Thermodynamic dissociation constants of N-phenylbenzohydroxamic acids and benzohydroxamic acid

Thermodynamic association constants of benzohydroxamic acid and several ortho-substituted N-phenylbenzohydroxamic acids have been determined by pH titration in aqueous dioxan media at 25 degrees and 35 degrees . Empirical pH corrections for mixed aqueous media have been applied. The pK(a) values do not vary linearly with the reciprocal of dielectric constant of the medium, but a plot of pK(a) vs. the mole fraction of dioxan is linear at a given temperature. Values of DeltaG degrees , DeltaH degrees and DeltaS degrees are tabulated.     

Thermodynamic stability constants of beryllium(II) and p-substituted N-phenyl benzohydroxamic acid complexes

The thermodynamic stability constants of beryllium(II) complexes of p-substituted N-phenylbenzohydroxamic acids have been determined in 50% v v aqueous dioxan at 35 degrees. The effect of methoxy, methyl, chloro, bromo, and nitro groups as substituents is discussed. There is a linear relationship between log K(1) and pK(a) and the Hammett equation is applicable. The beryllium complexes have been compared with those of Cu, Zn, Ni and Mn.     

Thermodynamic ionization constants of para-substituted N-phenyl-benzohydroxamic acids

Thermodynamic ionization constants of para-substituted N-phenylbenzohydroxamic acids have been determined in dioxan-water mixtures at 35 degrees . The plot of mole fraction of dioxan vs. pK(a) is linear at this temperature, whereas that of pK(a)vs. 100/D is linear over a narrow range of dielectric constants (D) but at higher mole fraction of dioxan is influenced by non-electrostatic factors.     

Proton-ligand stability constants of halo-N-arylhydroxamic acids

In sealed tube reactions bis(trifluoromethyl)mercury has been shown to exchange ligands with halogenated compounds such as GeBr₄ and SnBr₄ to produce a series of trifluoromethyl containing germanium and tin compounds including Ge(CF₃)₄ and Sn(CF₃)₂Br₂. These exchange reactions are shown to be synthically useful provided the desired products are stable at the required reaction temperatures.     

Determination of stability constants for rare earth elements and fulvic acids extracted from different soils

Fulvic acids (FAs) were extracted by alkali extraction from different soil samples in China, then purified using resins and characterized by Fourier transform infrared spectroscopy. The complexing ability of FAs was investigated by measuring the stability constants of rare earth elements (REEs) (La³⁺, Ce³⁺, Sm³⁺, Gd³⁺, Y³⁺) with FAs by the ion exchange technique. The results indicated that maximum binding ability forY³⁺ (4.414.44) was higher than other REEs (La³⁺, Ce³⁺, Sm³⁺, Gd³⁺) (0.721.03). There were two types of binding sites in the functional groups of fulvic acids. The complexing reaction followed two steps. The stability constants (K₁ and K₂) of REEs with FAs were calculated from experimental data by division of Scatchard plots into two straight-line segments. Y³⁺ (log K₁=5.72±0.05, log K₂=4.83±0.01) also has higher stability constants than the other four REEs (log K₁=4.37±0.16, log K₂=3.62±0.28).     

The stability constants of the rare earth complexes with trimetaphosphoric acid

The stability constants of the complexes formed between the rare earth metal ions and the anion of trimetaphosphoric acid have been determined at a temperature of 20 degrees C and an ionic strength of mu = 0.1 by the ion-exchange equilibrium method. The investigations indicate that stabilities of complexes increased from La to Lu. The highest and the lowest stability constant values (beta) were found to be 7.76 and 3.82 for Lu3+ and La3+ respectively.     

Activation analysis of rare earths : Separation of rare earths from accompanying elements

A scheme for the separation of rare-earth elements from gadolinite and tantalocolumbite minerals is discussed. The possibility of interference from traces of nonseparated elements in the subsequent separation of rare-earth elements from each other by cation exchange with α-hydroxyisobutyrate as the eluting agent is investigated.     

Potentiometric determination of rare earths with sodium ortho-vanadate

Ohne Zusammenfassung     

Solvent extraction-spectrophotometric determination of rare earths with chlorophosphonazo-III

The rare-earth chlorophosphonazo III chelates are easily extracted from an aqueous solution (pH 1.1-1.5) into n-butanol. The absorbance at the absorption maximum (at 668 nm) is about 3 times that in aqueous solution. The spectrophotometric determination of rare earths has been investigated.     

Double sulfates of some rare earths with tetramethylammonium

Double sulfates of rare earths and tetramethylammonium with empirical formula (CH₃)₄NLn(SO₄)₂ · 3H₂O (Ln=Ce, Pr, Nd, Eu, Gd, Tb and Dy) were synthesized and studied by the methods of TG, DTG and DTA in the temperature range from 20 to 500°C, and by X-ray powder diffraction and chemical analysis. Two isostructural groups were obtained: one from Ce to Eu and another from Gd to Dy. It was found that rare earth sulfates are obtained as final products at 500°C. For comparison, TG, DTG and DTA curves of the thermal decomposition of tetramethylammonium sulfate are given.

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Zusammenfassung Doppelsulfate von Seltenerden und Tetramethylammonium der empirischen Formel (CH₃)₄NLn(SO₄)₂ · 3H₂O mit Ln=Ce, Pr, Nd, Eu, Gd, Tb und Dy wurden synthetisiert und im Temperaturbereich 20–500°C mittels TG, DTG und DTA, weiterhin mittels Röntgenpulverdiffraktion und chemischer Analyse untersucht. Es wurden zwei isostrukturelle Gruppen erhalten, die eine von Ce bis Eu, die andere von Gd bis Dy. Man fand, daß man bei 500°C als Endprodukt die Seltenerdensulfate erhält. Zum Vergleich wurden die TG-, DTG- und DTA-Kurven der thermischen Zersetzung von Tetramethylammoniumsulfat gegeben.

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Financial support by the Research Council of Slovenia is gratefully acknowledged.     

Potentiometric determination of rare earths with sodium tungstate

Ohne Zusammenfassung     

Electrodeposition studies of rare earths

The combination of neutron activation analysis (NAA) and electrochemistry has been used to study the deposition behavior of rare earth elements, as it is reported that excepting La, no other rare earths are electrodeposited. The radiotracers of rare earth elements were electrolyzed in an aqueous medium on a graphite electrode by varying the voltage and time of electrodeposition, thereby optimizing the final experimental conditions for quantitative deposition of rare earth elements. The observations are reported in this work.     

Simultaneous spectrofluorimetric determination of the rare earths with calcein

The reactivity of the fluorescent reagent calcein with the trivalent cations of the rare earths has been spectrofluorimetrically studied in aqueous solution. Optimum excitation and emission wavelengths were 492-497 and 519-522 nm, respectively. Optimum pH was in the range 6.0-9.2. The stoichiometry of the complexes was 1:1. A direct, rapid and sensitive method for the determination of rare earth mixtures has been proposed with a detection limit of 4.49x10(-8) M and a coefficient of variation of 0.82%.     

Separation of thorium from rare earths

Summary A method for separation of thorium from rare earths in monazite based on the difference of stability of EDTA complexes towards oxine is described.     

The determination of the stability constants of uranyl and thorium with aminopolycarboxylic acids

The stability of uranyl and thorium ions with ligands N-(2′-carboxy phenyl) iminodiacetic acid (ADA), iminodiacetic acid (IDA) and [(ethylenedioxy)diethylenedinitrilo]tetraacetic acid (EGRA) have been studied using the potentiometric technique in 0.1M, KNO₃ solution at 25°C. The complexes of thorium (IV) ions with IDA and ADA are shown to be more stable than those for uranyl ions, while EGTA forms more stable complexes with uranyl ion.