Quinone-hydroquinone System Research Articles

Modification on Glassy Carbon Surfaces By Homogeneous Oxidation of Ferrocenecarboxilate in Presence of Ferrocenecarboxylic Acid and 1,4-Benzoquinone As Mediator

The quinone-hydroquinone system is one of the most important and well studied examples of organic redox couple. This system participates as electron and proton carrier in different mechanisms involved in some biological systems. In aqueous as well as in organic solvents, the quinone molecules can be reduced following a 2-electron exchange and due to their high basicity, protonation to yield the respective hydroquinone represent a significant thermodynamic driving force. On the other hand, the oxidation of carboxylates give rise to a transient acyloxy radical whose cleavage afford CO2 and a free radical that can dimerize. This process is also highly favoured from the kinetic and thermodynamic point of view. Therefore, the combination of quinones, carboxylates and the respective carboxylic acid, would be an interesting mixture to promote the spontaneous decarboxylation and hydroquinone formation. This proposal was confirmed in this work through the study of the interaction between 1,4-benzoquinone, ferrocenecarboxylic acid and ferocenecarboxylate in acetonitrile, mainly to promote the formation of an excess of free radicals that modify chemically glassy carbon electrodes with ferrocene groups. The study was performed using cyclic voltammetry, chronoamperometry, 1H-NMR and atomic force microscopy. Figure 1

Hydrogen bonding complexes in the quinone-hydroquinone system and the transition to a reversible two-electron transfer mechanism

The electrochemical reduction of 1,4-benzoquinone in acetonitrile in the presence of hydroquinone as a hydrogen bonding proton donor was studied. Different association modes and mechanistic regimes were found depending on the hydroquinone concentration. At stoichiometric concentrations, the formation of a dianionic quinhydrone linked by two-equivalent strong hydrogen bonds, was found. At higher concentrations of hydroquinone, the structure of this complex changes to another in which the monoprotonated quinone dianion is stabilized by interaction with hydroquinone and the supporting electrolyte cation. This complex is adsorbed on the glassy carbon electrode during its formation and the amount deposited is influenced by the concentration and size of the electrolyte cations. However, by further increasing of the hydroquinone concentration, the complex adsorption is totally inhibited and the cyclic voltammetry behaviour becomes reversible with the transfer of two-electrons.

Mechanistic Study on the Electrochemical Reduction of 9,10-Anthraquinone in the Presence of Hydrogen-bond and Proton Donating Additives

The electrochemical reduction of 9,10-anthraquinone (AQ) was investigated in CH(3)CN in both the absence and presence of the hydrogen-bond and proton donating additives, CH(3)OH, CH(CF(3))(2)OH, phenol, 4-methoxyphenol, 4-cyanophenol, 2,4,6-trichlorophenol, and benzoic acid (BA). Three clearly different types of electrochemical behavior were observed with increasing concentrations of the additives, and were simulated to analyze the reaction mechanisms. Type I was observed for weakly interacting additives, such as CH(3)OH, characterized by positive shifts of the two well-separated reduction waves, corresponding to the formation of AQ(•-) and AQ(2-), with no loss of reversibility. The second wave shifted more strongly, and finally merged with the first. These behaviors are explained by the association of AQ(2-) with the additives via strong hydrogen-bonding. Type II is attributed to a reduction mechanism involving quantitative formation of strong hydrogen-bonded complexes of AQ(2-) with additives, such as CH(CF(3))(2)OH, phenol and 4-methoxyphenol, showing a reversible or quasireversible two-electron reduction wave with increasing concentrations of the additives. The behavior of Type III, observed in the presence of strongly interacting additives, such as 2,4,6-trichlorophenol and BA, is characterized by a voltammogram composed of the 2-electorn cathodic and the broad anodic waves without keeping reversibility, facilitated by proton transfer in the hydrogen-bonded complexes, AQ(•-)-BA and AQ(2-)-BA. The effects of hydrogen-bonding and protonation on the electrochemistry of AQ have been systematically demonstrated in terms of the potentials and reaction pathways of the various species, which appear in quinone-hydroquinone systems.

The properties of graphite electrodes modified by the quinone-hydroquinone system

The standard states of quinone and hydroquinone were selected to be those of pure substances, which allowed us to introduce the solubility product of quinhydrone. This selection of the standard state made it possible to interpret both the interval and direction of changes in the oxidation potential of graphite electrodes whose pores were filled by these substances in aqueous solutions with a fixed acidity.

Influence of ultrasound on the kinetic parameters of electrochemical redox reactions

The aim of this work is to determine the Tafel parameters with and without ultrasound. The total overvoltage has been corrected for diffusion by using rotating disk technique and potentiostatic extrapolation to infinite rotating speed. Three well known redox systems have been selected regardless to their different electrochemical behaviour: the quinone-hydroquinone, the Fe(II)Fe(III) chlorides and Fe(II)Fe(III) cyanide systems. This work shows that the reversibility is higher with ultrasound only in the case of the quinone-hydroquinone system.

Extension of the voltammetric theory to inert, permeable thin-film coated rotating disc electrodes Part II. Behaviour of ferrocene—ferricinium ion and quinone—hydroquinone systems on polymer-coated electrodes

The voltammetric behaviour of ferrocene-ferricinium ion and quinone-hydroquinone systems is investigated on electrochemically thin film polymer coated electrodes. Ferrocene oxidation is studied in 0.1 M NBu 4 ClO 4 -nitromethane on rotating disc platinum electrodes coated with poly(2-hydroxymethyl-1,4-phenylene) oxide (I), poly-(2,6-dimethyl-1,4-phenylene) oxide (II), and poly[4-(2-aminoethyl)-1,2-phenylene] oxide (III) films. The quinone-hydroquinone system is investigated in aqueous medium (1 M HClO 4 ) with (I), (II) and poly-(2-cyano-1,4-phenylene) oxide films. Experimental results are in good agreement with the previously calculated voltammetric curves in steady-state mass transfer conditions. The charge transfer and diffusion parameters on these polymer-coated electrodes are calculated The quinone-hydroquinone system is rendered reversible by coating a platinum electrode with I.

Extension of the voltammetric theory to inert, permeable thin-film coated rotating disc electrodes: Part II. Behaviour of ferrocene-ferricinium ion and quinone-hydroquinone systems on polymer-coated electrodes

The voltammetric behaviour of ferrocene-ferricinium ion and quinone-hydroquinone systems is investigated on electrochemically thin film polymer coated electrodes. Ferrocene oxidation is studied in 0.1 M NBu 4 ClO 4-nitromethane on rotating disc platinum electrodes coated with poly(2-hydroxymethyl-1,4-phenylene) oxide (I), poly-(2,6-dimethyl-1,4-phenylene) oxide (II), and poly[4-(2-aminoethyl)-1,2-phenylene] oxide (III) films. The quinone-hydroquinone system is investigated in aqueous medium (1 M HClO 4) with (I), (II) and poly-(2-cyano-1,4-phenylene) oxide films. Experimental results are in good agreement with the previously calculated voltammetric curves in steady-state mass transfer conditions. The charge transfer and diffusion parameters on these polymer-coated electrodes are calculated The quinone-hydroquinone system is rendered reversible by coating a platinum electrode with I.

Oxidation-reduction polymers

Abstract

Thin-layer electrochemistry: steady-state methods of studying rate processes

Potential applications are considered for twin-electrode thin-layer electrolysis. Determination of diffusion coefficients, electron-transfer rate constants, and concentration of electroactive species are possible using steady-state currents attainable with the twin-electrode technique. The technique is applied to the Fe(II)-Fe(III) and the quinone-hydroquinone systems.

In-vitro-Versuche über die Methämoglobinbildung durch Chinonderivate

Heubner states that the oxidation of haemoglobin to methaemoglobin by quinones should be due to a tension between two oxidation-reduction systems, the quinone-hydroquinone system and the haemoglobin-methaemoglobin system. The authors tried to prove this statement by using various quinones with different oxidation-reduction potentials. An analysis of the results obtained suggests, however, that the oxidation-reduction potential is not the only factor determining the equilibrium. It seems that some other constitutionally conditioned factors also play an important role in this process. Experiments with non-haemolyzed erythrocytes show that all quinones tested are able to pass through the cellular membrane of the erythrocytes without undergoing any chemical reaction. Thus, the experiments with haemolyzed solutions and those with intact erythrocytes gave identical results.