mescalaniousmelvin
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Isolation of primary amines as HCL salt problem
To a 40mL beaker was added 5mL n-methyl-2-beta-ethylamine-pyyrole as a brown freebase oil. This was diluted with 10 mL of IPA and a stir bar was
introduced. 36% HCL as an aqueous solution is added dropwise until the pH is neutral. The resulting solution is poured over 100mL of anhydrous ether
with stirring. Ether becomes white and clouded and 2 distinct layers form. A layer of brown sits on the bottom. The white colouded ether doesn't
appear to be filterable.
At this point it was late and the salt didn't seem to want to come out of solution. I wonder how one could better make HCl salts, because I keep
failing at it. Gassing is not practical in my lab.
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cbfull
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From what I understand, the water introduced by the aqueous HCl quickly reduces the solubility of the oil in the solvent, and it precipitates the oil
forming a layer, a cloudy solution, or both. The acid is not able to react with the oil anymore because the water prevents it.
The acid stays dissolved in the water, and can't get to the oily, hydrophobic molecules. My recommendation is to use anhydrous reagents, including
HCl gas dissolved in cold, dry solvent.
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Organikum
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I dont get the idea of this method of crystallisation. You first dissolve in IPA which if I am not mistaken dissolves the base as the salt. Then you
add HCl to form the salt + water which will also dissolve the salt. Then you try to crash the salt with ether.
At least one solvent which dissolves the salt is unnecessary IMHO. Titration would perhaps be possible by dissolving the base in ether and adding HCl
36% to neutral. Then try crashing the salt with a huge amount of acetone - it will take some time standing in the fridge anyways.
But cbfull´s advise to prepare anhydrous HCl in either IPA or ether is of course best.
best of luck
/ORG
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XxDaTxX
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| Quote: | Originally posted by mescalaniousmelvin
To a 40mL beaker was added 5mL n-methyl-2-beta-ethylamine-pyyrole as a brown freebase oil. This was diluted with 10 mL of IPA and a stir bar was
introduced. 36% HCL as an aqueous solution is added dropwise until the pH is neutral. The resulting solution is poured over 100mL of anhydrous ether
with stirring. Ether becomes white and clouded and 2 distinct layers form. A layer of brown sits on the bottom. The white colouded ether doesn't
appear to be filterable.
At this point it was late and the salt didn't seem to want to come out of solution. I wonder how one could better make HCl salts, because I keep
failing at it. Gassing is not practical in my lab. |
Continuous azeotropic distillation should remove the excess water if gassing is not an option, provided your compound is relatively stable.
[Edited on 11-12-2006 by XxDaTxX]
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chemoleo
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Just dissolve the free amine in a minimum amount of HCl aq(conc). Then add a >15x excess of acetone. To my experience this preciptitates amine
salts well.
Never Stop to Begin, and Never Begin to Stop...
Tolerance is good. But not with the intolerant! (Wilhelm Busch)
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Sandmeyer
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I meen I also got sick and tired getting failures with Sasha's method of making HCl salts. IMO best way is to make sulfate by adding a dilute
H2SO4-EtOH soln. to freebase dissolved in ether until pH~4, allow to stirr for half an hour, filter, wash, filter and dry... It is foolproof...
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XxDaTxX
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Whats with everyone in here got against gassing?
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Sandmeyer
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I think people prefer simpler and safer solutions over more complicated and dangerous ones, that's all to it...
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