I have synthesized 1-phenylazo-2-naphthol in my laboratory tutorial and have to analyze it. I've done a thin layer chromatography (TLC) of it:

  • solvent: ethanol
  • eluent: toluene
  • stationary phase: silica gel plate

My only problem is, I need an theoretical value for comparison but haven't found any source.


2 Answers 2


Did you react aniline (or its hydrochloride) with sodium nitrite in the presence of 2-naphthol?

I'm afraid there will not be any table with $R_\mathrm{f}$ values. These values are not only dependent on the compounds and the mobile phases, but also on the stationary phase: e.g. silica, aluminium oxide, etc. Your best option is to use reference samples and measure the $R_\mathrm{f}$ value yourself for the conditions you want to apply or transfer from TLC to column chromatography.

My suggestion is to collect the crude reaction product (Büchner funnel, etc.) dry it, note the yield and measure the melting point.

For purification, recrystallize from ethanol. You should receive red needles with a melting point of $\pu{134 ^\circ C}$.

NOTE: Wear proper protection when handling the azo dye, which is a cancer suspect.


  1. IOC-Praktikum (PDF in German)
  2. GESTIS-database on hazardous substances
  • 2
    $\begingroup$ I agree 100%. Even if such tables existed, depending on how accurately you measure the solvents ratio, the $R_\mathrm{f}$ will change slightly. So the best bet is to leave a little room on the TLC plate and spot reference samples for comparison. $\endgroup$ Commented Sep 15, 2014 at 12:09

$R_\mathrm{f}$ is sensitive to particular stationary phase, up to having different $R_\mathrm{f}$ on different plates. Traditionally, it is done comparing $R_\mathrm{f}$ of freshly acquired sample and obtained previously in a different manner reference.

However, I agree with Klaus, use melting point of characterisation if possible.


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