Chemical Forums
Chemistry Forums for Students => Organic Chemistry Forum => Topic started by: m17 on May 06, 2018, 11:35:30 AM
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Hello!
Thank you in advance for reading my question and for helping me to solve my organic-practicals problem.
Recently, I had to separate three unknown organic compounds with TLC with silica gel on an aluminium plate as stationary phase. I had my substances dissolved in ethyl acetate.
I was thaught in my theoretical classes that if a spot doesn't occur on TLC plate it is suggested to vary the polarity of the eluent or the visualization method.
I tried different eluents by mixing petroleum ether and ethyl acetate (while increasing concentration of ethyl acetate up to 1:1 ratio) and also dichloromethane, chloroform and toluene (and mixtures of those substances).
As visualization method I used an UV-Lamp, KMNO4 and Phosphomolybdic acid.
However, I could always see just two spots instead of three.
Did you ever make such an experience or have an idea what could have been gone wrong?
Thank You very much for reading this and for your suggestions. :)
And sorry for my bad English, I am not native.
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Do you have access to the three unknowns individually?
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Unfortunately not, I was supposed to mix the compounds for the purpose of my experiment.
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what about using a different visualisation method such as permanganate stain
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OrganicDan96, The OP mentioned potassium permanganate.
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When nothing else works, misting the developed plate with conc. sulfuric acid and heating it will give you the charred spots. You can run the plate with parallel spots, and treat only one, if you need the invisible spot later for some reason. At any rate, you'll have your answer -- if one sport is not separating, or is degrading before you can visualize it.
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I had to do this once. Run in one solvent that separates two, turn TLC plate 90 degrees and use different solvent.
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Its called 2D TLC
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And to be frank, I think the most likely problem here is an incorrectly made sample being given to you, not an issue with visualization.
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Hey!
Thank You all for your replies.
The Idea of 2D TLC sounds reasonable, I will try it.