andre178
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removal of pyridine
Hello, I am trying to rid an aqueous solution from pyridine contaminants. I am trying to go the cleanest possible way without adding other things that
I cannot remove. I read that extraction with ether might solve my problem, but I tried it today and pyridine still remained in my aq. solution.
Any suggestions?
Andre
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chemrox
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what else is in the solution? depending on what else you've got you might run it through a resin column... but a lot hinges on what you have and wish
to keep..
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JohnWW
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If there are no other amines present, and you want to extract the pyridine from an aprotic organic solvent, a likely way could be to add some HCl or
H2SO4 to form a pyridinium salt, and then extract the salt with water.
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Nicodem
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JohnWWW, "aqueous solution" means a solution in water as solvent. Obviously water is not an "aprotic organic solvent".
Quote: Originally posted by andre178 | Hello, I am trying to rid an aqueous solution from pyridine contaminants. I am trying to go the cleanest possible way without adding other things that
I cannot remove. I read that extraction with ether might solve my problem, but I tried it today and pyridine still remained in my aq. solution.
Any suggestions? |
First of all you need to tell us the pH of the solution.
You can not remove pyridine from an aqueous solution with diethyl ether. I don't know who told you that, but the H2O/Et2O partition of pyridine is not
enough in favour of Et2O.
If the pH is above 6 then you might be able to remove most of the pyridine by washing several times with ethyl acetate (If the pH is much lower than
that then you can forget about removing it with washes). Then concentrate the aq. solution on a rotavap to half volume. This will remove the dissolved
ethyl acetate and the remaining pyridine which is gone via the pyridine/water azeotrope. Now dilute with water up to the original volume and you
should have your pyridineless original solution. If traces of pyridine are still present, then rotavap again to half volume and dilute again. If the
original concentration of pyridine is low enough, then you can skip the ethyl acetate washes and do the removal by azeotropic distillation only.
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scientific temper, not in the scientific defense of the theory. - Weston La Barre (Ghost Dance, 1972)
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andre178
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Thank you all for the answers, to summarize,
The other "stuff" in solution is functionalized fullerenes (ie. fullerenes with malonic acids stuck on them, enough to make it soluble in water).
the pH is basic.... ~11. I cannot add sulfuric acid because I don't know how to get rid of that... the fullerenes are somewhat temp sensitive so I
can't raise the mixture to anything above 60*C. I have a lot of sodium from the initial NaOH I added, so if I add HCl, it would get me a lot of NaCl
residues which again I don't want.
The Et2O extraction I got from my old college chem notebook in purification of pyridine from pyridinium chloride by
making the solution basic >8pH then 3x Et2O extraction, drying w/ NaSO4, then Hickman distillation to obtain pure Pyridine. <<==== I
really do appreciate your help but saying "who told you that...." doesn't get me far. It would've been more more helpful to point me to why pyridine
would not have a preference for ether over water; I understand that the compounds go by dielectric index in choosing solvents, is that correct?
I chose the ethyl acetate wash according to your advice since the pH is high, and then I will get rid of ethyl acetate by rotovapping. The fullerene
was processed in ethyl acetate before and with the help of the rotovap we were able to obtain pure compounds ~95% level.
[Edited on 1-14-2010 by andre178]
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Panache
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Mood: Instead of being my deliverance, she had a resemblance to a Kat named Frankenstein
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Continuous liquid-liquid extraction for a day using ethyl acetate followed by the rotovap seems like much less work and better efficacy (in relation
to the extraction, given your success already with the afermentioned advice re ethyl acetate), just 'set and forget'.
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Nicodem
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Quote: Originally posted by andre178 |
The Et2O extraction I got from my old college chem notebook in purification of pyridine from pyridinium chloride by
making the solution basic >8pH then 3x Et2O extraction, drying w/ NaSO4, then Hickman distillation to obtain pure Pyridine. <<==== I
really do appreciate your help but saying "who told you that...." doesn't get me far. It would've been more more helpful to point me to why pyridine
would not have a preference for ether over water; I understand that the compounds go by dielectric index in choosing solvents, is that correct?
|
Not really. The dielectric constant is just one of the molecular properties that affects the liquid/liquid distribution of a certain compound. Many
others can have a much more important role (H-bond donors/acceptors, ionizability, VdW volumes, flexibility, polarity of functional groups,
(a)symmetry: the whole structure in general). Good computational models exist for calculating the distribution coefficient for water/octanol, but
since all these effects are solvent specific, no general models exist for calculation of just any liquid/liquid system (water/octanol was chosen as a
model due to biochemists).
Anyway, the partition coefficient of pyridine for Et2O/H2O is 1.2 (Acta Chem. Scand., 3, 717-747). This means that in a biphasic system composed of
equal volumes H2O and Et2O, the amount of pyridine partitioned in Et2O will be only 1.2 as much as that remaining in H2O. Therefore there is no way to
quantitatively extract pyridine from its aqueous solution using diethyl ether, except for a continuous extraction. After a single wash 45% of the
original pyridine amount still remains in the aq. solution. After the second wash it is 20%. Third wash gives leaves about 9% and so on. So just
imagine that more than six diethyl ether washes are needed to reduce the pyridine content bellow 1% of the original, never minding a quantitative
removal.
PS: Are you sure the sodium salt of fulerenyldene malonic acid does not get extracted in ethyl acetate at least to some degree? I would expect this to
be the case given that it might have some limited surfactant properties. If so, then rather skip the washes and instead just do a few rotavaps to half
volume and back.
…there is a human touch of the cultist “believer” in every theorist that he must struggle against as being
unworthy of the scientist. Some of the greatest men of science have publicly repudiated a theory which earlier they hotly defended. In this lies their
scientific temper, not in the scientific defense of the theory. - Weston La Barre (Ghost Dance, 1972)
Read the The ScienceMadness Guidelines!
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Barium
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Reduce the volume of the solution to half, two or three times and it should be gone. In essence steam distillation is the way to go.
At a pressure of about 70mbar water boils at 40 deg C so you are well below your limit of 60 deg C.
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