ABSTRrlCTComparing reduction potentials of aromatic nitro compounds with those of corresponding nitroso compounds, by studying shifts o f half-wave and peak potentials with pH and by following the decrease of limiting current in buffered 35% DMF-water mixtures, the sequence of protons and electrons in the fourelectron reduction step was proved to be: H ', e, H ', c, Ze, 2H+. Arylhydroxylamines formed in the fourelectron reduction of nitro compounds can be protonated and further reduced, they can undergo dehydration (provided that the dehydration product is stable), they can undergo chemical reactions with intermediates of the reduction of the nitro group, like ArNO, they can be electrooxidized to nitrosobenzenes (which can undergo chemical reactions) or they can react with carbony1 groups when present. Stabilization of the dehydrated form can occur in quinonemethide (nifedipine) o r in some quinone-like heterocyclic derivatives. Side reactions of ArNHOH and ArNO are demonstrated by smaller peaks in CV and by controlled potential electrolysis. Reactions of ArNHOH with carbony1 groups were observed by formation of new waves of nitrones in the reduction of nitrobenzenaldehydes.

No abstract

1,2-Dialkyl-4-nitroimidazoles are reduced between pH 0 and 13 in a four-electron wave. The resulting arylhydroxylamine is stable and in acidic media reduced further to the amine. 1,2-Dialkyll-5nitroimidazoles and 2-alkyl-4( 5)-nitroimidazoles are reduced in alkaline media with the number of electrons approaching six. The hvdroxylamine derivative formed in these reductions can be dehydrated and yields an easily reducible, quinone-like ketiniine. The rate of the dehydration governs the heights of the first step and is base catalyzed. The sequence of electron and proton transfers for 2alkylsubstituted nitroimidazoles is the same as that observed for corresponding desalkyl compounds.l-Alkyl-4-amino-5-nitroimidazoles, as well as 1 -alky-4-nitro-5-aminoiiiiidazoles, are reduced in a single wave, the height of which approaches that of a six-electron process. The dehydration of the hydrolrylamino derivative is favored, probably due to an internal base catalysis. The shifts of half-wave potentials with pH differ principally from those of all other nitroimidazoles and indicate the predominant role of the amino group in the proton transfer.KEY WORDS: Nitroimidazoles, Reduction, Polarography.information useful in development of analytical procedures. EXPERXMENTM ApparatusPolarographic curves were recorded with Polarograph Sargent Model XV. Electrolytic cells enabling the use of three-electrode systems were used. Four capillaries were used: for the study of compounds I-V, VTI-X, and XII-XIV, the capillary characteristics were t, = 2.90 s, m = 2.30 mg s-l; for VI and XI, tl = 3.88 s, m = 2.26 mg s-I; for XV-XXIII, tl = 3.76 s, m = 2.00 mg s-l; and for Xxn:

No abstract

A method for the simultaneous quantitative polarographic determination of the three components in reaction mixtures has been proposed. The analysis is based on a separation of the half-wave potentials in strongly alkaline base solutions. The general polarographic behaviour of the three substances is also described. derivative 1-(2-hydroxyethy1)-2-methyl-5-nitro- HE nitroimidazole