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Author: Subject: Removing/neutralizing TFA from carbamate
Xylitol
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[*] posted on 28-3-2016 at 15:31
Removing/neutralizing TFA from carbamate


Let me start off by saying I'm a beginner and maybe missing something obvious.

I have synthesized a carbamate (3-methyl-3-pentyl carbamate) reacting approx 2 molar equivalents of Trifluoroacetic acid and Sodium cyanate with 3-methyl-3-pentanol.

Here is the problem: I've done the reaction several times and was only successful once. The problem is that if I don't use the exact right amount of acid, it is left over after the solvent (DCM) is evaporated. Here is the real problem: For some reason this excess of acid decomposes the carbamate when I try to neutralize it with sodium bicarbonate or try to recrystallize with water. As soon as the water or bicarbonate is added, the carbamate bubbles and turns into some unknown oil and ammonia.

I need to be able to remove this acid so that I can recrystallize and purify. I can't just distil it off because the bp is 70-something C and the carbamate breaks down and volatilizes at 50C.

Can someone help? I have a lot of this stuff sitting here, but I can't do anything without it decomposing.
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Metacelsus
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[*] posted on 28-3-2016 at 18:07


Maybe you could try adding solid anhydrous potassium carbonate to your DCM solution. I've used this to neutralize acids in the presence of water-senstive compounds. Sodium carbonate might also work.



As below, so above.
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[*] posted on 28-3-2016 at 18:44


You might also try dumping some pre washed/pre-dried weak base anion exchange resin in there. It should soak the TFA, which you could recycle later by eluting with dilute acid, probably sulfuric.

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Xylitol
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[*] posted on 29-3-2016 at 11:38


Quote: Originally posted by Metacelsus  
Maybe you could try adding solid anhydrous potassium carbonate to your DCM solution. I've used this to neutralize acids in the presence of water-senstive compounds. Sodium carbonate might also work.


So you think the problem has to do with the sodium bicarbonate not being anhydrous or do you think the potassium carbonate would work better for other reasons?

Also, any idea whats happening when it reacts with the water to produce ammonia and something else?

To be clear, my idea about the presence of TFA after the reaction being completed causing degradation of the compound is just a guess (and I'm a novice). Could something else be occurring here?

BTW thanks for the help!
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