. It's slightly damp and extremely hygroscopic. If I take a
few grains out on a spatula, they liquify before my eyes in less than a minute. I'm sure I can dry it out a little bit more with extended time under
vacuum, but I want to use my dessicator for other things, so this will do for now.
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Texium
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Thread Moved
2-8-2017 at 09:22 |
AJKOER
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An interesting simple approach would be to just add vinegar to CaCO3 until CO2 bubbling stops. This produces aqueous calcium acetate which, by
heating, one can concentrate without decomposition (unlike aqueous ammonium acetate). Add a source of NH3 (one could just place a beaker of
concentrated calcium acetate, which is shaken or stirred, in a larger sealed vessel containing household ammonia). Freeze and defrost to aid in
letting the Ca(OH)2 settle out of solution (or use more sophisticated equipment). Decant leaving concentrated aqueous ammonium acetate.
Following drying procedures described previously.
Note, one could concentrate the calcium acetate to the point of a moist salt/wet slurry. Treat the cold wet calcium acetate with an excess of NH3, and
then with hot CH3OH dissolving any formed ammonium acetate. Filter or distill off the latter hot methanol and ammonium acetate mix (see solubility in
hot methanol, which apparently sharply rises, per Wikipedia at https://en.m.wikipedia.org/wiki/Ammonium_acetate).
Also, in place of CaCO3, one can employ MgCO3. The latter can be formed, as I done on several occasion, as a MgCO3 white precipitate from the action
of NaHCO3 on heating (decomposing unstable aqueous Mg(HCO3)2) aqueous MgSO4 (Epsom Salts is sold in supermarkets, drug stores,..).
[Edit] This differs from the prior suggestion of NH3 and dilute acetic acid as it reduces the amount of problematic water present at the expense of
dealing with a Ca(OH)2 suspension (or not, per note above).
[Edited on 5-8-2017 by AJKOER]
[Edited on 5-8-2017 by AJKOER]
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JJay
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| Quote: Originally posted by AJKOER | An interesting simple approach would be to just add vinegar to CaCO3 until CO2 bubbling stops. This produces aqueous calcium acetate which, by
heating, one can concentrate without decomposition (unlike aqueous ammonium acetate). Add a source of NH3 (one could just place a beaker of
concentrated calcium acetate, which is shaken or stirred, in a larger sealed vessel containing household ammonia). Freeze and defrost to aid in
letting the Ca(OH)2 settle out of solution (or use more sophisticated equipment). Decant leaving concentrated aqueous ammonium acetate.
Following drying procedures described previously.
Note, one could concentrate the calcium acetate to the point of a moist salt/wet slurry. Treat the cold wet calcium acetate with an excess of NH3, and
then with hot CH3OH dissolving any formed ammonium acetate. Filter or distill off the latter hot methanol and ammonium acetate mix (see solubility in
hot methanol, which apparently sharply rises, per Wikipedia at https://en.m.wikipedia.org/wiki/Ammonium_acetate).
Also, in place of CaCO3, one can employ MgCO3. The latter can be formed, as I done on several occasion, as a MgCO3 white precipitate from the action
of NaHCO3 on heating (decomposing unstable aqueous Mg(HCO3)2) aqueous MgSO4 (Epsom Salts is sold in supermarkets, drug stores,..).
[Edit] This differs from the prior suggestion of NH3 and dilute acetic acid as it reduces the amount of problematic water present at the expense of
dealing with a Ca(OH)2 suspension (or not, per note above).
[Edited on 5-8-2017 by AJKOER]
[Edited on 5-8-2017 by AJKOER] |
I think this is rather unlikely to work. Evaporating concentrated ammonia and concentrated acetic acid off on a boiling water bath didn't seem to be a
very fruitful route either when I tried it. Or perhaps it is and I should have gone ahead and evaporated to dryness, but it didn't look like there was
much product left.
Perhaps you'd like to give it a try and post your results?
[Edited on 6-8-2017 by JJay]
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clearly_not_atara
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Calcium acetate decomposes at 160 C to acetone. I'm not sure if it can be dried below this temperature, but it seems like it would take a long time
with careful temperature control.
I do think the potassium acetate is most likely to be easy to dry than the sodium, because it loses water more easily; potassium acetate becomes a
hemihydrate above 42 C, whereas NaOAc remains a trihydrate up to 100 at least. But extrapolation like this is unreliable and I could certainly be
wrong here.
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JJay
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I think the reference that says 160 C (I remember seeing that) contains a typo and that it actually doesn't decompose below 260 C: http://pubs.acs.org/doi/pdf/10.1021/je60012a040
So it does look like it is possible to dehydrate calcium acetate with heat.
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JJay
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Oh, and I should probably mention that I finally found a paper that detected decomposition at just above 160 C, but it concluded that decomposition
was very slight below 400 C:
Distillation of Acetate of Lime.
E. G. R. Ardagh, A. D. Bbarbour, G. E. McClellan, E. W. McBride
Ind. Eng. Chem., 1924, 16 (11), pp 1133–1139
DOI: 10.1021/ie50179a013
Publication Date: November 1924
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