Mechanism of L-ascorbic acid oxidation and dehydro-L-ascorbic acid reduction on a mercury electrode. I. Acid medium

1977 ◽  
Vol 55 (15) ◽  
pp. 2799-2806 ◽  
Author(s):  
Juan José Ruiz ◽  
Antonio Aldaz ◽  
Manuel Dominguez
Keyword(s):  
Electron Transfer ◽  
Ascorbic Acid ◽  
Oxidation Process ◽  
Mercury Electrode ◽  
Oxidation Mechanism ◽  
Limiting Current ◽  
Acid Oxidation ◽  
Rate Determining Step ◽  
Reaction Orders ◽  
Electron Transfers

A polarographic study of the oxidation mechanism of L-ascorbic acid and of the reduction mechanism of dehydro-L-ascorbic acid was carried out in an acid medium.For L-ascorbic acid, the oxidation process involves a two electron transfer and obeys the overall reaction[Formula: see text]The polarographic curve shows that the limiting current is governed by diffusion. On the rising portion of the wave, the two electron oxidation process consists of two consecutive one electron transfers, the second being the rate determining step (rds). The reaction orders, together with the Tafel slopes, were calculated.The reduction of dehydro-L-ascorbic acid at the limiting current is kinetically controlled and involves a two electron transfer. The reaction kinetic pathways were studied and the reaction orders and Tafel slope were calculated. It is deduced that, for low overvoltages, the second one electron transfer is the rate determining step.

Mechanism of L-ascorbic acid oxidation on a mercury electrode. II. Basic medium

1978 ◽  
Vol 56 (11) ◽  
pp. 1533-1537 ◽  
Author(s):  
Juan José Ruiz ◽  
Antonio Aldaz ◽  
Manuel Dominguez
Keyword(s):  
Electron Transfer ◽  
Ascorbic Acid ◽  
Mercury Electrode ◽  
Oxidation Mechanism ◽  
Limiting Current ◽  
Basic Medium ◽  
Acid Oxidation ◽  
Acid Media ◽  
Rate Determining Step ◽  
Reaction Orders

A polarographic study of the oxidation mechanism of L-ascorbic acid is carried out in a basic medium and two oxidation waves are observed.An analysis of these waves shows that the limiting current is governed by diffusion and that in each reaction a two electron transfer takes place. On the rising portion of the waves, the oxidation process consists of two consecutive one electron transfers. In the first wave, the second transfer is the rate determining step, whilst in the second wave, a chemical stage subsequent to the second electron transfer is the rate determining step. The reaction orders, together with the Tafel slopes, are calculated.The oxidation mechanism of this acid in basic media is different from that in acid media.

Some Aspects of the Electroreduction of Niazid to Nicotinamide on Mercury Electrodes in Acidic Media

1992 ◽  
Vol 57 (9) ◽  
pp. 1836-1842 ◽  
Author(s):  
Rafael Marín Galvín ◽  
José Miguel Rodríguez Mellado
Keyword(s):  
Electron Transfer ◽  
Essential Role ◽  
Uv Spectroscopy ◽  
Acidic Media ◽  
Polarographic Wave ◽  
Rate Determining Step ◽  
Tafel Slopes ◽  
Reaction Orders ◽  
Mercury Electrodes ◽  
The Waves

The electroreduction of niazid on mercury electrodes has been studied in acidic media (pH < 6). Tafel slopes and reaction orders were obtained at potentials corresponding to the foot of the first polarographic wave. On the basis of both polarographic and voltammetric results it has been shown that the waves appearing at more negative potentials correspond to the reduction of nicotinamide. Protonation of niazid plays an essential role in its reduction and pK values of 1.4, 3.2 and 11.5 were obtained by UV spectroscopy. The process corresponding to the first wave is irreversible, being the second one-electron transfer the rate determining step. Above pH 4 the process is complex due to the overlapping of the waves caused by the occurrence of protonation reactions.

Electrochemical reduction of the nickel(II) dithiocarbamates at the mercury electrode

1976 ◽  
Vol 29 (6) ◽  
pp. 1191 ◽  
Author(s):  
TH Randle ◽  
TJ Cardwell ◽  
RJ Magee
Keyword(s):  
Electron Transfer ◽  
Chemical Reaction ◽  
Mercury Electrode ◽  
Electrode Reaction ◽  
Reduction Mechanism ◽  
Ece Mechanism ◽  
Controlled Potential ◽  
Nickel Species ◽  
Electron Transfers ◽  
Potential Conditions

The reduction mechanism of a series of nickel(11) dithiocarbamates has been investigated in dimethyl sulphoxide at the mercury electrode. Under controlled-potential conditions, the reduction proceeds initially by an ECE mechanism (electron transfer-chemical reaction-electron transfer) with n = 1 for both electron transfers. The chemical reaction involves a dissociation to produce a nickel species more easily reduced than the nickel(11) dithiocarbamate. However, for some derivatives, rate constants for the chemical step show a time dependence, at electrolysis times above 5 s, consistent with an ECCE mechanism of the type where the product of the first chemical reaction reacts further to produce a nickel species more difficult to reduce than nickel(11) dithiocarbamate. Exhaustive reduction of nickel(11) diethyldithiocarbamate at the mercury-pool electrode gave non-integral n-values (2 > n > 1) consistent with the ECCE mechanism, and demonstrated that the product of the second chemical reaction is reoxidized to nickel(11) diethyldithiocarbamate by oxygen. The nature of the complete electrode reaction suggests a metal-centred reduction.

A theoretical study on the oxidation mechanism of triose reductone in reference to L-ascorbic acid

1986 ◽  
Vol 64 (2) ◽  
pp. 360-365 ◽  
Author(s):  
Yasuo Abe ◽  
Hideo Horii ◽  
Setsuo Taniguchi ◽  
Shinichi Yamabe ◽  
Tsutomu Minato
Keyword(s):  
Ascorbic Acid ◽  
Functional Group ◽  
Theoretical Study ◽  
Oxidation Process ◽  
Gradient Methods ◽  
Vibrational Analysis ◽  
Oxidation Mechanism ◽  
Basis Set ◽  
Carbonyl Groups ◽  
Intermediate Species

The oxidation of triose reductone H—CO—C(OH)=C(OH)—H (which has the same functional group as L-ascorbic acid) to dehydroreductone is investigated by abinitio molecular orbital computations. The geometries of the substrate, oxidized product, and of six possible intermediate species are optimized by gradient methods at the STO-3G basis set level. All the species are found to be planar and stable molecules by the vibrational analysis. The most possible oxidation route is shown to consist of four steps. The combination of the enediol and carbonyl groups in the deprotonated molecule 2 gives an effective π conjugation for the electron removal. The oxidation process of L-ascorbic acid is discussed on the basis of the results for triose reductone.

scholarly journals Precise manipulation of electron transfers in clustered five redox sites

2021 ◽  
Author(s):  
Hitoshi Izu ◽  
Mio Kondo ◽  
Masaya Okamura ◽  
Misa Tomoda ◽  
Sze Koon Lee ◽  
...  
Keyword(s):  
Electron Transfer ◽  
Metal Ions ◽  
Metal Complexes ◽  
Oxidation Process ◽  
Metal Centre ◽  
Spectroscopic Investigations ◽  
Synthetic Strategy ◽  
Redox Sites ◽  
Electron Transfers

Electron transfers in multinuclear metal complexes are the origin of their unique functionalities both in natural and artificial systems. However, electron transfers in multinuclear metal complexes are generally complicated, and predicting and controlling these electron transfers is extremely difficult. Herein, we report the precise manipulation of the electron transfers in multinuclear metal complexes. The development of a rational synthetic strategy afforded a series of pentanuclear metal complexes composed of metal ions and 3,5-bis(2-pyridyl)pyrazole (Hbpp) as a platform to probe the phenomena. Electrochemical and spectroscopic investigations clarified the overall picture of the electron transfers in the pentanuclear complexes. In addition, unique electron transfer behaviours, in which the reduction of a metal centre occurs during the oxidation of the overall complex (reduction-upon-oxidation process), were discovered. We also elucidated the two dominant factors that determine the manner of the electron transfers. Our results provide comprehensive guidelines for interpreting the complicated electron transfers in multinuclear metal complexes.

Kinetic studies of electron-transfers between the mono- and dinegative ions of anthracene and 1,1-diphenyl ethylene

1965 ◽  
Vol 288 (1413) ◽  
pp. 224-239 ◽  
Keyword(s):  
Electron Transfer ◽  
Equilibrium Constants ◽  
Kinetic Studies ◽  
Side Reactions ◽  
Fast Process ◽  
Rate Determining Step ◽  
Self Consistent ◽  
Equilibrium Data ◽  
Rapid Equilibrium ◽  
Electron Transfers

Following the previously described study of the reaction of sodium anthracene, A., with 1,1- diphenyl ethylene, D, giving the sodium salt of the dimeric dianion, -C(Ph) 2 • CH 2 . CH 2 C(Ph) - 2 , nameIy 2A−. + 2D → 2A + − DD − we investigated now the reaction of disodium anthracene, A 2~ with D. It was shown that this extremely fast process produces a mixed dimer ~AD~, which decomposes reversibly into J7 The virtually irreversible dimerization of D7 into ~DD~ leads to complete decomposition of ~AD~ into AT* + ~DD~. The kinetic studies of these processes allowed us to evaluate the relevant rate and equilibrium constants and forced us to reconsider the results of the previous study. The previously proposed mechanism of conversion of A~ + D into A + ~DD~ was found to be correct, namely A* +D A+D* (rapid equilibrium), (i) D ^+ D --> DD• (rate determining step), (2) ~DD- + A~ --> ~DD~ (rapid electron transfer). (3) In addition, side reactions, A^ + A A 2~ + A, (4) A 2~ + D ~AD~, (5) -A D - *± A^+DT (6) form a small amount of the transient mixed dimer ~AD~. This transient was erroneously identified in the previous study as the monomeric radical-ion, and this mistake led to incorrect values of K l9 k2 and I£dig8>> DD~ 2D~, ...(I£di8s.). The corrected results derived from the present studies are K x « 10~7, k2 = 800 1. mole-1 s-1, Jfdi8S> « 10~15 mole/1. The scheme was proved to be self-consistent, and the value K x was confirmed by the potentiometric and equilibrium data.

A chronoamperometric study of the oxidative nucleation of niazid and isoniazid on mercury electrodes in basic solutions

2011 ◽  
Vol 76 (6) ◽  
pp. 755-762
Author(s):  
Mercedes Ruiz Montoya ◽  
Sara Pintado ◽  
José Miguel Rodríguez Mellado
Keyword(s):  
Electrode Surface ◽  
Oxidation Product ◽  
Oxidation Process ◽  
Mercury Electrode ◽  
Oxidation Mechanism ◽  
Electron Process ◽  
Basic Solutions ◽  
Mercury Electrodes

Using chronoamperometric measurements at pH 12 it is shown that the oxidation mechanism of niazid adsorbed on the mercury electrode changes with respect to the mechanism reported in the literature for the electrooxidation of the molecules reaching the electrode by diffusion. A compact monolayer of niazid molecules is formed on the electrode surface, being the hydrazide oxidized through a two-electron process. The oxidation product is not able to dissociate a H+ ion, and the oxidation process does not proceeds beyond. For isoniazid the monolayer never becomes compact.

Marcus-Hush Theory Revealed by Electron Tunneling Through Hexagonal Boron Nitride

2019 ◽  
Author(s):  
Matěj Velický ◽  
Sheng Hu ◽  
Colin R. Woods ◽  
Peter S. Toth ◽  
Viktor Zólyomi ◽  
...  
Keyword(s):  
Electron Transfer ◽  
Boron Nitride ◽  
Electron Tunneling ◽  
Hexagonal Boron Nitride ◽  
Large Body ◽  
Liquid Solution ◽  
Limiting Current ◽  
Electron Transfer Rate Constant ◽  
Electrochemical Parameters ◽  
Voltammetric Measurements

Marcus-Hush theory of electron transfer is one of the pillars of modern electrochemistry with a large body of supporting experimental evidence presented to date. However, some predictions, such as the electrochemical behavior at microdisk electrodes, remain unverified. Herein, we present a study of electron tunneling across a hexagonal boron nitride barrier between a graphite electrode and redox levels in a liquid solution. This was achieved by the fabrication of microdisk electrodes with a typical diameter of 5 µm. Analysis of voltammetric measurements, using two common redox mediators, yielded several electrochemical parameters, including the electron transfer rate constant, limiting current, and transfer coefficient. They show a significant departure from the Butler-Volmer behavior in a clear manifestation of the Marcus-Hush theory of electron transfer. In addition, our system provides a novel experimental platform, which could be applied to address a number of scientific problems such as identification of reaction mechanisms, surface modification, or long-range electron transfer.

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.

Sign in / Sign up

Export Citation Format

Share Document