I want to protonate the pyridinium nitrogen (BINOL derived phosphoramide containing pyridine ring) to prepare a salt. I do the reaction in dry DCM at room temperature using TfOH, HCl in Dioxane (4 M solution), HBr. In case of TfOH and HBr no salt formation occur...but in case of HCl in dioxane reaction happens but during precipitation it converts into the starting one. When tlc was checked from reaction mixture there is no starting material only one spot is there which in on bottom (does not move in pure ethyl acetate). But after precipitation only starting material is there.
Please suggest what to do.
You can try the reaction neat by mixing your pyridinium compound and acid in equivalent amounts, mixing together. Furthermore you can slowly warm the mixture and let it stand for a day or two.
As for upper floor 's opinions ,It‘s the method convicted by us to do the reaction ,but i don't know the reason that we should do it in the way .I'm thanks to you ,if you can acknowledge to me about it .
Without exact structure this is hard to tell, but protonation of phosphoramidates usually activates them for a nucleophilic attack. So in the presence of nucleophiles you may end up with substition products, with water e.g. a phosphoric acid and pyridinium salt. For purification purposes I recommend kugelrohr destillation instead of crystallization.
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