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DJF90
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Ah, sorry for spelling your name wrong buddy, but glad to have a reply from you what with the first hand experience and all. With the distillation, it
was a simple flask-claisen head-condenser affair, which differs from your arrangement by lack of a column. However, I'm not sure a vigreux would have
made all that difference, even with a variable take-off head.
What is interesting is that you mention the sample darkening. Even after a couple of hours the crystallised distillate had turned orange coloured. I
wasn't sure if it was my eyes playing tricks on me or not, but I have no doubt after your comment. I suspect this material will also go to waste; the
yield is terrible anyway but the important thing is that I now know how the TLC looks and so can monitor the reaction in progress for the appearance
of product/impurities. Purification by salt formation doesn't appear favourable due to the presence of other basic species in there (see ninhydrin
stain). Forming a crystalline derivative of the ketone might work nicely (oxime?) but its a fair bit of hassle to mess about with and potentially not
end up with product. Hydrate formation might be the ticket, but theres limited data about what its soluble/insoluble in. The patent does mention it
can be crystallised directly from the reaction mixture, so I may reconstitute a sample of the residue pre-distillation in acetone, add water, and see
what happens.
Cheers again for your reply.
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ziqquratu
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Depending on what you plan to do with it, reacting on may be OK. Reduction of the ketone with (say) NaBH4 should be no problem, or if you
planned to make the deoxygenated piperidine then making the hydrazone in preparation for the Wolff-Kishner should work well (and may give a
recrystallisable product, too).
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DJF90
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I had thought of telescoping it, but given the troubles that klute appeared to have with the subsequent reactions, I figured it would be best to
purify the material for the first time through. I've attached an excerpt from a book, which I found highly useful and I'd like to give this method a
go (lacking ammonium nitrate and time at the moment).
The distillates have all darkened now. I can imagine this is due to having an amine (base) and ketone in the same molecule (base catalysed aldol); as
the hydrate, the ketone is protected (geminal hydroxyls), and as the salt, the nitrogen is rendered inactive (protonation). It seems beneficial to
isolate the triacetoneamine as one of these species, rather than as the free base. Isolation by distillation as Ziqquratu and myself have done is
(probably) best followed by hydrate or salt formation.
Attachment: Triacetoneamine.pdf (603kB)
This file has been downloaded 1247 times
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bfesser
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Thread Copied
28-10-2013 at 17:55 |
Tornadyx
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TAA ketal derivative
Hey everyone
Some posts in this thread mentioned the ketalisation of TAA to form a TEMPO derivative. I have attempted this synthetic pathway a while back, because
when it came to synthesising TEMPO i did not want to use the Clemmensen reduction (mercury salts and harsh acidic conditions which hydrolyse TAA) or
the wolff-kishner reduction (free base hydrazine…) for deoxygenation and I don’t have NaBH4 to reduce to an alcohol and other methods are not
really viable in my situation. I also attempted transfer hydrogenation with ammonium formate and Pd/C but could not isolate any hydroxy or
deoxygenated derivative.
TAA was synthesized with similar methods described in this thread, I mainly used a writeup from Cheddite Cheese on SM, which I modified a bit:
Acetone (100 mL, 79 g, 1.4 mol), NH4Cl (6 g, 0.1 mol) added to RBF, bubbled dry NH3 (from 24 % ammonia, 110 mL, ca. 120 ml) through the rmx for 5h,
added acetone (200 mL) and heated for 15h at 50C. Acetone is distilled under vac. at 25C until 200 mL is collected. Rmx is acidified with HCl (7 M, 23
%) and continuously distilled under vac. A dark red/brown slurry forms, which when chilled to -21C yields crude dark crystals which are recrystallized
from IPA to yield off white crystals (12 g, 62 mmol, 5 % yield on NH3).
These reactions conditions are far from optimal, especially the distillation seems to destroy the products. Better conditions have been posted, of
which I wasn’t aware of at the time.
For the ketalisation, TAA (9.7 g, 50 mmol) was neutralized with aq. NaOH (3 g in 50 mL H2O) and extracted with toluene (2x 50 mL). Ethylene glycol was
distilled from car coolant (bp. 197C). Toluene (50 mL) was refluxed for 2h in a dean-stark setup with H2SO4 (2 mL, 3,68 g, 37 mmol) to form pTsOH in
situ. The toluene TAA extract and ethylene glycol (6 g, 0.1 mol) was added and the rmx refluxed overnight (ca. 16h). 3 mL water was collected total in
the dean stark. The rmx was basified using aq. NaOH (1 M) and the aq. layer was extracted with Et2O (3x 40 mL). The organic layer was dried with brine
and MgSO4 and all solvent was distilled of under vac. leaving a yellowish oil (4.0 g, 20 mmol, 40 %). Complete conversion was observed with TLC.
The ketalised TAA is generally insoluble, it only dissolves sparingly in acetone and almost not in water. This was a big problem for the formation of
the n-oxyl radical in the next step.
For the oxidation reaction, TAA ketal (4 g, 20 mmol) was suspended in H2O (50 mL) to which H2O2 (5 mL, 0.5 mol) and Na2WO4 (0.16 g, 0.1 mmol) was
added. The rmx was stirred for a day and no change was observed. NaOH (1 M, 10 mL), more peroxide (ca. 5 mL) and EtOH (50 mL) was added and the rmx
heated to 40C. The reaction was left to stir for 4 days, with the color slowly changing to an orange/red. The aq. solution was extracted with heptanes
(3x 50 mL), the organic layer dried with brine and MgSO4, distilled under vac. at 50C which yielded a red oil (3.16g, 15 mmol, 74 %). The conversion
of the starting material is incomplete, shown by TLC.
Because of the limited solubility of the TAA ketal, the oxidation proceeded very slowly, and incomplete conversion was the result. I will probably try
different conditions for this reaction (more peroxide, less polar solvents etc.).
If anyone has any suggestions or improvements, please write to me or answer this post. I also did not manage to attach pictures, im sorry for that.
Sources I used:
- Mahapatro, S. N.; Kallan, N. C.; Hovey, T. A.; De Dios, R. K.; Vergil, C.; Lai, T.; De Dios, R. C.; Tran, D.; McEvoy, J. P. TEMPO Synthesis,
Characterization and Catalysis: An Integrated Upper-Division Laboratory. J. Chem. Educ. 2024, 101 (12), 5449–5459. https://doi.org/10.1021/acs.jchemed.4c00739.
- TEMPO writeup from Cheddite Cheese on Science madness
- Tetrahedron Letters,Vol.29,No.31,pp 3741-3744,1988, reduction of aldehydes and ketones to methylene derivatives using ammonium formate as a
catalytic hydrogen transfer agent
- Patent EP0074607B1
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