nimgoldman
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Pyridine from Pyridine hydrochloride
I have some wet pyridine hydrochloride (Py.HCl) which I would like to turn back to pyridine base.
I guess this procedure is simple:
- dissolve Py.HCl in water
- add molar excess of dilute base (e.g. 10% NaOH)
- extract pyridine with pet ether or ethyl ether
- distill off solvent
- dry pyridine with NaOH, filter
- distill fresh pyridine over NaOH
Is this the correct procedure?
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Sigmatropic
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Why wouldn't you just skip all steps and distill over excess NaOH? The salt is free based and dried simultaneously.
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fusso
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Why not use conc/sat NaOH? Less water means less pyridine would dissolve in it, and less pet/diethyl ether needed.
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JJay
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Why wouldn't you dry the pyridine before distilling off the solvent? That way there would be less mechanical loss from product getting caught up in
the drying agent.
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nimgoldman
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Are you sure the molten pyridine hydrochloride will react with NaOH and the reaction won't be too vigorous?
I guess the side product would be NaCl which will stay dissolved in water, but using just molted pyridine.HCl could result in caking of the NaCl
precipitate.
Quote: Originally posted by JJay  | | Why wouldn't you dry the pyridine before distilling off the solvent? That way there would be less mechanical loss from product getting caught up in
the drying agent. |
Yes I would definitely dry the solvent containing pyridine and also wash the drying agent with fresh solvent to prevent losses.
I believe pyridine would have to further dried with at least a little NaOH/KOH as it is so hygroscopic.
[Edited on 7-10-2018 by nimgoldman]
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AvBaeyer
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It is relatively difficult to extract pyridine from water even if the aqueous solution is basic. The best thing to try is to add your HCl salt to
25-30% potassium carbonate solution (a few ml per gram of salt) in a sep funnel. Add ether and shake vigorously (cautiously). A second ether
extraction may be needed. Dry the extracts over potassium carbonate, remove the ether and distill the recovered pyridine. This is a method I have used
over the years to isolate amino acid esters from their HCl salts and works quite well. I cannot guarantee it will work for pyridine but I would try
it.
AvB
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nimgoldman
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| Quote: Originally posted by AvBaeyer | It is relatively difficult to extract pyridine from water even if the aqueous solution is basic. The best thing to try is to add your HCl salt to
25-30% potassium carbonate solution (a few ml per gram of salt) in a sep funnel. Add ether and shake vigorously (cautiously). A second ether
extraction may be needed. Dry the extracts over potassium carbonate, remove the ether and distill the recovered pyridine. This is a method I have used
over the years to isolate amino acid esters from their HCl salts and works quite well. I cannot guarantee it will work for pyridine but I would try
it.
AvB |
Thanks. I was thinking about salting out the pyridine from water. Potassium carbonate should work better than sodium chloride. I will try it.
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nimgoldman
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Just reporting the extraction was successful with a good yield.
Next time I have to be more sciencey and weight everything to actually quantify the yield...
[Edited on 17-10-2018 by nimgoldman]
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Tsjerk
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At least tell us what you did
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nimgoldman
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It's in the OP.
The only modification is that Py.HCl is dissolved in 25% K2CO3 solution instead of plain distilled water.
Etereal extract have been evaporated in a rotavap at atm. pressure. No ether came over up to 75 °C, leaving behind clear liquid of the characteristic
pungent smell of pyridine.
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