Xylitol
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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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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.
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Ozone
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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.
O3
-Anyone who never made a mistake never tried anything new.
--Albert Einstein
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Xylitol
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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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