Polarography of aromatic azo compounds. II. Kinetic study of the disproportionation of 4-Aminohydrazobenzene-4'-sulphonic acid

1965 ◽  
Vol 18 (5) ◽  
pp. 619 ◽  
Author(s):  
TM Florence
Keyword(s):  
Mercury Electrode ◽  
Sulphonic Acid ◽  
Azo Compounds ◽  
Rate Determining Step ◽  
A Value ◽  
Controlled Potential Electrolysis ◽  
Mercury Cathode ◽  
Dropping Mercury Electrode ◽  
Controlled Potential ◽  
Aromatic Azo Compounds

Solutions of 4-aminoazobenzene-4'-sulphonic acid were reduced by controlled potential electrolysis at a mercury cathode, and the disproportionation rate of the hydrazo derivative determined by spectrophotometry and polarography. The kinetics of the reaction were found to be first-order with respect to both hydrazo and hydrogen ion concentrations, although the overall reaction involved two molecules of the hydrazo compound. In the rate law, -d[hydrazo]/dt = k[H+][hydrazo], k was calculated to be (5.0�0.3) x 106 l. mole-1 sec-1 from spectrophotometric measurements, and (4.5�0.5) x 106 l. mole-1 sec-1 by polarography (25�). A reaction mechanism based on a rate determining step involving a quinonediimine intermediate has been proposed. Another value of the disproportionation rate constant was obtained from the effect of drop time on the limiting currents of 4-aminoazobenzene-4'-sulphonic acid at the dropping mercury electrode. A value of k of (22�5) x 106 l. mole-1 sec-1 was determined by this method. Reasons for the discrepancy between this result, and those found by direct measurement, are discussed.

Polarography and coulometry of Rh(III) in a pyridine – pyridinium chloride electrolyte

1969 ◽  
Vol 47 (12) ◽  
pp. 2123-2135 ◽  
Author(s):  
Leslie E. Johnston ◽  
John A. Page
Keyword(s):  
Mercury Electrode ◽  
Normal Wave ◽  
Bulk Solution ◽  
Pyridinium Chloride ◽  
Chloride Electrolyte ◽  
Catalytic Wave ◽  
Controlled Potential Electrolysis ◽  
Dropping Mercury Electrode ◽  
Controlled Potential ◽  
Electron Reduction

The polarography and coulometry of Rh(III) has been studied in an aqueous pyridine–pyridinium chloride–sodium chloride electrolyte at pH 5.30 and ionic strength 0.30 M at 25.0 °C. Two distinct types of polarographic behavior were noted as the total Py concentration was varied between 0.05 and 0.45 M, a "normal" wave with E1/2 of −0.43 V vs. a standard calomel electrode, and a second catalytic wave which under some conditions masked the normal wave.For both types of behavior, controlled potential electrolysis gave a well-defined two electron reduction but there was a definite H+ consumption in the electrolyses. It is postulated that hydride species are involved in the reduction according to the scheme[Formula: see text]surface reaction at dropping mercury electrode[Formula: see text]slow, bulk solution in controlled potential electrolysis

Polarography as an Analytical Tool

1964 ◽  
Vol 47 (1) ◽  
pp. 21-27
Author(s):  
John K Taylor
Keyword(s):  
Mercury Electrode ◽  
Selective Extraction ◽  
Analytical Tool ◽  
Diffusion Control ◽  
Oscillographic Polarography ◽  
Dropping Mercury Electrode ◽  
Anodic Stripping ◽  
Controlled Potential ◽  
Solid Electrodes ◽  
Practice Methods

Abstract Polarography is a useful analytical tool for determining many substances in solutions at small concentrations, and is frequently applied to analysis of minor constituents. Conventional polarography employs a dropping mercury electrode, can measure solutions in concentrations ranging from 10-2 to 10-5M, and requires only a few tenths of ml for analysis. Because of the difficulty of obtaining diffusion control in practice, methods are comparative and involve empirical calibrations with standard solutions. Practical tolerances have been worked out to insure that results are reliable to 2 relative per cent. Interferences have been lessened by several means, e.g., complexing, separation by electrolysis at controlled potential, selective extraction, and improvements in circuitry to permit use of relatively dilute supporting electrolytes. Modified polarographic methods include solid electrodes, derivative polarography, differential polarography, cathode ray polarography, anodic stripping polarography, and oscillographic polarography.

Electrochemical investigation of reduction of mercury complexes of 2-aminocyclopentene-1-dithiocarboxylic acid and some of its derivatives at mercury electrodes

1996 ◽  
Vol 74 (1) ◽  
pp. 95-102 ◽  
Author(s):  
A. Safavi ◽  
M. B. Gholivand
Keyword(s):  
Electrochemical Techniques ◽  
Mercury Electrode ◽  
Elemental Mercury ◽  
Redox Processes ◽  
Electrochemical Investigation ◽  
Controlled Potential Electrolysis ◽  
Mercury Complexes ◽  
Controlled Potential ◽  
Mercury Electrodes ◽  
Complementary Study

Electrochemical techniques of polarography, cyclic voltammetry, and controlled potential electrolysis at mercury electrodes have permitted a detailed investigation of the reduction reactions associated with mercury 2-aminocyclopentene dithiocarboxylate complexes, Hg(ACD)2, in dimethyl sulphoxide (DMSO). As a complementary study, the electrochemistry of the ligands themselves was investigated in DMSO solutions and at mercury electrodes. The lability of mercury(II) complexes and their rapid interaction with elemental mercury strongly influence the nature of the redox processes observed at mercury electrodes. Reduction of Hg(ACD)2 at a mercury electrode occurs in an overall two-electron step as:[Formula: see text]although mercury(I) is implicated as an intermediate. Key words: reduction, electrochemical techniques, mercury complexes.

The electrochemical oxidation of 2,5-dihydroxybenzoic acid on a mercury electrode in aqueous solutions

1986 ◽  
Vol 64 (1) ◽  
pp. 11-14 ◽  
Author(s):  
D. Sazou ◽  
N. Papadopoulos
Keyword(s):  
Oxidation Process ◽  
Electrochemical Behaviour ◽  
Mercury Electrode ◽  
The Other ◽  
Hanging Mercury Drop Electrode ◽  
Dihydroxybenzoic Acid ◽  
Current Function ◽  
Controlled Potential Electrolysis ◽  
Controlled Potential ◽  
Ph Range

The electrochemical behaviour of 2,5-dihydroxybenzoic acid (2,5-DHBA) has been studied in the pH range 5.5–12.7 at a hanging mercury drop electrode (HMDE). Voltammograms show the existence of one reversible wave of 2,5-DHBA governed by diffusion conditions. In the oxidation process a two-electron transfer takes place, as shown by the controlled potential electrolysis. From the calculation of the voltammetric parameters (peak width Ep − Ep/2, peak current function [Formula: see text]and from the other experimental data, a mechanism for the overall reaction in two different pH ranges, 5.5–9.5 and 9.5–12, is proposed.

scholarly journals Reduction of Cd(II) Ions in the Presence of Tetraethylammonium Cations. Adsorption Effect on the Electrode Process

Electrochem ◽  
2021 ◽  
Vol 2 (3) ◽  
pp. 415-426
Author(s):  
Juan Torrent-Burgués
Keyword(s):  
Mercury Electrode ◽  
Reduction Process ◽  
Inhibitory Effect ◽  
Electrode Process ◽  
Adsorption Effect ◽  
A Value ◽  
Half Wave ◽  
Dropping Mercury Electrode ◽  
Electrode Coverage ◽  
Isotherm Equations

The effect of the adsorption of tetraethylammonium (TEA) cations, which present both ionic and organic characteristics, on the reduction of Cd(II) ions have been studied from dc and ac measurements at the dropping mercury electrode. The resistance to the charge transfer (Rct) and Warburg coefficient (σ) parameters have been determined through impedance measurements. Thus, the global velocity constant has been obtained. The reduction process of Cd(II) in perchloric media is reversible and is affected by the adsorption of TEA cations, especially at high TEA concentrations. Values of E1/2, half wave potential, and DO, diffusion coefficient, obtained from both dc and ac measurements agree. The velocity constants show a decrease as TEA concentration increases, with values ranging from 0.6 to 0.01 cm·s−1. The inhibitory effect of TEA adsorption on the electrode process and the relationship between electrode coverage, θ, and velocity constants, K, using several isotherm equations, have been discussed. The best fit was obtained with the equation K = 0K(1 − θ)a with an a value close to three, indicating a blocking effect and electrostatic repulsion due to TEA.

Mechanism of 2-quinizarinsulphonic acid reduction on a mercury electrode

1981 ◽  
Vol 59 (8) ◽  
pp. 1201-1204 ◽  
Author(s):  
F. Capitan ◽  
A. Guiraum ◽  
J. L. Vilchez
Keyword(s):  
Mercury Electrode ◽  
Sulphonic Acid ◽  
Kinetically Controlled ◽  
Diffusion Controlled ◽  
Dropping Mercury Electrode ◽  
Reaction Orders ◽  
Second Wave ◽  
Acid Reduction

The reduction of the 1,4-dihydroxyanthraquinone-2-sulphonic acid (quinizarinsulphonic acid) at a dropping mercury electrode has been investigated. The reduction takes place in two monoelectronic steps and show E1/2 values vs. sce (E1/2)1 = −0.380 V and (E1/2)2 = −1.045 V at pH 4.60. The first wave is diffusion controlled, while the second wave is kinetically controlled. The reagent captures one electron and one proton to form the semiquinonic system. The semiquinone is dimerized. The dimer captures one electron and one proton, per molecule, to form the hydroquinone. The reaction orders, together with Tafel's slopes, have been calculated.

The electrochemistry and the kinetics of the formation of ruthenium(II) nitrogen complexes

1968 ◽  
Vol 46 (16) ◽  
pp. 2743-2747 ◽  
Author(s):  
I. J. Itzkovitch ◽  
John A. Page
Keyword(s):  
Mercury Electrode ◽  
Reduction Wave ◽  
Base Electrolyte ◽  
Mercury Cathode ◽  
Standard Calomel Electrode ◽  
Oxidation Wave ◽  
Dropping Mercury Electrode ◽  
Aqueous Base ◽  
Electron Reduction ◽  
Ar Gas

Electrolysis at a mercury cathode controlled at −0.50 V (vs. standard calomel electrode s.c.e.) in a H2SO4–K2SO4 electrolyte with pH of 2.6 and saturated with Ar gas has been used to prepare RuII–(NH3)5X. The reaction of this species with N2 in the aqueous base electrolyte at 26 °C has been studied and found to follow the equations:[Formula: see text]In base electrolyte saturated with N2 at 1 atm (CN2 ≈ 6 × 10−4 M) the value of the apparent first order constant, k′m is 4.4 × 10−5 s−1 and the value of kd is 4.2 × 10−2 1 mole−1 s−1.The electrochemistry of the various ruthenium species was also investigated in the H2SO4–K2SO4 electrolyte. At the dropping mercury electrode, RuIII (NH3)5Cl gave a well-defined one electron reduction wave with E1/2 = −0.27 V; RuII (NH3)5X gave a well-defined one electron oxidation wave with E1/2 = −0.25 V. The nitrogen complexes gave oxidation waves at a rotating platinum microelectrode, the monomer with E1/2 = +0.72 V and the dimer with E1/2 = +0.78 V.

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