For simplicity, perhaps. If you have other considerations (cost, etc.) then it depends.
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Microwave-assisted Tryptophan decarboxylation into Tryptamine
- Thread starter Hailstorm
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eagerstudent
Rising Star
Well I am looking for reliability, will this work the same if I reflux with carvone instead of microwave? I meant is it more reliable?
Yes and no. Traditional refluxing is definitely more controllable and repeatable. However, apparently microwave radiation assists tryptophan decarboxylation beyond merely heating the mixture, so in a microwave oven this reaction takes just a few minutes at low power.
I have not tried refluxing in carvone specifically, but people who refluxed tryptophan in acetophenone reported reaction times around 45 minutes. That is still an improvement over the traditional method where the ketone is only used in catalytic amounts: that takes hours and often results in lower yields due to thermal decomposition.
I have not tried refluxing in carvone specifically, but people who refluxed tryptophan in acetophenone reported reaction times around 45 minutes. That is still an improvement over the traditional method where the ketone is only used in catalytic amounts: that takes hours and often results in lower yields due to thermal decomposition.
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aizoaceous
Titanium Teammate
I've never done tryptophan to tryptamine, but I did tyrosine to tyramine in a loosely-capped test tube heated with a heat gun. An open beaker didn't work for me, tar. I've seen papers that ran under nitrogen, but the evolved carbon dioxide seems to provide some protection if it doesn't blow away. Reflux in acetophenone (bp 202 C) seems rather hot, and reflux in carvone (bp 231 C) seems very hot. I'd keep the temperature below the boiling point and/or mix the carvone with a lower-boiling solvent, limonene (bp 176 C) for me. The heating power required to maintain temperature may provide an indication of reaction progress if not at reflux, since the reaction is exothermic.
It is not that exothermic to provide reliable feedback. If you don't monitor it by TLC, you'd stop the reaction after the tryptophan has disappeared and CO2 is no longer evolving.
aizoaceous
Titanium Teammate
I think you're right. Around the time my reaction mixture looked completely melted, I had to adjust my heat gun from 240 C to 270 C to maintain 165-170 C at a thermocouple in the test tube. But calculating roughly now, that would imply megajoules per mole of exotherm, which is obviously not correct. I wonder if a fully melted reaction mixture changed the rate at which I lost heat from evaporating limonene or something. I ran twice and saw that effect both times so I do think it's real, just with a different cause.
I found it sometimes hard to distinguish bubbles of CO2 from bubbles of boiling limonene. Perhaps that's a benefit to running without additional solvent, well below the boiling point of carvone. The papers usually say to stop when the reaction mixture becomes homogenous, since the liquid amine is soluble/miscible with carvone but the solid amino acid isn't. I found that my tyramine still formed two layers, but the disappearance of the solid tyrosine still seemed reasonably obvious. I assume most amines go fully homogenous. TLC might require a pretty big sample (if you just reach in with a spatula, then does it get coated with liquid amine while the solid amino acid slides off?) but would be most confident.