TestTubeBoof
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Guidance on TLC Rf values
Hey guys, this is my third TLC I've done, the other two didn't work because I may have had a brain aneurysm when reading that the solution had to be
diluted before spotting.
The chemical on the left with the single spot is Benzyl alcohol, on the right is Benzaldehyde which I synthesized myself and am proud as it's the
first Aldehyde I've ever made.
I'm having a hard time figuring out exactly which spot is benzoic acid or benzaldehyde or even where to look to find out because different solvent
systems give different results.
The one I used was 95:5 Xylene/EtOAc, the Rf values are
Benzyl Alcohol: 0.25
Benzaldehyde lower spot 0.66
Benzaldehyde higher spot 0.79
A question I had was is doing TLC with aldehydes kind of weird because Benzaldehyde will decompose to the acid in air, will that kind of funk up the
results?
I'm assuming the larger spot is acid and above is the aldehyde. Any advice is or criticism appreciated, I know that Petroleum Ether is usually used
for non polar but I couldn't find any in Aus I may need to distill it from Shellite.
Edit: The reason for the line being so high up on the plate is that I overshot how much solvent I thought I put in the jar
[Edited on 13-3-2026 by TestTubeBoof]
[Edited on 13-3-2026 by TestTubeBoof]
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Texium
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Best way to know for sure is to get a sample of benzoic acid and spot that as well.
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DraconicAcid
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If your benzaldehyde was contaminated with benzoic acid, you'd see a spot much closer to the original line. Its Rf would be lower than that of benzyl
alcohol.
Please remember: "Filtrate" is not a verb.
Write up your lab reports the way your instructor wants them, not the way your ex-instructor wants them.
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