Dear Ionut-Marian Colbea thank you for asking this interesting technical question on RG. We are synthetic inorganic chemists, and personally I never worked with 2-naphthylhydrazine or its hydrochloride. It might be worth having a look at the following potentially useful patent:

Process for preparing 2-naphthylhydrazine in one step

https://patents.google.com/patent/CN1063170C/en

Unfortunately the original patent is written in Chinese, but the above link provides an English translation. Please see particularly the Embodiments. Once you have the free 2-naphthylamine, you can treat it with concentrated HCl to make the hydrochloride.

I hope this helps. Good luck and best wishes, Frank edelmann

Dear Frank,

Thank you for your answer! I haven studied that patent (any many more) and the yields for the final product are lower than they mention. That is why I was thinking if maybe someone with trained eye can see if there may be a hidden trick to use in order to raise these yields. I don`t quite understand the reaction mechanism; why the hydrazine (quite in excess) does not consume all the naphthol ?

BR,

Ionut

Dear Ionut-Marian Colbea thank you for your kind response and question. Perhaps one has to accept that not all reactions in organic chemistry proceed in very good yields. I just found a potentially useful hint in a Chinese patent (CN 1175571). It is stated there that 2-naphthylhydrazine was prepared by refluxing a mixture of 2-naphthol and 85% hydrazine hydrate in the presence of NaHSO3 as catalyst for 20 hours, cooling (or pouring into water), filtering, washing, and drying the product. The ratio of hydrazine : catalyst : naphthol was 1-10 : 0.8-1 : 1. Perhaps it might be worth a try to use this catalyst.

There is also a method known in the literature that uses 2-chloronaphthalene and hydrazine hydrate, but in that case you need a rather exotic catalyst.

P.S. 2-Naphthylhydrazine hydrochloride is also commercially available. 😎