Home About us Contact
|
Home About us Contact | ||
|
|
||
Electrochemical Reduction (electrochemical + reduction)
Selected AbstractsPrussian Blue-Modified Titanate Nanotubes: A Novel Nanostructured Catalyst for Electrochemical Reduction of Hydrogen PeroxideELECTROANALYSIS, Issue 19 2010Damir Ivekovi Abstract Prussian blue (PB) modified titanate nanotubes (PB-TiNT) have been synthesized by the reaction of Fe2+ -modified TiNT with hexacyanoferrate(III) ions. The rate constant for heterogeneous catalytic reaction between PB-TiNT and H2O2 was found to be k=2×104,dm3,mol,1,s,1, which is an order of magnitude higher than the values of k reported for conventionally prepared, electrochemically deposited PB films. On the PB-TiNT modified electrode with subnanomolar surface concentration of PB (,(PB)=2.8×10,11,mol/cm2), a stable, reproducible and linear response towards H2O2 was obtained in the concentration range 0.02,4,mM, with the sensitivity of 0.10,AM,1,cm,2 at ,150,mV. [source] Electrochemical Reduction of S(IV) Compounds in Water-Ethanol Solutions at Nafion/Tetraruthenated Porphyrins Glassy Carbon Modified ElectrodesELECTROANALYSIS, Issue 3 2010Karla Calfumán Abstract This work describes electrocatalytic detection of S(IV) compounds in water-ethanol solutions under acidic conditions, on a glassy carbon electrode modified with Co(II) tetraruthenated porphyrin electrostatically assembled onto a Nafion film. The Ipc current shows a linear relationship with the concentration of S(IV) oxo-anions. Controlled potential electrolysis shows that thiosulfate was detected as reaction product. Rotating disk electrode and UV-visible spectroelectrochemistry experiments showed a kinetic limitation to the electron transfer controlled by charge propagation in the film and the formation of an intermediary between Co center and S(IV) species. The reproducibility of the modification methodology presents a RSD of 4.1%. [source] Electrochemical Reduction of 4,4,-(2,2,2-Trichloroethane-1,1-diyl)- bis(chlorobenzene) (DDT) and 4,4,-(2,2-Dichloroethane-1,1-diyl)- bis(chlorobenzene) (DDD) at Carbon Cathodes in DimethylformamideELECTROANALYSIS, Issue 4 2006Mohammad Abstract In dimethylformamide containing tetramethylammonium tetrafluoroborate, cyclic voltammograms for reduction of 4,4,-(2,2,2-trichloroethane-1,1-diyl)bis(chlorobenzene) (DDT) at a glassy carbon cathode exhibit five waves, whereas three waves are observed for the reduction of 4,4,-(2,2-dichloroethane-1,1-diyl)bis(chlorobenzene) (DDD). Bulk electrolyses of DDT and DDD afford 4,4,-(ethene-1,1-diyl)bis(chlorobenzene) (DDNU) as principal product (67,94%), together with 4,4,-(2-chloroethene-1,1-diyl)bis(chlorobenzene) (DDMU), 1-chloro-4-styrylbenzene, and traces of both 1,1-diphenylethane and 4,4,-(ethane-1,1-diyl)bis(chlorobenzene) (DDO). For electrolyses of DDT and DDD, the coulometric n values are essentially 4 and 2, respectively. When DDT is reduced in the presence of a large excess of D2O, the resulting DDNU and DDMU are almost fully deuterated, indicating that reductive cleavage of the carbon,chlorine bonds of DDT is a two-electron process that involves carbanion intermediates. A mechanistic scheme is proposed to account for the formation of the various products. [source] Exploration of Stable Sonoelectrocatalysis for the Electrochemical Reduction of OxygenELECTROANALYSIS, Issue 12 2005Biljana S, ljuki Abstract A series of modified electrodes were prepared both via solvent evaporation and electrochemical cycling of azobenzene and derivatives and various quinones and assessed for their suitability as oxygen reduction electrocatalysts and sonoelectrocatalysts. Glassy carbon electrodes were modified via solvent evaporation with 1,2-dihydroxyanthraquinone and 1,2-diazonium-9,10-anthraquinone while edge plane and basal plane pyrolytic graphite electrodes were modified by the same procedure with 9,10-phenanthraquinone. The stability of the attached moiety was accessed in each case under ultrasound. For comparison the same electrode substrates were modified with 9,10-phenanthraquinone by electrochemical cycling and also exposed to ultrasound. The observed results suggest the use of the glassy carbon electrodes modified with azobenzene and derivatives via solvent evaporation as the optimal carbon based sonoelectrocatalysts for oxygen reduction in term of stability under insonation and high catalytic rate. [source] Electrochemical Reduction of Oxygen on Carbon Supported Pt and Pt/Ru Fuel Cell Electrodes in Alkaline SolutionsFUEL CELLS, Issue 4 2003E.H. Yu Abstract A study of O2 reduction in 1 M NaOH solution at gas diffusion electrodes made from carbon supported Pt and Pt/Ru catalysts is reported. Two Tafel regions were observed for both the Pt and Pt/Ru electrodes. Although the same mechanism was suggested for oxygen reduction on both Pt and Pt/Ru catalysts, the O2 reduction activity was lower on Ru. Electrochemical Impedance Spectroscopy (EIS) analysis was carried out at different potentials and showed the significant contribution of diffusion on the reaction process and kinetics. The effect of methanol on O2 reduction was investigated in solutions containing various concentrations of methanol. The electrode performance deteriorated with increasing methanol concentration because of a mixed cathode potential. The methanol tolerance, i. e., the methanol concentration which polarises the O2 reduction reaction for O2 reduction, at the Pt/C electrode with a Pt loading of 1.2 mg cm,2 is 0.2 M methanol in 1 M NaOH. [source] Polycyclic Aromatic Compounds-Mediated Electrochemical Reduction of Alkyl Mesylates.CHEMINFORM, Issue 27 2007Hisanori Senboku Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF. [source] Synthesis of Pinacols Through Electrochemical Reduction of Carbonyl Compounds at Platinum Cathode in Non-aqueous Weakly Acidic Medium.CHEMINFORM, Issue 14 2005K. L. Yadava Abstract For Abstract see ChemInform Abstract in Full Text. [source] Preparative Electrochemical Reduction of Decafluorobenzil.CHEMINFORM, Issue 13 2005N. V. Vasil'eva Abstract For Abstract see ChemInform Abstract in Full Text. [source] Electrochemical Reduction of 5-Oxoindeno[1,2-b]pyridinium Perchlorates in the Presence of Alkylating Agents.CHEMINFORM, Issue 42 2004B. Turovska Abstract For Abstract see ChemInform Abstract in Full Text. [source] Regioselective Radical Cyclization by Electrochemical Reduction Using an Arene Mediator.CHEMINFORM, Issue 51 2003Environmentally Benign Method. Abstract For Abstract see ChemInform Abstract in Full Text. [source] ChemInform Abstract: Structure of the Dimers Arising from One-Electron Electrochemical Reduction of Pyridinium Salts 3,5-Disubstituted with Electron-Withdrawing Groups.CHEMINFORM, Issue 25 2002Vincenzo Carelli Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source] ChemInform Abstract: Selective Electrochemical Reduction of Cinnamyl Ethers in the Presence of Other Allylic C,O Bonds.CHEMINFORM, Issue 22 2001Aida Solis-Oba Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source] Influence of pH on the Photochemical and Electrochemical Reduction of the Dinuclear Ruthenium Complex, [(phen)2Ru(tatpp)Ru(phen)2]Cl4, in Water: Proton-Coupled Sequential and Concerted Multi-Electron ReductionCHEMISTRY - A EUROPEAN JOURNAL, Issue 15 2005Norma R. de Tacconi Prof. Abstract The dinuclear ruthenium complex [(phen)2Ru(tatpp)Ru(phen)2]4+ (P; in which phen is 1,10-phenanthroline and tatpp is 9,11,20,22-tetraaza tetrapyrido[3,2-a:2,3,-c:3,,,2,,-l:2,,,,3,,,]-pentacene) undergoes a photodriven two-electron reduction in aqueous solution, thus storing light energy as chemical potential within its structure. The mechanism of this reduction is strongly influenced by the pH, in that basic conditions favor a sequential process involving two one-electron reductions and neutral or slightly acidic conditions favor a proton-coupled, bielectronic process. In this complex, the central tatpp ligand is the site of electron storage and protonation of the central aza nitrogen atoms in the reduced products is observed as a function of the solution pH. The reduction mechanism and characterization of the rich array of products were determined by using a combination of cyclic and AC voltammetry along with UV-visible reflectance spectroelectrochemistry experiments. Both the reduction and protonation state of P could be followed as a function of pH and potential. From these data, estimates of the various reduced species' pKa values were obtained and the mechanism to form the doubly reduced, doubly protonated complex, [(phen)2Ru(H2tatpp)Ru(phen)2]4+ (H2P) at low pH (,7) could be shown to be a two-proton, two-electron process. Importantly, H2P is also formed in the photochemical reaction with sacrificial reducing agents, albeit at reduced yields relative to those at higher pH. [source] Electrochemical Reduction and Carboxylation of Ethyl Cinnamate in MeCNCHINESE JOURNAL OF CHEMISTRY, Issue 9 2008Huan WANG Abstract The electrochemical reduction and carboxylation of ethyl cinnamate have been carried out in an undivided cell equipped with a Mg sacrificial anode using MeCN as solvent. Direct electroreduction led to the formation of the hydrodimers and saturated ester. And electrocarboxylation was carried out in the presence of CO2. The global yield and the ratio of mono- to dicarboxylic acids were strongly affected by various factors: electrode material, electrolysis potential, the substrate concentration and temperature. The high yield (78%) was obtained under an optimized reaction condition (cathode: Ni; electrolysis potential: ,1.7 V; substrate concentration: 0.1 mol·L,1; and temperature: ,10 °C). [source] Electrochemical, ESR and quantum chemical study of 1-substituted naphthalenes and their radical anions,,JOURNAL OF PHYSICAL ORGANIC CHEMISTRY, Issue 1 2008N. V. Vasilieva Abstract Electrochemical reduction and oxidation of a series of 1-substituted naphthalenes (1-X-naphthalenes) have been studied by the method of cyclic voltammetry (CV). The first reduction peak of the majority of these compounds corresponds to a one-electron transfer to form the relatively stable radical anion (RA). For these species, ESR spectra have been registered and interpreted, the life time has been estimated. The first oxidation peaks of 1-X-naphthalenes are irreversible and correspond to a transfer of two or more electrons. Copyright © 2007 John Wiley & Sons, Ltd. [source] Synthesis and Properties of a New Poly(arylene ethynylene) Containing 1,3,5-Triazine Units,MACROMOLECULAR CHEMISTRY AND PHYSICS, Issue 6 2004Qiang Fang Abstract Summary: A new photoluminescent poly(arylene ethynylene) containing 1,3,5-triazine units was prepared by polycondensation between 2,4-diphenyl-6- N,N -bis(4-bromophenyl)amino-1,3,5-triazine and 1,4-didodecyloxy-2,5-diethynylbenzene using Pd(PPh3)4 and CuI as the catalysts in the presence of triethylamine. The polymer showed good solubility in common organic solvents and had a number average molecular weight, , of 3,400, and a weight average molecular weight, , of 8,100. In toluene the polymer exhibited an intrinsic viscosity [,] of 0.11 dL,·,g,1 at 30,°C. The polymer showed photoluminescence (PL) with emission peaks at 479 nm in CHCl3 and at 509 nm in the solid state; quantum yield of the PL in CHCl3 was 21%. Electrochemical reduction (or n-doping) of the polymer started at about ,2.05 V versus Ag/AgNO3 and gave a peak at ,2.30 V versus Ag/AgNO3. The 1,2,3-triazine unit-containing poly(arylene ethynylene) (PATZ) polymer synthesized and investigated here. [source] Cyclic Control of the Surface Properties of a Monolayer-Functionalized Electrode by the Electrochemical Generation of Hg NanoclustersCHEMISTRY - A EUROPEAN JOURNAL, Issue 33 2006Michael Riskin Abstract Hg2+ ions are bound to a 1,4-benzenedimethanethiol (BDMT) monolayer assembled on a Au electrode. Electrochemical reduction of the Hg2+,BDMT monolayer to Hg+,BDMT (at E°=0.48 V) and subsequently to Hg0,BDMT (at E°=0.2 V) proceeds with electron-transfer rate constants of 8 and 11 s,1, respectively. The Hg0 atoms cluster into aggregates that exhibit dimensions of 30 nm to 2 ,m, within a time interval of minutes. Electrochemical oxidation of the nanoclusters to Hg+ and further oxidation to Hg2+ ions proceeds with electron-transfer rate constants corresponding to 9 and 43 s,1, respectively, and the redistribution of Hg2+ on the thiolated monolayer occurs within approximately 15 s. The reduction of the Hg2+ ions to the Hg0 nanoclusters and their reverse electrochemical oxidation proceed without the dissolution of mercury species to the electrolyte, implying high affinities of Hg2+, Hg+, and Hg0 to the thiolated monolayer. The electrochemical transformation of the Hg2+ -thiolated monolayer to the Hg0 -nanocluster-functionalized monolayer is characterized by electrochemical means, surface plasmon resonance (SPR), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), atomic force microscopy (AFM), and contact-angle measurements. The Hg0 -nanocluster-modified surface reveals enhanced hydrophobicity (contact angle 76°) as compared to the Hg2+ -thiolated monolayer (contact angle 57°). The hydrophobic properties of the Hg0 -nanocluster-modified electrode are further supported by force measurements employing a hydrophobically modified AFM tip. [source] Temperature-Dependent and Friction-Controlled Electrochemically Induced Shuttling Along Molecular Strings Associated with ElectrodesCHEMPHYSCHEM, Issue 10 2005Eugenii Katz Dr. Abstract The temperature and solvent composition dependence of the electrochemically stimulated rate of shuttling of the redox-active cyclophane, cyclobis(paraquat- p -phenylene), on a molecular string has been studied. The molecular string includes a ,-donor diiminebenzene-site that is associated on one side with an electrode, and stoppered on the other side with an adamantane unit. The cyclophane rests on the ,-donor site, owing to stabilizing ,-donor,acceptor interactions. Electrochemical reduction of the cyclophane units, to the bis-radical cation cyclophane, results in the shuttling of the reduced cyclophane towards the electrode, a process that is driven by the removal of the stabilizing donor,acceptor interactions, and the electrostatic attraction of the reduced product by the electrode. The latter process is energetically downhill, and is temperature-independent. Upon oxidation of the reduced cyclophane that is associated with the electrode, the energetically uphill shuttling of the oxidized cyclophane to the ,-donor site proceeds. The rate of this translocation process has been found to be temperature-dependent, and controlled by the solvent composition. The experimental results have been theoretically analyzed in terms of Kramers' molecular friction model. The theoretical fitting of the experimental results, using solutions of variable composition, reveals that the rate-constants for the uphill reaction in a pure aqueous solution follow the temperature-dependence of the viscosity of water. The results demonstrate the significance of friction phenomena in shuttling processes within molecular machines. [source] Electrochemical reduction of benzoylformic acid in ionic liquidCHINESE JOURNAL OF CHEMISTRY, Issue 9 2003Jia-Xing Lu Abstract Ionic liquids possess a number of unique properties that make them ideal electrolytes. Electrochemical reduction of benzoylformic acid in room temperature ionic liquids as reaction media could be conducted with excellent performances without any additional supporting electrolyte. Electrolysis at glassy carbon electrode results in the formation of mandelic acid in 91% yield. And the electrochemical behavior of benzoylformic acid was investigated with the technique of cyclic voltammetry. [source] A New Indirect Electroanalytical Method to Monitor the Contamination of Natural Waters with 4-Nitrophenol Using Multiwall Carbon NanotubesELECTROANALYSIS, Issue 9 2009Cruz Moraes, Fernando Abstract The electrochemical detection of the hazardous pollutant 4-nitrophenol (4-NP) at low potentials, in order to avoid matrix interferences, is an important research challenge. This study describes the development, electrochemical characterization and utilization of a multiwall carbon nanotube (MWCNT) film electrode for the quantitative determination of 4-NP in natural water. Electrochemical impedance spectroscopy measurements showed that the modified surface exhibits a decrease of ca. 13 times in the charge transfer resistance when compared with a bare glassy carbon (GC) surface. Voltammetric experiments showed the possibility to oxidize a hydroxylamine layer (produced by the electrochemical reduction of 4-NP on the GC/MWNCT surface) in a potential region which is approximately 700,mV less positive than that needed to oxidize 4-NP, thus minimizing the interference of matrix components. The limit of detection for 4-NP obtained using square-wave voltammetry (0.12,,mol L,1) was lower than the value advised by EPA. A natural water sample from a dam located in São Carlos (Brazil) was spiked with 4-NP and analyzed by the standard addition method using the GC/MWCNT electrode, without any further purification step. The recovery procedure yielded a value of 96.5% for such sample, thus confirming the suitability of the developed method to determine 4-NP in natural water samples. The electrochemical determination was compared with that obtained by HPLC with UV-vis detection. [source] Voltammetry as an Alternative Tool for Trace Metal Detection in Peloid Marine SedimentsELECTROANALYSIS, Issue 13 2007Irena Ciglene Abstract Here was demonstrated for the first time a possible application of abrasive stripping voltammetry in the direct measurement of trace metals in anoxic, sulfidic marine sediments (peloid mud) from a small and shallow (0.2,1,m) marine lagoon in Central Dalmatia, Croatia. Trace amounts of sample compounds are transferred to the graphite electrode surface and electrochemical reduction or oxidation processes are followed by the cyclic voltammetry in seawater or 0.55,M NaCl as electrolyte. After a preelectrolysis at potentials ranging from ,1.0 to ,1.5,V (vs. SCE) a well-defined anodic stripping peak corresponding to the oxidation of metal deposits generated at deposition potentials is obtained around ,0.74,V (vs. SCE). The same samples were studied by anodic stripping voltammetry at the Hg electrode and inductively coupled plasma-mass spectrometer (ICP-MS). ICP-MS showed higher concentrations of trace metals such as Al, Fe, Mo, Mn. A relatively high concentration of reduced sulfur species (RSS) (10,3 M) is determined electrochemically in porewater of the peloid mud, indicating that the magnitude of metal enrichment in the sediments is probably controlled by precipitation with sulfide. [source] Synthesis and Electrochemical Study of an Original Copper(II)-Capped Salen,Cyclodextrin ComplexEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 29 2010Elise Deunf Abstract A new metallocapped cyclodextrin (CD) was synthesized by the regioselective debenzylation, induced by diisobutylaluminium hydride (DIBAL-H), of perbenzylated cyclodextrins. This reaction allowed for the efficient preparation of an unprecedented CD,salen type copper(II) complex. The electrochemical behavior of both the bound and unbound CD,salen compounds was investigated by cyclic voltammetry. Notably, it was shown that the presence of tert -butyl groups at the ortho - and para -positions of the salen aromatic rings stabilized the copper(II) phenoxyl radical species that was generated upon the one-electron oxidation of the starting compound. Importantly, this stabilization remained effective when the salen-type ligand was covalently attached to the CD. This allowed for investigations of the reactivity of the copper(II) phenoxyl radical complex towards a primary alcohol to be performed by cyclic voltammetry. This reaction can be considered as mimicking the behavior of galactose oxidase. However, under these conditions, no reactivity was observed in the presence of benzyl alcohol. This may be due to distortion, either of the initially square planar salen ligand after its grafting to the CD primary face, and/or of the CD itself. On the other hand, the electrochemical reduction of the un-grafted copper(II) salen-type ligand led to a transient anionic species that exhibited significant stability on the time-scale of the slow cyclic voltammetry measurement in the absence of the CD, but was unstable in the presence of the CD. In the latter case, it was demonstrated that the anionic species was protonated by the CD. Importantly, this protonation was not fast enough to prevent catalytic activation of iodomethane by the electro-generated copper(I)-capped salen CD complex. [source] Substituent effects in reductions of heteroaromatic cationsJOURNAL OF PHYSICAL ORGANIC CHEMISTRY, Issue 10 2002David Heyes Abstract A set of 11 each of 2,4,6-triphenylpyrylium, -thiopyrylium and - N -methylpyridinium tetrafluoroborates carrying a range of substituents in the phenyl rings were prepared. First and second wave reduction potentials were determined. For the thiopyrylium series there are linear correlations between scaled potentials (E°/0.05915) and summed Hammett constants for substituents in the pendant phenyl groups (,,=,2.29 and 3.38 for first and second waves respectively). For the pyrylium series, a good linear relationship (,,=,2.79) is obtained for all substituent patterns for the first wave reduction potentials, but for the second wave there are separate correlations for salts carrying substituents in the 4-phenyl and for those carrying substituents in 2- and 6-phenyls. For the pyridinium series, the first wave potentials show separate correlations for salts carrying substituents in the 4-phenyl and for those carrying substituents in 2-and 6-phenyls, but a single linear relationship for the second wave potentials. These are related to particular structural features in the cations, radicals and anions in each series. Rates and products were determined for reductions of the pyrylium and thiopyrylium cations by sodium cyanoborohydride and of all cations by sodium borohydride in acetonitrile solution. Reactions are first order in reducing agent and cation. Primary kinetic isotope effects were determined for borohydride reduction of the least reactive of each of the series of cations. Plots of logarithms of second-order rate constants against summed Hammett constants for substituents in the pendant phenyl groups are linear for all combinations of reagent and cation with 0.91 < , < 1.50 across all substituent patterns. For parent pyrylium and thiopyryliums, kBH4/kCNBH3,=,8.4,×,104 and 1.5,×,104, respectively, and for reductions by borohydride the reactivities of the pyrylium, thiopyrylium and pyridinium, series decrease in the order 1.4,×,105:8.8,×,103:1. Constant selectivities are not observed. Comparison of the correlations for electrochemical reduction and for hydride addition leads to the conclusion that charge neutralization in the hydride addition transition states runs ahead of bonding changes at the originating B,H bond. Copyright © 2002 John Wiley & Sons, Ltd. [source] Polyquinolines containing both spirobifluorene and cardofluorene units: Synthesis and characterizationJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 13 2004Ching-Hsin Chen Abstract We have synthesized aromatic polyquinolines containing both spirobifluorene and cardofluorene moieties in the main chain by applying acid-catalyzed Friedländer quinoline synthesis. The incorporation of these rigid nonplanar structures into the polymer backbone, which restricts segmental mobility, significantly increases both the glass-transition temperature and thermal stability, while providing enhanced solubility as a result of a decrease in the degree of molecular packing and crystallinity. We have also examined the optical and electrochemical properties of these polyquinolines. The low-lying lowest unoccupied molecular orbital energy level and quasireversible electrochemical reduction of these polyquinolines suggest their potential for use as electron-injecting/transporting materials in polymer light-emitting diodes. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 3314,3322, 2004 [source] | |||||||||||||