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Author: Subject: Tryptamine synthesis: workup woes
National Hazard

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[*] posted on 15-7-2015 at 13:24
Tryptamine synthesis: workup woes

I am using this paper as a reference: "Chemistry Letters 893-896 (1986)"

My goal was to replicate the procedure from this reference using cyclohexanone (versus cyclohexenone) as a catalyst. Ten grams of tryptophan were suspended 75 mL of cyclohexanol. A quantity of cyclohexanone was added (one Pasteur pipette-full) and the reaction was heated to ~150oC with stirring (nearly boiling). By the end of ~14 hours, I had cooled the reaction mixture down to RT. The result was a dark, nearly black oil in which a some crystalline sediment formed. The sediment was isolated via filtration and washed with water and then ethanol. As the sediment was washed, silvery, flat crystals were observed. That went well, however, a large amount of dark oil remained. This oil was washed with 1.2 M HCl which was collected and rapidly made basic with solid NaOH. Unfortunately, the pesky brown oil remained. I then proceeded to extract it with 2x100 mL DCM which I pooled and boiled down to a concentrated oil. I treated this oil with HCl to pH 3 and stirred for 2-3 minutes. The aq layer was a yellow-brown color. The insoluble oil was extracted with acidic water again. The pooled extracts were treated with NaOH. The extracts immediately became turbid. They were placed in a freezer for ~1 h.

After that point they were set out to sit overnight. I checked on them this morning only to find that one extract (~200 mL) had a layer of brown solid precipitated at the bottom. The other extract (~300 mL) had a thin layer of flat solid floating in it. There was some brown solid (not as much) at the bottom. I plan to extract that material with DCM again, but I am worried that tryptamine is not soluble in DCM. This would mean that I discarded much of the product. A patent I found suggests that it is soluble in DCM (US #2943093) -- this patent states that the tryptamine can be dissolved in DCM and treated with CO2 gas. Moreover, I'm wondering if it's worth it to extract with DCM. Is tryptamine soluble in very, very alkaline water? If it isn't, then I could just filter the product out, wash it with cold water and recrystallize from toluene.
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International Hazard

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[*] posted on 16-7-2015 at 12:56

Provided you have successfully hydrolyzed any imines present and removed all of the Cyclohexanone, it might be possible to purify your material via vacuum distillation.

Steam distillation would be dependent on how insoluble Tryptamine actually is, in water. It isn't a super high boiler, so it might not be impossible. Just difficult?

Tryptamines when impure, can be very tough to crystallize. I've had some long fruitless waits.

[Edited on 16-7-2015 by zed]

[Edited on 16-7-2015 by zed]
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