E.N. Rizkalla

Metal chelates of phosphonate-containing ligands-V Stability of some 1-hydroxyethane-1,1-diphosphonic acid metal chelates.

A detailed study of the complexes formed between 1-hydroxyethane-1,1-diphosphonic acid and twelve metal ions, including the alkaline earth and transition non-transition metal ions, is reported. The formation constants of the protonated and unprotonated complexes are measured from potentiometric data and possible structural formulae are given. The results reveal that only mononuclear (1:1) di-, mono- and unprotonated metal chelates are formed and that the general order of stability for the unprotonated complexes is Zn > Mn > Ca > Cu > Cd > Pd > Ni > Co reverse similar Sr > Mg > Ag > Ba.

The kinetics of decomposition of hydrogen peroxide in the presence of ethylenediaminetetraacetatoiron(III) complex

Abstract The rate of decomposition of hydrogen peroxide in the presence of ethylenediaminetetraacetatoiron(III) complex is investigated under variable conditions of hydrogen peroxide and iron-EDTA concentrations, pH, ionic strength and temperature. The following rate law holds: Rate = k4K3 [FeY(OH) 2−][H2O2] + + k3K1K2 [FeY(OH) 2− ][OOH − [H + ] The rate constants and the related thermodynamic parameters are calculated. Substitution controlled mechanisms are suggested to account for the formation of the violet peroxy intermediate.

Metal chelates of azo-pyridazine dyes: Chelating tendencies of benzoylacetone-monohydrazone-3-hydrazino-4-benzyl-6-phenylpyridazine (bahp)

The synthesis, acid-base equilibria and metal-ion chelating tendencies of BAHP are reported. From potentiometric equilibrium measurements of hydrogen-ion concentration at 30 degrees and ionic strength 0.10M (KNO(3)), in 75% dioxan-water medium, the values of the stability constants of some BAHP complexes with transition, non-transition and lanthanide ions have been evaluated. Probable structures of the metal chelates are inferred from the electronic absorption spectra and infrared examination of the solid copper complex. The use of BAHP as an analytical reagent for the spectrophotometric determination of copper, nickel and cobalt ions is discussed.

Metal chelates of azo-pyridazine dyes-II : Chelating tendencies of diacetyl-, benzil- and benzoylethane-monohydrazone-3-hydrazino-4-benzyl-6-phenylpyridazine

Abstract The diacetyl-(DAHP), benzil-(BHP) and benzoylethane-(BEHP) derivatives of 3-hydrazino-4-benzyl-6-phenylpyridazine have been prepared and characterized. Their acid-base properties and their equilibria with transition metal ions in 75% dioxan-water solvent at 30°C have been investigated by pH titrimetry. The role of proton and metal ion solvation by the organic solvent has been discussed in view of the results obtained for the lanthanide-BHP systems in different media. Probable structures of the metal chelates are given based on potentiometric data and spectral results for the solid copper chelates. The possibility of forming MHL species were inferred from electronic absorption measurements at different pH values. The use of BHP as an analytical reagent for the determination of copper spectrophotometrically or as a metallochrom indicator in the complexometric titration of Cu(II) ion is also discussed.

The kinetics and mechanisms of the catalysed decomposition of hydrogen peroxide by ethylenediaminetetra(methylenephosphonato) complex of manganese(II)

The decomposition of H2O2 in the presence of ethylenediaminetetra(methylene-phosphonato)manganate(II) complex, [Mn(II)Y] (Y represents the (CH2-N(CH2PO3H2)2)2 anion), was studied at various temperatures. The rate law: −d[H2O2]dt =Ka[H+](k2 + k1K1[H+])(1 + Ka[H+])(1 + K1[H+]) [MnY]aq[H2O2]T holds over the pH range 9.0–10.30. A mechanism involving Mn(IV) and peroxy intermediates is suggested. In strongly alkaline solutions, Mn(IV) species hydrolyse to give colloidal MnO2. At 30°C, the specific rate constants for the reactions: [Mn(III)Y(OH)]6− + H2O2 k1→ [Mn(III)Y(OOH)]6− + H2O and [Mn(III)Y]5− + H2O2 k2→ [Mn(III)Y(H2O2)]5− were determined to be k1 = 33 M−1S−1 and k2 = 2.2 M−1S−1. The corresponding activation parameters are, δH1⦵ = 17 ± 4 kJ mol−1;δS1⦵ = −165 ± 15 J K−1 mol−1; δH2⦵ = 83 ± kJ mol−1 and δS2⦵ = 37 ± 55 J K−1 mol−1.

Kinetic studies on the reaction of ethylenediaminetetraacetatochromium(III) complex with hydrogen peroxide

The rate of reaction of [Cr(III)Y]aq (Y is EDTA anion) with hydrogen peroxide was studied in aqueous nitrate media [μ = 0.10 M (KNO3)] at various temperatures. The general rate equation, Rate = k1 + k2K1[H+]−11 + K1[H+]−1 [Cr(III)Y]aq[H2O2] holds over the pH range 5–9. The decomposition reaction of H2O2 is believed to proceed via two pathways where both the aquo and hydroxo-quinquedentate EDTA complexes are acting as the catalyst centres. Substitution-controlled mechanisms are suggested and the values of the second-order rate constants k1 and k2 were found to be 1.75 × 10−2 M−1 s−1 and 0.174 M−1 s−1 at 303 K respectively, where k2 is the rate constant for the aquo species and k2 is that for the hydroxo complex. The respective activation enthalpies (ΔH*1 = 58.9 and ΔH*2 = 66.5 KJ mol−1) and activation entropies (ΔS*1 = −85 and ΔS*2 = −40 J mol−1 deg−1) were calculated from a least-squares fit to the Eyring plot. The ionisation constant pK1, was inferred from the kinetic data at 303 K to be 7.22. Beyond pH 9, the reaction is markedly retarded and ceases completely at pH ⩾ 11. This inhibition was attributed in part to the continuous loss of the catalyst as a result of the simultaneous oxidation of Cr(III) to Cr(VI).

THE DECOMPOSITION KINETICS OF HYDROGEN PEROXIDE CATALYSED BY ETHYLENEDIAMINE-TETRAKIS(METHYLENEPHOSPHONATO)IRON(III)

Abstract The catalysed decomposition of hydrogen peroxide in the presence of ethylenediaminetetrakis(methylene-phosphonato)iron(III) was studied at various temperatures. The observed rate law is given by -d[H2O2]/dt = k1K/([H+] + K) [Fe(CENTMP)]. where K is the acid-dissociation constant of the aquo complex. A mechanism involving the aquation of the ternary hydroxo complex as the rate-determining step is suggested. The values of k1 and pK were determined at 35°C to be 0.62 × 10−2 and 10.09 repectively. Activation enthalpy and activation entropy for the aquation reaction were determined from Arrhenius plots and found to be ΔH‡ = 74.57 kJ mol−1 and ΔS‡ = 202 J K−1 mol−1. The results are compared with previously reported data on catalysis by the structurally related [Fe(EDTA)] species.

Metal chelates of phosphonate-containing ligands—VI Complexes of ethylenediaminetetra(methylenephosphonic) acid with Cd, Mg, Ca and Ba

A correction is made to results previously obtained, as a result of further calculations.

Metal chelates of azo-pyridazine dyes III chelating tendencies of pyruvic and hippuric monohydrazone-3-hydrazino-4-benzyl-6-phenylpyridazine

The synthesis and quantitative equilibrium studies of two new azo-pyridazine ligands, namely the pyruvic (PHP) and hippuric (HipHP) acid derivatives are described in detail. Their acid-base and metal-ligand equilibrium constants in 75% dioxan-water solvent at 30 °C have been calculated from potentiometric and spectrophotometric data. The probable structures are inferred from electronic and vibrational spectral results. Evidence is presented for the formation of protonated complexes withPHP.ZusammenfassungDie Synthese und quantitative Gleichgewichtsuntersuchungen von zwei neuen Azo-pyridazin-Liganden, die von Brenztraubensäure (PHP) bzw. Hippursäure (HipHP) abzuleiten sind, werden im Detail beschrieben. Die entsprechenden Säure-Base- und Metall-Ligand-Gleichgewichtskonstanten in 75% Dioxan-Wasser bei 30 °C wurden aus potentiometrischen und spektrophotometrischen Daten ermittelt. Die wahrscheinlichen Strukturen wurden von Elektronen- und IR-spektroskopischen Daten abgeleitet. Es sind Beweise vorhanden, daß mitPHP protonierte Komplexe gebildet werden.

X-ray photoelectron studies of some phosphates

Abstract The X-ray photoelectron spectra of sodium, potassium, magnesium and calcium salts of orthopyro- and triphosphate were measured. The O (1S) electron spectra of the different salts showed the presence of only one king of oxygen except in the case of acid phosphates where two types of oxygen were distinguished to account for the presence of protonated and non-protonated oxygen sites. The values of the binding energies measured were correlated were correlated with the calculated charges by applying an iterative Paulings method. The chemical shift is P (2p) electron energies have been empirically correlated with the common logarithm of stability constants.