paraguay
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Removing excess anime from enamine condensation?
I'm thinking of the procedure used in the attached paper in which enamines are formed using molecular sieves in ChCl3. Given their ease of hydrolysis,
is there any feasible way to wash the enamine of any residual amine?
I'm not a chemist by any means, please correct me if I'm wrong but my understanding is that any brine or dilute acid washes would lead to losses given
the water content. From what I can tell it seems that pyrrolidine is more soluble in primary alcohols than chloroform, could dry methanol or IPA be
effective? It seems that most of the literature points to distillation of the enamine itself, perhaps it's unavoidable.. any thoughts would be much
appreciated!
-J
Attachment: jo0611061.pdf (108kB)
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[Edited on 1-10-2020 by paraguay]
[Edited on 1-10-2020 by paraguay]
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karlos³
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Can you not distill the excess amine of from the enamine?
The enamine should be much higher boiling anyway.
Are you going to reduce that enamine later on?
If so, why not remove the residual amine after the reduction instead, as then you can simply try washing it out, or in case of pyrrolidine, to remove
it via mild steam distillation from the products freebase is what has worked well for me in the past.
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paraguay
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Was thinking that as well, I imagine the bp would increase with the size of the enamine, making it easier for separation, yes?
Ultimately I worry about heating the enamine and I can't find any info on general heat sensitivity, but I suppose if this reaction is done classically
with a dean-stark, the enamine would get pretty warm anyways correct?
[Edited on 2-10-2020 by paraguay]
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karlos³
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Quote: Originally posted by paraguay  | | Was thinking that as well, I imagine the bp would increase with the size of the enamine, making it easier for separation, yes?
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Yes, in general I would agree on this
| Quote: Originally posted by paraguay |
Ultimately I worry about heating the enamine and I can't find any info on general heat sensitivity, but I suppose if this reaction is done classically
with a dean-stark, the enamine would get pretty warm anyways correct? |
Right, I was thinking the same, I mean if its already formed under reflux conditions, in a high boiling solvent like usually toluene, then it won't
hurt to remove the excess amine via distillation.
You would probably still benefit from using reduced pressure.
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