Simultaneous determination of N-unsubstituted and N-substituted nitroazoles and criteria for their identification-II Chromatographic separation and polarographic determination of nitropyrazoles.
The N-unsubstituted nitropyrazoles have an imino hydrogen atom, in contrast to the N-substituted derivatives, and react with hydroxide to give nitropyrazole anions. The strongly negative shift of E(1 2 ) for these anions makes possible simultaneous polarographic determination of any pair of compounds, one of which is an N-unsubstituted nitropyrazole and the other a corresponding N-substituted derivative. Simultaneous polarographic determination of three compounds [3(5)-, 3- and 5-nitropyrazoles] is also possible with 0.1M sodium hydroxide as supporting electrolyte, but only when DeltaE(1 2 ) between the N-substituted isomers is at least 100 mV. In this case adequate DeltaE(1 2 ) is caused by the different electron densities of the nitro-groups of isomers. In the medium mentioned it is possible to determine simultaneously even four compounds [1-, 3(5)-, 3- and 5-nitropyrazoles], because the E(1 2 ) value of 1-nitropyrazole does not change with pH, contrary to other nitropyrazoles. Developers for the chromatographic separation are proposed. Some criteria are given for the distinction of the N-unsubstituted- and the corresponding N-substituted nitropyrazoles. The structures of two new compounds have been determined. Methods are recommended for the simultaneous identification and determination of the compounds appearing together in the reaction mixtures during the substitution of the imino hydrogen atom, or during the rearrangements of the 1-nitropyrazoles to the N-unsubstituted ones.
Dumanović
D
D
Research Laboratory "Galenika", Zemun, Yugoslavia.
Maksimović
R
R
Cirić
J
J
Jeremić
D
D