We are confirming the substitution of pentafluorophenyl groups with amine in the PPPFA polymer by monitoring the appearance of free pentafluorophenol in the reaction mixture with 19NMR spectroscopy. However, the signals of appeared after the reaction pentafluorophenol are shifted in comparison with the pure reagent we purchased. Why is that?
pentafluorophenol anion in slightly basic condition and pentafluorohhenol neutral form (pure), maybe! ? Did you use base, such as TEA, in your reaction?
The phenol proton is very acidic so I agree with the above. Furthermore, you're coupling an amine so it's possible (and I would say likely) this is sufficiently basic to deprotonate your acidic phenol (or perhaps you use a base like TEA in your reaction). You could NMR your pentafluorophenol and the amine you're coupling to see if this is what is deprotonating your phenol and moreover recapitulate your shifted 19F NMR findings. How big of shift are you seeing? Is it possible you're seeing a shift in the 19F NMR due to some side reaction with the pentafluorophenol, perhaps an esterification?
Thank you very much for your comments. We didn't use TEA in our reaction, but we do see that only half the amount of the amine we are using for the substitution is reacting with the polymer every time. So I think, as you suggested, this amine can play the dual role of the reagent and a base at the same time. We are now checking the NMR of the mixture of the pentafluorophenol and the amine to see if it does cause deprotonation and change in the spectrum. Thank you again.
Hi Dr. Kharbash, you're very welcome. Glad I could be helpful. Did this work? Was this in fact the answer?
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