[gingi85]

I've been following a procedure for the production of azoaryl compound. The starting material is a naphthylamine derivative that is converted to the corresponding diazonium salt and then reacted with a tertiary phenylamine for the final azoaryl product-- a deep red compound.

Recently, I switched to a new vendor for the starting material. Apparently, as the final step in the product of the napthylamine derivative they recrystallized it using either HCl or sulfuric acid, so the final product is the either the hydrochloric salt of the amine or the sulfate salt. At any rate, when I follow this procedure, the product of my diazotation is different than the intended product. It gives me an entirely different peak by HPLC and somewhat different (although similar) chemical shifts by proton NMR.

When I take this product on to the next step, I again get an entirely different product -- a bright orange solid. Again the HPLC peak is has a different retention time than the intended azoaryl. Proton NMR is also different, but all my protons are accounted for.

If I slurry the naphthylamine in NaOH solution to convert it back to the free amine, it performs as intended.

Any ideas what might be going on over here? How is the naphthylamine salt affecting the diazotization (if that's indeed what's going on)? Ideas? References?

Much thanks!

[Dan]

Are you saying that treatment of the batch produced from the hydrochloride salt with NaOH gives the same product as treatment of the sulfate batch with NaOH?

It sounds like you are just carrying a different salt through the synthesis (sulfate instead of chloride).

[gingi85]

I'm not sure whether this naphthylamine is hydrochloride salt or the sulfate salt (i.e. it was marketed as the free amine). What I do know is that when I treat it with NaOH, i get the same result as I did with the naphthylamine that I now to be a free amine.

The reason I don't think that it is just a different salts of the same compound is because a) the HPLC solvents are buffered, so even if they were different salts I should still get the same retention time and b) the final azoaryl product is neutral species (not a salt at all) and still gives me two different materials

I hope this clarified things somewhat.

[opsomath]

Honestly, the simplest answer may be that the naphthylamine you think is just the salt of the correct stuff is actually the salt of the incorrect stuff. Have you positively confirmed that you get the correct material after treatment with base to get the free amine?

The other thing I can think of is that the different salt could be promoting the formation of the ortho-linked azobenzene instead of the para-linked form, which is the one we usually assume forms. I could potentially see something like that happening if you had, for instance, a sulfate counterion which promoted hydrogen bonding in a certain way...

The good news is, it should be pretty easy to tell from NMR. Just look at the coupling patterns on the tertiary phenylamine ring.