If the sodium sulfite-diazonium salt mixture is acidified before warming or before becoming dark, the red color of the solution does not disappear on heating, and the precipitated phenylhydrazine hydrochloride obtained is colored red.
"Organic-Syntheses"
Conant, James Bryant
The rapid addition of the diazonium salt solution to the sodium sulfite seems to be advantageous.
"Organic-Syntheses"
Conant, James Bryant
The most feasible method consists in the reduction of diazonium salts with sodium sulfite.
"Organic-Syntheses"
Conant, James Bryant