NOPR Collection:

Transition metal substituted 12-tungstophosphates:Characterization and evaluation of their performance as oxidation catalysts

Mon, 01 Jun 1998 00:00:00 GMT

Title: Transition metal substituted 12-tungstophosphates:Characterization and evaluation of their performance as oxidation catalysts Authors: Indira, V; Joy, P A; Gopinathan, Sarada; Gopinathan, C Abstract: Tetrabutylammonium salt of [PW₁₂O₄₀]^3- and its transition metal (Mn²⁺, Fe²⁺, CO²⁺ and Cu²⁺) substituted compounds are characterized by elemental analysis, thermogravimetric and spectroscopic techniques. Thermal stability of these compounds decreases after metal ion substitution, but the cobalt substituted compound is relatively more stable. The cobalt substituted compound is found to be a good catalyst for the oxidation of cyclohexanol and the catalytic activity of the transition metal substituted compounds decreases in the order: CO²⁺>> Mn²⁺> Fe²⁺³ Cu²⁺. Detailed studies of the reaction in the presence of Co²⁺and Mn²⁺ substituted compounds reveal that the transition metal ions are initially oxidized to a higher oxidation state which then act as the catalytic centre for the reaction. The enhanced catalytic activity of Co²⁺ substituted compound is due its oxidation to Co²⁺ in the presence of H₂O₂ which is evidenced from EPR and UV-VIS spectroscopic studies. Page(s): 473-481

Reactions of polyhomofunctional organic compounds: 2-Kinetics of hydrolysis of four azomethine sites in a trinuclear cobalt(II) complex

Mon, 01 Jun 1998 00:00:00 GMT

Title: Reactions of polyhomofunctional organic compounds: 2-Kinetics of hydrolysis of four azomethine sites in a trinuclear cobalt(II) complex Authors: Raju, S Suryanarayana; Ramachandraiah, A Abstract: Kinetic studies on the hydrolysis of a novel trinuclear cobalt(II) complex, (CoBAMC-Sal)₂ Co(DMF)₂⁺²(2) in buffered 90 : 10 aqueous /DMF (v/v) mixtures are reported. Repetitive spectral scans of the reaction mixture exhibit isosbestic points at all pH’s. The hydrolysis follows pseudo - first order kinetics with respect to the complex. The rate constants are compared to those reported earlier for the ligand, BAMC - Sal (1) under similar conditions. The difference between the rates of hydrolysis of complex and those of the pure ligand is found to be due to steric factors and stability of the complex. The studies indicate different modes of cleavage of the trinuclear complex at different pH's before the ligand moieties undergo hydrolysis at their azomethine sites. Activation energy, E _a, and thermodynamic parameters such as ΔH^#, ΔG^# and ΔS^# are evaluated by Arrhenius and Eyring methods. Page(s): 482-488

Kinetics and mechanism of oxidations of [N-(2-hydroxyethyl) ethylene-diamine-N,N',N'-triacetato] chromium (III) by N- bromosuccinimide

Mon, 01 Jun 1998 00:00:00 GMT

Title: Kinetics and mechanism of oxidations of [N-(2-hydroxyethyl) ethylene-diamine-N,N',N'-triacetato] chromium (III) by N- bromosuccinimide Authors: Abdel-Khalek, Ahmed A.; Sayyah, El-Said M.; Khaled, Eman S. H. Abstract: The kinetics of oxidation of [N-(2-hydroxyethyl)ethylenediamine- N,N' -Nvtnacetato] chromium (III) complex [Cr^III (H₂O)(TOH) by N-bromosuccinimide(NBS) in aqueous solution to yield chromium (IV) has been studied spectrophotometrically at 20-40°C range. The reaction is first order each in [NBS] and [Cr^III], and the rate increases with increase in pH between 6.30 and 7.33. The thermodynamic activation parameters have been calculated. The experimental rate law is consistent with a mechanism in which the deprotonated [Cr^III(OH)(TOH)^- ] is considered to be the most reactive species compared to its conjugate acid. It is assumed that electron transfer takes place via an inner-sphere mechanism. Page(s): 489-492

Kinetics and mechanism of oxidation of n-butyric and iso-butyric acid hydrazides by hexacyanoferrate(lll) in acidic medium

Mon, 01 Jun 1998 00:00:00 GMT

Title: Kinetics and mechanism of oxidation of n-butyric and iso-butyric acid hydrazides by hexacyanoferrate(lll) in acidic medium Authors: Hongekar, M L; Patil, J B Abstract: The title reaction, studied spectrophotometrically, exhibits first order rate dependence each on [hexacyanoferrate (III)]_o and [hydrazide]_o. The effect of [HClO₄] on oxidation rate is a curious one. On increasing [HClO₄], initially the rate decreases but tends to attain limiting value at higher concentration of HCIO₄. The reaction rate is slightly enhanced by an increase in ionic strength. However, at constant ionic strength, rate is insensitive to the added salts like NaNO₃, NaCIO₄, NaCl, KCI, LiCI and K₄ Fe(CN)₆. The entropy of activation is negative whereas dielectric effect of the binary solvent (water + methanol) is positive. Carboxylic acid and N₂ are identified as oxidation products. A suitable mechanism and a rate law consistent with the experimental results are proposed. Page(s): 493-497