Electroreduction Products Research Articles

AN ESR STUDY OF ELECTROCHEMICAL REDUCTION OF NITROBENZENE

By means of a highly sensitive electrolytic cell installed in the ESR cavity, the authors investi-gated in situ the kinetic behavior of the primary electroreduction product (a radical anion) in a sol-vent mixture of water and ethanol over a wide range of pH. For the first time they observed somefurther complex kinetic behaviors of the electroreduction process of nitrobenzene. Through a study ofthe behavior of the radical anion (φ-NO_2~-.) with variations of pH, concentration of nitrobenzene(φ-NO_2) and electroreduction potential, they advanced a reaction scheme of the electroreduction ofnitrobenzene and simulated the experimental curves in order to evaluate the kinetic parameters of thereaction steps concerned.

Electrochemical behaviour of the bisazo dye, Direct Red-81

The electroreduction of the bisazo dye, Direct Red-81, occurs at two azo groups at the dropping mercury electrode and at the pyrolytic graphite electrode. A comparison of the redox couple III a/III c observed in cyclic voltammetry with p-phenylenediamine indicated the formation of p-phenylenediamine as a product of electroreduction. The analysis of products at various pH's and potentials indicated that the 4 e −, 4 H + reduction of the first azo group occurs with cleavage of the α-naptholazo derivative and is followed by the 4 e −, 4 H + reduction of the second azo group in 4-amino-4-sulfoazobenzene.

Differential pulse polarographic behaviour of nitrate, nitrite and hydroxylamine

We have observed several differential pulse polarographic peaks in buffered or unbuffered solutions in the presence of ammonium and Yb(III) ions and compared these with the results on classical polarography for nitrate, nitrite, and hydroxylamine respectively. It was ascertained that the Yb(III) ion serving as multivalent cation may electrocatalyse the nitrate and nitrite waves quite adjacent to the reduction wave of Yb(III) itself on the one hand, while the electroreduction product Yb(III) may be reoxidized to Yb(III) to produce a kineiit wave, especially at higher concentrations of nitrate or nitrite on the other hand. The mechanism and electrode process of these waves have been studied and discussed.

252 - Electrochemical Studies on Trans- and Cis-Retinal and Bacteriorhodopsin

A study has been made of the polarographic behaviour, and the mechanism of electroreduction, of all- trans and 13- cis- retinals. Both compounds exhibit the same redox pattern of two successive one-electron additions. The initial step involves the simultaneous addition of an electron and a proton, with formation of a free radical, which then dimerizes. The electroreduction products resulting from the two reduction steps of all- trans retinal were identified by means of UV, IR and mass spectroscopy. Bacteriorhodopsin isolated from halobacteria was investigated in buffered aqueous medium by d.c. polarography. This gives a single polarographic wave with a pH-dependence of U 1 2 similar to that for the first reduction step of all- trans- and 13- cis- retinals.

Photochemically Reversible Dimer Electroreduction Product of 2-Oxopurine

Abstract The electrochemical reduction of 2-oxopurine in buffered aqueous medium was found to proceed via two successive one-electron additions. The initial one-electron step involves the addition of a proton, leading to formation of a free radical which rapidly dimerizes. At more negative potentials, reduction leads to formation of 1,6-dihydro-2-oxopurine. The product of reduction on wave I was isolated and identified by various spectroscopic techniques as the dimer 6,6′-bis-(1,6-dihydro-2-oxo-purine). In neutral aqueous medium this dimer reduction product (but not the product of reduction on wave II, 1,6-dihydro-2-oxopurine) underwent quantitative photochemical dissociation to the parent 2-oxopurine, with a quantum yield at 254 nm of 0.03. The dimer reduction product also quantitatively regenerated the parent monomer in an alkali-catalyzed reaction at room temperature. The proposed mechanism of the reduction reaction, and susceptibility of the reduction product to photodissociation, is compared with the corresponding behaviour of other purine, and pyrimidine, derivatives.

Electrochemically induced pyrimidine dimerization

A study has been made of the polarographic behaviour and the mechanisms of electroreduction of N-methyl derivatives of pyrimidone-2 and 4-methylthiouracils. One of the major electroreduction products of all the foregoing is a 6,6′-bis(3,6-dihydro-pyrimidone-2) dimer similar to that previously described as the major reduction product of the parent pyrimidone-2. The properties of the dimers are described, including their ability to undergo photodissociation to the parent pyrimidone-2 derivatives. The mechanisms of the electroreductions and their significance in relation to the photochemistry of some nucleic acids and their constituents is discussed.

Study of the kinetics of electrode processes by means of electrolysis with constant current. XII. A chemical change of the electroreduction product to a reversibly oxidizable substance

Study of the kinetics of electrode processes by means of electrolysis with constant current. XII. A chemical change of the electroreduction product to a reversibly oxidizable substance

Electrolytic Reductive Coupling: XV . Electroreductions of Aqueous Concentrated Solutions of Diethyl Maleate in the Presence of Sodium or Tetraethylammonium Cations

Concentrated solutions of diethyl maleate in dimethylformamide‐water containing sodium or tetraethylammonium p‐toluenesulfonate were electrolyzed at constant current. The yields of diethyl succinate and of tetraethyl butanetetracarboxylate were determined. At a given concentration of supporting cation and of bulk water less hydrodimer is formed in the presence of sodium than in the presence of tetraethylammonium cations. These results are related to previous suggestions concerning the influence of the degree of hydration of the supporting cations upon the nature of the electroreduction products.

Problems in the polarography of chromate

The mechanism of electroreduction of chromate was investigated by applying complexing agents and polyelectrolytes that bind trivalent chromium (the electroreduction product) thus affecting the current in the polarographic prewave. It was found that amounts of adsorbed polyelectrolytes so minute as to be insufficient to affect any preceding reactions, caused an increase in the polarographic current, until, under suitable conditions, the theoretical diffusion current could be recovered. Similar augmentation of the current was observed when agents that could solubilize the barely soluble layer possibly formed by the products of the electrode process, were added. It was concluded that the thin layer formed near the surface is responsible for reducing the polarographic current in the prewave. Its impeding effect is a function of its structure, thickeness and charge.