Nitro groups, mercury electrode

Controlled-potential coulometry also can be applied to the quantitative analysis of organic compounds, although the number of applications is significantly less than that for inorganic analytes. One example is the six-electron reduction of a nitro group, -NO2, to a primary amine, -NH2, at a mercury electrode. Solutions of picric acid, for instance, can be analyzed by reducing to triaminophenol. 

Conditions for reducing pyridine N-oxides to pyridines have been worked out1S4>. In general, this reaction proceeds with good yields in 20 % aqueous sulfuric acid under constant current conditions at mercury or lead electrodes, provided there is no easily reducible group present in the molecule (e.g., the nitro group). 

Nitro compounds are reduced by amalgams in a manner similar to that found at a mercury electrode. Aliphatic nitro compounds [75] are thus reduced to alkylhydroxyla-mines by NH4(Hg), whereas aromatic nitro compounds may form amines, hydrazo, azo, or azoxy compounds and even nitroso compounds [75,76]. Aliphatic, tertiary vicinal dini-tro compounds may be reduced to alkenes by elimination of the nitro groups as nitrite [77]. 

In the case of the A -nitrosamines, the easy electrochemical reduction of the nitro group has allowed the development of direct electrochemical methods for their determination. The reductive amperometric determination has been described using dropping mercury electrodes or hanging mercury drop electrodes. Likewise the oxidative amperometric determination using... 

The nitro group, having a strong tendency to absorb electrons, is reversibly reduced at a dropping mercury electrode. The reduction usually takes place in two steps, to amine via... 

The analytical method described here is based on the results obtained with dc polaro-graphy and differential pulse polarography at dropping mercury electrode. The detection and determination of the drug metronidazole (I) continues to be of interest, particularly because of its status as a drug of abuse. The nitro group in metronidazole is useful in electrochemical analysis. 

The basis of the application of polarography to the chemistry of explosives are the reducibility of the nitro-group at the dropping mercury electrode to hydroxylamino or amino derivatives, of organic nitrates in which the N-0 bond is reduced to form the nitrate ion and the possibility of the determination of amines. 

Compared to oxidation, EC reduction has not been not widely used with HPLC. Reducible groups include hydroxylamines, nitrosamines, -oxides, peroxides, quinones, aromatic nitro compounds and disulfides. The antibiotic chloramphenicol can be assayed in blood by EC reduction using a mercury film electrode. ... 

A pendent mercury drop electrode has been used to reduce the 4,5-azomethine group in 1,4-benzodiazepines There were additional contributions from partial reduction of nitro moieties, as in nitrazepam, and A -oxides, as in chlordiazepoxide. The 5-lipoxygenase inhibitor methyl 2-[(3,4-dihydro-3,4-dioxo-l-naphthalenyl) aminojbenzoate (CGS 8515) has been measured in ethyl acetate extracts of plasma from animals treated with the drug using an ODS-modified silica column with methanol-aq. acetate buffer (0.15 mol L, pH 4.5) (60 -f 40) as eluent and EC... 

The redox behaviour has been determined, in acetonitrile solution at a mercury and platinum electrode, of 3,4-disubstituted and fused 1,2,5-thiadiazoles, including 2,1,3-benzothiadiazoles. All ring systems and their derivatives are reversibly reduced initially in a one-electron step to their radical anion, but nitro- and bromo-derivatives are reduced preferentially at the substituent group. ... 

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