I am conducting an organic synthesis. Below is the TLC image. TLC image of reaction mixture

I used dichloromethane:methanol:triethylamine=10:1:0.15 as eluent, but I stored it during 3 days, so it may be a little bit concentrated.

  • Question 1. I used toluene to dissolve sample. If I spot only toluene and run TLC, and stain the plate, then there emerges brown color near the solvent front. I waited enough time to let toluene evaporate before staining, but are there chances that spot 1 is of toluene?

  • Question 2. I am assuming that my desired product is basic, so I used triethylamine. When I fixed ratio of dichloromethane and methanol and changed only ratio of triethylamine, only the position of spot 7 changed and the others are unchanged. Then can I conclude that spot 7 is not part of spot 6 or tailing 2?

TLC comparison for Et3N

(sample is more concentrated than first image)

  • Question 3. There are some tailings. Does existence of tailing always mean the band widening when I run the column chromatography? I heard that when I do the column, I had better use as minimum solvent as possible. But to prevent tailing, should I dilute the sample more? (I think the size of spot was small enough)

  • Question 4. In UV, spot 6 looks like one big spot, but after staining it seems that middle is empty. Does this mean there are two or more other compounds in same position?

  • Question 5. Is spot 4 and tailing 1 is same compound? Is spot 6 and tailing 2 is same compound? If I can't determine in this result, what should I do?

another TLC image

Another TLC image. Spot 4 is more identifiable. (sample is more concentrated than first image)

  • Question 6. I assume that the longer distance spot moves, the more nonpolar it is. Even in very polar solvent system (i.e. dichloromethane:methanol=10:1) many spots are close to solvent front. To separate spot 1, 2, 3, and 4, how can I change the solvent system?

additional information

  • starting material : aza-crown ether, bromothiophene, Pd catalyst, P ligand.
  • expected product : N-substituted thiophene.
  • aza-crown ether and spot 7 is not drawn up by solvent without (aza-crown ether is detectable only by ninhydrin) So I think I should use Et3N to separate these two.
  • spot 3 is assumed to be Pd catalyst. bromothiophene and P ligand is not detectable by formaldehyde/H2SO4 staining.
  • $\begingroup$ Better you refer to some senior colleague at your place. I won't start any column using those conditions but what is the crude the material the amount the columns around etc it is crucial, togheter with possible major changes of the eluent. As for 1 answer should be no. #2 not really important #3a likely #3b no 4# likely but it might depend on the handling of the plate. #5&6 reduce polarity. Note that this is an attempt to help,only. Otherwise I would have answered. Also one should know if the reactants are there. The entire tlc is messy. Tailing is due to Et3N. $\endgroup$
    – Alchimista
    Aug 9 at 9:20
  • $\begingroup$ Finally the start line might have been to far from the eluent surface level. Togheter with a not well dried plate this means bigger spots. And to all: the capillaries for TLC should be extremely thin, not those called "for ematocrito". $\endgroup$
    – Alchimista
    Aug 9 at 9:22
  • $\begingroup$ @Alchimista Oh Is that start line too far? I line position at 1 cm from the bottom of the plate. $\endgroup$
    – Krang Lee
    Aug 9 at 9:26
  • $\begingroup$ I have just guessed from the pics. And this would be important only if one doesn't dry the plate after deposition (and not existing with volatile eluents). But it is the last problem with your TLC $\endgroup$
    – Alchimista
    Aug 9 at 9:30
  • 1
    $\begingroup$ think about it. At least they won't be gases. The plate must be dry even after deposition. Otherwise the spot starts the process. $\endgroup$
    – Alchimista
    Aug 9 at 9:41

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