Ahmed A. Abdel-Khalek

Kinetics of the oxidation of (N-(2-hydroxyethyl)-ethylene-diamine- N,N',N'-triacetato)cobalt(II) by N-bromosuccinimide

SummaryThe kinetics of the oxidation of [N-(2-hydroxyethyl)-ethylene-diamine-N,N′,N′-triacetato] cobalt(II), [CoII-(HEDTA)]−, by N-bromosuccinimide, NBS, have been studied in aqueous solutions and water-methanol solvent mixtures under various conditions. The reaction stoichiometry indicates that one mole of NBS reacts with one mole of [CoII(HEDTA)]−. In aqueous solutions the reaction obeys the following rate law:

KINETICS AND MECHANISM OF OXIDATION OF CHROMIUM (III)-L-ARGININE COMPLEX BY PERIODATE

Rate = \left\{ {k_2 + k_3 /\left[ {H^ + } \right]} \right\}\left[ {Co^{11} \left( {HEDTA} \right)^ - } \right]\left[ {NBS} \right]

Kinetics and mechanism of oxidation of (ethylenediaminediacetato)chromium(III) by N-bromosuccinimide

An inner sphere mechanism is proposed for pathway oxidation of both the protonated and deprotonated species of the complex, with the formation of an intermediate which slowly forms the final oxidation product, [CoIII(HEDTA)]. In water-methanol solvent mixtures the reaction rate decreased as the methanol content was increased. An appropriate mechanism, consistent with the kinetic results, is suggested.

Kinetics and mechanism of oxidation in the diaqua(nitrilotriacetato)cobaltate(II)/N-bromosuccinimide reaction: evidence for iron(II) catalysis

SummaryA kinetic study of the oxidation of chromium(III) by N-bromosuccinimide (NBS) in aqueous solutions and H2O-MeOH solvent mixtures were performed. The kinetics in aqueous solutions obeyed the rate law: d[CrVI]/dt = {k4KhK2[NBS][CrIII]T}/[+]{1 + Kh/[H+] + (K1 + KhK2/[H+][NBS])} where Kh, K1 and K2 are the hydrolysis constant of [CrIII(H2O)6]3+, and pre-equilibrium formation constants for the protonated and deprotonated precursor complexes, respectively. An innersphere mechanism is proposed. An argument based on isokinetic correlations among activation parameters for the oxidation of a series of cobalt(II) and chromium(III) complexes including [Cr(H2O)6]3+ is presented in support of a common mechanism for these reactions.

Kinetics and mechanism of the oxidation of diaqua(nitrilotri- acetato)chromium(III) complex by N-bromosuccinimide

Oxidation of the chromium(III)-l-arginine complex [CrIII(L)2(H2O)2]+ by periodate has been investigated. In aqueous solutions, [CrIII(L)2(H2O)2]+ is oxidized by IO−4 according to the rate law: d[CrVI]/dt=k2K5[CrIII]T [IVII]T/1 +([H+]/K1)+K5[IVII]T where k2 is the rate constant for the electron transfer process, K1 the equilibrium constant for the dissociation of [CrIII(L)2- (H2O)2]+ to [CrIII(L)2(H2O)(OH)]+H+, and K5 the pre-equilibrium formation constant. Values of k2= 4.02×10−3s−1, K1=5.60×10−4m and K5=171m−1 were obtained at 30°C and I=0.2m. Thermodynamic activation parameters were calculated. It is proposed that electron transfer proceeds through an inner-sphere mechanism via coordination of IO−4 to chromium(III).

Kinetics and mechanism of oxidation of the chromium(III)-dl-valine complex/periodate reaction. Evidence for iron(II) catalysis

SummaryThe kinetics of oxidation of [CoII(EDTA)]2- (EDTA = ethylenediaminetetraacetate) by N-bromosuccinimide (NBS) in aqueous solution obey the equation: Rate = k2K3[CoII]T[NBS]/{1 + [H+]/K2 + K3[NBS]} where k2 is the rate constant for the electron-transfer process, K2 the equilibrium constant for the dissociation of [CoII(EDTAH)(H2O)]− to [CoII(EDTA)(OH)]3− and K3 the pre-equilibrium formation constant. The activation parameters are reported. It is proposed that electron transfer proceeds via an inner-sphere mechanism with the formation of an intermediate which slowly generates hexadentate[CoIII(EDTA)]−.

Kinetics and mechanism of oxidation of tris(ethylenediamine)-chromium(III) by N-bromosuccinimide

The kinetics of oxidation of (ethylenediaminediacetato)-chromium(III), [Cr(EDDA)(OH2)2]+, by N-bromosuccinimide (NBS) in aqueous solution to yield CrVI have been studied spectrophotometrically over the 20–40°C range. The reaction rate is first order with respect to both [NBS] and [CrIII], and increases with pH over the range 4.8–5.8. The activation parameters were calculated. A mechanism in which deprotonated [CrIII(EDDA)(OH2)(OH)] is the reactive species is suggested. The electron transfer may proceed via an inner sphere mechanism through bridging of the two reactants by the hydroxo ligand.

Kinetics and mechanism of oxidation of chromium(III)-tetraoxalylurea complex by periodate

SummaryOxidation of the diaqua(nitrilotriacetato)cobaltate(II) complex, [CoIInta(H2O)2]-, by NBS has been studied in aqueous medium. The kinetics of the reaction in the presence of an iron(II) catalyst obey the rate law:Catalysis by iron(II) is believed to be due to the oxidation of iron(II) to iron(III), which acts as the oxidizing agent. The thermodynamic activation parameters were calculated and we propose that electron transfer proceeds through an inner-sphere mechanism.