Doc B
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Tricky isolation
I am considering the theory of a reaction upon an aromatic in the salt form (to limit by-product formation) conducted in a polyethylene amine solvent,
probably EDA, and have hit a few hurdles with extraction and isolation that you mad scientists may be able to offer advice upon.
1) The first hurdle is if the aromatic is reacted as a salt, will the strongly basic solvent render the reactant and subsequent aromatic product basic
and therefore isolatable by non-polar extraction?
2) Considering the above to be the case and that the reaction is stopped by slowly quenching with an equal volume of water, the second hurdle presents
itself. Given the parameters of solubility of both the product and the solvent. It seems to me required that the reaction be diluted several times
more, to a total of about 5 volumes, so that the amine is well in aqueous solution for isolation of the product by NP liquid-liquid extraction.
However if this is to be done using for example toluene, which is miscible in the amine until it is well dilute or ether which is partially miscible
until dilution then the product to solvent ratio is up to 1:180 if a x5 dilution is performed. This somewhat unusual solubility factor seems to be the
case, more or less, with most other NP solvents suited to the extraction of the product in this particular solvent. Therefore is the liquid NP
extraction of such a dilute product too inefficient to proceed via this method of isolation?
3) The other options I can offer is if the reaction is not stopped by quenching with water and one were to proceed to isolation by condensation under
reduced pressure or should the quencing be done using a minimal volume of water then to proceed to isolation by condensation under reduced pressure.
Which would seems optimal?
The formation of unwanted by-products formed during the evaporation will require significant work up to remove. Additionally the first hurdle needs to
be addressed to ascertain how to treat the residue.
Any other suggestions?
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Nicodem
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I would like to help you, but judging from your post only, it is uncertain that you actually want help. In other words: Rather than telling us
everything but the essential, give us the essential information first.
It seems to me that this is your first experience with developing an isolation procedure and you don't how to begin with it. The very first thing to
do, is to realize that the isolation is a reaction specific process. Only when you will realize this, and why is it so, you will be able to develop
one yourself and we will be able to give you suggestions.
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Doc B
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Yay, a reply!!!
No wait don't go, I really do want help...
Thank you for replying Nicodem, there is a rather zen like quality to your post that I am struggling to comprehend fully. Possibly because its 03:30
and I should be sleeping or because the realization as such hasn't yet occured to me. You are correct in that this is the first time I am unable to
develop an extraction method that is, for lack of a better word, intuitive. Well at least not as straight forward as is common to my experience.
The essential information I think you may refer to is that I am contemplating a somewhat general reaction, being akin to the reduction reaction.
Theoretically effecting the general reductive deoxygenation or catalytic hydrogenation of mono/polycyclical aromatic hydrocarbons. If I am off the
mark in addressing the essentials please accept my apologies advise of any further clarification I may offer.
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watson.fawkes
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I'll be more
blunt. Name names. IUPAC, CAS, common name, whatever. What is the name of what you want to extract, and what are you extracting it from?
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zed
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You are being extremely circuitous. If you want a usable response, tell folks exactly what you are trying to do....EXACTLY!
We aren't mind-readers, and so far you have only provided a bunch of mumbo-jumbo.
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Doc B
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I have no idea what happened but the specific data has been removed from my second post... Strange! I will edit it and hope that it makes more sense,
sorry for the confusion folks.
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Doc B
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Ok it won't let me edit so let's just try posting the amended version...
Yay, a reply!!!
No wait don't go, I really do want help...
Thank you for replying Nicodem, there is a rather zen like quality to your post that I am struggling to comprehend fully. Possibly because its 03:30
and I should be sleeping or because the realization as such hasn't yet occured to me. You are correct in that this is the first time I am unable to
develop an extraction method that is, for lack of a better word, intuitive. Well at least not as straight forward as is common to my experience.
The essential information I think you maybe referring to is that I am contemplating a somewhat general reaction, being akin to the Benkeser reduction
reaction. Theoretically able to effect the general reductive deoxygenation for example phenylethanolamine to phenylethylamine or catalytic
hydrogenation of mono-cyclical to poly-cyclical aromatic hydrocarbon but I haven't thought of an example for this yet. As mentioned previously
isolation is from a polyethylene amine, most probably ethylenediamine.
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Doc B
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Some experimental results...
Upon quench and dilution the reaction mixtureis strongly alkaline.
Proceeding NP extraction and subsequent acidification has no yielded.
Condensing alkaline mixture to residue. To be repeated due to reaction anomaly but experimented with regardless in the following manner.
NP extraction shows that something has moved into the NP solvent by its change from clear to milky.
Upon attempting to extract with acid and crystallization thereof to isolate any product. There is no yield and NP solvent remains milky. I may try
acid extraction with a stronger concentration of acid or condensation of the NP solvent to dryness. Any suggestions?
I read that in such amine reactions the product can be locked up in a quaternary amine structure and suggested to acidify the residue with 5% dilute
HCl(aq). I therefore acidified the condensation residue accordingly. While however this was done on the anomalous reaction, the residue did dissolve
into the dilute acid and is awaiting condensation.
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