抄録
Polarographic behavior of the N-O groups in 1-oxides, 4-oxides, and 1, 4-dioxides of quinoxaline, 2-methylquinoxaline, 2-phenylquinoxaline, and 2-quinoxalinecarboxylic acid is discussed. The reduction wave of quinoxaline ring showed reversibility, but that of the N-O groups was found to be irreversible. Except in 2-quinoxalinecarboxylic acid 1-oxide and 1, 4-dioxide, variation of pH did not show any effect on the wave height of the N-O reduction. However, the limiting current of the first reduction wave of 2-quinoxalinecarboxylic acid 1-oxide and 1, 4-dioxide decreased in the neutral solutions, but the total limiting current of the first and second waves remained constant. These behaviors of the N-O groups can be interpreted by considering that the rate of proton addition to the N-O groups is very fast. By the introduction of a carboxyl, phenyl, or methyl group into the quinoxaline ring, both reductions of quinoxaline ring and the N-O group took place at more positive potentials in the order of COOH>H>C6H5≈CH3. The phenyl and carboxyl groups produced a stronger effect on the reduction potentials of 1-N→O than those of 4-N→O, while a reverse effect was observed for the methyl groups. This order of facility of the N-O reduction can be correlated to the yield of synthetic N-oxidation in the reverse way. The carboxyl and phenyl derivatives of quinoxaline 1, 4-dioxides showed two reduction waves due to the corresponding N-O groups, which were assigned by comparing the half-wave potential and limiting current of their monoxide derivatives, and the reduction mechanisms for these derivatives were suggested.
