Polarography of 4-nitrodiphenylamine (DPA) in methanol-water mixtures⋆

Electrochemical behaviour of 2-nitrobenzidine in N,N-dimethylformamide

Abstract: The electrochemical reduction of 2-nitrobenzidine (I) has been investigated in N,N-dimethylformamide solutions. Two well-defined polarographic waves in the ratio 1:3 were obtained. The first wave was found to be a reversible, diffusion-controlled, single electron wave while the second was the result of a diffusion-controlled, irreversible, three-electron process with chemical complications. The nitro and nitroso anion radical intermediates of I formed during the CPE experiments were detected by an ESR technique and confirmed later by cyclic voltammetry. The “current oscillations” observed in the cyclic voltammograms of I are discussed. An eece-type of sequence is suggested for I reduction leading to the formation of 2-hydroxylaminobenzidine.

Electrochemical reduction of 2,4,6-trinitro diphenylamine in buffered and unbuffered methanolic solutions

Abstract: The polarographic reduction of 2,4,6-trinitro diphenylamine was found to give three waves of nearly equal height in all pH regions in buffered solutions and also in unbuffered methanol—water mixtures The waves were shown to be diffusion-controlled and irreversible on the basis of the usual criteria Controlled-potential electrolysis at the limiting region of the third wave gave n app = 18 and thus it was shown that n app = 6 for each of the waves It was concluded that each of the nitrogroups in the compound is reduced to the corresponding amino group, the nitro groups ortho to the  NH group in the parent compound being reduced first followed by the other Cyclic voltammetric experiments in unbuffered solutions gave evidence for a new redox system which was attributed to amine-quinone diimine intermediate couple It was inferred that each of the nitro groups in the compound is reduced to the amino function via this intermediate

Electrochemical reduction of 2,3'-dinitrobenzidine in buffered aqueous methanol

Abstract: 2,2′-dinitrobenzidine (2,3′-DNB) gives a single diffusion-limited irreversible polarographic wave in buffered aqueous methanol. Microcoulometric experiments indicate a transfer of ten electrons in the reduction and cyclic voltammetric studies show direct proof for the existence of a nitroso intermediate. Based on the results obtained, a suitable mechanism is proposed for the reduction of 2,3′-DNB in buffered methanolic solutions.

Polarographic behaviour of 2,4-dinitrodiphenylamine in amphiprotic media

Abstract: Two six-electron diffusion-controlled irreversible waves are obtained for the polarographic reduction of 2,4-dinitrodiphenylamine (DPA) in buffered and unbuffered media in all compositions of methanol-water mixtures. Based on the polarographic and coulometric data, it is suggested that each of the nitro groups is reduced to the corresponding amine in a single stepvia the diimine intermediate to give 2,4-diamino DPA as the final product. The influence of various factors such as structure of the depolariser, pH and composition of methanol on the reduction of the compound is also discussed.

Electrochemical reduction of 2-nitrobenzidine in methanol-water mixtures

Abstract: The electroreduction of 2-nitrobenzidine (2-NB) in buffered methanol-water mixtures in the composition range 20–80% (v/v) and pH range 2.80–12.00 gave a single six-electron diffusion-controlled irreversible wave. On the basis of the results obtained, a diphenoquinone-diimine intermediate is suggested in the mechanism of 2-NB reduction in methanol-water mixtures.

Strongly basic systems: iii. the h− function for various solvent systems

Abstract: The Hammett acidity function concept has been used to determine simultaneously the pKa values of 24 substituted anilines and diphenylamines and the H− values of various solvent systems. The following solvent systems were examined (the most basic H− value obtained for each is shown in parentheses): water containing benzyltrimethylammonium hydroxide (16.20); pyridine–water containing tetramethylammonium hydroxide (18.91); sulpholane–water containing tetramethylammonium hydroxide (19.18); dimethyl sulphoxide–water containing tetramethylammonium hydroxide (18.61); water containing lithium hydroxide (14.31).In addition to these results adjustments have been made to previously published scales for hydrazine–water (15.08) and ethylenediamine–water (15.48).

Studies of the polarographic and coulometric behaviour of aromatic nitro-compounds: I. Nitrobenzene in ethanol

Abstract: Summary A detailed polarographic (a.c. and d.c.) and coulometric investigation of nitrobenzene has been made at various pH values in the presence of different concentrations of ethanol. Below pH 4.7, two waves are apparent but above this pH, the second wave does not appear. Coulometric evidence indicates that the first and second waves correspond to the four-and two-electron processes, respectively. The coulometric method was not applicable in sodium hydroxide and sodium acetate solutions. When the diffusion coefficients (from the diaphragm cell) are used in the Ilkovic equation, no reliable conclusions can be reached for the number of electrons involved in the reduction process in alkaline solutions. The a.c. polarographic method gives evidence for the formation of species such as: C 6 H 5 NO 2 H 2 2+ , C 6 H 5 NO 2 − and C 6 H 5 NO 2 2− . Analysis of d.c. polarographic data by Delahay's treatment of irreversible waves, indicates that the number of electrons involved in the rate-determining step is 2. In sodium hydroxide solutions, however, the first main wave is split indicating more than one rate-determining step. The results presented in this paper indicate that the first wave in the reduction of nitrobenzene is a four-electron process at all pH values. The second wave, which appears below pH 4.7, corresponds to a two-electron process irrespective of wave heights. The difference in the a.c. polarographic behaviour in acid and alkaline solutions has given evidence for the formation of species like C 6 H 5 NO 2 H 2 , C 6 H 5 NO 2 − , and C 6 H 5 NO 2 2− .

The H_ acidity function in ethylene and propylene glycols

Abstract: The H_ acidity function has been determined for solutions of sodium and lithium glycollates in ethylene and propylene glycols with a series of nitrodiphenyl-amines as indicators. The validity of the H_ function has been established in basic solutions of ethylene glycol but not in propylene glycol. Equilibrium constants have been reported for the ionization of some nitrodiphenylamines in basic solutions of the two glycols.