The Electroreduction of Substituted Benzofurazans

1972 ◽  
Vol 50 (2) ◽  
pp. 263-269 ◽  
Author(s):  
W. R. Fawcett ◽  
P. A. Forte ◽  
R. O. Loutfy ◽  
J. M. Prokipcak
Keyword(s):  
Electron Transfer ◽  
Molecular Orbital ◽  
Double Layer ◽  
Rate Constants ◽  
Hyperfine Splitting ◽  
Platinum Electrode ◽  
Hückel Theory ◽  
Layer Effect ◽  
Standard Rate ◽  
Anion Radicals

The electroreduction of 4- and 5-substituted benzofurazans was investigated at a platinum electrode in acetonitrile. Standard potentials for the reactions were linearly related to the energy of the lowest vacant molecular orbital as estimated by Hückel theory. Standard rate constants for electron transfer decreased as standard potentials in the series became more cathodic. This decrease is attributed to a double layer effect. No correlation was obtained between standard rate constants and observed hyperfine splitting constants for the anion radicals.

Unusual Influence of the Temperature on the Standard Rate Constants of Charge Transfer for the Eu(III)/Eu(II) Redox Couple in Chloride-Bromide Melts

2007 ◽  
Vol 62 (7-8) ◽  
pp. 445-451 ◽  
Author(s):  
Sergey A. Kuznetsov ◽  
Marcelle Gaune-Escard
Keyword(s):  
Electron Transfer ◽  
Cyclic Voltammetry ◽  
Charge Transfer ◽  
Kinetic Parameters ◽  
Rate Constants ◽  
Redox Reaction ◽  
Electron Transfer Mechanism ◽  
Standard Rate ◽  
Standard Rate Constant ◽  
The Eu

The influence of bromide ions and temperature on the standard rate constants of the Eu(III)/Eu(II) redox reaction was determined. Cyclic voltammetry was used for the calculation of the kinetic parameters. It was shown that in NaCl-KCl (equimolar mixture)-NaBr (15 wt%)-EuCl3 melts increase of the temperature from 973 K up to 1023 K leads to a drastical decrease of the standard rate constant ks for the Eu(III)/Eu(II) redox reaction. This unusual influence of the temperature on the ks value was explained by a change of the electron transfer mechanism. It is suggested that at 1023 K another mechanism becomes dominant - the transfer of electrons through dissolved bromine in the melt. Bromine appeared in the melt due to the decomposition of chloride-bromide or bromide complexes of Eu(III), and the concentration of bromine in the melt increased with the growth of temperature.

Comparison of Gold and Platinum Electrode Responses in Activated Sludge

1993 ◽  
Vol 28 (11-12) ◽  
pp. 473-480
Author(s):  
A. Heduit ◽  
B. Martin ◽  
I. Duchamp ◽  
D. R. Thevenot
Keyword(s):  
Electron Transfer ◽  
Activated Sludge ◽  
Gold Electrode ◽  
Platinum Electrode ◽  
Electrochemical Determination ◽  
Exchange Current ◽  
Experimental Conditions ◽  
Equilibrium Exchange ◽  
Prolonged Contact ◽  
Current Densities

Gold and platinum were compared to ascertain how they expressed a stabilized potential in activated sludge. The comparison was based on electrochemical determination of the electron transfer rate (i.e. equilibrium exchange current density) and recording of potentials against time. When both metals are treated in the same way, platinum gives equilibrium exchange current densities approx. 10 times higher than gold, both in aerated activated sludge and in treated water. For platinum, the equilibrium exchange current densities range from 0.1 to 0.25 µA/cm2 immediately after polishing and decrease during prolonged contact with activated sludge subjected to alternating aeration/anoxia sequences. The lower kinetics of electron transfer on gold go together with significant differences in response:- In an aerobic medium a gold electrode potential is lower than that of a platinum electrode. In a strongly anaerobic medium, the reverse is true. Consequently, the amplitude of the potential variation between aerobic and anaerobic media is smaller for gold than for platinum. Under our experimental conditions this amplitude was approx 350 mV for gold and 850 mV for platinum.- The slopes of the linear relationships between potential and pH or potential and the logarithm of the dissolved oxygen concentration are two or three times greater for platinum than for gold. Although the values obtained with platinum electrodes cannot represent a veritable equilibrium state, the platinum electrode zero-current potential would seem to be far more sensitive to variations in the medium than that of the gold electrode; it is, therefore, more suitable for use in activated sludge.

The Effect of p-Toluidine on the Two-Step Electroreduction of Zn(II) in Water-Methanol and Water-Dimethylformamide

1999 ◽  
Vol 64 (4) ◽  
pp. 585-594 ◽  
Author(s):  
Barbara Marczewska
Keyword(s):  
Electron Transfer ◽  
Binary Mixtures ◽  
Rate Constant ◽  
Rate Constants ◽  
Electrode Surface ◽  
Mercury Electrode ◽  
Forward Rate ◽  
Solvent Molecules ◽  
Activated Complex

The acceleration effect of p-toluidine on the electroreduction of Zn(II) on the mercury electrode surface in binary mixtures water-methanol and water-dimethylformamide is discussed. The obtained apparent and true forward rate constants of Zn(II) reduction indicate that the rate constant of the first electron transfer increases in the presence of p-toluidine. The acceleration effect may probably be accounted for by the concept of the formation on the mercury electrode an activated complex, presumably composed of p-toluidine and solvent molecules.

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