nimgoldman
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Separating L-tryptophan/tryptamine from taurine
I am attempting L-tryptophan decarboxylation to tryptamine. Unfortunately, my source of tryptophan comes with 1% taurine mixed in.
I looked up solubilities and haven't found a good washing solvent to remove just taurine (except maybe for hot absolute alcohol). Tryptophan and
taurine have similar solubility profiles.
I was therefore thinking about proceeding with decarboxylation of the impure tryptophan in Tetraline, then purifying the residue instead.
After removing the solvent in vacuo, the residue might consists mostly of tryptamine base and taurine, provided the taurine won't interfer with
tryptamine (which I am afraid of, since it is an acid...)
Separating tryptamine from taurine might be easier since the taurine (and residual tryptophan) can be simply washed out with water.
Another method could be recrystallization or tryptamine, leaving taurine in solvent.
Yet another method could be dissolving both tryptamine and taurine in suitable solvent and then saturating the solvent with gaseous HCl. Tryptamine
HCl will then precipitate while taurine will stay in solution.
What would be your preferred method of separation in this case?
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Elrik
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Distilled water?
L-Tryptophan has a nice steep solubility curve going from 0.23g/l at 0° to 49.9 g/l at 100°
According to the paper 'Determination and Correlation of the Solubility for Taurine in Water', which uses maddening kelvin and 10x mole fraction units
[insert rant], taurine is soluble to the extent of 1g per 18g H2O at 0°C, around 2g/18g at room temp, going up to 8g/18g at 80°C.
So, while the two compounds may have a roughly similar solubility at room temperature, taurine is much more soluble in ice cold water and two rounds
of recrystallization should remove it.
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nimgoldman
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Quote: Originally posted by Elrik  | Distilled water?
L-Tryptophan has a nice steep solubility curve going from 0.23g/l at 0° to 49.9 g/l at 100°
According to the paper 'Determination and Correlation of the Solubility for Taurine in Water', which uses maddening kelvin and 10x mole fraction units
[insert rant], taurine is soluble to the extent of 1g per 18g H2O at 0°C, around 2g/18g at room temp, going up to 8g/18g at 80°C.
So, while the two compounds may have a roughly similar solubility at room temperature, taurine is much more soluble in ice cold water and two rounds
of recrystallization should remove it. |
This does not seem to work. I dissolved 30 g of L-tryptophan in about 1 000 ml of near boiling water, then left it to cool down to room temperature
and then overnight in the fridge (4 °C).
Only a handful of crystals appear, maybe few grams.
The solution is clearly oversaturated and stays like that, even after scraping the beaker.
I think it will eventually crash out, but over the course of several days, which is very inconvenient for my application.
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Elrik
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In that case, dual solvent crystallization. Heat the crystallizing solution up and add alcohol.
Ethanol and isopropanol should both help push tryptophan out of ice cold solution at a faster rate. The same [attached] paper I mentioned previously
charts the effects of ethanol and isopropanol on taurine solubility curves. 5% Isopropanol or 10% ethanol would leave taurine sufficiently soluble in
cold water to remove it while probably encouraging tryptophan to leave solution.
Another thing I would mix in to the purification process as a step 1 would be to add the powder to ice water, shake the hell out of it, and hope much
of the taurine dissolves.
I would not try to run a decarboxylation on the mixture prior to separation. Who knows how the taurine would react. You could get polymeric
sulfonamides, taurine-tryptamine sulfonamide, ethylamine, nasty tar gunk, who knows what.
Attachment: Determination and Correlation of the Solubility for Taurine in Water.pdf (117kB)
This file has been downloaded 252 times
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nimgoldman
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Thanks.
So far I managed to crash out most of the tryptophan by cycling the beaker between fridge (4 °C) and the freezer (-18 °C).
When the water started crystallizing to ice, the beaker have been moved to fridge to slowly thaw. Each cycle crashed out substantial amount of
tryptophan. It crystallized along the scrape lines and around the ice crystals.
Finally, I filtered the solution, which takes a quite a while time even with a fast paper and full vacuum. The filtrate have been washed with cold
water once even though this caused some loss of tryptophan.
Tryptophan formed wet crumbles resembling a cottage cheese.
I tried vacuum drying but this was not effective, so I transfered the crumbled tryptophan in the oven at 100 °C, then powdered in a mortar (still
somewhat wet) and the powder dried again at 110 °C.
Finally, this yield a powdered tryptohan, somewhat free of taurine. I will weight the product but it seems I lost over half of it, but not having time
to tune up the recrystallization (I will improve that later based on your advice).
The powder will be put in a vacuum desiccator for final drying.
I guess the water content is not such a big problem (most will escape in the decarboxylation process) but I need powder to increase the surface area
to aid speed up the decarboxylation process.
I will then follow with ketone-catalyzed decarboxylation (using Teralin/MEK).
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