Electrochemical reduction of tricarbonyl compounds: Reduction mechanism of alloxan on a mercury electrode

A study has been carried out on the reduction mechanism of alloxan over a DME corresponding to the first two-electron transfer over the pH range 0–12.Polarographic and voltammetric results show the reduction process to be kinetically controlled. Rate and equilibrium constant data for the prior chemical reaction have been evaluated and several reaction mechanisms for different pH zones have been proposed.     

苯亚甲基丙二腈在汞阴极上的还原反应

本文应用了多种电化学方法(循环伏安法,微分脉冲极谱法等)及UV光谱,GC-MS手段研究了苯亚甲基丙二腈(BDMN)在汞阴极上的还原过程.在0.03mol.L^-1四乙基溴化铵(TEAB),50%二氧六环-水介质中BDMN还原的微分脉冲极谱图上有两个峰,第一个峰是此分子中的双键还原,生成苄基丙二腈引起的,峰电位在-0.98V(vs.SCE).第二个峰的峰电位在-1.55V(vs.SCE),此峰是BDMN的水解产物苯甲醛还原为苯甲醇产生的.BDMN的整个电极反应为ECEC过程.此处,对BDMN及二氧六环在汞电极上的吸附现象也进行了研究.     

Electrochemical reduction of cefminox at the mercury electrode and its voltammetric determination in urine

The electrochemical behaviour of cefminox in phosphate buffers solutions over pH range 2.0-9.0 using differential-pulse polarography, DC-tast polarography, cyclic voltammetry and linear sweep voltammetry (staircase) has been studied. In acidic media, a non reversible diffusion-controlled reduction involving two electrons occurs and the mechanism for the reduction was suggested. A differential-pulse polarographic method for the determination of cefminox in the concentration range 5.8×10⁻⁶-6.0×10⁻⁵ M with a detection limit of 1.76×10⁻⁶ M was proposed. Also, a method based on controlled adsorptive pre-concentration of cefminox on the hanging mercury drop electrode followed by linear sweep voltammetry, allows its determination in the concentration range 8.3×10⁻⁸-1.5×10⁻⁶ M with a detection limit of 2.47×10⁻⁸ M. These methods have been used for the direct determination of cefminox in human urine with recoveries between 98 and 103%, and precision around ±2%.     

Electrochemical reduction of a mixture of 1,4- and 1,6-dinitrocyclooctatetraenes on a dropping mercury electrode

Conclusions The limiting current of the first wave on the polarograms in the reduction of a mixture of 1,4- and 1,-dinitrocyclooctatetraenes corresponds to the transfer of two electrons. The reduction may be stopped at this step. The wave shape is determined by the reversible transfer of the first electron.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 8, pp. 1911–1913, August, 1985.     

Electrochemical reduction mechanism of 5(1H)-pyrromethenones in dimethylformamide on a mercury electrode

The mechanism of the electrochemical reduction of some 5(1H)-pyrromethenones and their aryl analogs (5-arylmethylene-3,4-dimethyl-3-pyrrolin-2-ones) in dimethylformamide on a mercury electrode, using LiClO₄) as supporting electrolyte, has been investigated. Polarographic and voltammetric experimental data show that 5(1H)-pyrromethenones undergo a reductive electrodimerization only through an EC mechanism, whereas their aryl analogs can also be reduced through an ECE mechanism. This different behaviour gives information about the reactivity of the bridge carbon atom of these compounds.     

Electrochemical behavior of kryptand 222 on a mercury electrode

The electrochemical behavior of kryptand 222 at the interface between a mercury electrode and an aqueous solution is studied by the impedance spectroscopy, polarography, and cyclic voltammetry methods. It is established that kryptand 222 possesses high surface activity at this interface. Adsorption parameters of kryptand 222 are found on the basis of the model of two parallel capacitors supplemented by the Frumkin isotherm by the regression analysis method. The potential dependences of the differential capacitance (C,E curves), calculated using these parameters satisfactorily agree with experiment. It is shown that the maximum in the C,E curves in the region of negative potentials is caused by catalytic process of hydrogen evolution.     

Electrochemical studies of technetium at a mercury electrode

The electrochemistry of technetium was studied by polarography, cyclic voltammetry and coulometry in chloride and sulfate media as a function of pH in the range 1.5–13. Compounds of Tc(III) and Tc(IV) are produced by reduction of pertechnetate, and the system Tc(III)/Tc(IV) was investigated in acidic media. The potential—acidity diagram of technetium is described for two total pertechnetate concentrations. Evidence for the dismutation of Tc(III) below pH 4 is discussed.     

Electrochemical reduction of ciprofloxacin at the mercury electrode and its voltammetric determination in tablet and urine

In this study a reduction square wave voltammetric method was developed and validated for the direct determination of ciprofloxacin (CIP) in pharmaceutical formulation and biological fluid using hanging mercury dropping electrode (HMDE) surface. Best results were obtained for the quantitative determination of CIP in 0.02 M Britton-Robinson buffer at pH 2.5 and at a potential of ?1300 mV vs. Ag/AgCl reference electrode. Various experimental and instrumental parameters affecting the peak current and potential of CIP electrochemical reduction were investigated and optimized. The monitored peak current was directly proportional to the concentration of CIP, where it exhibited a linear response in the range 3.0 × 10^?7–2 × 10^?6 M (r = 0.99). The accuracy of the proposed method was concluded based on the value of mean recovery of 98 ± 0.72 % with RSD of 0.181 % at a detection limit of 7 × 10^?9 M. Possible interferences by various substances usually present in pharmaceutical formulations have been also evaluated. After validating the proposed method, the applicability of this voltammetric method was demonstrated by estimating CIP in its pharmaceutical formulation and spiked human urine, where values of mean recoveries of 97 ± 1.0% and 108.0 ± 2.0% were obtained, respectively.     

Electrochemical determination of 2,4-D at a mercury electrode

An indirect electrochemical determination of 2,4-dichlorophenoxyacetic acid (2,4-D), has been presented. The method is based on the adsorption and desorption of 2,4-D on mercury electrode. Also, the electrochemical behavior of 2,4-D in aqueous solutions at different pH values and different 2,4-D concentrations were studied. A simple and rapid method has been developed for its extraction from water and soil. The subsequent determination was carried out by a tensammetric method. Three calibration curves could be obtained from different parts of voltammogram. Under the optimum conditions (pH = 2.3; E_acc = −1100 mV; t_acc = 60 s; alternative current mode; ν = 40 mV s⁻¹; pulse height = 20 mV; modulation frequency = 60 Hz; phase angle = 90°) the limit of detection was 50 μg L⁻¹. The proposed method was applied to the determination of 2,4-D in real samples such as soil and water.     

Electrochemical reduction of hydrogenated 2-pyrimidones on a graphite electrode

A rotating disk-ring, graphite electrode was used to show that the first step in the electrochemical oxidation of substituted 2-oxo-1,2,3,4-tetrahydropyrimidines in anhydrous acetonitrile corresponds to a two-electron process and leads to the formation of the corresponding substituted 2-oxo-1,2-dihydropyrimidines. The electroreduction wave of 2-oxo-1,2-dihydropyrimidines on the ring electrode which appears at about –1.0 V is related to the reduction of the protonated oxidized species arising in the electrolysis. The electrochemical oxidation potentials of 11 hydrogenated 2-pyrimidones and electrochemical reduction-potentials of two 2-pyrimidines were determined.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 1, pp. 117–121, January, 1985.     

Electrochemical reduction of decafluorobenzil in DMF on a platinum electrode

The mechanism of electrochemical reduction of decafluorobenzil on a platinum electrode in DMF was investigated by cyclic voltammetry. The first reduction peak corresponded to a reversible single-electron transfer leading to the formation of a relatively stable anion-radical whose ESR spectrum was registered and characterized. The second peak corresponded to the reduction of the anion-radical into an unstable dianion that quickly reacted with initial decafluorobenzil, and the arising species (or its transformation product) at the given potential underwent further reduction. The effect of fluorine on the potentials and on the mechanism of the electrochemical reduction of decafluorobenzil was considered.     

Electrochemical behaviour of low-potential electron-transferring proteins at the mercury electrode

This paper reports on a pulse polarographic study of low-potential electron-transferring proteins at the mercury electrode. The proteins studied were the negatively charged iron-sulphur cluster containing ferredoxins from spinach, and from Megasphaera elsdenii, the iron-containing rubredoxin and the FMN-containing flavodoxin both from M. elsdenii. Furthermore, the positively charged, four haem-containing cytochrome c₃ from Desulfovibrio vulgaris strain Hildenborough was studied. It was observed that the electrode reaction of these proteins could be made much more efficient when a polymer or surfactant was added, with a charge opposite to the protein. The reduction efficiency of these proteins reaches an optimum when the net charge of the protein times its concentration is about equal to the same amount of opposite charges, which was added as a polymer or surfactant.     

Electrochemical behaviour of tilmicosin at the hanging mercury drop electrode

The electrochemical behaviour of tilmicosin (TIM) was investigated using cyclic voltammetry and square-wave voltammetry in Britton-Robinson buffers (pH 2–12). The voltammograms of TIM showed one-irreversible peak which attributed to reduction of the >C=C< group in the entire pH values. However, an additional peak was shown over the pH range 2.00 to 4.00. Its peak potential is more positive potential from that of >C=C< group, and its potential was not practically dependent on the pH. On the other hand, the peak potential of >C=C< group was shifted to the more negative values with increasing pH. According to the obtained voltammetric data, the probable reaction mechanism for the reduction of TIM was proposed. Moreover, the adsorption of TIM on the mercury electrode surface by means of square-wave adsorptive stripping voltammetry measurements is studied at different pH values. The peak current variations with the deposition time and TIM concentration were observed.     

槲皮素在悬汞电极上的伏安行为研究

应用循环扫描伏安法考察槲皮素在悬汞电极上的电化学行为,并用线性扫描伏安法测定其含量。在0.1mol/LNa2CO3-NaHCO3(pH9.51)缓冲溶液中,槲皮素在-1.33V(vs.Ag/AgCl)处出现灵敏的还原峰,峰电流与其浓度在2.0×10-6～2.0×10-5mol/L(r=0.9989)范围内呈良好的线性关系。该方法可直接用于罗布麻叶中槲皮素的含量测定。     

Electrochemical reduction of the perfluoro-n-Hexyl iodide on mercury,in dimethylformamide

The electrochemical reduction behaviour of perfluoro-n-hexyl iodide, C₆F₁₃I, has been studied at the mercury electrode in dimethylformamide as a solvent. The major reaction product of the controlled-potential electrolysis of C₆F₁₃I is the organomercuric compound (C₆F₁₃)₂Hg. Using conventional polarography and linear sweep voltammetry, it is concluded that a chemical prereaction occurs between the perfluoro-n-hexyl iodide and polarized mercury, yielding the perfluoro-n-hexyl mercury iodide C₆F₁₃HgI, which is itself reducible in two separate steps. A detailed mechanism of the electrochemical reduction of C₆F₁₃I is proposed and discussed.     

Electrochemical study of potassium isobutyl xanthate at a mercury electrode.

Polarographic studies of potassium isobutyl xanthate at a mercury electrode reveal that the product of an anodic reaction is strongly adsorbed at the mercury surface, as indicated by a prewave. The adsorbed film greatly affects the characteristics of the anodic wave of xanthate in an aqeous medium. The current of total wave is proportional to the concentration of xanthate from 0.32 to 1.6 mM.