Controlled Potential Electrolysis Research Articles

Electrochemical and structural properties of 1,3-substituted (–Cl, –Br) phenyl-5-phenylformazans

In this study, 1-[ o-, m-, p-(chloro, bromo)]-3-( m-nitrophenyl)-5-phenylformazans were synthesized. Their structures were elucidated and spectral behaviors were investigated using elemental analysis, GC–mass, 1H NMR, 13C NMR, FTIR and UV–vis spectra. Electrochemical properties of formazans such as number of electrons transferred ( n), diffusion coefficient ( D) and heterogeneous rate constant ( k s ) of the compounds were determined and possible mechanisms were proposed with the use cyclic voltammetry, ultramicrodisc electrode and chronoamperometry. The relation between their absorption properties and electrochemical properties was sought. The redox characteristics of these compounds have been investigated in nonaqueous dimethylsulfoxide at platinum and ultramicro platinum (10 μm) electrodes. Through controlled potential electrolysis, the oxidation products of each class of compounds can be separated and identified. The oxidation mechanism is suggested and it is proved. A correlation was obtained between λ max with Hammett substituent coefficient, E ox1 and E red1.

Fixation of CO2 by Electrocatalytic Reduction and Electropolymerization in Ionic Liquid–H2O Solution

The electrocatalytic synthesis of low-density polyethylene (LDPE) from carbon dioxide on a nanostructured (ns)TiO2 film electrode was investigated by controlled potential electrolysis in a solvent mixture of water and the ionic liquid 1-ethyl-3-methylimidazolium tetrafluoroborate ([EMI]BF4) at room temperature under ambient pressure. Under these conditions, the nsTiO2 film is remarkably efficient and selective for the electroreduction of CO2. The current efficiency for the formation of the electrolytic product is about 8-14% at -1.50 V (vs SCE). The electrocatalytic activity of the electrode in the electrochemical reduction of CO2 was investigated by cyclic voltammetry (CV), and the probable electrode reaction mechanism is discussed.

Electrochemical and spectroscopic properties of 1:2 Ni complexes of 1,3-substitued (CH 3, OCH 3) phenyl-5-phenylformazans

In this study, new 1:2 nickel complexes of 1-[ o-, m-, p-(methyl, metoxyphenyl)]-3-( p-metoxyphenyl)-5-phenylformazans were synthesized. Their structures were elucidated and spectral behaviors were investigated with the use of elemental analysis, GC–mass, 1H NMR, 13C NMR, IR, and UV–vis spectra. The redox characteristics of these compounds have been investigated in nonaqueous dimethylsulfoxide at platinum and ultramicro platinum (10 μm) electrodes. Through controlled potential electrolysis, the oxidation products of each class of compounds can be separated and identified. The oxidation mechanism is suggested and it is proved. It was observed the oxidation mechanism take place in a single step two-electron or one-electron transfer to a disproportionation or dimerization reactions following the radical formation step. Eventually the relation between their absorption properties and electrochemical properties was examined.

A strategy for the electro-organic synthesis of new hydrocaffeic acid derivatives

Electrochemical treatment processes can significantly contribute to the protection of the environment through the minimization of waste and toxic materials in effluents. From a pharmaceutical point of view and due to the existing resemblance between the electrochemical and biological reactions, it can be assumed that the oxidation mechanisms on the electrode and in the body share similar principles. In this paper, the application of electrochemical studies in the design of an environmentally friendly method was delineated for the new hydrocaffeic acid (HCA, 3,4-dihydroxy hydrocinnamic acid) derivatives synthesis at carbon electrodes in an undivided cell. In this cell, the EC mechanism reaction was involved, comprising two steps alternatively; (1) electrochemical oxidation and (2) chemical reaction. In particular, the electro-organic reactions of HCA, an important biological molecule, were studied in a water–acetonitrile (90:10 v/v) mixture in the presence of benzenesulfinic acid (3) and p-toluenesulfinic acid (4). The research included the use of a variety of experimental techniques, such as cyclic voltammetry, controlled-potential electrolysis and product spectroscopic identification.

Electro-Organic Synthesis and Characterization of New Dihydroxybenzene Dinitrile Derivatives with Fluorescent Properties

Novel fluorescent molecules were synthesized by designing an environmentally friendly method involving the bulk electrolysis technique. This electrochemical treatment process helps protect the environment by minimizing the toxic waste component of effluent. The electrochemical oxidation of 3,6-dihydroxybenzene-1,2-dinitrile (DBD) in the presence of benzenesulfinic acids was studied in an aqueous solution (H(2)O : AN, 90 : 10), which included an acetate buffer (pH=5.0). This research utilized a variety of experimental techniques, including cyclic voltammetry, controlled-potential electrolysis as well as spectroscopic identification of compounds produced as products. In addition, our fluorescent studies offered results in line with existing findings. At the wavelength of 205 nm, DBD and compound (6) were excited and their fluorescent emissions were monitored.

Study of the electrochemical reduction of amoebicide teclozan and its amperometric determination in pharmaceutical formulations

The electrochemical reduction of amoebicide Teclozan (TEC) was studied on a glassy carbon electrode in acetonitrile. Controlled-potential electrolyses were performed for coulometric and preparative purposes. The electrogenerated products were isolated by liquid-liquid extraction and characterized by ¹H NMR. It was observed that TEC presents two voltammetric peaks, each one associated with the cleavage of two C-Cl bonds. In presence of a proton donor it was observed that the first peak at -1.8 V promotes mainly the reduction of the groups CHCl2 to CH2Cl and the second one at -2.2 V promotes the reduction of the groups CH2Cl to CH3 giving as the sole product the completely dechlorinated TEC derivative with yields between 82 and 97%. In addition, a comparative study between the analytical performance of voltammetric techniques and amperometric detection of TEC in hydrodynamic conditions was performed. The amperometric detection was more sensitive than all evaluated voltammetric techniques, providing a detection limit of 8.9 × 10-6 mol L-1.

The inducing NO-vasodilation by chemical reduction of coordinated nitrite ion in cis-[Ru(NO2)L(bpy)2]+ complex

The synthesis of [Ru(NO(2))L(bpy)(2)](+) (bpy = 2,2'-bipyridine and L = pyridine (py) and pyrazine (pz)) can be accomplished by addition of [Ru(NO)L(bpy)(2)](PF(6))(3) to aqueous solutions of physiological pH. The electrochemical processes of [Ru(NO(2))L(bpy)(2)](+) in aqueous solution were studied by cyclic voltammetry and differential pulse voltammetry. The anodic scan shows a peak around 1.00 V vs. Ag/AgCl attributed to the oxidation process centered on the metal ion. However, in the cathodic scan a second peak around -0.60 V vs. Ag/AgCl was observed and attributed to the reduction process centered on the nitrite ligand. The controlled reduction potential electrolysis at -0.80 V vs. Ag/AgCl shows NO release characteristics as judged by NO measurement with a NO-sensor. This assumption was confirmed by ESI/MS(+) and spectroelectrochemical experiment where cis-[Ru(bpy)(2)L(H(2)O)](2+) was obtained as a product of the reduction of cis-[Ru(II)(NO(2))L(bpy)(2)](+). The vasorelaxation observed in denuded aortic rings pre-contracted with 0.1 mumol L(-1) phenylephrine responded with relaxation in the presence of cis-[Ru(II)(NO(2))L(bpy)(2)](+). The potential of rat aorta cells to metabolize cis-[Ru(II)(NO(2))L(bpy)(2)](+) was also followed by confocal analysis. The obtained results suggest that NO release happens by reduction of cis-[Ru(II)(NO(2))L(bpy)(2)](+) inside the cell. The maximum vasorelaxation was achieved with 1 x 10(-5) mol L(-1) of cis-[Ru(II)(NO(2))L(bpy)(2)](+) complex.

Electro-Fenton treatment of dye solution containing Orange II: Influence of operational parameters

The electro-Fenton process was used to assess the decoloration of Orange II in aqueous solutions. Hydrogen peroxide (H 2O 2) was electro-generated by reduction of dissolved oxygen (DO) in acidic solutions containing dilute supporting electrolyte. This oxidation process allows the production of active intermediates, which react on the organic compounds, leading to their mineralization. Decoloration experiments were performed in the presence of perchlorate, chloride and sulfate electrolyte media at pH 3.0 under potential controlled electrolysis conditions. Effect of operational parameters such as cathodic potential, oxygen mass flow rate and inert supporting electrolyte type and concentration were investigated to find the best experimental conditions for achieving overall dye decoloration. Complete decoloration of Orange II occurs in less than 90 min. In addition, effect of cathode surface area and electrolyte concentration in the accumulation of H 2O 2 and behavior of the Fe 3+/Fe 2+ in the electro-Fenton system was examined. Results show that potential of −0.5 V vs. SCE, 0.05 M NaClO 4 electrolyte, O 2 sparging rate of 8 ml/min and diluted dye concentration were the best conditions for decoloration of the Orange II by electro-Fenton process. The mineralization of the initial pollutant was investigated by total organic carbon measurements that show a 75% mineralization of 2 × 10 −5 M dye at 180 min. Also, degradation by-products were identified with GC–MS analysis.

Electrochemical Studies on New Chelating Compounds of the Mono‐ and Bis(imidazolyl)pyridine Type

AbstractRecently designed and synthetized mono‐imidazolinone (I and III) and bisimidazolinone (II and IV) chelating ligands were electrochemically characterized at mercury and carbon paste electrodes. Based on polarographic, voltammetric and coulometric investigations in buffered aqueous media, the general reduction pathway has been suggested. Reduction of the mono‐imidazolinone derivatives proceeds in acidic and neutral media in two two‐electron steps. In the first step, the 2,3‐CN double bond of the imidazolone ring is reduced yielding a mixture of two diastereoisomers (V and VI). In the second step, the 2,3‐CN single bond (in protonated form) is further reductively split and as the only final product the compound VII was formed. Both intermediates (V and VI) as well as the final product (VII) were prepared using controlled potential electrolysis on the first and second wave, respectively, isolated and identified by means of NMR. The reduction of bis‐derivatives proceeds most probably in an analogical way: in the first step, both imidazoles are reduced simultaneously at the same potential, whereas the following reduction (ring‐opening) proceeds stepwise. In the case of compound III, the covalent hydration of the parent compound takes place in acidic media, partially preventing its reduction. Finally, voltammetric behaviour of mono‐ and bisimidazolinones at carbon paste electrode is also discussed and, in prospect, possible electroanalytical applications outlined.

Electrochemical Control of the Bioluminescence by Bacterial Luciferase Using Platinum-mesh Electrode

Bioluminescence reaction by bacterial luciferase has been successfully controlled by a controlled-potential electrolysis using platinum-mesh electrode to regenerate the reduced form of flavin mononucleotide (FMNH2), which is one of the substrates of the reaction. It was found that the regeneration of FMNH2 is facilitated by the adsorbed hydrogen atoms formed on a platinum electrode surface in the presence of phosphate ions.

Voltammetric behavior of cefdinir in solubilized system

The voltammetric behavior of cefdinir has been studied in different surfactant media viz. anionic, neutral, and cationic surfactants over the pH range 2.5–12 in phosphate buffer (0.2 M). Addition of cationic surfactant (citrimide) to the cefdinir containing electrolyte enhanced the reduction current signal while anionic surfactant (sodium lauryl) and neutral surfactant (Tween-20) 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, coulometry and spectral analysis. An analytical method with adequate precision and accuracy was developed for the determination of cefdinir in linear concentration range 2 × 10 −4 – 1 × 10 −5 mol L −1 with detection limit 0.3 × 10 −6 mol L −1 . The analysis of cefdinir in its pharmaceutical formulation resulted in mean recoveries of 99 and 98% for both the reduction peaks.

Design of carbon nanotube-polymer frameworks by electropolymerization of SWCNT-pyrrole derivatives

Single-walled carbon nanotubes (SWCNTs) have been functionalized by electropolymerizable pyrrole groups following covalent and non-covalent strategies. The covalent pyrrole grafting was carried out by ester formation between pyrrole alcohol and chemically oxidized SWCNT. The strong π-interactions between pyrene and SWCNT were exploited for the non-covalent adsorption of a new pyrene-pyrrole derivative on the pristine nanotube surface. The pyrrole-ester-SWCNT was solubilized in THF and electropolymerized by controlled potential electrolysis at 0.95 V. The pyrene-pyrrole SWCNT was spread on an electrode surface and electropolymerized in its adsorbed state at 0.95 V in CH 3CN. The reinforced nanostructured polypyrrole SWCNT-framework was investigated with scanning electron microscopy.

The Bis((trifluoromethyl)sulfonyl)imide-Based Room Temperature Ionic Liquids Used for Several Electrochemical Applications

Two room temperature ionic liquids based on the bis ((trifluoromethyl)sulfonyl)-imide anion (TFSI anion), the tributylmethylammonium-TFSI (Bu3MeN-TFSI) and the butylmethylpyrrolidinium-TFSI (BuMePy-TFSI), have been prepared for the electrochemical study of Li+/Li redox couple, the electrodeposition of Mn, Zn-Mn alloys and Cu-Mn alloys, and the extraction of Cu(II) ions from aqueous solutions, respectively. The best coulombic efficiency of Li+/Li couple is 97%. Mn(II), Zn(II) and Cu(I) species were introduced into the Bu3MeN-TFSI or BuMePy-TFSI by the anodic dissolution of the respective metallic electrodes. Coatings containing Mn, Zn, Cu, Zn-Mn or Cu-Mn can be obtained by controlled-potential electrolysis. The current efficiencies of Mn electrodeposition in either ionic liquid approach 100%. The Zn-Mn and Cu-Mn alloy deposits obtained in this study were compact and adherent. The surface morphology of these deposits depended on the Mn/Zn and Mn/Cu ratio, respectively. The BuMePy-TFSI ionic liquid containing N,N,N',N'-tetrakis-(2-pyridin-2-yl-ethyl)- butane-1,4-diamine (N4Py2) exhibits good ability of extracting Cu(II) ions from aqueous solution. The electrochemical study revealed that both Cu(I) and Cu(II) can form strong coordinated compounds with N4Py2 because the redox potentials of Cu(II)/Cu(I) and Cu(I)/Cu(0) couples shift to much more negative values, respectively.

Catalytic reduction of hexachlorobenzene and pentachlorobenzene by cobalt(I) salen electrogenerated at vitreous carbon cathodes in dimethylformamide

Abstract Cyclic voltammetry and controlled-potential electrolysis have been used to investigate the catalytic reduction of hexachlorobenzene and pentachlorobenzene by cobalt(I) salen that is electrogenerated at a carbon cathode in dimethylformamide containing 0.050 M tetramethylammonium tetrafluoroborate. Cyclic voltammograms for the reduction of cobalt(II) salen in the presence of either hexachlorobenzene or pentachlorobenzene show an enhanced cathodic peak for the catalyst–substrate reaction as well as loss of the anodic peak for reoxidation of cobalt(I) salen, revealing the effectiveness of the catalyst. However, cobalt(I) salen shows no catalytic activity toward tetrachlorobenzene or any less-chlorinated species. Controlled-potential electrolyses of cobalt(II) salen–hexachlorobenzene mixtures give both pentachlorobenzene and three isomers of tetrachlorobenzene, whereas bulk catalytic reduction of pentachlorobenzene affords three different tetrachlorobenzenes; for both substrates, substantial starting material remains unreduced. To account for the formation of the various products, a mechanistic scheme is proposed and discussed.

Voltammetric and potentiometric studies of some sulpha drug-Schiff base compounds and their metal complexes

Abstract The electrochemical behavior of some sulpha drug-Schiff bases at a mercury electrode was examined in the Britton-Robinson universal buffer of various pH values (2.5–11.7) containing 20% v/v) of ethanol using DC-polarography, cyclic voltammetry and controlled-potential electrolysis. The DC-polarograms and cyclic voltammograms of the examined compounds exhibited a single, 2-electron, irreversible, diffusion-controlled cathodic step within the entire pH range which is attributed to the reduction of the azomethine group-CH=N- to -CH2-NH-. The symmetry transfer coefficient (α) of the electrode reaction and the diffusion coefficient (D 0) of the reactant species were determined. The electrode reaction pathway of the compounds at the mercury electrode was suggested to follow the sequence: H+, e−, e−, H+. The dissociation constant of the sulpha drug-Schiff bases, the stability constant and stoichiometry of their complexes with various divalent transition metal ions (Mn2+, Co2+, Ni2+, Cu2+ and Zn2+) were determined potentiometrically at room temperature.

REDOX PROPERTIES OF RUTHENIUM COMPLEX WITH CATECHOL ARE INVOLVED IN TOXICITY TO GLIAL CELLS

ABSTRACT Since the biological activity of [Ru III (NH 3 ) 4 (catechol)] + has never been tested, its cytotoxicity to glial cells was assayed and correlated with its redox properties. Coordinated catechol oxidizes faster than catechol in the presence of oxygen, but controlled potential electrolysis showed that its oxidation involves only one-electron. However, the oxidation of the free ligand by oxygen involves two electrons, which could generate more reactive oxygen species. Indeed, catechol was more cytotoxic than [Ru III (NH 3 ) 4 (catechol)] + complex to human glioblastoma GL-15 cells and also to rat astrocytes. [Ru III (NH 3 ) 4 (catechol)]-induced cytotoxicity was related to the generation of reactive oxygen species and [Ru II (NH 3 ) 4 (quinone)] 2+ . However, other mechanisms should be involved since antioxidant enzymes and deferoxamine only partially protected GL-15 cells. INTRODUCTION Ruthenium is an element that has industrial, pharmaceutical and medical applications. Ruthenium can be used in the reduction of noxious oxides from industrial emissions

Study of the Electrochemical Redox Characteristics of Some Triazolopyrimidines

An electrochemical study related to the redox characteristics of Ethyl-3-acetyl-6-methyl-1, 4-diphenyl-4, 3a-dihydro-1, 3, 4-triazolino[3, 4-a] pyrimidine-5-carboxylate ester and its derivatives (1a-f) and (2a-e) in nonaqueous solvents such as 1, 2-dichloroethane (DCE), dichloromethane (DCM), acetonitrile (AN), dimethylsulphoxide (DMSO) and tetrahydrofurane (THF) using <TEX>$0.1\;mol\;dm^{-3}$</TEX> tetrabutylammonium perchlorate (TBAP) as a supporting electrolyte at platinum, glassy carbon and gold electrodes, has been performed using cyclic voltammetry (CV). Controlled potential electrolysis (CPE) is also carried out to elucidate the course of different electrochemical reactions through the separation and identification of the intermediates and final electrolysis products. The redox mechanism is suggested and proved. It was found that all the investigated compounds in all solvents are oxidized in a single irreversible one electron donating process following the well known pattern of the EC-mechanism to give a dimer. On the other hand, these compounds are reduced in a single irreversible one electron step to form the anion radical, which is basic enough to proton from the media forming the radical which undergoes tautomerization and then dimerization processes to give also another bis-compound through N-N linkage formation.

Nickel(I) Salen-Catalyzed Reduction of 1-Haloalkyl-2-oxocycloalkanecarboxylates: Three- and Four-Carbon Ring Expansions

Cyclic voltammetry and controlled-potential electrolysis have been employed to study the catalytic reduction of methyl 1-(4-halobutyl)-2-oxocyclopentanecarboxylate and ethyl 1-(3-halopropyl)-2-oxocyclohexanecarboxylate by nickel(I) salen electrogenerated at carbon cathodes in dimethylformamide containing tetramethylammonium tetrafluoroborate. Electrocatalytic reduction of the aforementioned compounds, in either their bromo or iodo forms, affords the corresponding ring-expanded products (methyl cyclononanone-5-carboxylate and ethyl cyclononanone-5-carboxylate) in up to 26% yield, along with the dehalogenated species (methyl 1-butyl-2-oxocyclopentanecarboxylate and ethyl 1-propyl-2-oxocyclohexanecarboxylate) and their unsaturated counterparts [methyl 1-(but-3-enyl)-2-oxocyclopentanecarboxylate and ethyl 1-allyl-2-oxocyclohexanecarboxylate]. However, the principal products are dimers—dimethyl -(octane-1,8-diyl)bis(2-oxocyclopentanecarboxylate) derived from methyl 1-(4-halobutyl)-2-oxocyclopentanecarboxylate, and diethyl -(hexane-1,6-diyl)bis(2-oxocyclohexanecarboxylate) arising from ethyl 1-(3-halopropyl)-2-oxocyclohexanecarboxylate—obtained in yields ranging from 52% to 83%. A mechanistic scheme, involving alkyl radicals formed via nickel(I) salen-catalyzed cleavage of the carbon-halogen bond of each substrate, is proposed to account for the formation of the various products.

Anodic carbon–boron bond cleavage through the intermediacy of electrogenerated bromonium ion

The electrochemical properties of a series of cyclic arylboronic esters, XC 6H 4B(OR) 2 [RR = CH 2CH 2; X = H ( 1a); p-Me ( 1b); p-OMe ( 1c); p-Cl ( 1d); p-Ph ( 1e); m-Cl ( 1f); m-OMe ( 1g); CF 3 ( 1h); OMe ( 1i); 2,6-dimethyl ( 1j); 1b with RR = (CH 2) 3, ( 1k); 1b with RR = CMe 2CMe 2, ( 1m)] has been studied in acetonitrile by cyclic voltammetry (CV) and controlled-potential electrolysis (CPE). The CV of representative examples of aryl borates with different substituents show one irreversible oxidation wave on a Pt cathode, at 1.8–1.9 V (vs. Ag/AgCl), with a negligible substituent effect. The cathodic CPE process led to small amounts of biaryls only, whereas the direct anodic CPE could not be carried out practically due to low currents. However, in the presence of electrogenerated bromonium (or iodonium) ions a C–B bond cleavage does take place to yield the corresponding bromoaryls, brominated phenols, and arylboronic acids as the major products.

On the role of the surfactant aliquat ® 336 on the kinetics of oxygen reduction reaction and on the rate of hydrogen peroxide electrosynthesis

This paper reports an investigation on the effect of the surfactant aliquat ® 336 (A336) on the mass transport parameters of the oxygen reduction reaction and on H 2O 2 electro-generation rate. Results have shown that most of the positive effects of adding A336 to the electrolyte are observed at concentrations around the critical micelle concentration (CMC). Results analyzed in this paper have shown that adding A336 at CMC shifted half-wave potential for O 2 reduction by 80 mV more negative and, furthermore, extended limiting current plateaus for the reaction O 2 → H 2O 2 over extra 100 mV more negative. Limiting currents for O 2 reduction are higher in the presence of A336, and the O 2 diffusion coefficient increased from 2 × 10 −6 cm 2 s −1 to 9 × 10 −6 cm 2 s −1. All these findings were verified by controlled potential electrolysis in a flow electrochemical reactor, where it was also found that the H 2O 2 electro-generation rate reached a maximum for A336 concentrations close to the CMC.