Wednesday, February 20, 2013

Thin Layer Consternation

Earlier today, I was involved in a minor dust-up with some commenters over at Derek's blog. A central issue concerned my (admittedly quick'n'dirty) TLC, which meant to indicate the complete consumption of the acrylate starting material for Blog Syn #002.

Well, since I was already running another entry for #003, I decided to pause and take stock of my TLC tool-box: yes, I should use a ruler, and yes, a classic TLC would have lots more info (solvent system, stain, clearer labels, etc).

So, I took a sample from my IBX oxidation of methylnaphthalene to 2-naphthaldehyde (12 h timepoint, set up in straight DMSO with 0.1 volume of H2O). Results below:


Before anyone goes crazy, that's DMSO / H2O on the baseline, and the SM at Rf ~0.8. It's stained in potassium permanganate, which forms pale yellow spots upon heating. I circled the "UV-only" spots with a pencil before staining.

I'm guessing that the tiny new spot (Rf ~0.45) represents trace aldehyde. But, as you can tell, we're still a long, long way away from completion. Sad, because it was a lot more homogeneous this time!

Readers: How's my technique? Have any more pointers?

12 comments:

  1. The "o" in "spots" is too small! Your handwriting is terrible! I reject you and your witch hunt!

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  2. It's TLC, whatever. Those dudes in the comments at derek's blog have something up their ass. Mark down the shit that's important in your notebook and move on.

    It looks perfectly fine. What do they want?

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  3. CoulombicExplosionFebruary 20, 2013 7:13 PM

    I think one of the commenteers over at ItP may have been the Dowager... http://www.quickmeme.com/meme/3t2pad/

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    Replies
    1. CoulombicExplosionFebruary 20, 2013 10:31 PM

      *facepalm* Couple of typos in there, but you get the point.

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  4. dinitrophenylhydrazine for ketones and aldehydes!

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    Replies
    1. True dat. Maybe I'll publish a TLC retraction...

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    2. Vanillin is great too and smells so good :)

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  5. I can't understand why anybody would care how you do a TLC. The only time I might even think about using a ruler is when the spots are really close (but even then I probably wouldn't bother because you can still usually tell). Write down whatever info you think is important to you. It's only a TLC....

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  6. It's always interesting to me what some people choose to do with anonymity. (I say from an anonymous log in, but mostly just because I am lazy.)

    The first TLC was fine for what it was. Does anyone REALLY make pretty and perfect TLC plates every time they run one? o.O

    And for what it's worth, like so many (perhaps less vocal) others, I really love the BlogSyn project!

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  7. You should tell your TLC to be careful with exposure to UV - she got pink all over. A lotion with higher SPF should be applied next time

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  8. (yes, gratuitous corporate shill) but I do like the tlc drawing tool in chemdraw nowadays - for those plates there is nothing like a visual. Of course, photos are easy too now also.

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  9. I don't use a ruler, I don't even use a line. 3 crosses at the bottom, if you can't get them relatively aligned you probably can't do the reaction you're TLC-ing.

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