Jacqueline Courtot-Coupez

Electrochemical behaviour of a binary cofacial dicobalt porphyrin in aprotic media under a nitrogen atmosphere: Formation of mixed-valence compounds

Abstract The electrochemical behaviour of the binary cofacial dicobalt porphyrin Co 2 FTF 4 was investigated in benzonitrile under a pure nitrogen atmosphere. The two cobalt(II) centres of the molecule are oxidized or reduced separately in two different monoelectronic steps giving rise, for the first oxidation and reduction reactions, to mixed-valence compounds: [Co III Co II ] and [Co II Co I ] respectively; further oxidation or reduction leads to the [Co III Co III ] and [Co I Co I ] derivatives. All the redox systems are nearly reversible and diffusion-controlled, even the Co(III)/Co(II) ones. Except for the [Co I Co I ] species, all the redox states of the dicobalt bisporphyrin were generated by electrolysis and characterized by spectrophotometry and/or ESR spectroscopy. Whereas the [Co II Co II ] compound displays metal—metal interaction, the [Co III Co II ] is a valence-localized mixed-valence compound i.e., the odd electron is localized on one cobalt. Such multistep charge transfers for the two nearly equivalent cobalt nuclei of the molecule are explained by the existence of interactions between the two cobalt(II) centres. The results of this study clearly demonstrate that the proximity of the two(II) atoms induces different properties of the CO 2 FTF 4 porphyrin with regard to cobalt monoporphyrins.

Determination of Humic Substances in Seawater by Electrochemistry (Mechanisms)

Abstract A new method for the measurement of the concentration of humic substances (HS) in seawater is described. The peak obtained by differential cathodic sweep voltammetry after HS adsorption in the presence of traces of molybdenum(VI) can be used for quantitative determination. Measurements using various electrochemical techniques (ACP, CV, ADPV, DPP) would indicate that the film adsorbed onto the electrode is the result of the adsorption of the organic substance in a first step followed in a subsequent step by the formation of a surface complex (Mo(VI)-HS)ads rather than the direct adsorption of the dissolved complex. The electrochemical mechanism corresponds to a one-electron reduction of the adsorbed (Mo(VI)-HS)ads complex to the corresponding (Mo(V)-HS)ads complex.

Dosage Des Traces De Detergents Non-Ioniques Dissous Par Spectrophotometrie D' Absorption Atomique

Abstract A novel procedure for the analysis of non-ionic surfactants is reported. The method relies on extraction of a cobaltithiocyanate adduct from an aqueous sample into a benzene phase. The amount of cobalt extracted was determined by atomic absorption and correlated linearly with the corresponding surfactant concentration in the aqueous specimen. Relevant pollution levels in the Atlantic Ocean were estimated rapidly with a precision and accuracy of 10% or better.

Etude physicochimique de la chloration de l'eau de mer artificielle contenant de l'azote ammoniacal

Abstract Chlorine added to ammonia-free sea-water gives rise to a fast and quantitative oxidation of bromide to hypobromite and hypobromous acid. However as ammonia nitrogen levels commonly found in coastal and estuarine sea-water are sufficiently high and thus not negligible compared to the chlorine dose introduced formation of monochloramine to compete with oxidation of bromine leading to bromamines. The relative importance of these two reactional pathways is estimated considering both bromine determination and study of the electron absorption spectra of chlorinated seawater. In order to avoid substitution reactions taking place in the presence of organic compounds, preliminary experiments have been carried out in artificial and u.v. photo-oxidized sea-water. The nature of the species formed depends on the molar ratio added chlorine vs ammonia-nitrogen concentration of seawater. With Cl/N larger than 1.5, only bromide derivatives are obtained: dibromamine, tribromamine and bromine(I) (HBrO + BrO − ). Cl/N smaller than 1.5 leads to a mixture of monochloramine, dibromamine and some monobromamine: monochloramine clearly predominates when ammonium concentrations reach higher values. Stoichiometry of ammonia to nitrogen oxidation by chlorine explains this ratio of 1.5 and a strong decrease of the total oxidant concentration is observed under these conditions. Bromamines decompose within the following 30–60 min; only stable compounds remain: either bromine(I) or monochloramine according to Cl/N values. A similar behaviour is observed in natural seawater previously doped with ammonia as to the nature of the products formed for a given Cl/N ratio; however, bromamines decompose more rapidly due to bromination of organic components.

Calibration of the hydrogen electrode in propylene carbonate Potentiometric studies of acid-base reactions

Abstract The dissociation of hydronium trifluoromethanesulfonate (H3OSO3CF3), hydronium perchlorate (H3OClO4) and anhydrous perchloric acid has been investigated using conductimetry in propylene carbonate. HClO4 (KA=10−1.3 mol l−1) and H3OSO3CF3 (KD=10−1.7 mol l−1) are not completely dissociated; H3OClO4 is found to behave as a strong electrolyte in the solvent. The determination of the conditional potential of H+/H2 couple (E′H20), has been achieved using the hydrogen electrode in solutions of perchloric and trifluoromethane-sulfonic acids. Potentiometric titrations of molecular and anionic bases with HSO3CF3, with hydrogen or glass electrodes, yield the pKA values of the acid-base couples used; in the case of HA acids (sulfuric, nitric, acetic, picric and hydrogen chloride) homoconjugation equilibria have been investigated. The acidity scale so obtained in propylene carbonate is correlated with the water one using the transfer coefficient of the proton between the two solvents.

Influence de la Matière Organique des Milieux Naturels sur la Redissolution Cathodique [Agrave] l'électrode [Agrave] Goutte Pendante de Mercure

Abstract At pH 2 the cathodic stripping of seawater at the HMDE displays two peaks (-0.520V and -0.260V). If the peak at -0.520V is due to humic and fulvic acids the other one is probably associated to traces of organic compounds (10−7M) having the thiocarboxylic functional group .

Etude physicochimique de la chloration de l'eau de mer artificielle

Abstract Inorganic reactions occurring during ammonia-free sea-water chlorination have been considered. Experiments have been carried out in artificial or UV-photooxidized sea-water in order to avoid slow reactions of chlorine and bromine with organic compounds in sea-water. Results obtained either from bromine determination, using phenol red as a reagent, or from electronic absorption spectra of chlorinated sea-water show a fast and quantitative oxidation of bromide to hypobromite and hypobromous acid. No bromate formation was detected in our experimental conditions.

Électrochimie dans le carbonate de propylène: I. Oxydation anodique de quelques hydrocarbures aromatiques polynucléaires

Abstract In propylene carbonate, the two consecutive one-electron oxidations of the aromatic compounds: 9,10-diphenyl anthracene, perylene and thianthrene are quasi-reversible. The cation radicals formed during the first step are very stable; on the other hand, the dications react very rapidly with nucleophilic species such as water. These results are similar to those obtained in acetonitrile or dichloromethane.

Protonation of water in propylene carbonate

Abstract The protonation of water in propylene carbonate in the presence of perchloric and trifluoromethanesulfonic acids (HClO4 and HSO3CF3) has been investigated using voltammetry, conductimetry and potentiometry. Three protonated forms of water exist in these solutions: (H2O)H+ or H3O+, (H2O)2H+ or H5O2+ and (H2O)3H+ or H7O3+. The 1–4 complex (H2O)4H+ or H9O4+ seems not to be formed in detectable amount in this aprotic solvent. The hydrates of perchloric acid are extensively dissociated, contrary to those of trifluoromethanesulfonic acid. The determination of the pK of the complexes H3O+, H5O2+, H7O3+, has been achieved from solutions of perchloric acid and of its hydrates by potentiometry with hydrogen and glass electrodes. The distribution of the proton between the different species present in the medium has been plotted as a function of total concentration of water. These results obtained in propylene carbonate are compared to those in other dipolar aprotic solvents.

Dosage Des Detergents Anioniques Dans L'Eau De Mer. Generalisation De La Methode Aux Eaux Douces Et A La Determination Des Detergents Cationiques

Abstract A procedure for determination of anionic surfactants in sea water is described for concentrations in the range 10–500 ug/1. This method involves formation of an ion-pair between orthophenahthroline-copper (II) cation and anionic surfactant which is extracted by methylisobutylketone; copper being determined in the solvent by atomic absorption spectrophoto-raetry. The procedure can been also used to determine anionic surfactant in fresh water. Determination of cationic surfactants is possible after changes of the original experimental conditions.