Thin Lead Chromatography help

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  • #1
chem_tr
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Main Question or Discussion Point

Hello everyone,

I was poor on TLC before, and am poor now :smile: I want to ask a question to you guys.

Please look at the attached zip file with a tif image.

My question is very simple: Is it possible to fully isolate the impurities (yellow spot and light olive-mustard-colored streaking) from my ester, which is immobilized on the start point? I have very poor knowledge on chromatography, and I have a limited amount of ester sample. I don't want to make a mistake while performing the column chromatography. More simply, can I avoid the streaking from involving my ester sample and drive off from the column completely?

If you want to know, thf alone elutes my ester with elution solvent (Rf is about 1). thf:MeOH mixtures cause some streaking effects. I am planning to isolate the impurities by eluting through the column with MeOH first to drive off the yellow spot, and then employing 1:1 MeOH:thf mixture to isolate the mustard-colored streaking, and after these have gone, eluting with thf alone to obtain my purified ester sample.

Thank you for your time on even reading this post.
 

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  • #2
Bystander
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"Zip file corrupted or invalid," so, I don't get to look at it. Is your ester solid? (Hope against hope) Sounds like you've got a perfect opportunity to practice your fractional recrystallization technique; dissolve it in "hot" THF, let it cool and add a little MeOH.

If not, what you've described as an approach sounds about as good as anything.
 
  • #3
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You can usually get better separation with preparitive TLC, but you can't purify very much material at a time.

Have you looked at solvent systems extensively? The particular solvents can have a big effect on both Rf and the amount of streaking.

Also, using concentrations of methanol over about 10% you can start to dissolve the silica gel, which is a real pain to get rid of later.
 
  • #4
chem_tr
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I will try my best, thank you.

PS: What is the result if MeOH starts to dissolve some silica gel? I have not seen any "holes" on TLC plate.
 
  • #5
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You wouldn't see holes on the plate, but if you were to run a flash column you would end up with silica gel in your product material after you stripped down your fractions.
 
  • #6
chem_tr
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I see. I will not use a flash column, mine will be a simple and short column at ambient conditions.
 

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