Controlled-potential Coulometry Research Articles

Electrochemical Study of Catechol Derivatives in the Presence of β-diketones: Synthesis of Benzofuran Derivatives

The electrochemical oxidation of 4-(1,3-dithiolan-2-yl)benzene-1,2-diol was studied in the presence and absence of acetylacetone (2a), dimedone (2b) and 4-hydroxycoumarin (2c) as nucleophiles in aqueous solution by means of cyclic voltammetry and controlled-potential coulometry. The results indicate that these nucleophiles participate in Michael addition reaction with the oxidized form of catechol derivatives, and then convert it to the corresponding new benzofuran derivatives. The electrochemical synthesis of compounds has been successfully performed at a carbon rod electrode and in two-compartment cell. The observed homogeneous rate constants (kobs) of the reaction of oxidized form of catechol derivatives with 2a-c as nucleophiles were estimated by comparing the experimental cyclic voltammograms with the digital simulated results. The calculated kobs was found to vary in the order 4-hydroxycoumarin (2c) < dimedone (2b) < acetylacetone (2a).

Electrochemical Oxidation of 4-(Piperazin-1-yl)phenol in the Presence of Aryl Sulfinic Acids

Electrochemical oxidation of 4-(piperazin-1-yl)phenol has been studied in the presence of aryl sulfinic acids as nucleophiles in ethanol/water mixture (10/90) using cyclic voltammetry and controlled-potential coulometry methods. The results indicate that the electrochemically generated p-quinone-imine participates in Michael type addition reaction with aryl sulfinic acids and via an EC mechanism converts to the new 2-(phenylsulfonyl)-4-(piperazin-1-yl)phenol derivatives. The present work has led to the development of a facile and environmentally friendly electrochemical method for the synthesis of some new 2-(phenylsulfonyl)-4-(piperazin-1-yl)phenol derivatives under green conditions.

Voltammetric Peak Enhancement of Cefpirome in Cetyltrimethylammonium Bromide

The objective of the present work is to develop a voltammetric method for the determination of cefpirome in bulk and pharmaceutical formulations and it also deals with the beneficial use of surfactants in the catalysis of electrode reactions. The voltammetric behaviour of cefpirome in Britton Robinson buffer solutions over the pH range 2.0-12.0 using differential pulse voltammetry and cyclic voltammetry has been studied in surfactant media. In the entire pH range a well defined cathodic and anodic peak were observed in cyclic voltammetry. Number of electron transferred in the reduction process was calculated and the reduction mechanism has been postulated on the basis of controlled potential electrolysis and coulometry. The proposed differential pulse voltammetric method allows quantitation over the range 1.0 mgmL-1 and 62 mgmL-1 with detection limit of 1.2 mgmL-1 respectively. The analysis of cefpirome in pharmaceutical formulation exhibited the mean recoveries of 99.7% for the reduction peak.

Diversity in electrochemical oxidation of dihydroxybenzenes in the presence of 1-methylindole

Electrochemical oxidation of some catechol derivatives (1a–e) have been studied in water/ acetonitrile solution containing 1-methylindole (3) as a nucleophile, using cyclic voltammetry and controlled-potential coulometry. An interesting diversity in the mechanisms has been observed in electrochemical oxidation of catechol derivatives (1a–e) in the presence of 3. In this work, we have proposed reaction schemes ECEC, ECECE and ECECECE for oxidation of 1a–e in the presence of 3. Electrochemical oxidation of catechol derivatives has been studied in the presence of 1-methylindole using cyclic voltammetry and controlled-potential coulomertry.We have proposed reaction schemes ECEC, ECECE and ECECECE for oxidation of catechol derivatives in the presence of 1-methylindole.

A promising green method in cyclization reaction. Oxidation of 3-methylcatechol in the presence of 1,10-phenanthroline

Abstract Electrochemical oxidation of 3-methylcatechol as a model compound has been studied in the presence of 1,10-phenanthroline as a bi-dentate nucleophile in water/acetonitrile (70/30, v/v) solution using cyclic voltammetry and controlled-potential coulometry. The results revealed that anodically generated 3-methylcyclohexa-3,5-diene-1,2-dione participates in inter and intramolecular Michael addition reactions with 1,10-phenanthroline and via an ECEC pathway converts to the corresponding heterocyclic compound. The present work has led to the development of a facile and one-pot method with high atom economy under ambient conditions and in an undivided cell using a carbon electrode.

Voltammetric studies of some azo compounds derived from 4-methyl-6,7-dihydroxy coumarin in microemulsion and aqueous media

The cyclic voltammetric(CV) behavior of some azo compounds based on coumarin derivatives was investigated in microemulsion systems and in aqueous solutions. The obtained results indicated that these compounds undergo an irreversible 4-electron reduction step leading to cleavage of the N=N center with the formation of amine compounds in all media. The effect of medium on the CV parameters was discussed. The total number of electrons involved in the reduction process was determined by controlled potential coulometry. Also, The effect of substituents on the electrode reaction pathway and the kinetic parameters of the electrode process were calculated and discussed. Based on the data obtained the electroreduction mechanism was suggested and discussed.

The Determination of N-Values for Some Amino-Acridines by Controlled Potential Coulometric Reduction

Abstract The reduction of some aminoacridines has been investigated by controlled potential coulometry. The number of electrons involved in the first reduction stage has been determined by a graphical treatment of the current-time values obtained using a divided electrolysis cell. With the exception of 5-aminoacridine the results confirm the values obtained indirectly by Kaye5.

The controlled potential reduction of crystal violet and brilliant green at the stirred mercury cathode.

Abstract The application of controlled potential coulometry to the electro-reduction of the triphenylmethane dyestuffs crystal violet and brilliant green is described below. The polarographic work by Kaye and Stonehill (1952) indicated that, like the aminoacridines previously examined (Wilson, Butler, Ingle and Taylor, 1960), these were reduced in two stages each involving the uptake of one electron. The aim of the present work was to seek confirmation of this by direct measurement of the quantities of electricity involved in the reduction of a known amount of dyestuff.

A convergent paired electrochemical synthesis of new heterocyclic compounds. Reaction of benzoquinones with 3-Amino-4-hydroxycoumarin

Electrochemical oxidation of catechols (1) has been studied in the presence of cathodically generated 3-amino-4-hydroxycoumarin (3a) as a nucleophile in aqueous solutions, using cyclic voltammetry and controlled-potential coulometry. The results indicate that the o-benzoquinones derived from catechols (1) participate in Michael addition reaction with 3-amino-4-hydroxycoumarin (3a) to form the corresponding new heterocyclic compounds (7) (oxidized form of coumestan derivatives). The electrochemical process consists of a multi-step including (a) cathodic reduction of 4-hydroxy-3-nitrocoumarin (3) to 3-amino-4-hydroxycoumarin (3a), (b) anodic oxidation of catechols (1) to related o-benzoquinone (2), (c) the Michael addition reaction of 3-amino-4-hydroxycoumarin (3a) to o-benzoquinone (2), and (d) anodic oxidation of formed adduct. The paired electrochemical synthesis of compounds 7a and 7b has been successfully performed in a one-pot process at carbon rods as working and counter electrodes in an undivided cell.

Electrochemical oxidation of 4-morpholinoaniline in aqueous solutions: Synthesis of a new trimer of 4-morpholinoaniline

Electrochemical oxidation of 4-morpholinoaniline has been studied in various pHs using cyclic voltammetry and controlled-potential coulometry. The electrochemical trimerization of 4-morpholinoaniline is described and its mechanism has been studied in aqueous solution. This method provides a green, reagent-less, and environmentally friendly procedure with high atom economy, for the synthesis of “ 4-morpholinoaniline- trimer” using a carbon electrode in an undivided cell in good yield and purity.

Synthesis and complexes of an N4 Schiff-base macrocycle derived from 2,2′-iminobisbenzaldehyde

An N(4) tetradentate [1 + 1] Schiff base metal free macrocycle HL was prepared, by 1 : 1 condensation of 2,2'-iminobisbenzaldehyde (1) and diethylenetriamine, and characterised. Seven mononuclear complexes, [Zn(II)L(py)](BF(4)) (2), [Cu(II)L](BF(4))]·H(2)O (3), [Ni(II)L](BF(4))·H(2)O (4), [Co(II)L](BF(4))]·H(2)O (5), Fe(III)L(BF(4))(2)·2H(2)O·MeCN (6), [Co(III)L(NCS)(2)]·0.3py (7) and [Fe(III)L(NCS)(2)] (8), of L(-) are reported. The Cu(II) and Ni(II) complexes were prepared by a template approach whereas the others were accessed by metallation of pre-formed HL. The X-ray crystal structure determinations show that [Cu(II)L](BF(4)) and [Ni(II)L](BF(4)) feature square planar N(4) coordinated Cu(II) and Ni(II) centres, respectively, whereas [Fe(III)L(NCS)(2)]·NO(2)Me features an octahedral N(6) coordinated Fe(III) centre (two NCS anions bound axially) and the Zn(II) complex, which crystallised as 2{[Zn(II)L(py)](BF(4))}·py, features square pyramidal Zn(II) ions (a pyridine molecule bound axially). In all cases the N(4) macrocycle is bound equatorially to the metal ion. Cyclic voltammograms of the soluble BF(4) complexes, 2-5, were carried out in MeCN vs. 0.01 mol L(-1) AgNO(3)/Ag and revealed multiple, mostly irreversible or quasi-reversible, redox processes. The Zn(II) complex 2 exhibited two irreversible oxidation processes and one irreversible reduction process, all of which are ligand-centered. The Ni(II) complex 4 showed a process with a weak return wave at E(m) = +0.57 V (ΔE = 0.05 V). Interestingly, after controlled potential coulometry experiments on 2, 3 and 4 (at +0.48, +0.61 and +0.71 V which transferred 1.2, 1.0 and 1.6 e(-) equiv. per complex, respectively), a new reversible or quasi-reversible process was obtained, with a lower potential than beforehand (E(m) (ΔE)/V = +0.16 (0.08), +0.31 (0.13) and +0.45 (0.11) respectively).

Electrochemical determination of antihypertensive drug irbesartan in pharmaceuticals

A sensitive voltammetric method has been developed for the determination of irbesartan in a Britton–Robinson buffer medium. Irbesartan exhibited a well-defined cathodic peak over the entire pH range from 2.0 to 12.0. The mechanism of reduction was postulated on the basis of controlled potential electrolysis, coulometry, and spectral analysis. Under optimal conditions, a linear response of irbesartan was obtained in the range from 3.0×10−5 to 5.7×10−3molL−1 and with a limit of detection of 5.33×10−7molL−1. The effect of cationic surfactant on the voltammetric reduction peak of irbesartan in Britton–Robinson buffer is also described.

Electrooxidation of the calix[4]arenedihydroquinone mechanistic investigation and electrodeposition of the oxidised form on platinum grid

The electrochemical behaviour of 5,17-di-tert-butyl-11,23,25,27-di-dihydroxy-26,28-dimethoxy calix[4]arene has been investigated at a platinum electrode in aprotic solvent by cyclic, square wave and rotating-disk voltammetry as well as by controlled potential coulometry. By comparing to the ferrocene, the height of the first irreversible transfer process involves only one-electron transfer, which corresponds to the formation of the radical cation. However, the last substance undergoes a fast chemical reaction and follows an ECHE sequence. But, the large scale electrolysis at the first anodic peak required a consumption of 2.25 Faradays per molecule. When we interrupt the electrolysis after consumption of 1 Faraday per molecule, an intermediate compound was formed, which is the calix[4]arenequinhydrone (X4Me2(H2Q)Q) through a partial reduction of the start product. Furthermore, the reaction may evolves in solution following an ECHECH redox process for generating the calix[4]arenediquinone (X4Me2Q2). On the other hand, the voltammetric follow-up shows the electrogeneration to the departure product during the macroscale electrolysis according an ECHE-disproportionation mechanism. When the electrolysis was performed after the third oxidation peak, (X4Me2Q2) was electrogenerated in solution and was deposit, afterward, on the platinum grid.

Electrochemical synthesis of the new substituted phenylpiperazines

Abstract Electrochemical oxidation of 1-(4-(4-hydroxyphenyl)piperazin-1-yl)ethanone ( 1 ) has been studied in the presence of arylsulfinic acids ( 3a–c ) as nucleophiles in aqueous solutions using cyclic voltammetry and controlled-potential coulometry methods. The results revealed that quinone-imine derived from oxidation of 1 participates in Michael type addition reaction with 3a–c and via an EC mechanism converts to the corresponding new phenylpiperazine derivatives. The present work has led to the development of a facile and environmentally friendly reagent-less electrochemical method for synthesis of some new phenylpiperazine derivatives in aqueous solutions with high atom economy and safe waste under ambient conditions and in an undivided cell using a carbon electrode.

Electrochemical dimerization of 4-methylesculetin: Synthesis and kinetic study of a highly-oxygenated dimer

This paper describes the electrochemical dimerization of 4-methylesculetin via anodic oxidation. The voltammetric data show that electrochemically generated ortho-benzoquinone participates in Michael addition reaction with starting molecular (4-methylesculetin) forms the corresponding highly-oxygenated dimer. The mechanism of dimerization has been studied in water/acetonitrile mixture using cyclic voltammetry and controlled-potential coulometry. The electrochemical synthesis of this highly-oxygenated dimer has been successfully performed in an undivided cell in good yield and purity. Furthermore, the observed homogeneous rate constants of the chemical reaction between ortho-benzoquinone and 4-methylesculetin were estimated by comparing the experimental cyclic voltammetric curves with the digitally simulated ones.

Electroanalytical studies of sulfentrazone in protic medium, its degradation by the electro-Fenton process, and toxicity assessment using ss-DNA

Sulfentrazone is an herbicide used as a pre-plant incorporated or pre-emergence treatment. The electrochemical oxidation of sulfentrazone was studied, by cyclic, differential and square-wave voltammetry on unmodified and on glassy carbon nanotube-modified electrodes, and by controlled-potential coulometry and electrolysis. The voltammograms of sulfentrazone showed a main irreversible diffusion-controlled pH-dependent oxidation peak. The in situ DNA-damaging capacity of sulfentrazone was also investigated, employing double stranded ds-DNA-modified glassy carbon electrode, without evidence of interaction. On the other hand, in a solution of sulfentrazone and single stranded ss-DNA, the oxidation signals of the respective bases decreased concentration-dependently, indicating binding of sulfentrazone to guanine and adenine. The electro-Fenton method was employed to promote decontamination by eliminating the herbicide, resulting in almost 60% of mineralization.

ChemInform Abstract: Production, Spectroscopy, and Electronic Structure of Soluble Fullerene Ions.

Taking advantage of the well-separated redox potentials of the mono-, di-, and trianions of C{sub 60} and C{sub 70}, their room-temperature-stable, soluble monoanion radicals have been selectively prepared in bulk quantities by controlled-potential coulometry. Upon reduction, strong bands in the near-IR are observed for C{sub 60}{sup {minus}} but not for C{sub 70}{sup {minus}}. Absorptions at 1,064, 995, and 917 nm are tentatively assigned to the allowed HOMO-LUMO t{sub 1u}-t{sub 1g} transition of C{sub 60}{sup {minus}}, in agreement with theoretical calculations. Vibrational (Raman) bands of excited C{sub 60}{sup {minus}} radical anions at 1,507 and 652 cm{sup {minus}1} and/or t{sub 1g} orbital splittings of similar magnitudes can be calculated from the electronic spectrum. For C{sub 70}{sup {minus}} the allowed HOMO-LUMO 3{sub 1}-a{sub 1} transition is calculated to occur in the IR region. ESR signals with g values below the free electron value are observed for solutions of both C{sub 60}{sup {minus}} and C{sub 70}{sup {minus}}. For C{sub 60}{sup {minus}} the occurrence of facile electron self-exchange in solution is suggested.

Synthesis and electrochemical, in situ spectroelectrochemical, electrical and gas sensing properties of ball-type homo- and hetero-dinuclear phthalocyanines with four [1a,8b-dihydronaphtho[b]naphthofuro[3,2-d]furan-7,10-diyl] bridges

The new mono-nuclear Fe II 2 and ball-type homo-dinuclear Fe II–Fe II 3 phthalocyanines have been synthesized from the corresponding 4,4′-(1a,8b-dihydronaphtho[b]naphthofuro[3,2-d]-furan-7,10-diyl)bis(oxy)diphthalonitrile 1 while ball-type hetero-dinuclear Fe II–Co II phthalocyanine 4 was synthesized from 2. The compounds have been characterized by elemental analysis, UV–vis, IR and MALDI-TOF-mass spectroscopies. The redox behaviours of the complexes were identified by controlled-potential coulometry, cyclic voltammetry and differential pulse voltammetry measurements on Pt in dimethylsulfoxide containing tetrabutylammonium perchlorate. The assignments of the redox processes and the understanding of the interactions between the metal phthalocyanine units in 3 and 4 were achieved by the combined evaluation of the voltammetric and in situ spectroelectrochemical outcomes. Complex 3 showed ring-based mixed-valence behaviour as a result of the considerable interaction between the phthalocyanine rings. On the other hand, the interactions between the two metal phthalocyanine units of 4 were found to be much weaker than those in 3. The potential application of molecular organic semiconductors needs the control adjustment of conductivity. Ac and dc conductivity measurements were performed with the applied external electric filed. At high frequency, the conduction follows the universal power law and conduction mechanism can be explained by classical hopping barriers mechanism for the system.

Kinetics study of electrochemically induced michael reaction of benzoquinones with triphenylphosphine

The electrochemical oxidation of 3,4-dihydroxybenzaldehyde (1), 3,4-dihydroxybenzoic acid (2) and 2,5-dihydroxybenzoic acid (3) were studied in the presence of triphenylphosphine (4) as a nucleophile using cyclic voltammetry and controlled-potential coulometry. The results indicate that the quinones derived from oxidation of 3,4-dihydroxybenzaldehyde, 3,4-dihydroxybenzoic acid and 2,5-dihydroxybenzoic acid participate in Michael addition reaction with triphenylphosphine (4). In this work, based on an EC mechanism, the observed homogeneous rate constants (kobs) of the reaction of produced benzoquinones with triphenylphosphine (4) were estimated by comparing the experimental cyclic voltammograms with the digitally simulated results.

Square-wave adsorptive stripping voltammetric behaviour of entacapone at HMDE and its determination in the presence of surfactants

The objective of the present work is to develop a voltammetric method for the determination of entacapone based on the enhancement effect of Tween 20. Addition of neutral surfactant (Tween 20) to the entacapone containing electrolyte enhanced the reduction current signal while anionic surfactant (sodium lauryl sulphate) and cationic surfactant (cetrimide) showed an opposite effect. The reduction process was irreversible over the entire pH range studied (2.5–12). The mechanism of reduction has been postulated on the basis of controlled potential electrolysis and coulometry. The current–concentration plot was rectilinear over the range from 5 × 10 −4 mol L −1 to 1.8 × 10 −5 mol L −1 with a correlation coefficient of 0.996 for differential pulse voltammetry (DPV) and 1.6 × 10 −4 mol L −1 to 1.6 × 10 −5 mol L −1 with correlation of 0.999 M for square ware voltammetry (SWV) in Britton Robinson buffer at pH 2.5. The lower limit of quantification (LOQ) and the lower limit of detection (LOD) were found to be 0.42 ng mL −1 and 0.13 ng mL −1 respectively. The analysis of entacapone in its pharmaceutical formulation exhibited the mean recovery of 99% for the reduction peak.