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Topic: Methyl ester deprotection  (Read 7429 times)

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Offline Dan

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Re: Methyl ester deprotection
« Reply #15 on: March 01, 2017, 02:48:21 AM »
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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Offline Optimist

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Re: Methyl ester deprotection
« Reply #16 on: March 01, 2017, 06:01:20 AM »
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

Offline Optimist

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Re: Methyl ester deprotection
« Reply #17 on: March 01, 2017, 06:04:03 AM »
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.

Offline rolnor

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Re: Methyl ester deprotection
« Reply #18 on: March 01, 2017, 07:22:35 AM »
It should be said that this resin is strongly acidic so be carefull not hydrolysing the isocyanide.

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