Electrosynthesis Conditions Research Articles

The Importance of Batch Electrolysis Conditions during the Reduction of L-Cystine Hydrochloride

During the constant-current batch electrolysis of L-cystine hydrochloride to produce L-cysteine hydrochloride in 2 mol dm−3 HCl at 298 K, a simple mathematical model can describe reactant conversion. Initially, the reduction is under charge-transfer control; as electrolysis proceeds, the process shows mixed control, then eventually pure mass-transport control (due to convective-diffusion of the reactant). A parametric study of the major process variables (the current density and the catholyte flow rate) has suggested favored electrosynthesis conditions at a range of cathodes. Selection of the applied current density is a compromise between achieving higher rates of reduction as the current density is raised, balanced against the lower current efficiencies that result due to the increased rates of hydrogen evolution. High hydrogen overpotential cathodes such as mercury-plated copper and lead are favored. At a practical current density (2 kA m−2) titanium cathodes show comparable performance to mercury-plated copper and lead. The relative performance of titanium is much poorer at low current densities. Prolonged electrolysis highlighted problems with electrode stability at mercury-plated copper, lead, and titanium cathodes. In contrast, carbon is inert; the use of reticulated vitreous carbon and carbon felt provides a high surface area and moves mass-transport control to lower reactant concentrations and higher fractional conversions during the batch electrolysis. This produces much more favorable figures of merit. Under mass-transport controlled conditions, high catholyte flow rates are favored at all cathodes, as is the inclusion of a plastic mesh turbulence promoter in the catholyte channel. © 2005 The Electrochemical Society. All rights reserved.

Properties of Films Electropolymerized from an Aniline–Acrylamide Mixture

Conditions for electrosynthesis of co-polymers of aniline and acrylamide and the aniline role in it are established.

Electropolymerization Mechanism and Electrochemical Properties of Polypyrrole Film Doped with a Large Anion

Using the galvanostatic method the polypyrrole films doped with common low molecular weight inorganic anions and with the large surfactant anions were obtained. The electrochemical behaviour of polypyrrole films electrosynthesised in the presence of 1,2 dihydroxybenzenedisulfonic(3,5)acid disodium salt(1,2 DHBSAS)was investigated by cyclic voltammetry. The study has been focused on the evaluation of the effects of electrosynthesis conditions on the electroresponse of the PPY films as well as on the role of the nature of the electrolyte on the doping process and on the interface properties of the polymer electrode.The results indicate that the kinetics of the redox process are mainly governed by diffusion of the cations and anions of the supporting electrolyte(cycling electrolyte), while the large anions remain immobilized in the polymer structure. Therefore, the kinetics of the process can be monitored by changing the nature of the electrolyte and this may allow modulation of the electrical and optical properties of PPY/1,2 DHBSAS film.

Electrochemical investigations of the oxidation–reduction of furfural in aqueous medium: Application to electrosynthesis

The present study concerns the electrochemical properties of furfural in aqueous medium on noble (Au and Pt) and non-noble (Pb, Cu and Ni) metal electrodes. The anodic and cathodic reactions are investigated by cyclic voltammetry on Au, Pt and Ni electrodes and during prolonged electrolyses on Pt, Pb and Cu in order to find the optimum conditions for a paired electrosynthesis. Anodic reactions are controlled by diffusion in the range of the stability of the solvent (water). Beside these limits, the gas evolution competes with the conversion of furfural. The best conditions for preparative electrooxidation (Ni anode, 0.5 M NaOH, j=0.8 mA cm −1) gave furoic acid in a 80% yield and furfuryl alcohol was obtained by electroreduction in a 55% yield on Cu cathodes at pH 10 and 30 mA cm −2.

Theoretical Foundations and Implementation of the High-Temperature Electrosynthesis of Molybdenum Carbide in Ionic Melts

A thermodynamic analysis and a voltammetric study of molybdenum- and carbon-containing melts were performed. The melt composition and electrosynthesis conditions were optimized to obtain molybdenum carbide powders and coatings.

Effect of electrosynthesis conditions on the structure and optical properties of the polyphenylacetylene films

The method of electrochemical synthesis of conducting polyphenylacetylene (PPA) layers on Pt, Cu, SnO 2 , ITO-surfaces was developed. The influence of electrosynthesis conditions on the structure, morphology, optical spectra and conductivity of PPA films have been studied. The influence of electrosynthesis condition on the electron spectra of PPA films allow to propose the possibility of electrochemical generation in PPA films the free charge carriers by the mechanism of electrochemical doping.

Direct Electrochemical Synthesis of Diaziridines

The possibility of direct electrosynthesis of mono- and bicyclic diaziridines is studied using, respectively, 1,2-dimethyldiaziridine and 1,5-diazobicyclo[3,1,0]hexane as an example. In either case the process is realized in a galvanostatic electrolysis in the anodic space of a diaphragm cell and proceeds through intermediate formation of alkylchloramines; other electrosynthesis conditions depend on the structure of the source aminoalkane. In the synthesis of monocyclic diaziridines, for the electrolyte, a 4 M solution of NaCl in water was used, which contained high concentrations of 0.5 and 2.0 M of, respectively, CH2O and MeNH2, and the amine excess served, in particular, for binding protons in the reaction of diaziridine synthesis. The process occurs in a homogeneous phase, and the current efficiency for 1,2-dimethyldiaziridine amounted to 40–50% in optimum conditions. In the synthesis of bicyclic diaziridines, the electrolyte was a 4 M solution of NaCl in a 20-% aqueous methanol, containing a low—0.1 M concentration of H2N(CH2)3NH2 and an equimolar quantity of CH2O, and additives of NaHCO3 were used for binding protons in the reaction of diaziridine synthesis. The process occurs in a heterophase environment because of an incomplete dissolution in the conditions of experiment of NaCl and intermediately-formed chloraminoalkane. The current efficiency for 1,5-diazobicyclo[3,1,0]hexane reached 80–85% in optimum conditions, but the loads of the source aminoalkane were 20 times lower than in the synthesis of monocyclic diaziridines. Compared are the results of a direct and an earlier-described indirect method of electrosynthesis of mono- and bicyclic diaziridines.

Quartz crystal microbalance study of electrochemical deposition of poly(3-dodecylthiophene) films on Au electrodes

Poly(3-dodecylthiophene) films were synthesised electrochemically from a propylene carbonate solution of the monomer, by galvanostatic method and cyclic voltammetry. Electrochemical properties of the resulting polymers were compared with the properties of regioregular head-to-tail (HT) polymer synthesised chemically. The first part of the work is focused on the electrochemical characteristics of HT polymer, namely on dependence of the shape of cyclic voltammograms obtained for redox reaction of the polymer on the film thickness and mean conjugation length. In the second part, the optimum conditions of electrosynthesis have been established. The quartz crystal microbalance measurements carried out during potentiodynamic polymerisation of 3-dodecylthiophene (by cyclic voltammetry) showed that deposition of the polymer film was preceded by dissolution of the gold substrate. At the later stage of the film formation, the oligomers that were initially accumulated in the vicinity of the electrode, attained the crucial lengths and precipitated on the electrode surface. In the case of a slow diffusion of the monomer to the electrode the growing film may be irreversibly overoxidised or/and crosslinked.

Direct electrochemical synthesis of novel transition metal chelates of tridentate azomethinic ligands

New chelates of the type ML(L 1) n ·MeOH ( n=1, 2) were obtained on the basis of the tridentate azomethinic ligands 2- N-tosylamine(2′-hydroxybenzal)aniline (L) and 2- N-tosylamine(2′-tosylaminobenzal)aniline (L 1) and zero-valent transition metals (Co, Ni, Cu, Zn, Cd) under electrosynthesis conditions. The mononuclear character of these products and the participation of N 2O- or N 3 groups of the azomethinic ligands in the coordination are demonstrated by IR, 1H NMR spectral and magnetic data (77–293 K).

Electrochemically synthesized polypyrrole nanotubules: effects of different experimental conditions

Nanotubules of polypyrrole (PPy) were electrochemically synthesized using the pores of nanoporous polycarbonate (PC) particle track-etched membranes (PTM) as templates. The influence of some conditions of electrosynthesis (electrochemical method, monomer concentration, electrolyte concentration and nature) on the kinetics of pyrrole electropolymerization and on the morphology of the obtained nanomaterials has been investigated. In particular, the empirical kinetics of the electrochemical generation of polypyrrole–perchlorate (PPy–ClO 4) from aqueous solution, at 0.8 V (vs SCE) was followed by electrical charges measurement. The orders with respect to pyrrole and LiClO 4 are 0.34 and 0.70 respectively. The electrogeneration of polypyrrole–polystyrenesulfonate (PPy–PSS) was also followed and shows that an increase of the electrolyte concentration increases the polymerization rate at constant potential. Finally, the morphology of PPy nanotubules doped with LiClO 4 and NaPSS has been studied by high resolution emission SEM and by TEM.

Electrosynthesis of poly(3‐methylthiophene) films with high strength and stabile conductive properties

AbstractThe electrochemical polymerization of 3‐methylthiophene was significantly facilitated by the presence of freshly distilled boron fluoride‐ethyl ether as supporting electrolyte and stainless steel as electrode during the polymerization. The lower oxidation potential of the monomer led to high overall stereoregularity and stacking order of poly(3‐methylthiophene) chains. A current density of 1 mA/cm2 and a monomer concentration of 35–70 mmol/L turned out to be optimal electrosynthesis conditions. Poly(3‐methylthiophene) films had high tensile strength (73 MPa) and flexibility. The high stereoregularity of poly(3‐methylthiophene) resulted in high conductivity with improved environmental stability.

Influence of synthesis conditions on polypyrrole-poly(styrenesulphonate) composite electroactivity

The influence of the conditions of electrosynthesis (potential, monomer and electrolyte concentrations) on the electroactivity of polypyrrole-poly(styrenesulphonate) (PPy-PSS) composite films was determined. This electroactivity was evaluated by the charge storage ability of the polymer (amount of electrical charge stored (millicoulombs) per unit mass (milligrams) of polymer). A parallel kinetic study on PPy-PSS electrogeneration was followed. The charge storage ability of electrogenerated PPy-PSS films increased when films were electrogenerated from increasing concentrations of monomer. Films generated from increasing concentrations of polyelectrolyte or at high potentials showed lower charge storage abilities. Increasing monomer concentration favours the monomer oxidation at lower overvoltages, increases the polymerization rate at constant potential and retards the passivation-degradation processes towards high anodic overvoltages. An increase of the electrolyte concentration retards the monomer oxidation towards higher overvoltages, increases the polymerization rate at constant potential, once the monomer oxidation was initiated, and favours passivation processes. The empirical kinetics of the electrochemical generation of composite films of PPy-PSS from aqueous solution, at 800mV (vs. SCE), were followed by ex situ ultramicrogravimetry. The orders with respect to pyrrole and NaPSS are 0.35 and 0.70 respectively.

Electrosynthesis of Nitrosobenzenes Bearing Electron Withdrawing Substituents

Optimum conditions for electrosynthesis of nitrosobenzenes bearing in meta or para position electron withdrawing groups (, , , , ) were found using dc polarography, cyclic voltammetry, and the recording of current‐voltage curves using mercury and carbon electrodes. Electroreduction was best carried out in an acetate buffer pH 5.7 containing 20 to 40% dimethylformamide using a porous carbon electrode. This was followed by electro‐oxidation on an anode of a similar composition in the same solution. Two consecutive batch electrolyses are possible, but yields with a flow‐through cell were better due to a smaller effect of consecutive condensations, yielding azoxy or azomethine compounds. At pH 5.7, which was used in this study, the rates of these competitive processes were lowest.

Electrochemistry of conjugated organic polymers

The electrochemistry of conjugated organic polymers such as polyaniline, polythiophene, and polypyrrole has been reviewed. The physical chemistry and, especially, the electrochemistry of conducting polymers (CP) are largely determined by their electrosynthesis conditions. The effects of such factors as the dopant, solvent, and base electrolyte on the preparation and electrochemical n- and p-doping of CP have been considered. The outstanding features of the electrochemistry of CP have been delineated. The prospects for the use of CP as active cathode and anode materials in chemical cells have been discussed.

Recent developments in the synthesis and functionalization of conducting poly(thiophenes)

AbstractThe mechanism of the electropolymerization of thiophene derivatives has been investigated by varying the electrosynthesis conditions and the monomer structure. The results of these analyses led to the definition of optimized electrosynthesis conditions allowing the control of the electrical and electrochemical properties of poly(thiophenes). On the basis of these results, the properties of these polymers have been modified by means of a new one‐step electrosynthesis of conducting composite materials and by the direct electropolymerization of tailor‐made functionalized monomers. For this purpose, the steric conditions associated to the various possibilities of covalent derivatization have been analyzed, leading to the definition of a “functionalization space”, compatible with the preservation of high conductivity and electrochemical reversibility in the resulting polymers. This concept has been applied to the synthesis of highly conducting chiral poly(thiophenes) on which an effect of enantioselective molecular recognition has been demonstrated for the first time.

Recent developments in the synthesis and functionalization of conducting poly(thiophenes)

AbstractThe mechanism of the electropolymerization of thiophene derivatives has been investigated by varying the electrosynthesis conditions and the monomer structure. The results of these analyses led to the definition of optimized electrosynthesis conditions allowing the control of the electrical and electrochemical properties of poly(thiophenes). On the basis of these results, the properties of these polymers have been modified by means of a new one‐step electrosynthesis of conducting composite materials and by the direct electropolymerization of tailor‐made functionalized monomers. For this purpose, the steric conditions associated to the various possibilities of covalent derivatization have been analyzed, leading to the definition of a “functionalization space”, compatible with the preservation of high conductivity and electrochemical reversibility in the resulting polymers. This concept has been applied to the synthesis of highly conducting chiral poly(thiophenes) on which an effect of enantioselective molecular recognition has been demonstrated for the first time.

Effects of steric factors on the electrosynthesis and properties of conducting poly(3-alkylthiophenes)

Two series of thiophene monomers 3-substituted with linear and branched alkyl chains have been synthesized, and their electropolymerization has been investigated together with the properties of the resulting polymers. An analysis of the effects of the electrosynthesis conditions by visible absorption spectroscopy shows that the mean conjugation length presents an increasing dependence on the applied electrical conditions as the length of the alkyl chain increases. In the case of linear alkyl substituents (R3 = CH/sub 3/ to C/sub 18/H/sub 37/), the length of the alkyl chain affects slightly the polymerization reaction but produces important modifications on the structure and on the properties of the polymers. Thus, the mean conjugation length and the electrochemical reversibility admit an optimum for the polymers containing 7-9 carbons in the alkyl chain while the polymer films remain highly conductive up to R3 = C/sub 10/H/sub 21/. In contrast, the steric hindrance to conjugation caused by branched alkyl substituents totally inhibits the polymerization (isopropyl) or leads to weakly conjugated polymers (isobutyl). It is shown that the distance between the thiophene ring and the branched alkyl chain is the determining parameter which governs the aptitude for electropolymerization and the properties of the resulting polymer.

Polythienothiophene as cathode active material. A comparative study with polythiophene and polydithienothiophene

Polythienothiophene (pTT) electrode performance is dependent on electrosynthesis conditions of the polymer film. A comparative performance study of pTT, polythiophene (pT) and polydithienothiophene (pDTT) in relation to their use as cathode-active materials in lithium-LiClO 4-propylene carbonate batteries, showed that pTT polymer electrode was not competitive; as the kinetic of its doping—undoping process was the slowest and the value of its specific charge capacity, was the lowest.

Characteristics of electrochemically synthesized polymer electrodes in lithium cells—IV. Effects of the synthesis conditions on the performance of polypyrrole

The performance of polymer electrodes in lithium cells strongly depends on the conditions of electrosynthesis. In this work we describe the role of current density and of total charge of preparation on the cyclability of polypyrrole electrodes in a 1 M LiClO 4 solution in propylene carbonate.

Réduction électrochimique de γ-nitrocétones. Conditions expérimentales d'accès à des dérivés de la pyrroline et de la pyrrolidine

Optimal conditions for electrosynthesis, at a mercury cathode in hydroalcoholic media, of three classes of nitrogen heterocyclic compounds are set up from an exhaustive study of the electrochemical behaviour of γ-nitroketones 1 and their reduction products.Pyrroline-N-oxides 3 are obtained by cyclization of the hydroxylamine when the nitro compounds are reduced at sufficiently low cathodic potentials. Quantitative yields are achieved in the case of tertiary nitro compounds. In other cases (primary and secondary nitro compounds), simultaneous formation of ketone-oximes 6 occurs.According to the nature of the α-substituent of the carbonyl, the other heterocyclic derivatives can be prepared as follows. In the case of a methyl substituent, pyrrolines 4 can be obtained by reduction of nitro compounds 1 or of N-oxyde pyrrolines 3. Pyrrolidines 5 are prepared by reduction of 1, or 3 and 4 in the case of tertiary compounds. In the case of a phenyl substituent, pyrrolines 4 can only be obtained by reduction of compounds 3 arising from a tertiary nitro compound. Pyrrolines 5 are prepared by direct reduction of 1 (primary and secondary nitro compounds) or of 3 and 4 (tertiary nitro compounds).