Electrocarboxylation of benzyl chlorides at silver cathode at the preparative scale level

The electrocarboxylation of benzyl chlorides to the corresponding carboxylic acids performed at silver cathodes was investigated both theoretically and experimentally in order to find the influence of the operative parameters on the selectivity and on the Faradic efficiency of the process. Theoretical considerations were confirmed by the electrocarboxylation of 1-phenyl-1-chloroethane performed in undivided cells equipped with sacrificial anodes both in a bench-scale electrochemical batch reactor and in a continuous batch recirculation reaction system equipped with a parallel plate electrochemical cell. Selectivity and Faradic yields higher than 80% and 70%, respectively, were obtained by working under anhydrous conditions both under amperostatic and potentiostatic alimentation at appropriate values of either current density or applied potential.     

Electrocarboxylation of chloroacetonitrile by a Cobalt(I) complex of terpyridine

The electrocarboxylation of chloroacetonitrile (NC–CH₂–ClRCl) mediated by [Co^IIL₂]²⁺ (L = terpyridine) was investigated by cyclic voltammetry. Electrochemical studies under argon atmosphere showed that the monoelectronic reduction of [Co^IIL₂]²⁺ yielded a Cobalt(I) complex which after the loss of a terpyridine ligand reacted with chloroacetonitrile. The oxidative addition of chloroacetonitrile on [Co^IL]⁺ gave an alkylCobalt(III) complex [R–Co^IIIL]²⁺ which was reduced into an alkylCobalt(II) complex, highly unstable and decomposed into an alkyl anion and a Cobalt(II) complex. Under carbon dioxide atmosphere, Cobalt(I) complex was shown to be unreactive towards CO₂ but CO₂ insertion was observed in the alkylCobalt(III) complex [R–Co^IIIL] ²⁺ giving probably a CO₂ adduct [R–Co^IIIL(CO₂)]²⁺. This adduct presented a strong adsorption at the carbon electrode and was reduced at potential less cathodic than the one of alkylCobalt(III) complex. After reduction, the carboxylate RCO₂⁻ (NC–CH₂–CO₂⁻) was released and a catalytic bielectronic carboxylation of chloroacetonitrile took place. Controlled potential electrolyses confirmed the catalytic process and gave for cyanoacetic acid faradic yields up to 60% under low overpotential conditions.     

Electrochemical reduction of benzyl halides at a silver electrode

The electrochemical reduction of benzyl halides PhCH₂X (X = Cl, Br and I) has been investigated at Ag and glassy carbon (GC) electrodes in CH₃CN + 0.1 M Et₄NClO₄. At both electrodes reduction of PhCH₂X involves irreversible electron transfer concerted with breaking of the carbon-halogen bond. All three halides exhibit a single 2e⁻ reduction peak at GC, whereas up to three peaks can be observed at the Ag electrode. Silver exhibits remarkable catalytic properties for the reduction process, which is positively shifted by 0.45-0.72 V with respect to GC. The mechanism of reduction of the organic halides at Ag involves adsorption of both the starting reagents and their reduction products. Adsorption of PhCH₂Cl and PhCH₂Br is weak and slow, whereas PhCH₂I is more rapidly and strongly adsorbed, so that two distinct peaks can be observed for the reduction of the dissolved and adsorbed molecules. Controlled-potential electrolyses at Ag have shown that the process may be directed to the production of bibenzyl or toluene, depending on the applied potential.     

Factors influencing the formation of 2-hydroxy-6-naphthoic acid from carboxylation of naphthol

The synthesis of 2-hydroxy-6-naphthoic acid (2,6-HNA) from carboxylation of alkali-naphthoxide was studied with varying alkali cation types and reaction conditions such as reactant concentration, reaction time, temperature, and pressure. The product selectivity was strongly affected by the types of alkali cation, reaction time, and temperature, while the product yield was governed by reaction pressure. The maximum HNA yield, 28.6%, was achieved with 2,6-HNA selectivity of 81.6% at 6 atm of CO₂, 543 K, and 6 h of reaction. The addition of K₂CO₃ led to further increase in the productivity of 2,6-HNA via suppression of the decarboxylation of HNA.     

Electrocatalytic and simultaneous determination of isoproterenol, uric acid and folic acid at molybdenum (VI) complex-carbon nanotube paste electrode

This paper describes the development, electrochemical characterization and utilization of a novel modified molybdenum (VI) complex-carbon nanotube paste electrode for the electrocatalytic determination of isoproterenol (IP). The electrochemical profile of the proposed modified electrode was analyzed by cyclic voltammetry (CV) that showed a shift of the oxidation peak potential of IP at 175 mV to less positive value, compared with an unmodified carbon paste electrode. Differential pulse voltammetry (DPV) in 0.1 M phosphate buffer solution (PBS) at pH 7.0 was performed to determine IP in the range from 0.7 to 600.0 μM, with a detection limit of 35.0 nM. Then the modified electrode was used to determine IP in an excess of uric acid (UA) and folic acid (FA) by DPV. Finally, this method was used for the determination of IP in some real samples.     

Electrocatalytic oxidation of thioglycolic acid at carbon paste electrode modified with cobalt phthalocyanine: application as a potentiometric sensor

The voltammetric behavior of thioglycolic acid (TGA) was studied at a carbon paste electrode modified with cobalt phthalocyanine (CoPc). The CoPc-modified electrode shows high electrocatalytic activity toward oxidation of TGA, lowering substantially the overpotential of anodic reaction. Results of the cyclic voltammetry show that TGA undergoes a two-step oxidation (each step with one electron) resulting the dimer of thiol. Enhancement of the rate of electron transfer results in a near-Nernstian behavior of modified electrode to the concentration of TGA and makes it as a suitable potentiometric sensor for the detection of this compound. This electrode shows a near-Nernstian response in a wide linear range of the concentration TGA (4 orders of magnitude). The modified electrode was used successfully for the determination of TGA and its salts in hair-treatment products and also in culture media. The modified electrode exhibited a fast response time (<10 s), very good stability, and had an extended lifetime.     

电化学合成邻苯二甲酸和邻甲苯酸

以邻二氯苯、邻氯甲苯、二氧化碳为原料,N,N-二甲基甲酰胺为溶剂,铝、镍网及化学镀镍膜为阳极,不锈钢网为阴极,牺牲阳极法制备邻苯二甲酸、邻甲苯甲酸,邻苯二甲酸的产率为16%,电流效率为48%。     

Cavity microelectrodes for the voltammetric investigation of electrocatalysts: the electroreduction of volatile organic halides on micro-sized silver powders

In this work the use of cavity-microelectrodes is described for the study of the electrocatalytic properties of silver powders in the electroreduction of trichloromethane, taken as model compound. The key role played by the Ag surface status has driven the research towards the use of micro- and nanosized materials, whose exploitation requires the full understanding of the complex behaviour of multiphasial interfaces, and the development of the appropriate investigation methodologies. Moreover, comparison with electrodeposited silver macroelectrodes demonstrates the advantages of using cavity-microelectrodes, especially in terms of improvement of the electrocatalytic activity, insignificance of ohmic drop and double layer capacitance in the voltammetric response, and simplicity offered by the experimental procedure for renovating the electrode material and surface.     

Effect of silver on the photocatalytic degradation of humic acid

In this study, humic acid was mineralized and degraded photocatalytically in presence of bare TiO₂ and silver loaded TiO₂ (0.5–5.0 at.% Ag). X-ray diffraction (XRD) and inductive coupled plasma (ICP) analysis confirm the complete photodeposition of silver over TiO₂ by photodeposition method. X-ray photoemission spectroscopy (XPS) studies confirmed the presence of Ag⁰ in all Ag–TiO₂ samples and the absence of Ag⁺ ions. Silver loading over TiO₂ improved the rate of mineralization and degradation of humic acid with a maximum loading of 1.0 at.% Ag. Ninety percent carbon from humic acid was mineralized to CO₂ only after 60 min by using bare TiO₂ as a photocatalyst. However, this conversion was possible within 40 min by using 1.0 at.% Ag-loaded TiO₂. This observation verifies that coating of metals like silver over TiO₂ acts as an electron sink and can improve the redox reaction by preventing electron–hole recombination reaction. The optimum 1.0 at.% Ag loading in the current work is indicative that the blocking of the TiO₂ surface active sites by silver also plays an important role in the photocatalytic mineralization and degradation of humic acid. As the silver loading is increased, less number of active site are available over the surface of photocatalyst TiO₂ for redox reaction. This finding was supported by the TEM analysis of the photocatalyst samples.     

Electrocatalytic oxidation of some anti-inflammatory drugs on a nickel hydroxide-modified nickel electrode

The electrocatalytic oxidation of several anti-inflammatory drugs (mefenamic acid, diclofenac and indomethacin) was investigated on a nickel hydroxide-modified nickel (NHMN) electrode in alkaline solution. This oxidation process and its kinetics were studied using cyclic voltammetry, chronoamperometry, and electrochemical impedance spectroscopy techniques. Voltammetric studies indicated that in the presence of drugs, the anodic peak current of low-valence nickel species increases, followed by a decrease in the corresponding cathodic current. This pattern indicates that drugs were oxidized on the redox mediator immobilized on the electrode surface via an electrocatalytic mechanism. A mechanism based on the electrochemical generation of Ni(III) active sites and their subsequent consumption by drugs was also investigated. The corresponding rate law under the control of charge transfer was developed and kinetic parameters were derived. In this context, the charge-transfer resistance accessible both theoretically and through impedancemetry was used as a criterion. The rate constants of the catalytic oxidation of drugs and the electron-transfer coefficients are reported. A sensitive, simple and time-saving amperometric procedure was developed for the analysis of these drugs in bulk form and for the direct assay of tablets, using the NHMN electrode.     

One-step large-scale synthesis of micrometer-sized silver nanosheets by a template-free electrochemical method

We have synthesized micrometer-sized Ag nanosheets via a facile, one-step, template-free electrochemical deposition in an ultra-dilute silver nitrate aqueous electrolyte. The nanosheet growth was revealed to occur in three stages: (1) formation of polygonal Ag nuclei on a substrate, (2) growth of {112}-faceted nanowire from the nuclei, and (3) anisotropic growth of (111)-planar nanosheets, approximately 20 to 50 nm in thickness and 10 μm in width, in the <112>−direction. The vertical growth of the facet nanowire was induced by the strong interface anisotropy between the deposit and electrolyte due to the ultra-dilute concentration of electrolyte and high reduction potential. The thickness of Ag nanosheets was controllable by the adjustment of the reduction/oxidation potential and frequency of the reverse-pulse potentiodynamic mode.     

Voltammetric investigation of the dissociative electron transfer to polychloromethanes at catalytic and non-catalytic electrodes

The electrochemical behavior of CCl₄, CHCl₃ and CH₂Cl₂ has been investigated by cyclic voltammetry at glassy carbon and silver electrodes in DMF + 0.1 M Et₄NClO₄ in the absence and presence of a good proton donor. At both electrodes, each compound exhibits a series of reduction peaks which represent sequential hydrodechlorination steps up to methane. The nature of the electrode material and the proton availability of the medium affect drastically the voltammetric pattern of the compounds. Silver exhibits extraordinary electrocatalytic properties toward the reduction process, with positive shifts of the peak potentials of about 0.57-0.95 V as compared to glassy carbon. Reduction of any polychloromethane, CH_nCl_(4−n) (n = 0-2), yields the carbanion CH_nCl_(3−n)⁻ which partitions into two reaction channels: (i) protonation and (ii) Cl⁻ elimination to give a carbene :CH_nCl_(2−n). If a strong proton donor is added into the solution, sequential hydrodechlorination becomes the principal reaction route at both electrodes. When, instead, purposely added acid is not present in solution, both reaction pathways ought to be considered. In these conditions, when possible, self-protonation reactions play an important role in the overall reduction process.     

The chemistry involved in the loading of silver(I) into poly(amic acid) via ion exchange: A metal-ion-induced crosslinking behavior

Metal-ion-induced crosslinking of poly(amic acid) (PAA) was observed in the incorporation of silver ions into PAA through ion exchange. Studies on the interaction of silver ions with 3,3′,4,4′-benzophenonetetracarboxylic acid/4,4′-oxidianiline (BTDA/ODA)-based PAA suggest that the ion exchange reactions between poly(amic acid) and silver ions are not so simple as what we generally believed. It involves not only the formation of silver carboxylate but also the generation of diversified silver chemical entities arising from the strong chemical bonding of metal ions with the functional groups, such as carbonyl groups and amide groups, in the polymer chain, which are suggested to be responsible for the crosslinking behavior. Moreover, silver ions loaded into the film are readily self-reduced and provides us a convenient route to disperse very small metal nanoparticles into the polymeric matrix. Meanwhile, strong accelerating effect of silver ions was observed on the hydrolysis of PAA molecules and the characterization results indicate that about 14-16 wt% precursors were dissolved during the ion exchange in the aqueous silver ion solutions. Fortunately, it is found that the metal-ion-induced crosslinking structure formed in the silver-doped film has helped to prevent the damaging effect of silver ions and the essential structural features of PAA were retained in the remaining polymer matrix.     

Using an electrode with renewable surface for study of silver reduction from acid thiourea solutions

Sulfur-containing thiourea (TU) decomposition products exert a considerable effect on the silver electroreduction rate in TU solutions. The technique of removing a thin layer from a metal electrode in-situ at a fixed electrode potential makes it possible to minimize the influence of adsorbed impurities on the rate of the process under study. The values of the exchange current and transfer coefficient for silver reduction from TU solutions have been determined using this technique. Impurities in acid TU solution substantially increase the reduction rate for potentials more positive than about −0.5 V vs. Ag/AgCl.     

Hydrothermal synthesis of well-stable silver nanoparticles and their application for enzymeless hydrogen peroxide detection

We reported on a facile hydrothermal synthesis of well-stable silver nanopartiles (AgNPs) from an aqueous solution of AgNO₃ and poly[(2-ethyldimethylammonioethyl methacrylate ethyl sulfate)-co-(1-vinylpyrrolidone)] (PQ11), a kind of cationic polyelectrolyte, at 100 °C without the extra introduction of other reducing agents and protective agents. Transmission electron microscopy (TEM) observation reveals that the AgNPs thus formed mainly consist of small nanoparticles about 5 nm in diameter. It is found that such dispersion can form stable AgNPs-embedded films on bare electrode surfaces and these nanoparticles exhibit remarkable catalytic performance for hydrogen peroxide (H₂O₂) detection. The sensor has a fast amperometric response time of less than 2 s. The linear range is estimated to be from 1 × 10⁻⁴ M to 0.18 M (r = 0.998) and the detection limit is estimated to be 3.39 × 10⁻⁵ M at a signal-to-noise ratio of 3, respectively.     

Effect of sulphuric acid and copper sulphate concentrations on the morphology of silver deposit in the cementation process

The silver ion cementation on copper was investigated in the presence or absence of oxygen in solutions containing 1.85 × 10⁻⁴ M Ag⁺ at 25 °C. The influence of sulphuric acid and copper sulphate concentration (0.005-0.5 M) on the silver cement morphology was studied in details and results were linked with the previously determined kinetics data of the process. The morphology of silver deposit was found to be independent of the presence of oxygen in the system as well as the sulphuric acid concentration. Contrary, the concentration of copper sulphate strongly influenced the morphology of silver deposit. At the beginning of the cementation process silver covers uniformly the copper surface. Afterwards, a growth of dendrites is initiated on preferential parts of the surface. The growing dendrite behaves as cathodic sites, with relatively huge surface area and promotes the creation of anodic sites in a close neighbourhood. Finally, the anodic site encloses the dendrite island and develops its area inward the copper material. Copper ions at low concentration modified slightly silver dendrites but the increase in concentration up to 0.5 M Cu²⁺ leads to completely disappearance of dendrites from the surface. The lack of dendrites on the surface is a result of the competitive process that consumes additional silver ions, occurring in the bulk of the solution. The morphology of silver deposit cemented in the deoxygenated solution containing 0.5 M H₂SO₄ + 0.5 M CuSO₄ depends strongly on the mechanism of the process.     

Platinum-modified titanium anodes for the electrolytic destruction of nitric acid

Three sets of electrodes, namely Pt electroplated Ti (PET) and diffusion annealed PET (DAPET) of plating thickness 3, 5, 7 and 10 μm and thermochemically glazed mixed oxide coated titanium anode (MOCTA-G) were evaluated for their performance, with a view to optimizing the current density conditions for maximum efficiency during the electrolytic destruction of nitric acid. In the acid killing by electro-reduction process, concentration of nitric acid in the high level waste (HLW) from the spent nuclear fuel reprocessing plant was brought down from about 4 to 0.5 M in order to reduce the amount of HLW by subsequent evaporation and to minimise the corrosion in waste tanks during storage of the concentrated waste solution. The electrochemical reduction of 4 and 8 M nitric acid to near neutral conditions was carried out with the above-said anodes and Ti cathode at various cathodic current densities ranging from 10 to 80 mA cm⁻². At current densities below 15 mA cm⁻² MOCTA-G electrode worked satisfactorily, whereas PET and DAPET electrodes could withstand and function well at much higher cathodic current densities (up to 80 mA cm⁻²). The life assessment of a 3 μm thick PET electrode at a cathodic current density of 60 mA cm⁻² in 8 M HNO₃ for a period of 110 h showed no failure. Phase identification of the plated electrodes was done by XRD measurements and their surface morphology was investigated by SEM.     

Effect of both protective and reducing agents in the synthesis of multicolor silver nanoparticles

In this paper, the influence of variable molar ratios between reducing and loading agents (1:100, 1:50, 1:20, 1:10, 1:5, 1:2, 1:1, 2:1) and between protective and loading agents (0.3:1, 0.75:1, 1.5:1, 3:1, 7.5:1, 30:1, 75:1) in the synthesis of silver nanoparticles by chemical reduction has been evaluated to obtain multicolor nanoparticles with a high stability in time. The protective agent poly(acrylic acid, sodium salt) (PAA) and reducing agent dimethylaminoborane (DMAB) play a key role in the formation of the resultant color. Evolution of the optical absorption bands of the silver nanoparticles as a function of PAA and DMAB molar ratios made it possible to confirm the presence of silver nanoparticles or clusters with a specific shape. The results reveal that a wide range of colors (violet, blue, green, brown, yellow, red, orange), sizes (from nanometer to micrometer), and shapes (cubic, rod, triangle, hexagonal, spherical) can be perfectly tuned by means of a fine control of the PAA and DMAB molar concentrations.     

Electrocatalytic carboxylation of 2-amino-5-bromopyridine with CO2 in ionic liquid 1-butyl-3-methyllimidazoliumtetrafluoborate to 6-aminonicotinic acid

A new electrochemical procedure for the electrocatalytic carboxylation of 2-amino-5-bromopyridine with CO₂ in ionic liquid, 1-butyl-3-methyllimidazolium tetrafluoborate (BMIMBF₄), to 6-aminonicotinic acid was investigated for the first time. The experiments were carried out in three electrodes undivided cell under mild conditions, and the use of volatile and toxic solvents and catalysts, as well as any other additional supporting electrolytes, was avoided. The electrochemical reduction behavior of 2-amino-5-bromopyridine in BMIMBF₄ had been studied by cyclic voltammetry with a reduction peak at −1.6 V (vs. Ag). 6-Aminonicotinic acid was obtained in 75% yield and 100% selectivity, under the optimized condition. Moreover, the ionic liquid was successfully recycled.     

Large-scale synthesis and self-organization of silver nanoparticles with Tween 80 as a reductant and stabilizer

Tween 80 (polysorbate 80) has been used as a reducing agent and protecting agent to prepare stable water-soluble silver nanoparticles on a large scale through a one-pot process, which is simple and environmentally friendly. Silver ions can accelerate the oxidation of Tween 80 and then get reduced in the reaction process. The well-ordered arrays such as ribbon-like silver nanostructures could be obtained by adjusting the reaction conditions. High-resolution transmission electron microscopy confirms that ribbon-like silver nanostructures (approximately 50 nm in length and approximately 2 μm in width) are composed of a large number of silver nanocrystals with a size range of 2 to 3 nm. In addition, negative absorbance around 320 nm in the UV-visible spectra of silver nanoparticles has been observed, probably owing to the instability of nanosized silver colloids.