Electrooxidation of simulated wastewater containing pharmaceutical amoxicillin on thermally prepared IrO2/Ti

<p>The electrooxidation of amoxicillin (AMX) on the iridium oxide electrode thermally prepared (400°C) has been investigated by cyclic voltammetry and preparative electrolysis. Physical characterization by Scanning Electron Microscopy (SEM) showed that the IrO₂ electrode has a rough surface with pores' presence. In cyclic voltammetry, the oxidation of AMX occurs directly at the anode's surface or via the higher degree oxide of iridium oxide (IrO₃). It is noted that the oxidation process of AMX can be controlled by diffusion combined with the phenomenon of adsorption. In preparative electrolysis, the effect of several parameters has been investigated. These are the current density, the support medium, the initial pH. The findings obtained show a weak degradation of amoxicillin. The Chemical Oxygen Demand (COD) reduction rate is less than 11% under our experimental conditions, indicating that the IrO2 electrode leads to the parent compound's conversion. Also, the degradation of the organic compound is favored in a very acidic medium.<strong></strong></p><p>Furthermore, the effect of inorganic ions such as SO₄^2-, PO₄^3-, NO₃^-, Cl^- was evaluated. Investigations show that these ions' effects are diverse, with COD reduction rates ranging from 2.47%; 2.68%; 7.7%; 16.41%, and 71.65%, respectively, in the absence and the presence of SO₄^2-, PO₄^3-, NO₃^-, Cl^-ions. SO₄^2- have virtually no effect on enhancing the degradation of amoxicillin. PO₄^3- ions provide a slight improvement in amoxicillin degradation. As for nitrate ions, their influence is 2.31 times that of phosphate ions. Chloride ions improve the performance of the electrooxidation of amoxicillin on IrO2 very significantly. The presence of chloride ions makes it possible to go from 2928.35 (absence of inorganic ions) to 33.19 kWh per Kg of COD. This represents an energy gain of over 98%.</p>

Electrochemical oxidation and electroanalysis of paracetamol on a boron-doped diamond anode material in aqueous electrolytes

Electrochemical oxidation of paracetamol on boron-doped diamond (BDD) anode has been studied by cyclic voltammetry and preparative electrolysis. Quantification of paracetamol during electrolysis has been mainly realized by differential pulse voltammetry technique in the Britton-Robinson buffer solutions used as the supporting electrolyte. Various parameters such as current intensity, nature of the supporting electrolyte, temperature, and initial concentration of paracetamol have been investigated. The electrochemical characterization by the outer sphere Fe(III)/Fe(II) redox couple has also been performed, showing the metallic character of BDD electrode. The obtained linear dependency of the oxidation peak current intensity and paracetamol concentration indicates that BDD electrode can be used as an electrochemical sensor for the detection and quantification of paracetamol. The investi­gation of paracetamol degradation during preparative electrolysis showed that: (i) the degradation rate of paracetamol increases with increase of current intensity applied; (ii) for the initial concentrations of 10, 6 and 1 mM of paracetamol, its oxidation rate reaches 60, 78 and 99 % respectively, after 1 h of electrolysis in 0.3 M H2SO4 (pH 0.6) at applied current density of 70 mA cm-2; (iii) at temperatures of electrolyte solution of 28, 55 and 75 °C, paracetamol oxidation rate reached 85, 92 and 97 % respectively, after 2 h at applied current density of 70 mA cm2. From the investigation of the effect of pH value of electrolyte solution, it appears that oxidation of paracetamol is more favorable in acidic solution at pH 3 than solutions of higher pH values.

ELECTROCHEMICAL OXIDATION OF DIMETHYL SULFONE IN ALKALINE MEDIUM

In this paper the electrochemical oxidation of dimethyl sulfone (DMSO2) on a platinum electrode in an alkaline medium has been studied by cyclic voltammetry. It is shown that during the electrochemical oxidation of dimethylsulfone in an alkaline medium on a smooth platinum electrode, a significant suppression of the oxygen evolution (O2) occurs in the potential range of E = 1.3-2.0 V. By scanning electron microscopy methods, Raman scattering and infrared spectrometry it is shown that the main substance is the dimethyl disulfone (DMDSO2) during the anodic oxidation of DMSO2 on a platinum electrode. By the preparative electrolysis of aqueous solutions of various concentrations of DMSO2 in 0.1 M NaOH solution at controlled potentials E = 1.6 and 1.8 V it is established that the current yield of the base material is not more than 84%. Based on the data of the physicochemical analysis of the final products of preparative electrolysis, a mechanism is proposed for the formation of dimethyl disulfone in an alkaline medium. It has been shown that the oxidation of dimethyl sulfone proceeds in the oxygen region by breaking C-S bonds in the DMSO2 molecule to form methyl (CH3•) and methylsulfonic (CH3S•(O)2) radicals. It is assumed that the methylsulfone radicals readily dimerize with the formation of stable DMDSO2 molecules and are desorbed in the bulk of the solution, and the methyl radicals bind to the HO radicals to form methanol molecules. The latter is well chemisorbed on the surface of platinum with the formation of adsorbed COH particles that are oxidized on a platinum electrode with the formation and evolution of carbon dioxide (CO2) from the volume of the anolyte solution. The formation of molecules of methanol was identified by the method of chromato-mass -spectrometry, and the emission of carbon dioxide by the gravimetry.

Synthesis of naturally-derived macromolecules through simplified electrochemically mediated ATRP

The flavonoid-based macroinitiator was received for the first time by the transesterification reaction of quercetin with 2-bromoisobutyryl bromide. In accordance with the “grafting from” strategy, a naturally-occurring star-like polymer with a polar 3,3',4',5,6-pentahydroxyflavone core and hydrophobic poly(tert-butyl acrylate) (PtBA) side arms was synthesized via a simplified electrochemically mediated ATRP (seATRP), utilizing only 78 ppm by weight (wt) of a catalytic CuII complex. To demonstrate the possibility of temporal control, seATRP was carried out utilizing a multiple-step potential electrolysis. The rate of the polymerizations was well-controlled by applying optimal potential values during preparative electrolysis to prevent the possibility of intermolecular coupling of the growing polymer arms. This appears to be the first report using on-demand seATRP for the synthesis of QC-(PtBA-Br)5 pseudo-star polymers. The naturally-derived macromolecules showed narrow MWDs (Đ = 1.08–1.11). 1H NMR spectral results confirm the formation of quercetin-based polymers. These new flavonoid-based polymer materials may find applications as antifouling coatings and drug delivery systems.

Electrochemical behaviour of 1-{[(3-halophenyl)imino]methyl}-2-naphthol Schiff bases on graphite electrodes

An electrochemical study of the reduction of 1-{[(3-halophenyl)imino]methyl}-2-naphthol compounds on graphite electrodes was carried out. All the compounds were dissolved in a 1:4 (volume fraction) mixture of tetrahydrofuran (THF) and methanol. NaClO4 (0.1 mol L–1) was used as the supporting electrolyte. Cyclic voltammetry, chronoamperometry, constant-potential coulometry (bulk electrolysis), and constant-potential preparative electrolysis were employed. The cyclic voltammetric data revealed that the reduction on graphite was irreversible and followed an EC mechanism. The diffusion coefficients and the number of electrons transferred were determined using the chronoamperometric Cottrell slope and the ultramicro electrode steady-state current. The number of electrons was also determined by bulk electrolysis. The products of the electroreduction were synthesized in milligram quantities by the use of constant-potential preparative electrolysis. These products were purified and characterized by spectroscopic methods. Based on these findings, a mechanism for the electroreduction process is proposed.Key words: electrochemical reduction, hydroxynaphthylideneaniline Schiff bases, cyclic voltammetry, ultramicro electrode.

Electroreduction of 1-methyl 5-nitroindole, 5-nitrobenzofurane, and 5-nitrobenzothiophene in acidic and basic hydroorganic media: Generation and trapping of iminoquinone-type intermediates and electrosynthesis of ring-substituted amino derivatives

Preparative electrolysis of 1-methyl-5-nitroindole (1b, X = NCH3), 5-nitrobenzofurane (1c, X = O), and 5-nitrobenzothiophene (1d, X = S) at Hg, in acidic hydromethanolic media, leads to the formation of the corresponding 4-substituted amino derivatives 5, which result from the 100% regioselective addition to iminoquinone-type intermediate 4 of methanol or of any other good nucleophile present in the electrolytic solution. In acidic medium, the iminoquinonium intermediates 4b and 4c were trapped in a cycloaddition reaction with cyclopentadiene added to the electrolysis medium. The regiochemistry of the nucleophilic addition is discussed in light of AM1 calculations. Key words: 1-methyl-5-nitroindole, 5-nitrobenzofurane, 5-nitrobenzothiophene, iminoquinone, electrosynthesis.

Mechanism of Reduction of Cymantrene (Tricarbonyl η5-Cyclopentadienylmanganese) and Its Methyl Carboximidate Derivative

The mechanisms of electrochemical reduction of cymantrene, [Mn(CO)3(η5-Cp)], and its ring-substituted methyl carboximidate derivative, [Mn(CO)3(η5-C5H4C(NH)OMe)], were studied by voltammetry, in situ IR spectroelectrochemistry and preparative electrolysis. The product of one-electron reduction undergoes further chemical reactions. Comparison of the data obtained under atmosphere of argon and that of carbon monoxide leads to the conclusion that a ligand substitution reaction and dimerization participate in the overall reaction sequence. FTIR spectra recorded in situ suggest product dimerization, the formation of [Mn(CO)5]- and, to a lesser extent, other unstable species. The dimer formation was not observed in the course of the reduction of the carboximidate.