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I've completed my reactions, and based on the stoichiometry and TLC analysis, I think my mixture should contain 3-4 compounds:

  1. Ethyl gallate (my product)
  2. Gallic acid (the reagent/starting material)
  3. Dicyclohexylurea (by-product from my reaction)
  4. Pyridine (catalyst that I used)

Here's my TLC result (please look carefully there are 3-4 spots):

  • Spot No. 1 = gallic acid

  • Spot No. 2 = my successful mixture

  • Spot No. 3 = my semi-successful mixture (it's not completely successful because there are still pretty much gallic acid remaining)

  • Solvent A = chloroform : methanol => 100 : 1

  • Solvent B = n-hexane : ethyl acetate => 1 : 3

TLC

Based on that, I must do purification by doing column chromatography. However, I've very little experience in doing column chromatography and I'm unsure about the appropriate solvent for my column.

My questions:

  1. Based on the TLC result, which solvent is more suitable for my column chromatography to separate compounds? And could you explain why it's more suitable, please?
  2. Do you have any suggestions regarding the mixture ratio for my solvent system? (like should I lower the ethyl acetate etc.)

Feel free to add other suggestions/advice that you've for me.

Note: I also don't know which spot on the TLC plate corresponds to my product.

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    $\begingroup$ Your product is most likely the high running spot on system B. Try running another tlc of 1:1 hexane/EtOAc which should bring your gallic acid SM down to approx baseline and your product to Rf 0.3-0.4 $\endgroup$
    – Waylander
    Mar 24 at 13:09
  • $\begingroup$ I see, but could you share your thoughts on my TLC result using chloroform:methanol (1:1)? What are the issues with that TLC? Is my product spot (Rf) too low?" $\endgroup$
    – Jonathan
    Mar 24 at 13:21
  • $\begingroup$ Try another tlc with a bit more MeOH (2%) to try to separate out the product. Note that the DCHU does not really stain with most reagents $\endgroup$
    – Waylander
    Mar 24 at 13:28
  • $\begingroup$ Okay, I kind of get it now. Regarding DCHU not staining, could I use KMNO4 or Ninhydrin to make the DCHU spot appear? $\endgroup$
    – Jonathan
    Mar 24 at 15:05
  • $\begingroup$ @Jonathan You wrote you used 1 Percent methanol. 1:1 would be 50 and at this point most compounds will not show any retention. It would make sense to run a stepwise gradient from 10 to maybe 50 Percent EtAc to purify your product. You can check fractions by running them on a TLC and check which fractions will be pure and and separated from the starting material/ side product. $\endgroup$
    – raptorlane
    Mar 24 at 15:12

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