The reduction of 1-phenylazo-2-naphthol-3,6-disulphonic acid (disodium salt) at the dropping mercury electrode has been investigated. The reduction takes place in a two-electron step. The process is diffusion controlled. The reagent captures two electrons and one or two hydrogen ions depending on whether the pH is higher or lower than 7, producing 1-phenylhydrazo-2-naphthol-3,6-disulphonic acid, in both cases. A disproportionation reaction of the hydrazo compound takes place, and amines are the final reduction products. The reaction orders, together with Tafel’s slopes have been calculated.

The reduction of 7-chloro-1,3-dihydro-1-methyl-5-phenyl-2H-1,4-benzodiazepine-2-one at the dropping mercury electrode has been investigated. The process is diffusion controlled; furthermore, the reduction wave enables the quantitative determination of the drug both in acid and basic media. The reagent captures two electrons and two hydrogen ions. A disproportionation reaction of the hydrazo-compound takes place, and amines are the final reduction products.