Electrochemical investigations on some potential antibacterials, I

Electrochemical behaviour of the medicinally important 4-(4′-sulphonamoyl)hydrazono-1-phenyl-3-methyl-2-pyrazolin-5-ones has been studied at d.m.e. and glassy carbon electrodes. At d.m.e., all six compounds exhibited a single, well-defined, four-electron wave in the pH range 2.5–12.0. Polarographic four-electron wave was found to be diffusion-controlled and irreversible. Similarly, cyclic voltammetry of these compounds at glassy carbon electrode exhibited a single peak. Peak potential shows shifts towards negative potential with pH, with linear segments up to pH 8.2 and are practically pH independent at higher pH values. An anodic peak at far-off positive potential was observed in the reverse scan, indicating the irreversible nature of the electrode process. Controlled potential electrolysis and coulometric studies gave the value of n as 4.0 ± 0.1 in the pH range 2.5 to 10.0. Out of the two major end products formed, one was identified as sulphanilamide and the other as 1-phenyl-3-methyl-4-amino-2-pyrazolin-5-one on the basis of IR and NMR studies. On the basis of DCP, LSV, CV, CPE, coulometry and spectral analysis, a mechanism has been postulated for the reduction of these compounds at d.m.e. and glassy carbon electrodes. Keywords: polarography, cyclic voltammetry, antibacterials, pyrazolin-5-ones.