Collect. Czech. Chem. Commun. 1992, 57, 1836-1842

Some Aspects of the Electroreduction of Niazid to Nicotinamide on Mercury Electrodes in Acidic Media

Rafael Marín Galvín and José Miguel Rodríguez Mellado

Departamento de Química Física y Termodinamica Aplicada, Facultad de Ciencias, Universidad de Cordoba, 14004 Cordoba, Spain


The electroreduction of niazid on mercury electrodes has been studied in acidic media (pH < 6). Tafel slopes and reaction orders were obtained at potentials corresponding to the foot of the first polarographic wave. On the basis of both polarographic and voltammetric results it has been shown that the waves appearing at more negative potentials correspond to the reduction of nicotinamide. Protonation of niazid plays an essential role in its reduction and pK values of 1.4, 3.2 and 11.5 were obtained by UV spectroscopy. The process corresponding to the first wave is irreversible, being the second one-electron transfer the rate determining step. Above pH 4 the process is complex due to the overlapping of the waves caused by the occurrence of protonation reactions.