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I am trying to monitor the esterification of a non UV active amino acid.I used thionyl chloride and Methanol as reagents.

As amino group is unprotected, Ninhydrin should give positive result for both reactant and products. However, I believe there should be Rf difference between reactant and product.When I performed TLC and stained with ninhydrin, the reactant was strong brown and one spot at very high Rf value showed pale brown coloration.Now can I think that pale brown spot as my target ester?

I am doubtful because reactant and product both supposed to show strong coloration as amino group is not affected.On the other hand, will just methylating the acid result in high Rf change? Because I feel amino group is also polar, it would not allow spot to raise till high Rf end.

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  • $\begingroup$ On what medium did you perform TLC? Silica? $\endgroup$ – Waylander Feb 14 at 8:28
  • $\begingroup$ Yes Silica.CHCl3/MeOH $\endgroup$ – Science123 Feb 14 at 8:29
  • $\begingroup$ You could use a bromcresol green stain which is indicative of carboxylic acids, details here silicycle.com/faq/thin-layer-chromatography/… Do you have access to alumina plates? $\endgroup$ – Waylander Feb 14 at 8:30
  • $\begingroup$ Unfortunately I don't have access to Alumina plate. To add some more information the top spot is tailing. Is it due to free amine? $\endgroup$ – Science123 Feb 14 at 8:39
  • $\begingroup$ I doubt it is free amine, you normally need to add NH3 to your eluent to get free amine off the baseline. How much MeOH are you using in the eluent? $\endgroup$ – Waylander Feb 14 at 8:50

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