Nitro group polarographic reduction

A pulse polarographic method to determine dantrolene sodium and its major metabolites in urine after ethyl acetate extraction has been reported [181]. The ethyl acetate is brought to a residue and the dantrolene plus the total extract-able metabolites are analyzed for reduction of the azomethine linkage at -0.86 V in a DMF-acetate buffer (pH 4.0). The nitro compounds are simultaneously determined in the same media as dantrolene equivalents from the reduction of the nitro group at -0.26 V (see Fig. 26.13). The difference between the two determinations represents the metabolites not containing the nitro group. Levels as low as 0.1 fig/mL can be determined for either functional group. 

Polarographic reduction gives three reduction waves, the first of which is reversible (77ZOB2730). Nitro compounds show four waves, one associated with reduction of the nitro group. 

Dumanovic with colleagues carried out polarographic investigation of various derivatives 3-, 5-nitropyrazoles and 2-, 4-, 5-nitroimidazoles in aqueous buffer solutions (pH 1.8-9.3) and 0.1 M solution NaOH [903-912], On polarograms all the investigated nitroazoles have one or two waves of reduction both in acid and neutral medium. The first four-electron wave corresponds to reduction of nitro group to hydroxylamine one. The second two-electron wave corresponds to further reduction of hydroxylamine derivative to aminoazole (Scheme 3.34). 

Polarographic reduction of pH dependence of metronidazole [931], 2-nitroimidazoles, 4(5)-nitroimidazoles, 4-nitro- and 5-nitro-l-methylimidazoles [932-936] A-nitroimidazoles [937], and l-aryl-4-nitroazoles [938] has been investigated. A smaller diffusive current for 2-nitroimidazoles in comparison with other isomers noted by the authors is thought to be possibly due to its increased acidity [932], Electrochemical reduction of the nitro group in l-aryl-4-nitroazoles occurs in... 

Polarographic reduction of a nitro group at the 2-position showed96 that 2-nitrofuran was the easiest to reduce, while 2-nitrothiophene and 2-nitroselenophene required 20-30 mV, and nitrobenzene 40 mV higher potential. The reduction potentials of the five-membered heterocyclic isologs may increase with a decrease in electron shifts produced by the lone-pair of the heteroatom in the series 0 > S > Se. Hence, in its polarographic behavior 2-nitroselenophene is closer to nitrobenzene than to nitrofuran. 

Several furan aldehydes and ketones without a heterocyclic nitro group have been investigated polarographically and the intervention of ketyl radicals or their conjugate acids confirmed. Their involvement in amalgam reductions of furan carbonyl derivatives was also shown. 

A polarographic investigation of trichloronitromethane [42] shows a stepwise removal of chlorine under these conditions before the reduction of the nitro group occurs. Whether the difference in reduction path reflects the difference in the electrode material, electrode potential, or medium is not known. 

Several dinitronaphthalenes have been investigated polarographically [158,159]. The first wave is usually a four-electron reduction. The 1,2- and 1,4-dinitronaphthalenes behave like o and / -dinitrobenzenes, whereas 2,3-dinitronaphthalene does not exhibit a conjugation effect similar to that of (9-dinitrobenzene. Nitro groups in c -positions are reduced in preference to those in y3-positions. 

Kemula and co-workers (163) developed the polarographic reduction of the nitro group as an analytical method. 

The 6-nitrodihydrodiazepinium perchlorate (9n) can also be reduced under these conditions. The main polarographic wave in this case arises from the reduction of the nitro group to a hydroxyamino group.38... 

For the determination of keto-acids, e.g. pyruvic, a-ketoglutaric and oxalacetic acids in mixtures and in biological materials, a method has been proposed employing paper electrophoretic separations of the 2,4-dinitrophenylhydrazones of these acids.< ) After elution, the polarographic wave corresponding to the reduction of the nitro-groups (in the 2,4-dinitrophenylhydrazone formed) was followed in 0-1 N HCl and the first wave at —0T4 V measured. 

Since the latter are useful sources of pyridine derivatives, methods for their deoxygenation have been much studied. These compounds lack the oxidizing properties found with some amine oxides. Polarographic studies show that in acid media pyridine 1-oxide has a much lower reduction potential than oxides of tertiary amines with exocyclic nitrogen atoms -. The half-wave potentials are not useful guides to the abilities of the N-O bonds in pyridine oxides to take part in oxygen transfer reactions, and in 4-nitropyridine 1-oxide the nitro group is reduced first . 

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