guy
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Chromatography of acetone condensation products
I did a paper chromatography of the mixture of condensation products. It was from acetone and H2SO4 and left over night. The solution is dark brown.
The chromatography was done with 70% EtOH and chromatography paper.
I need help identifying which colors belong to which compounds. There are two "yellow" compounds I know come from acetone, isophorone and phorone.
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DDTea
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When I run TLC's, I always make three rows to spot:
-Starting Material
-Mixture
-Products
Naturally, one would spot the starting material (acetone) in the "starting material" lane. A mixture of the starting material and the products would
be spotted in the "mixture" lane, and the products would be spotted in the "products" lane. Pretty self-explanatory.
This made comparisons and identifications a lot easier, when the spots migrated cleanly and stayed in their lanes, that is.
In this case, identifying acetone would be easy if you ran a second chromatography test with a separate lane including the original acetone.
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Klute
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What stain did you use to develop the paper?
What you could do is try a few reactions with different quantites of acid (and a lighter acid) and different times of reaction, the higher
condensation products (isophorone) could appear in the longer reaction times. Or just follow the reaction with TLC, the first products appearing would
be the lighter ones. Just an idea.
I'm actually surprised there so few reaction products. I was under the impression that aldol reaction with acetone, especially wwith H2SO4, produces
tons of aldol/addition/deshydratation products, and mostly tar. The room temp must leed to fewer reaction products.
PS: raw guess, but I would think the bottom stains would be the isopherone
[Edited on 21-8-2007 by Klute]
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Nicodem
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| Quote: | Originally posted by DDTea
Naturally, one would spot the starting material (acetone) in the "starting material" lane. |
You can not spot a compound more volatile than the mobile phase due to it obviously evaporating. Acetone moves practiacaly on the front in just about
any mobile phase anyway.
| Quote: | Originally posted by Klute
What stain did you use to develop the paper? |
I think Guy just separated the colored crap from acetone self condensation. It does not look like he used any reagent to develop the TLC. Phorone
should not be yellow enough for such visual identification without staining. Those spots are probably some higher condensation products. Phorone,
mesitylene and similar are however UV-absorbing so they should be visible on normal flouroscent TLC plates.
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Klute
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That would explain why there is only 3 stains 
I guess UV would reveal much more products, or simply I2 vapors.
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guy
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Since I used a kind of polar solvent, I think most of the nonpolar stuff like the tar products stayed at the bottom in that red dot.
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guy
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Can naptha be used as a substitute for hexane in chromatography?
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Ozone
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I have used ligroin, and that is pretty close (~ 60-90°C, C7-C11, fraction), but... you have to be patient with its evaporation--and it takes longer
to develop.
Pet ether, or the 35°C fraction of "naptha" (when I was younger I accidentally blew up a fireplace with this as I had mistaken it for the heavier
cut) also works, but the primary isomer range around C5 makes volatility something to consider.
Oh yes, don't "let it soak in" and do use a match on the end of a looong stick .
I hate to call it "reference", but Wiki has:
"The 60 to 80 °C fraction is often used as a replacement for hexane."
Cheers,
O3
[Edit] Fractionated gasoline (petrol C5-C8>>C10) should also work quite nicely, OTC. The fractionation serves to remove oxygenates (forerun)
whilst leaving the surfactants, lacquer, etc. behind.
[Edited on 21-8-2007 by Ozone]
[Edited on 21-8-2007 by Ozone]
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Klute
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My favourite eluant when purifying sulfurated heterocycles was pentane or haxanes wiht 1-5% of DCM or ether, the seperations where often much better
(and elution quicker) than simply hydrocarbons. I nearly always use similar eluant mixtures now. You could try low boiling naphta (you might need to
distill it if it leaves some higher boiling liquids on evaporation) and 1% DCM on TLC and gradually increase the % of DCM until you have the optimal
seperation.
Keep us posted, I find this interesting.
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guy
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For the moment I have run out of equipment and reagents, but I'm sure many of are more qualified to do this. It would be cool if someone else could
contribute to this.
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Klute
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I'll give it a try when I have time, on TLC and using different times/catalyst (silica gel and a few days should be a very mild catalyst and could
yield only lighter products)
But I can't acces GC-MS, IR or NMR (don't think I'll be able to use the NMR for this though) until next month at best...
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WizardX
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If you can, purchase TLC plates that fluorescence.
http://inst.sfcc.edu/chemscape/catofp/chromato/tlc/tlc.htm
http://www.chemguide.co.uk/analysis/chromatography/thinlayer...
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Klute
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I personnaly use only UV 254nm silica plates, it's so practical, and a small UV lamp used in board etching can be had for cheap..
It makes TLC so much easier
And the prices of the UV plates aren't that different from "normal" ones
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