E. Merciny

Étude thermodynamique de la complexation des lanthanides trivalents avec l'acide hydroxyéthyl-éthylénediaminetriacétique et d'autres acidesn aminoacétiques

Several polyaminoacetic acids have been studied by potentiometry at an ionic strength 1 (KCl) and 25° C, in order to determine their acidity constants. The pK values found are: 2.48, 9.67 (glycine); 1.84, 2.57, 9.27 (iminodiacetic acid); 1.03, 1.75, 2.31, 9.34 (nitrilotriacetic acid); 1.50, 1.95, 2.45, 6.21, 9.79 (ethylenediaminetetraacetic acid). The pK values of the lanthanide complexes Ln—EDTA—H are: 3.1, 2.14, 2.03, 1.89, 1.82, 1.44, 1.35, 1.27, 1.19, 1.17, 1.15 (Ln = La, Nd, Sm, Eu, Gd, Dy, Ho, Er, Tm, Yb, Lu).

Contribution a la determination potentiometrique des constantes de stabilite des complexes 1:2 avec les acides aminopolyacetiques MeHnY2

An extension of the potentiometric method based on pH measurement is applied to the determination of the stability constants of addition complexes. On the one hand, the polybasic chelating agent HnY, and on the other hand the same acid in presence of an equimolar concentration of the entity to be complexed, are titrated with standard sodium hydroxide in a medium of constant ionic strength. By means of a least-square computer program, the stepwise stability contants of the addition complexes are obtained. This method is applied to the 1:2 complexes formed between several trivalent lanthanides and hydroxyethylethylenediaminotriacetic acid (HEDTA).

Etude de la complexation des lanthanides trivalents par les isomères de l'acide diaminocyclohexanetétraacétique: Partie 2. Les Constantes d'Acidité et les Constantes de Formation des Complexes 1:1 avec l'Acide trans-1,4-Diaminocyclohexane-N,N,N′,N′-Tétraacétique

Abstract (Study of the complexation of trivalent lanthanides by the six isomers of diaminocyclohexanetetraacetic acid. Part 2. Acidity constants and formation constants of the 1:1 complexes of trans-1,4-diaminocyclohexane-N,N,N′,N′-tetraacetic acid) Potentiometric measurements of the acidity constants of trans-1,4-diaminocyclohexane-N,N,N′,N′-tetraacetic acid (trans-1,4-DCTA) and of the stability constants of its 1:1 complexes with the trivalent lanthanides are reported for an ionic strength of 1 (KCl) at 25°C. The behaviour of this ligand is similar to that of monoaminodiacetic acids, suggesting that only one N(CH2COO−)2 group participates in chelation. The selectivity of trans-1,4-DCTA for the lanthanides is better than that reported for the monoaminodiacetic acids.

Étude de la complexation des lanthanides trivalents par les six isomères de l'acide diaminocyclohexane-tétraacétique : Partie 3. Relation entre les Constantes d'Acidité et la Structure Moleculaire des Chélatants

(Study of the complexation of trivalent lanthanides by the six isomers of diaminocyclohexanetetraacetic acid. Part 3. Relationship between the acidity constants and the molecular structure of the ligands.) Potentiometric measurements of the acidity constants of the six isomers of diaminocyclohexane-N,N,N′,N′-tetraacetic acid (DCTA) are reported for an ionic strength of 1 mol l−1 (KCl) at 25°C. The values of the two constants Ka3 and Ka4 are correlated with the maximum N—N distance for each ligand. Ethylenediamine-N,N,N′,N′-tetraacetic acid (EDTA) and some homologous ligands, including specially synthesized, 1,8-diaminooctane-N,N,N′,N′-tetraacetic acid and 1,10-diaminodecane-N,N,N′,N′-tetraacetic acid, are studied under the same conditions. It is proved that there is a relationship between the molecular structure and the affinity for protons.

Constant-current coulometric determination of uranium in the pure metal

Abstract A new method is proposed for the highly precise and accurate constant-current coulometry of uranium in high-purity uranium. Precisely weighed amounts of uranium and pure iron are dissolved in 7 M sulfuric acid containing some hydrogen peroxide (40% v v ). The solution is quantitatively transferred to the coulometric cell by rinsing with 1 M H 2 SO 4 , saturated with cerium(III) sulfate. The first step is the quantitative electro-chemical reduction to U(IV), Fe(II) and Ce(III) on a gold gauze electrode at constant current (100 mA) until evolution of hydrogen is observed. The hydrogen is then removed by flushing the solution with very pure nitrogen until the potential of a platinum gauze electrode reaches a constant value. Oxidation on the gold gauze electrode is carried out under precisely controlled constant current; after the quantitative oxidation of U(IV) to U(VI) and Fe(II) to Fe(III), and crossing the end-point, this end-point is determined very precisely potentiometrically through back-titration by successive current injections of 10 mA during 1 s. The method was tested on a NBS reference material, uranium (NBS 960).

Determination des constantes de stabilite des complexes des lanthanides trivalents avec les macrocycles polyaza polycarboxyliques : Etude des Propriétés Complexantes de la Résine Chélatante Chelite-N vis-à-vis des Lanthanides Trivalents

Abstract ( Determination of the stability constants of trivalent lanthanide complexes with polyazapolycarboxylic macrocycles. Study of the complexing properties of the chelating resin Chelite-N for trivalent lanthanides. ) The complexing properties of the chelating resin Chelite-N, which is characterized by amidoxime-type functional groups, for neodymium and holmium are described. The conditioning of the resin, its chelating capacity and its acid-base properties are examined first. To evaluate the formation constants of trivalent lanthanide complexes with the chelating resin, the resin is equilibrated with the lanthanide ions and then with an aqueous solution of ethylenediaminetetraacetic acid.

Étude de la complexation des lanthanides trivalents par l'isomère trans-1,3 de l'acide cyclopentanediaminotétraacétique

(Study of the complexation of the lanthanides by the trans-1,3 isomer of cyclopentanediaminotetraacetic acid.) The various steps of the synthesis of trans-1,3-cyclopentanediaminotetraacetic acid are briefly discussed and the acidity constants of this chelating agent are reported, together with the stability constants of its 1:1 complexes with the trivalent lanthanides; the results are obtained at 25° C for an ionic strength of 1 mol l−1 (KCl) by coulometric titrations with potentiometric detection. The values reported are compared with the corresponding data obtained with other polyaminopolyacetic acids.