Cation and anion electrochemically assisted solid-state transformations of malachite green

The possibility of the electrochemical promotion of different solid-to-solid transformations including the performance of successive cation and anion insertion processes has been tested using malachite green, a triphenylmethane dye, in contact with aqueous NaCl electrolyte. Electrochemical data using the voltammetry of microparticles methodology reveal significant differences with the solution phase electrochemistry of the dye. Voltammetric data, combined with atomic force microscopy, focusing ion beam-field emission scanning electron microscopy, and high-resolution field emission scanning electron microscopy permit characterization of the oxidative dissolution, oxidation with anion insertion, reduction with cation insertion and reduction with anion issue processes, whose thermochemical aspects, involving separate ion and electron transport contributions, are discussed.

A comprehensive study on the electrocatalytic degradation, electrochemical behavior and degradation mechanism of malachite green using electrodeposited nanostructured β-PbO2 electrodes

This work has investigated the electrocatalytic degradation of malachite green (MG) in aqueous solution with G/β-PbO₂, SS316/β-PbO₂, Ti/β-PbO₂ and Pb/β-PbO₂ electrodes. These electrodes show high oxygen evolution over-potential and excellent electrochemical degradation efficiency for organic pollutants. The optimum conditions for the degradation of MG were obtained by studying the effects of different parameters, such as initial current densities and initial MG concentration. The remaining organic compounds concentrations (color) and chemical oxygen demand (COD) removal efficiency were investigated and compared. The results indicate that the efficiency of G/β-PbO₂ electrode for both color and COD removals is more than those of other electrodes. At the optimum conditions, the color and COD removal efficiencies of MG reached up to 100% and 94%, respectively. The observed degradation rate of MG was found to vary in the order G/β-PbO₂> SS316/β-PbO₂> Ti/β-PbO₂> Pb/β-PbO₂. Moreover, in this paper, the electrochemical behavior and adsorption characteristic of MG in aqueous solutions with different pH values were studied in details at glassy carbon electrode using both constant-current coulometry and cyclic voltammetry techniques. This study has led to the proposed mechanism for the oxidation pathway of MG and determine the absorption properties of MG in acidic, neutral and basic solutions. We also proposed the mineralization pathway of MG at β-PbO₂ electrode.

Electron-Transfer Mechanism in the N-Demethylation of N,N-Dimethylanilines by the Phthalimide-N-oxyl Radical

The reactivity of the phthalimide N-oxyl radical (PINO) toward the N-methyl C-H bond of a number of 4-X-substituted N,N-dimethylanilines (X = OMe, OPh, CF(3), CO(2)Et, CN) has been investigated by product and kinetic analysis. PINO was generated in CH(3)CN by reaction of N-hydroxyphthalimide (NHPI) with Pb(OAc)(4) or, for the kinetic study of the most reactive substrates (X = OMe, OPh), with tert-butoxyl radical produced by 266 nm laser flash photolysis of di-tert-butyl peroxide. The reaction was found to lead to the N-demethylation of the N,N-dimethylaniline with a rate very sensitive to the electron donating power of the substituent (rho(+) = -2.5) as well as to the oxidation potential of the substrates. With appropriately deuterated N,N-dimethylanilines the intermolecular and intramolecular deuterium kinetic isotope effects (DKIEs) were measured for some substrates (X = OMe, CO(2)Et, CN) with the following results. First, intramolecular DKIE [(k(H)/k(D))(intra)] was found to be always different and higher than intermolecular DKIE [(k(H)/k(D))(inter)]; second, no intermolecular DKIE [(k(H)/k(D))(inter) = 1] was observed for X = OMe, whereas substantial values of (k(H)/k(D))(inter) were exhibited by X = CO(2)Et (4.8) and X = CN (5.8). These results, while are incompatible with a single step hydrogen atom transfer from the N-C-H bond to the N-oxyl radical, as proposed for the reaction of PINO with benzylic C-H bonds, can be nicely interpreted on the basis of a two-step mechanism involving a reversible electron transfer from the aniline to PINO leading to an anilinium radical cation, followed by a proton-transfer step that produces an alpha-amino carbon radical. In line with this conclusion the reactivity data exhibited a good fit with the Marcus equation and a lambda value of 37.6 kcal mol(-1) was calculated for the reorganization energy required in this electron-transfer process. From this value, a quite high reorganization energy (>60 kcal mol(-1)) is estimated for the PINO/NHPI(-H)(-) self-exchange reaction. It is suggested that the N-demethylated product derives from the reaction of the alpha-amino carbon radical with PINO to form either a cross-coupling product or an alpha-amino carbocation. Both species may react with the small amounts of H(2)O present in the medium to form a carbinolamine that, again by hydrolysis, can be eventually converted into the N-demethylated product.