Chemical electrochemical mechanism. Electrochemical reduction of some pyrazolidine-3,5-diones in DMSO. Relation between voltammetric behavior and 1H nuclear magnetic resonance spectra

Abstract

In DMSO (TEAP), phenylbutazone, oxyphenbutazone, and kebuzone, pyrazolidine-3,5-dione species are irreversibly reduced in two steps at the mercury electrode. The total reduction process is monoelectronic with production of the enolate carbanion. A chemical–electrochemical mechanism is proposed, each step is attributed to one of the tautomeric forms, ketoenol (E) and diketone (D). The tautomeric equilibrium constants (K = [E]/[D]) are reached both by linear sweep voltammetry at 30 V s−1 and by FT 1H NMR and the global apparent acidity constants are determined by potentiometry.