Electrochemical Studies on Eriochrome Violet B and Its Lanthanide Complexes. II. Controlled-potential Coulometric Studies

Abstract

Controlled-potential coulometric studies of Eriochrome Violet B (5-sulpho-2-hydroxy-benzeneazo-2-naphthol) using a stirred mercury pool cathode have shown that four electrons per molecule of dye are required for the reduction and that the amines are the final reduction products both in acidic and basic media. The lanthanide-dye complexes are reduced in a similar manner to the free dye. The reduction of Eriochrome Violet B does not obey first-order kinetics, and the observed reaction rate may be related qualitatively to a disproportionation mechanism involving an unstable hydrazo compound. The coulometric and polarographic behaviour of Eriochrome Violet B has been compared with that of the uranium system, which is well known to involve a disproportionation step.