Electrochemical Characteristics of Nitro-Heterocyclic Compounds of Biological Interest IV. Lifetime of the Metronidazole Radical Anion

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Abstract
Electrochemical studies on metronidazole using mixed aqueous/dimethylformamide (DMF) solvents have allowed us to generate the one-electron addition product, the nitro radical anion, RNO−2. Cyclic volt-ammetric techniques have been employed to study the tendency of RNO−2 to undergo further chemical reaction. The return-to-forward peak current ratio. ip/ipf. was found to increase towards unity with increasing DMF content of the medium, indicating the extended lifetime of RNO−2. Second order kinetics for the decay of RNO−2 were established at all DMF concentrations examined. Extrapolation has allowed the rate constant and a first half-life of 8.4 × 104dm2/mol-sec and 0.059 seconds respectively, to be determined for the decay of RNO−2 in a purely aqueous media. This is impossible by direct electrochemical measurement in water. due to a different reduction mechanism, giving the hydroxylamine derivative in a single 4-electron step. The application of the technique to other nitro-aromatic compounds is discussed.