Chemical Forums
Chemistry Forums for Students => Organic Chemistry Forum => Organic Chemistry Forum for Graduate Students and Professionals => Topic started by: Optimist on February 27, 2017, 10:43:34 PM
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I have done deprotection of methyl ester using 1N KOH in methanol resulted in potassium salt of my compound. To get carboxylic acid i adjust the pH of solution (2~3) with Acetic acid, and tried to extract the compound using DCM or E.A I couldn't able to recover my compound.
it's seems that my compound have high solubility in water as well.
So, my question is how can i recover my compound from aqueous layer ?
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It is very difficult to obtain pH 2-3 with acetic acid since acetate buffer is formed. Better use HCl, otherwise a large excess of acetic acid is needed.
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It is very difficult to obtain pH 2-3 with acetic acid since acetate buffer is formed. Better use HCl, otherwise a large excess of acetic acid is needed.
Actually, I used 1N HCl before but i was not able to recover my compound. May be the compound having solubility in water.
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Compound with 3 carboxy group and ureido group and mass ~300 is for sure good soluble in water.
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If you use HCl and then evaporate thorough, you can extract your compound with ethyl acetate, potassium chloride would be insoluble.
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I doubt if derivative of Glu-ureido-Lys would show sufficiently solubility in ethylacetate. Rather protection of carboxylic group should be changed.
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If you use HCl and then evaporate thorough, you can extract your compound with ethyl acetate, potassium chloride would be insoluble.
Gul-urea-lysine compound having isocyanide group which is sensitive toward acid, so I can't keep it for longer period of time. Isocyanide group will be hydrolyzed to formamide.
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I doubt if derivative of Glu-ureido-Lys would show sufficiently solubility in ethylacetate. Rather protection of carboxylic group should be changed.
If i use tert-butyl protected Gul-Urea-lysine derivative, finally step is deprotection using TFA and Isocyanide group is sensitive to acid that's why i changed to Methyl ester instead of t-butyl group.
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Acidify the saponification step with an acidic resin (e.g. Dowex, Amberlite), filter, concentrate. This gives you a salt-free crude, it may be pure enough depending on what you plan to do with it.
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Acidify the saponification step with an acidic resin (e.g. Dowex, Amberlite), filter, concentrate. This gives you a salt-free crude, it may be pure enough depending on what you plan to do with it.
I have never use acidic resin, would you please explain the procedure or kindly let me know the reference if you have.
thanks for your help.
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I have used Amberlyst-pyridinumsalt to remove methoxide, works very well.
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I have used Amberlyst-pyridinumsalt to remove methoxide, works very well.
how can i use cation exchange resin in hydrogen form to convert potassium salt of compound to free acid? do you have any standard procedure>
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You just pour the resin in and stir it for a while then filter off the solid resin. Its basically just crosslinked polystyrenesulfonic acid.
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You just pour the resin in and stir it for a while then filter off the solid resin. Its basically just crosslinked polystyrenesulfonic acid.
What i understand, I just dissolve my post. salt in water and add resin into it and stirr for a while. The resin will exchange H+ with K+ and I just filter off my product.
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Ah ok no. You said you hydrolyze the ester with 1M KOH in MeOH. After that step pour in enough resin to neutralize the KOH and protonate your product. It won't be an instantaneous pH change like you get with HCl solution. After the base is neutralized there will be no salt ions in solution, they will all be bound to the resin. Filter off the solid resin, then take your product solution in MeOH and evaporate off the MeOH (and bit of water generated during KOH neutralization) to get pure product.. Save the resin, its a bit expensive but it can be regenerated easily.
Try not to use too huge an excess of KOH solution, because you have to neutralize it all with resin.
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Acidify the saponification step with an acidic resin (e.g. Dowex, Amberlite), filter, concentrate. This gives you a salt-free crude, it may be pure enough depending on what you plan to do with it.
I have never use acidic resin, would you please explain the procedure or kindly let me know the reference if you have.
thanks for your help.
Just think of it as a solid acid. You just add it to your reaction. The resin capacity can be found on the suppliers website, usually expressed in meq/g - this is milliequivalents per gram, for a monoprotic acid this is the same as mmol/g, and is usually in the 1-2 range. I would use an excess vs the KOH to make sure you get all the potassium out of solution.
As stated above, try to avoid using a huge excess of KOH if you're working on multigram scale or higher, otherwise you will need a lot of resin (but it can be regenerated, so this is not a massive problem). After adding the resin, stir the solution gently or you risk breaking the beads and creating fines that can block filter frits. Another option that avoids this potential problem is to pour your crude onto a column of resin and allow it to slowly drip through under gravity (resin contact time of 1 h should be plenty) and rinse off the resin with 2-4 bed volumes of MeOH. I favour this method, especially on larger scale, because it doesn't risk damaging the resin, which is important if you plan to regenerate and reuse it several times.
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Ah ok no. You said you hydrolyze the ester with 1M KOH in MeOH. After that step pour in enough resin to neutralize the KOH and protonate your product. It won't be an instantaneous pH change like you get with HCl solution. After the base is neutralized there will be no salt ions in solution, they will all be bound to the resin. Filter off the solid resin, then take your product solution in MeOH and evaporate off the MeOH (and bit of water generated during KOH neutralization) to get pure product.. Save the resin, its a bit expensive but it can be regenerated easily.
Try not to use too huge an excess of KOH solution, because you have to neutralize it all with resin.
thanks for your comments, Stay blessed. I hope this procedure would help
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Acidify the saponification step with an acidic resin (e.g. Dowex, Amberlite), filter, concentrate. This gives you a salt-free crude, it may be pure enough depending on what you plan to do with it.
I have never use acidic resin, would you please explain the procedure or kindly let me know the reference if you have.
thanks for your help.
thanks for your response, stay blessed
Just think of it as a solid acid. You just add it to your reaction. The resin capacity can be found on the suppliers website, usually expressed in meq/g - this is milliequivalents per gram, for a monoprotic acid this is the same as mmol/g, and is usually in the 1-2 range. I would use an excess vs the KOH to make sure you get all the potassium out of solution.
As stated above, try to avoid using a huge excess of KOH if you're working on multigram scale or higher, otherwise you will need a lot of resin (but it can be regenerated, so this is not a massive problem). After adding the resin, stir the solution gently or you risk breaking the beads and creating fines that can block filter frits. Another option that avoids this potential problem is to pour your crude onto a column of resin and allow it to slowly drip through under gravity (resin contact time of 1 h should be plenty) and rinse off the resin with 2-4 bed volumes of MeOH. I favour this method, especially on larger scale, because it doesn't risk damaging the resin, which is important if you plan to regenerate and reuse it several times.
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It should be said that this resin is strongly acidic so be carefull not hydrolysing the isocyanide.