Reduction Of Perchlorates Research Articles

Cyclic voltammogram analysis of the 3,3´- (1,4-phenylene) perchlorates

As a consequence of a three-stage synthesis from terephthalic aldehyde, a series of 3,3 '- (1,4-phenylene) perchlorates including methyl, hydrogen, acetyl, bromio, methoxy and nitro groups (R = Br, H, Me). The matching formazans were reacted with formalin in dioxane in the presence of perchloric acid to produce tetrazin ium salts. Formazans were synthesized by reacting terephthalic aldehyde phenylhydrazone with ar ene diazonium tosylates in a DMF/pyridine combination. The use of ar ene diazonium tosylates greatly simplified the separation and purification of formazans. The p henylhydrazone was produced in aqueous dioxane using the usual approach from terephthalic aldehyde and phenylhydrazine/hydrochloric acid. Individual f ormazans and tetrazinium perchlorates were isolated and characterized by elemental analysis, IR, NMR, UV spectroscopy. The electrochemical reduction of tetrazinium perchlorates was investigated using cyclic voltammetry (CV). Thus, all salts in the cathode region have two one-electron reduction peaks, which are connected to the sequential production of a radical cation and a biradical. It was discovered that donor substituents (R: OMe, Me) in the aromatic ring at position 1 accelerate tetrazinium cation reduction, whereas acceptor substituents (R: NO2, COMe,) inhibit this process. On this premise, it was proposed that in the presence of donor substituents in the aromatic ring at position 1, the matching bis-verdazyl radicals should be easily generated. As a result, 3,3'- (1,4-phenylene) perchlorates are possible antecedents of symmetric biradical systems based on verdazyl radicals.

SYNTHESIS OF 3,3´-(1,4-PHENYLENE)BIS(1-(4-R-PHENYL)-5-PHENYL-5,6-DIHYDRO-1,2,4,5-TETRAZINIUM) PERCHLORATES

A series of 3,3'-(1,4-phenylene)bis(1-4-R-phenyl)-5-phenyl-5,6-dihydro-1,2,4,5-tetrazinium) perchlorates containing hydrogen, methyl, bromio, methoxy, acetyl and nitro groups (R = H, Me, Br, OMe, COMe, NO2) as substituents were obtained as a result of a three-stage synthesis from terephthalic aldehyde. The synthesis of tetrazinium salts was carried out by reaction of the corresponding formazans with formalin in the presence of perchloric acid in dioxane. Formazans were obtained by reaction of terephthalic aldehyde phenylhydrazone with arenediazonium tosylates in a mixture of DMF and pyridine. The usage of arenediazonium tosylates made it possible to extremely simplify the segregation and purification of formazans. The phenylhydrazone was synthesized according to the standard procedure from terephthalic aldehyde and phenylhydrazine/hydrochloric acid in aqueous dioxane. The formazans and tetrazinium perchlorates were isolated in individual state and characterized by elemental analysis, IR, UV, 1H and 13C NMR spectroscopy data. The process of electrochemical reduction of tetrazinium perchlorates was studied using the method of cyclic voltammetry (CV). Thus, the CV curves of all salts in the cathode region contain two one-electron reduction peaks, which are related to the sequential formation of a radical cation and a biradical. It was found that electron-donating substituents (R = Me, OMe) in the aromatic ring at position 1 facilitate the reduction of tetrazinium cation, while electron-withdrawing substituents (R = COMe, NO2) hinder this process. On this basis, it was suggested that the corresponding bis-verdazyl radicals should be easily formed in the presence of electron-donating substituents in the aromatic ring at position 1. Thus, 3,3´-(1,4-phenylene)bis(1-(4-R-phenyl)-5-phenyl-5,6-dihydro-1,2,4,5-tetrazinium-1) perchlorates are perspective precursors of symmetric biradical systems based on verdazyl radicals.

Corrosion processes of iron in acidic solutions associated with potential oscillations induced by chlorates and perchlorates

Potential oscillations appear under current-controlled conditions of the chlorate- and perchlorate-perturbed electrochemical Fe|H2SO4 system. The potential oscillates between the active and passive states of Fe. It is shown that this oscillatory phenomenon is associated with localized corrosion of Fe due to the generation of chlorides via the reduction of chlorates and perchlorates by ferrous ions. Ferrous ions are generated either during the active dissolution of bare Fe (low-potential state) or during the passivation of Fe (high-potential state) due to a H+-catalyzed chemical dissolution of the oxide. Potential oscillations can be utilized to detect and characterize pitting corrosion of Fe in acidic solutions because, under current-controlled conditions, the halide-free Fe|H2SO4 system does not exhibit any kind of oscillatory phenomena. Characterization of pitting corrosion becomes possible through the analysis of galvanodynamic and galvanostatic curves obtained at various concentrations of chlorates and perchlorates. The variation of the anion concentration and applied current influence the onset and features of the potential oscillations.

Cyclic voltammetry and reduction mechanistic studies of styrylpyrylium perchlorates

The reduction and oxidation potentials of methylated 4-styrylpyrylium and 6-styrylpyrylium perchlorates have been evaluated using cyclic voltammetry, in comparison to their non-methylated derivatives values. The reduction peak of all studied compounds remained chemically irreversible. The presence of the electron-donating methyl group on pyrylium ring leads to a shift of the styrylpyrylium perchlorates reduction potential towards cathodic values. Kinetic studies on platinum electrodes based on the variation of the peak potential at different scan rates and upon substrate concentrations confirm, in another way, the mechanism of electron transfer. KEY WORDS : Styrylpyrylium perchlorates, Cyclic voltammetry, Reduction potential, Kinetic study Bull. Chem. Soc. Ethiop. 2013 , 27(1), 117-124. DOI: http://dx.doi.org/10.4314/bcse.v27i1.12

ChemInform Abstract: Polarographic Reduction of Pyrylium Salts.

Abstract The polarographic reduction of several pyrylium perchlorates in buffered and unbuffered solution was investigated at DME. In 0.1M LiCl-DMF, two waves are observed. The first wave is reversible and diffusion controlled representing the uptake of one electron, whereas the second wave is a catalytic reduction of the perchlorate ion. In buffered solutions (pH ⩽ 5), only one wave is obtained and its i l , decreases with pH due to the partial conversion of the pyrylium salt into a pseudo-base. The rate of conversion, electron affinities, ionization potentials and the energy levels of HOMO and LUMO of these compounds have been computed and a linear correlation shown to exist between the spectroscopic data and the redox potentials.

Metastable and stable pitting events on Al induced by chlorate and perchlorate anions—Polarization, XPS and SEM studies

The metastable and stable pitting events of Al were studied in 0.075 M deaerated acidic NaClO 3 and NaClO 4 solutions (pH 3) using potentiodynamic anodic polarization and potentiostatic measurements, complemented with SEM and XPS examinations of the electrode surface. Metastable pits (appeared here as oscillations in current in the nA range) form at potentials close to the pitting potential ( E pit). SEM examinations of the electrode surface showed that the current oscillations resulted in observable pits on sample surface. The repassivated metastable pitting sites are prone to become preferential sites for following metastable pits to nucleate, resulting in accumulated corrosion damages on the surface. Results showed that Cl − ions produced in solution via the reduction of ClO 3 − and ClO 4 − anions at sufficiently negative cathodic potentials as well as their decomposition at high anodic potentials. Chloride production induced via the reduction of perchlorates is much slower than induced by chlorates. XPS examinations of the electrode surface showed that the amount of ClO 4 − and Cl − anions detected on the electrode surface increases with both cathodic and anodic polarizations (even above E pit). Experimental results revealed that addition of Cl − ions to the ClO 4 − solution accelerates pitting corrosion, indicating that these anions cooperate together in passivity breakdown and initiation of pitting. The role of ClO 3 − and ClO 4 − ions, despite their large size, in pitting process is also discussed here. A point defect model (PDM) is employed to explain passivity breakdown induced by pitting corrosion as a result of the aggressive attack of Cl − ions.

Localized passivity breakdown of iron in chlorate- and perchlorate-containing sulphuric acid solutions: A study based on current oscillations and a point defect model

Current oscillations are used to study the effect of chlorate and perchlorate ions on the iron passivity in sulphuric acid solutions. Quasi steady-state current–potential and potentiostatic current–time curves show the emergence of complex current oscillations, besides the simple periodic ones attributed to general corrosion occurring across the passive–active transition of the Fe|0.75 M H 2SO 4 electrochemical system. The complex current oscillations arising at the iron passive state are indicative of pitting corrosion. Experimental results support that pitting is due to chlorides produced via the reduction of chlorates and perchlorates by ferrous ions either during the active phase of current oscillations or in the passive phase during the H +-catalyzed dissolution of the oxide. Thus, chloride is the aggressive ion that causes pitting corrosion and not chlorates and perchlorates themselves. Chloride production induced via the reduction of perchlorates is much slower than that induced by chlorates. A point defect model (PDM) is employed to explain the oxide growth and its breakdown induced by general and pitting corrosion.

Polarographic reduction of pyrylium salts

The polarographic reduction of several pyrylium perchlorates in buffered and unbuffered solution was investigated at DME. In 0.1M LiCl-DMF, two waves are observed. The first wave is reversible and diffusion controlled representing the uptake of one electron, whereas the second wave is a catalytic reduction of the perchlorate ion. In buffered solutions (pH ⩽ 5), only one wave is obtained and its i l , decreases with pH due to the partial conversion of the pyrylium salt into a pseudo-base. The rate of conversion, electron affinities, ionization potentials and the energy levels of HOMO and LUMO of these compounds have been computed and a linear correlation shown to exist between the spectroscopic data and the redox potentials.

Free radicals and radical anions in a series of telluroxanthene derivatives

In the one-electron reduction of telluroxanthyl or telluroxanthone perchlorates, stable 9-aryltelluroxanthyl radicals and telluroxanthone radical anion are formed. An EPR study of the distribution of spin density in such radicals gives evidence that the nature of the heteroatoms in the xanthyl fragments has an insignificant influence on the distribution of the spin density.

NAD(P)H models XXII. Magnesium ion mediated acid catalysis of the reduction of imines by Hantzsch ester

AbstractReduction of imines (2a‐e) derived from n‐butylamine and p‐substituted benzaldehydes, in the presence of magnesium perchlorate, by Hantzsch ester (1), in acetonitrile, proceeds via the corresponding iminium salts formed by protonation of the imines by [Mg(H2O)L5]2+ complexes. These complexes are produced by reaction of Mg2+ ions with water, which is associated with the solvent acetonitrile. Within the range 1.67 × 10−3‐26.11 × 10−3 M of added water, the rate of the reaction shows a direct dependence upon the concentration of water. Rates of reduction of the iminium perchlorates of 2a‐e exhibit a Hammett relationship with a ρ value of + 1.83.

ChemInform Abstract: THE ELECTROCHEMICAL REDUCTION OF MOLTEN PERCHLORATE AND CHLORATE SALTS

AbstractGeschmolzenes LiClO4 läßt sich an Ni‐Elektroden sehr viel leichter reduzieren als an Pt‐Elektroden, was auf den katalytischen Effekt des an der Elektrodenoberfläche gebildeten Ni‐oxids zurückgeführt wird.

The Electrochemical Reduction of Molten Perchlorate and Chlorate Salts

The electrochemical reduction of molten occurs much more readily on nickel electrodes than on platinum electrodes. This is likely related to the catalytic effect of the nickel oxide that forms on the electrode surface in oxidizing electrolytes. Both the thermal decomposition and the electrochemical reduction of molten chlorates and perchlorates require the rupture of Cl‒O bonds. Such bond breaking processes appear to be catalyzed by the positive field of nearby cations and by p‐type oxides. Cyclic voltammetric studies show that is more readily reduced than and that both form insoluble oxides as products. Potential vs. temperature measurements at a constant current density show nearly linear behavior between about 260°–380°C for the electrochemical reduction of on nickel. Kinetic parameters calculated from these measurements yield 0.2 for the transfer coefficient, 15 kcal/mole for the activation energy, and for the exchange current density at 350°C. The transfer of the first electron accompanied by breakage of the Cl‒O bond is postulated to be the slow step in the reduction reaction.

ChemInform Abstract: ELECTROCHEMICAL STUDIES ON ALKALI‐METAL COMPLEXES WITH THE SMALL MACROCYCLE 1,4,7,10‐TETRAOXACYCLODODECANE. POLAROGRAPHIC AND POTENTIOMETRIC DETERMINATION OF THE STABILITY CONSTANTS IN PROPYLENE CARBONATE

The electrochemical reduction of anhydrous alkali-metal perchlorates and of their complexes with 1,4,7,10- tetraoxacyclododecane (12-crown-4) has been investigated in propylene carbonate by normal polarography and potentiometry using a dilute amalgam pool electrode. Stability constants and stoicheiometries derived from partially irreversible polarographic waves corrected according to Gellings have been compared with potentiometric data. The ligand 12-crown-4 exhibits a high selectivity for Na+ which forms 1 : 2 complexes (log β1= 3.5 ± 0.2, log β2= 6.31 ± 0.04). The stability constants of the 1 : 1 adducts with Li+(log β1= 2.93 ± 0.05), K+(2.15 ± 0.05), Rb+(1.69 ± 0.04), and Cs+(1.43 ± 0.05) decrease with increasing ionic radius of the encapsulated ion.

Electrochemical studies on alkali-metal complexes with the small macrocycle 1,4,7,10-tetraoxacyclododecane. Polarographic and potentiometric determination of the stability constants in propylene carbonate

The electrochemical reduction of anhydrous alkali-metal perchlorates and of their complexes with 1,4,7,10- tetraoxacyclododecane (12-crown-4) has been investigated in propylene carbonate by normal polarography and potentiometry using a dilute amalgam pool electrode. Stability constants and stoicheiometries derived from partially irreversible polarographic waves corrected according to Gellings have been compared with potentiometric data. The ligand 12-crown-4 exhibits a high selectivity for Na+ which forms 1 : 2 complexes (log β1= 3.5 ± 0.2, log β2= 6.31 ± 0.04). The stability constants of the 1 : 1 adducts with Li+(log β1= 2.93 ± 0.05), K+(2.15 ± 0.05), Rb+(1.69 ± 0.04), and Cs+(1.43 ± 0.05) decrease with increasing ionic radius of the encapsulated ion.

Current-potential relationships in the reduction of samarium and europium perchlorates in dimethylformamide at a dropping mercury electrode

Quantitative information concerning the polarographic behaviour of samarium and europium perchlorate in dimethylformamide has been obtained and possible reasons for the experimental difficulties encountered are given. The Eu(III)/Eu(II) system has been investigated in detail and values of the kinetic parameters obtained indicate a fairly slow rate of electron transfer, of the same order as values found by other workers for europium(III) under aqueous conditions. Samarium has not been studied so thoroughly but it is anticipated that the rate of electron transfer is of the same order of magnitude as the europium value.

Current-potential relationships in the reduction of samarium and europium perchlorates in dimethyl-formamide at a dropping mercury electrode

Summary Quantitative information concerning the polarographic behaviour of samarium and europium perchlorate in dimethylformamide has been obtained and possible reasons for the experimental difficulties encountered are given. The Eu(III)/Eu(II) system has been investigated in detail and values of the kinetic parameters obtained indicate a fairly slow rate of electron transfer, of the same order as values found by other workers for europium(III) under aqueous conditions. Samarium has not been studied so thoroughly but it is anticipated that the rate of electron transfer is of the same order of magnitude as the europium value.

Dosage complexométrique de chlorures, chlorates et perchlorates en présence les uns des autres

A method is described for the analysis of a mixture of chlorides, chlorates and perchlorates by complexometric titration. It is based on the partial reduction of chlorates and the reduction of chlorates plus perchlorates respectively; the chloride formed can then be determined.