Claude Bied-Charreton

ELECTROCHEMISTRY OF CONDUCTING POLYPYRROLE FILMS CONTAINING COBALT PORPHYRIN

The electrochemical polymerisation of pyrrole-substituted cobalt tetraphenylporphine complex on a vitreous carbon electrode has been performed in acetonitrile+tetrabutylammonium tetrafluoroborate solution. The redox properties of the film have been examined by cyclic voltammetry and compared to those of cobalt-porphyrin monomer in solution. Voltammograms of these films exhibit a reversible process for the Co(II)/Co(I) reaction at a formal potential of −0.87 V/SCE. The cobalt-porphyrin content of the films has been estimated by cyclic voltammetry, and the conductivity of the polymers has been assessed by studying well-known electrochemical processes in solution at these modified electrodes. Thus, it appears that thick polyporphyrin films act as insulators in low potential range E < −1 V/SCE. Copolymerisation of the pyrrole-substituted cobalt porphyrin with pyrrole and 3-(pyrrol-1-ylmethyl)pyridine has been achieved. No improvement of the electrochemical properties has been noted for the copolymers obtained. We have also proved that interchain complexation reaction of the cobalt(III) sites occurs by the pyridine moieties of the copolymer films.

Metalloporphyrin-polypyrrole film electrode: characterization and catalytic application

Abstract The visible electroreflectance (ER) technique, coupled to capacitive and voltammetric measurements, has been used to characterize the redox properties of polypyrrole-modified electrodes, doped with meso -tetrakis (4-carboxyphenyl) porphine cobalt, iron and manganese (PP/TCPPM). The ER spectra give direct evidence for the location of a reversible electron/transfer reaction and allow us to determine the redox potential of the TCPPM(III)/M(II) process in the polypyrrole film (in 0.1 M CH10 4 solution). The values obtained ( + 0.200 V vs SCE for TCPPCo(III)/Co(II); −0.100 V for TCPPFe(III)/Fe(II) and −0.200 V for TCPPMn(III)/Mn(II) are compared to those determined by ER for the same species. TCPPM, adsorbed on gold electrodes. The catalytic application of 2,6-diterbutylphenol oxidation by molecular oxygen in acetonitrile with PP/TCPPMn(III) is tested. The catalytic species TCPPMn(II) is obtained by electrolysis of the modified electrode PP/TCPPMn at −0.300 V. The results show that the entire heterogeneous catalytic oxidation process of phenol, with a Mnue5f8oxygen adduct as intermediate, can be developed without damaging the PP/TCPPMn film.

Electropolymerized nickel macrocyclic complex-based films: design and electrocatalytic application

The voltammetric behaviour of electropolymerized nickel macrocyclic ncomplexes in alkaline aqueous solution is described. The nickel-based nmodified electrodes were prepared by oxidative polymerization of nickel nporphyrin, nickel salen and nickel cyclam complexes by repeated potential nscans in 0.1 m NaOH solution. All the electroformed films exhibited the nsame behaviour which is similar to that shown by nickel hydroxide-modified nelectrodes. In addition, the nickel complex-based polymers act as nefficient materials for the electrocatalytic oxidation of methanol, nethanol and hydrazine.

Electrocatalysis of the oxidation of alcohol and phenol derivative pollutants at vitreous carbon electrode coated by nickel macrocyclic complex-based films

The voltammetric behavior of carbon electrodes coated by a nickel macrocyclic complex-based film in alkaline aqueous solution is described. The nickel-based modified electrodes were prepared by anodic oxidation of nickel porphyrin and nickel cyclam complexes by repeated potential scans in 0.1 M NaOH aqueous solution. The nickel-based films act as efficient materials for the electrocatalytic oxidation of alcohols and phenol derivatives in aqueous 0.1 M NaOH and prevent the electrode from irreversible passivation during the electrocatalytic oxidation of phenols in neutral aqueous solution.

Zeolite-porphyrin modified electrodes

Etudes sur les proprietes des electrodes de Pt recouvertes dun melange de polystyrene et de zeolite ou graphite et de zeolite et modifiees par de la meso-tetrakis (4-N-methylpyridyl) porphine de Mn(III), Co(III) ou Fe(III)

Electropolymerized manganese porphyrin films as catalytic electrode materials for biomimetic oxidations with molecular oxygen

Some recently published results on the electrocatalytic oxidation of hydrocarbons, olefins and a thioacetamide derivative by molecular oxygen are described. The catalytic process involves electropolymerized manganese porphyrin films as electrode materials in acetonitrile or dichloromethane solution containing 1-methylimidazole and benzoic (or acetic) anhydride, with acceptable catalytic efficiency (up to 500 turnovers of the catalyst per hour) and faradaic yield (up to 98%). Confinement of the catalyst on the electrode surface markedly improves its stability compared with that of homogeneous electrocatalytic systems and makes the supported porphyrin stable and reusable.

Redox and electrocatalytic properties of cobalt-bipyridyl-polypyrrole film electrodes

Abstract The electrochemical polymerisation of Co(L)3(BF4)2 (where L = 4-methyl,4′(2.pyrrol-1-ylethyl)-2,2′-bipyridine) on a gold electrode has been performed in CH3CN + tetraethylammonium perchlorate solution. The properties of the film have been examined by means of voltammetric techniques and compared to those of Co(L)3(BF4) and Co(Bipy)3(BF4)2 in solution. The redox potentials of the three systems on the modified electrode are: Co(III)/Co(II), E°′ = 0.240 V; Co(II)/Co(I), E°′ = −1.090 V and Co(I)/Co(−I), E°′ = −1.80 V. The systems appear to be quasi-reversible and are similar to those observed with the corresponding Co(L)3(BF4)2 complex in solution. The variations of the redox potentials of the polymer vs. the concentration of ligands (Bipy, acrylonitrile, allyl chloride) in solution show that exchange between L linked to the polypyrrole matrix and ligands can be observed inside the polymeric film. This property allows the film to be used in the catalytic reduction of allyl chloride at −1.2 V.

Grafting of cobalt porphyrins in sol–gel matrices: application to the detection of amines

Abstract Grafting in a sol–gel matrix is of interest since it provides materials which are transparent with a good optical quality and which are compatible with the use of optical fibers in spectroscopic detection. Grafting of cobalt(II)porphyrins in a sol–gel matrix was realized using a porphyrin substituted by a triethoxysilyl group and pure tetramethoxysilane as the precursor. Comparison was achieved between grafted and non-grafted porphyrins. Preliminary results on pyridine sensing show that the diffusion of pyridine occurs with a lower rate than in organic matrices.

Incorporation Of Water-Soluble Porphyrins In Sol-Gel Matrices And Application To pH Sensing

Abstract The incorporation of H 2 TPPS 4− into sol–gel materials has been used to determine the pH inside a sol–gel matrix.

Oxidation of phenols by molecular oxygen catalysed by transition metal complexes. Comparison between the activity of various cobalt and manganese complexes and the role of peroxy intermediates

The oxidation reactions of hindered phenols by molecular oxygen catalysed by monomeric and polymeric cobalt–Schiff base complexes, cobalt and manganese porphyrins, and (pyridine)cobaloxime are described; the rate and selectivity of these reactions are very dependent on the catalyst and on the solvent.A new product has been isolated, 1,3,5-tri-t-butyl-4-oxocyclohexa-2,5-dienylperoxy(pyridine)co-baloxime, and was fully characterised by its elemental analysis and spectroscopic methods. The reactivity of peroxy compounds derived from 2,4,6-tri-t-butylphenol which are postulated as intermediates in the oxidation of this phenol has been studied. Thermal decomposition of 1,3,5-tri-t-butyl-4-oxocyclohexa-2,5-dienyl(pyridine)cobaloxime indicates that the formation of this complex from the phenol, O2, and (pyridine)cobaloxime(II) is reversible and that it is converted into 2,6-di-t-butyl-1,4-benzoquinone only in the presence of a proton source. The corresponding hydroperoxide is probably an intermediate in this transformation as its decomposition in the presence of the cobalt(II) or manganese(III) complexes yields the same final products as the overall oxidations.