POLAROGRAPHIC AND ELECTROCHEMICAL STUDIES OF SOME AROMATIC AND HETEROCYCLIC NITRO-COMPOUNDS .4. POLAROGRAPHIC-REDUCTION OF 2-ALKYLNITROIMIDAZOLES AND AMINONITROIMIDAZOLES

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-Dialkyl-5-nitroimidazoles and 2-alkyl-4(5)-nitroimidazoles are reduced in alkaline media with the number of electrons approaching six. The hydroxylamine derivative formed in these reductions can be dehydrated and yields an easily reducible, quinone-like ketimine. The rate of the dehydration governs the heights of the first step and is base catalyzed. The sequence of electron and proton transfers for 2-alkylsubstituted nitroimidazoles is the same as that observed for corresponding desalkyl compounds. 1-Alkyl-4-amino-5-nitroimidazoles, as well as 1-alkyl-4-nitro-5-aminoimidazoles, are reduced in a single wave, the height of which approaches that of a six-electron process. The dehydration of the hydroxylamino 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.