Controlled-potential Coulometry Research Articles

Millisecond Coulometry via Zeptoliter Droplet Collisions on an Ultramicroelectrode

AbstractWe show that discrete collisions of zeptoliter emulsion droplets on an ultramicroelectrode (UME) can be used as individual controlled potential coulometry experiments, lasting between 100 and 500 milliseconds. By loading a highly hydrophobic toluene droplet with a hydrophobic analyte of interest and knowing the volume of the droplet to a high degree of precision, Faraday's Law can be employed to calculate the number of electrons passed during the electrolysis. Monodisperse (±15 % of the average size) emulsion systems were created by ultrasonication followed by filtering through a 200 nm porous filter. Discrete droplet collision events were observed in the amperometric i‐t curve. Each of these collisions are interpreted as individual coulometry experiments, implying that several bulk electrolyses can be carried out over the course of one collision experiment. Herein, we show calculations of the electron stoichiometry for the ferrocene oxidation reaction, which agrees well with the expected value of 1 electron. We further extend the methodology to more complicated systems, such as the oxidation of tetrathiafulvalene (TTF), tertiary aliphatic amines, such as tripropylamine (TPrA), and a 1,2‐diphenylhydrazine (DPH) molecule. This electroanalytical methodology allows for fast, nanoscale electrolysis in low dielectric media.

Environmentally Friendly, One-pot, Catalyst-free, and Facile Electrochemical Synthesis of New SupraN- andO-Heterocycles

In the present study, electrochemical oxidation of 4-aminophenol (1a) has been studied in the presence of cyanoacetate derivatives 3a and 3b as nucleophile in a mixture of ethanol and phosphate buffer solution (0.15 M, pH 7) as green media using cyclic voltammetry and controlled-potential coulometry techniques. The obtained results indicate that the corresponding 4-iminocyclohexa-2,5-dienone (2a) formed from 4-aminophenol (1a) participates in the Michael addition reaction to yield new N- and O-heterocycles. The electrosynthesis of these new heterocycle compounds has been performed successfully in an undivided cell in good to excellent yields and high purity under mild conditions without any catalyst and toxic solvent.

Insight into the electrochemical oxidation of N,N-dialkyl-p-phenylenediamines in the presence of malononitrile and methyl cyanoacetate. A convergent paired electrochemical method for the synthesis of cyanide and dicyanide derivatives of phenylcarbonimidoyl

The electrochemical oxidation of N,N-dialkyl-p-phenylenediamines has been studied in the presence of malononitrile and methyl cyanoacetate as nucleophiles in water/ethanol (80:20, v/v) mixture using some electrochemical techniques (cyclic voltammetry, chronoamperometry, chronocoulometry and controlled-potential coulometry). Diagnostic criteria of the electrochemical methods in keeping with spectroscopic data of the isolated products revealed that N,N-dialkyl-p-phenylenediamines in the presence of malononitrile and methyl cyanoacetate via a convergent paired electrochemical process are converted to cyanide and dicyanide derivatives of phenylcarbonimidoyl. The present work has led to development of a green and one-pot method for the synthesis of the title compounds.

Advancing the Chemistry of CuWO4 for Photoelectrochemical Water Oxidation.

Photoelectrochemical (PEC) cells are an ongoing area of exploration that provide a means of converting solar energy into a storable chemical form (molecular bonds). In particular, using PEC cells to drive the water splitting reaction to obtain H2 could provide a clean and sustainable route to convert solar energy into chemical fuels. Since the discovery of catalytic water splitting on TiO2 photoelectrodes by Fujishima and Honda, significant efforts have been directed toward developing high efficiency metal oxides to use as photocatalysts for this reaction. Improving the efficiency of PEC cells requires developing chemically stable, and highly catalytic anodes for the oxygen-evolution reaction (OER). This water oxidation half reaction requires four protons and four electrons coupling in two bond making steps to form O2, which limits the rate. Our group has accelerated efforts in CuWO4 as a candidate for PEC OER chemistry. Its small band gap of 2.3 eV allows for using visible light to drive OER, and the reaction proceeds with a high degree of chemoselectivity, even in the presence of more kinetically accessible anions such as chloride, which is common to seawater. Furthermore, CuWO4 is a chemically robust material when subjected to the highly oxidizing conditions of PEC OER. The next steps for accelerating research using this (and other), ternary phase oxides, is to move beyond reporting the basic PEC measurements to understanding fundamental chemical reaction mechanisms operative during OER on semiconductor surfaces. In this Account, we outline the process for PEC OER on CuWO4 thin films with emphasis on the chemistry of this reaction, the reaction rate and selectivity (determined by controlled-potential coulometry and oxygen-detection experiments). We discuss key challenges with CuWO4 such as slow kinetics and the presence of an OER-mediating mid-gap state, probed by electrochemical impedance spectroscopy. We propose that this mid-gap state imparts the observed chemoselectivity of OER on CuWO4. We introduce insights into the chemical mechanism of PEC OER on CuWO4 using Tafel analysis of electrochemical polarization. We measure Tafel slopes of ∼161 mV/dec, showing that PEC OER proceeds at a slower rate on CuWO4 than on common electrocatalysts for this reaction. Moreover, the observed photocurrent is independent of the borate buffer concentration, signaling that the buffer plays no role in the rate-determining elementary step of the reaction. Finally, we explore some recent developments in doping this material with Co (a known electrocatalytically active metal) and in coupling it with a transparent manganese phosphate (MnPO) electrocatalyst. We find that introducing Co into the wolframite structure leads to detrimental recombination of photogenerated charge carriers. However, coupling CuWO4 with MnPO increases the photocurrent density. Despite some of these challenges, CuWO4 proves to be a robust, visible light absorbing photoanode that can oxidize water with a high degree of selectivity and is therefore worthy of further exploration. Even if new compositions emerge that show better reactivity, this material serves as an excellent proving ground for the common challenges in developing ternary-phase oxides and other compositionally complex materials.

Electrochemical and in situ spectroelectrochemical properties of metal-free and metallophthalocyanines containing α-naphtholbenzein groups on the peripheral positions

Phthalocyanine (Pc) compounds-containing α-naphtholbenzein units have been synthesized and characterized by spectroscopic data and elemental analysis. The redox properties of the compounds were investigated by cyclic and square wave voltammetry, controlled-potential coulometry and in situ spectroelectrochemistry in DMSO and compared with the free phthalonitrile ligand. The Pc compounds displayed common metal and/or ring-based reduction and oxidation processes. However, electrochemical measurements clearly suggested that the substituents involving anthraquinone units are redox active and so have a considerable effect on the redox processes of these compounds.

Kinetics study and electrochemical synthesis of arylsulfinic acid derivatives of clozapine in green media

The electrochemical oxidation of clozapine (CLZ) has been studied in the presence of toluenesulfinic acid (TSA) and benzenesulfinic acid (BSA) as nucleophiles in aqueous solution, using cyclic voltammetry and controlled-potential coulometry. The results indicate the participation of electrochemically produced dibenzodiazepine in the Michael addition type reaction with TSA or BSA to form the corresponding new dibenzodiazepin derivatives. On the basis of the EEC mechanism, the observed homogeneous rate constants (kobs) of the chemical reaction between oxidized clozapine with TSA and BSA were estimated by comparing the experimental cyclic voltammograms with the digitally simulated results. Also the effective parameters such as type of nucleophile, scan rate and pH on the rate constants of chemical reactions are investigated. The electrochemical synthesis of new dibenzodiazepine derivatives (3a and 3b) has been successfully performed in an undivided cell at biological pH. The product has been characterized by IR, 1H NMR, 13C NMR and MS methods.

Создание эталонной установки на основе метода кулонометрии с контролируемым потенциалом в рамках совершенствования государственного первичного эталона ГЭТ 176 и ее измерительные возможности

The results of developing of reference installation, based on a controlled-potential coulometry, in the frame of improving the State primary standard of the units of mass (molar) fraction and mass (molar) concentration of a component in the liquid and solid substances and materials GET 176 are presented. The physical principles of controlled-potential coulometry, content and metrological characteristics of the developed installation are considered. Measurement results of copper, iron and lead contents in the certified reference materials of metals' solutions and CRM of brass produced by BAM, Germany, obtained using reference installation are given.

Electrochemical Synthesis and Kinetic Evaluation of Electrooxidation of Acetaminophen in the Presence of Antidepressant Drugs.

With the aim of obtaining information about drug-drug interaction (DDI) between acetaminophen and some of antidepressant drugs (fluoxetine, sertraline and nortriptyline), in the present work we studied the electrochemical oxidation of acetaminophen (paracetamol) in the presence of these drugs by means of cyclic voltammetry and Controlled-potential coulometry. The reaction between N-acetyl-p-benzoquinone-imine (NAPQI) produced from electrooxidation of acetaminophen and antidepressant drugs (see scheme 1) cause to reduce the concentration of NAPQI and decreases the effective concentration of antidepressants. The cyclic voltammetric data were analyzed by digital simulation to measure the homogeneous parameters for the suggesting electrode mechanism. The calculated observed homogeneous rate constants [Formula: see text] for the reaction of electrochemically generated N-acetyl-para benzoquinn-imine with antidepressant drugs was found to vary in the order [Formula: see text] > [Formula: see text] > [Formula: see text] at biological pH.

Cost-effective electrosynthesis of a series of edaravones through an electrochemical-assisted domino heteroannulation and paired electrochemical process

A series of novel edaravone structures was successfully synthesized through the anodic oxidation of catechols in the presence of edaravone in aqueous solution. The cyclic voltammetric results indicate that a one-pot multi-step sequential reaction occurs between edaravone and the electrochemically derived ortho- and para-benzoquinones affording fused poly-heterocyclic compounds. Using controlled potential coulometry, it has been proved that this catalyst-free, tandem reaction occurs via EC, ECECi, and ECECiCi mechanisms. The paired electrochemical synthesis of compound 5g has been successfully performed in a one-pot process with carbon rods as working electrodes and RVC as counter electrodes in an undivided cell. In addition, the electrosynthesis of edaravone derivatives has been successfully performed in ambient conditions in an undivided cell using an environmentally friendly method with high atom economy. All of the obtained compounds were fully characterized by spectroscopic methods such as FT-IR, 1H NMR, 13C NMR, and MS.

Thermodynamic and electrochemical study of some dihydroxybenzenes in the presence of different nucleophiles

In the current study, effects of thermodynamic on the reaction mechanisms of the electrochemical oxidation of hydroquinone and catechol in the presence of various nucleophiles have been investigated both experimentally and theoretically, using cyclic voltammetry, controlled-potential coulometry, and density functional theory. The theoretical results were calculated at DFT (B3LYP) level of theory and 6-311+G(p,d) basis set. Calculated ΔG tot of the oxidation of the intermediates and products indicated that thermodynamic is one of the important parameters on the reaction mechanisms. The results of this work show that depending on the ΔG tot of electrochemical oxidation, the intermediates which are produced on the surface of electrode will participate in the electrochemical or chemical following reactions.

Green and One-Pot Electrochemical Synthesis of New Benzofurans Based on an ECC Mechanism

The electrochemical oxidation of quinizarine has been studied in the presence of methyl cyanoacetate and ethyl cyanoacetate acting as a nucleophile in acetate buffer solution mixed with ethanol (30/70 v/v) using cyclic voltammetry and controlled-potential coulometry methods. The results revealed that anthracene-1,4,9,10-tetraone derived from the electro-oxidation of quinizarin participates in 1,4-Michael addition reactions with cyanoacetate derivatives. The adducts formed convert to the corresponding benzofuran derivatives through an ECC (Electrochemical, Chemical, Chemical reaction) mechanism. In the present study, benzofuran derivatives were synthesised in good yields using controlled potential electro-oxidation at three graphite electrode in an undivided cell under mild conditions.

A Facile and Efficient One‐Pot Electrochemical Synthesis of Thiazole Derivatives in Aqueous Solution

AbstractIn the present work, the electrooxidation of hydroquinones 1a and 1b, and catechols 1c and 1d was studied in the presence of rhodanine (3) as nucleophile in a mixture of EtOH and phosphate buffer solution as ‘green’ media using cyclic voltammetry and controlled‐potential coulometry. The results indicated that the corresponding p‐ and o‐quinones formed from the hydroquinones and catechols, respectively, participate in Michael addition reaction to yield new thiazole derivatives. The electrochemical syntheses of these new thiazole derivatives were performed successfully at three graphite rod electrodes in undivided cells in good‐to‐excellent yields at room temperature without any catalyst.

Electrochemical oxidation of catechols in the presence of 4-mercapto-benzoic acid, to synthesis sulfanyl compounds and their biological studies

Electrochemical oxidation of catechols in the presence of 4-mercapto-benzoic acid as nucleophile have been studied in aqueous acetate buffer solution using cyclic voltammetry and control potential coulometry. The cyclic voltammetric results showed that an electro oxidative/Michael type sequential reaction occurs between the 4-mercaptide anion and electrochemically generated o-bezoquinones leading to the corresponding products 4a–4b.The mechanism electrochemical reaction is proved as an EC pathway using controlled-potential coulometry. The antimicrobial activity of these newly synthesized compounds were screened against Gram-positive and Gram-negative bacteria namely, Bacillus subtilis, Staphylococcus aureus, Escherichia coli. These newly syntheses compounds showed good antimicrobial activity.

Mechanistic Investigation of the Electro-Oxidation of Catechols in the Presence of N-Methylbenzylamine at Room Temperature: Synthesis of New Quinone Derivatives

Electro-oxidation of catechol derivatives has been studied in the presence of N-methylbenzylamine as nucleophile in phosphate buffer (c=0.15 M, pH=7)/ethanol solution using cyclic voltammetry and controlled-potential coulometry (CPC). Voltammetric data indicate that a 1,4-Michael addition of N-methylbenzylamine from its NH group to the electrochemically derived o-quinone via an ECE mechanism has occurred. Moreover, the progress of coulometry confirmed our electrochemical mechanism. The electrochemical synthesis of quinone derivatives has been successfully accomplished using CPC in a two-compartment cell and the products were characterised by FTIR and NMR spectroscopy and elemental analysis.

Efficient synthesis of diethyltetrahydroquinoxalinediones

Chemical and electrochemical oxidation of different catechols were studied in the presence of N,N′-diethylethylenediamine in phosphate buffer solution, using cyclic voltammetry, constant-current coulometry and controlled-potential coulometry. The quinones derived from catechols participate in Michael addition reactions with N,N′-diethylethylenediamine via the ECECE mechanism to form the corresponding new diethyltetrahydroquinoxalinedione derivatives.

Electrochemical, Electrocatalytic Dioxygen Reducing and Dielectric Relaxation Properties of Non-Peripheral Tetra-2,3-dihydro-1H-inden-5-yloxy Substituted Phthalocyanines

Novel metal-free and metallophthalocyanines were synthesized by cyclotetramerization of 3-(2,3-dihydro-1H-inden-5-yloxy)phthalonitrile and characterized. The redox properties of these compounds were investigated by cyclic voltammetry, square-wave voltammetry, controlled-potential coulometry and in situ spectroelectrochemistry in dimethylsulfoxide and dichloromethane. The compounds displayed metal and/or phthalocyanine ring-based reduction and oxidation processes. The color changes associated with these redox processes and electrogenerated anionic and cationic redox species were recorded with in situ electrocolorimetric measurements. The electrocatalytic performances of the compounds toward oxygen reduction reaction having vital importance for fuel cell applications were determined by hydrodynamic rotating disk and bipotentiostatic rotating ring-disk voltammetry measurements. The Vulcan XC-72/Nf/FePc modified glassy carbon electrode showed much higher catalytic performance toward oxygen reduction than those of the other modified ones. Furthermore, the field dependence of dielectric response and the conductivity of the samples were measured as a function of frequency and temperature. Dielectric relaxation behaviors of the phthalocyanines were also investigated. The ITO/ZnPc/Au sample showed the highest value of ɛ′(ω) as compared to the other samples. The analysis of the real and imaginary parts of the dielectric permittivity with frequency was carried out assuming a distribution of relaxation times as well as the scaling behavior of the dielectric loss spectra.

Electrochemical oxidation of catechol derivatives in the presence of 3-acetyldihydro-2(3H)-furanone: efficient and green method for synthesis of new butyrolactone derivatives

Electro-oxidation of catechols has been studied in the presence of 3-acetyldihydro-2(3H)-furanone as a nucleophile in water–ethanol solution (90:10 v/v), using cyclic voltammetry and controlled-potential coulometry. The results indicate that the electro-generated o-benzoquinone participates in a Michael addition reaction with this nucleophile and via EC mechanism pathway, converted to corresponding catechol derivatives. The products have been characterized after purification by IR, 1H NMR, 13C NMR, and elemental analysis method. .

None-catalyst and clean synthesis of symmetric and asymmetric indoles from electrochemical oxidation of 4-aminophenol and p-phenylenediamine in the presence of malononitrile in green media

The mechanism of electrochemical oxidation of p-phenylenediamine and 4-aminophenol in the presence of malononitrile, as a nucleophile is studied in a phosphate buffer solution (0.15M) mixed with ethanol (v:v) using the cyclic voltammetry, controlled-potential coulometry and UV-spectroscopy methods. The results obtained indicate that the oxidation form of p-phenylenediamine and 4-aminophenol participate in the 1,4-michael addition reactions with malononitrile via the ECECCC mechanism (E: electrochemical and C: chemical) for the electrochemical synthesis of new indole derivatives with good yield under controlled potential conditions. The products obtained were characterized after purification by the FT-IR, 1H NMR, 13C NMR, mass spectroscopy and elemental analysis.

The effect of electronic structure on electrocatalytic behaviors of cobalt Schiff base complexes: Electrosynthesis of 2-phenylacetic acid using carbon dioxide

Electrochemical fixation of carbon dioxide was used as an efficient method to synthesize 2-phenylacetic acid. The electrochemical carboxylation of benzyl bromide by two cobalt Schiff base complexes of [N,N′-bis(salicylaldehyde)-1,2-phenylenediimino cobalt(II)], [Co(II) salophen], and [N,N′-bis(benzoylacetone) ethylenediimino cobalt(II)], [Co(II) bzaen], in N,N-dimethylformamide and in the presence of carbon dioxide was investigated using cyclic voltammetry method. The electrocatalytic reduction mechanism of benzyl bromide is dependent on the electronic structure of the complexes. Moreover, the presence of CO2 improves the catalytic efficiency and stability of the complexes. Finally, controlled potential coulometry (CPC) and constant current coulometry (CCC) were carried out in the absence and the presence of CO2. The electrosynthesis yields of 2-phenylacetic acid from benzyl bromide are obtained by 50% and 55% using CPC and 60% and 70% using CCC under mild conditions using [Co(II) salophen] and [Co(II) bzaen] complexes respectively. DFT calculations along with Mulliken/NBO studies have been carried out, in order to support the experimental results.

Facile and one-pot, electro-organic synthesis of a new bis-quinone by the ECCE mechanism in green media

Abstract Electrochemical oxidation of 4-methyl catechol (1a) is investigated in the presence of 1,3-indandione (3) as nucleophile in phosphate buffer solution (0.2 mol/L, pH 6) mixed with ethanol as organic green solvent (50/50) using cyclic voltammetry and controlled-potential coulometry. The results indicated that quinones derived from electro-oxidation of 1a, participated in a 1,4-Michael addition reaction with 1,3-indandione (3) under ECCE mechanism. In this direction, a new bis-quinone was synthesized in high yield and good purity using a facile and convenient electrochemical pathway by carbon anode electrodes in an undivided cell.