Palladium(II) inhibition during cerium(IV) oxidation of aldoses: a kinetic study

Summary The kinetics of oxidation of aldoses, namely xylose, arabinose, galactose and glucose, by Ce^IV have been studied in HClO₄ + H₂SO₄ medium and in the presence of Pd^II. The reactions exhibit a first order rate dependence with respect to oxidant. The rate is inversely dependent on the [HSO _inf4 ^sup– ][H⁺] ratio. The order of reaction with respect to aldose decreases at higher [aldose]. Due to the formation of a complex between Ce^IV and Pd^II, a retarding effect of [Pd^II] on the rate of disappearance of [Ce^IV] has been observed. A mechanism consistent with the observed kinetic data is proposed.     

The kinetics of oxidation of N(2-hydroxyethyl)ethylenediaminetriacetatocobaltate(II) by peroxodisulfate ion in aqueous acidic solutions

Summary Peroxodisulfate ion readily oxidises Co^II-YOH [YOH =N(2-hydroxyethyl)ethylenediaminetriacetate] with the formation of an intermediate complex. The kinetics of the electron-transfer step follow the rate law: Rate = 2k_HK_H[H⁺][S₂O₈]²-[Co^II-YOH]/(1 + K_H[H⁺]) where [S₂O₈]^2– is the total peroxodisulfate concentration, k_H is the rate constant for the electron-transfer process, and K_H is the pre-equilibrium protonation constant. Activation parameters have been evaluated. The intermediate, which was identified spectrophotometrically, slowly rearranges to the quinquedentate species Co(YOH)(H₂O). The rate of this rearangement has also been measured.     

Kinetics and mechanisms of oxidation by metal ions. Part XIII. Osmium(VIII)-catalysed oxidation of cycloalkanols by alkaline hexacyanoferrate(III)

Summary The kinetics of OsO₄-catalysed oxidation of cyclopentanol, cyclohexanol and cyclooctanol by alkaline hexacyanoferrate(III) have been studied at low [OH^–] so that the equilibrium between alcohol and alkoxide ion is not unduly shifted towards the latter. The reaction shows a first-order dependence in [OH^–]. The order of the reaction with respect to cycloalcohol is fractional, indicating the formation of an intermediate complex with Os^VIII since the order with respect to hexacyanoferrate(III) ion is zero. The order with respect to Os^VIII may be expressed by the equation k_obs=a+b[Os^VIII]. The analysis of the rate data indicates a significant degree of complex formation between [OsO₃(OH)₃]^– and ROH. It was found that the bimolecular rate constant k for the redox reaction between complex and OH^–k₁, the forward rate constant for the formation of alkoxide ion. The activation parameters of these rate constants are reported.     

Unusual stabilization of manganese(III) during the cooxidation of dimethylformamide and manganese(II) by chromium(VI)

The kinetics of the formation and decomposition of Mn^III have been investigated spectrophotometrically in acidic media at 25 °C. The complete rate law for Mn^III formation isCr^VI + DMF + Mn^II {H⁺} Mn^III + CO₂ + Me₂NH + Cr^III ... (1)Mn^III + DMF {H⁺} Mn^II + CO₂ + Me₂NH ... (2)expressed by k _obs1 = k ₁ k₁ K _a1[H⁺][DMFH⁺][Mn^II]/{1 + K _a1[H⁺]}. Mn^III reduction by DMF follows the rate law k _obs2 = k ₂ K _h[DMF][H⁺]²/{[H⁺] + K _h}. The above results are accounted for by a mechanism involving the intermediacy of Cr^IV.     

Mechanistic Study of Oxidation of Palladium(II) by Cerium(IV) in Aqueous Acid

The kinetics of oxidation of Pd^II by Ce^IV have been studied spectrophotometrically in HClO₄ media at 40 °C. The reaction is first order each in [Ce^IV] and [Pd^II] at constant [H⁺]. Increasing [H⁺] accelerates the reaction rate with fractional order in [H⁺]. The initially added products, palladium(IV) and cerium(III) do not have any significant effect on the reaction rate. At constant acidity, increasing the added chloride concentration enhances the rate of reaction. H₃Ce(SO₄)₄⁻ and PdCl₄²⁻ are the active species of oxidant and reductant respectively. The possible mechanisms are proposed and the reaction constants involved have been determined.     

Inner-sphere oxidation of ethylenediaminetetraacetatocobaltate(II) by N-bromosuccinimide

Summary The kinetics of oxidation of [Co^II(EDTA)]^2- (EDTA = ethylenediaminetetraacetate) by N-bromosuccinimide (NBS) in aqueous solution obey the equation: Rate = k ₂ K ₃[Co^II]_T[NBS]/{1 + [H⁺]/K ₂ + K ₃[NBS]} where k ₂ is the rate constant for the electron-transfer process, K ₂ the equilibrium constant for the dissociation of [Co^II(EDTAH)(H₂O)]^– to [Co^II(EDTA)(OH)]^3– and K ₃ 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[Co^III(EDTA)]^–.Abstracted from the M.Sc. thesis of Eman S. H. Khaled.     

Kinetics of tetraamminecopper(II)-catalysed oxidation of sulphur(IV) by peroxodisulphate in ammonia buffer

The kinetics of tetraamminecopper(II)-catalysed oxidation of SO^2– ₃ to SO^2– ₄ in ammonia buffers and in a nitrogen atmosphere obeys the rate law: –d[S^IV]/dt = k ₂[Cu^II][SO₃ ^2–][NH₃]^–1. There is spectrophotometric evidence for the formation of the intermediate complex [Cu(NH₃)₃(SO₃)] in a pre-equilibrium.     

Kinetics and mechanism of bromide ions oxidation by cerium(IV) in sulphuric acid solutions revisited

Kinetics of Br⁻ anion oxidation by cerium(IV) species in aqueous H₂SO₄ solutions have been reexamined. The rate of reaction was determined spectrophotometrically based on a factor analysis of the absorbance – time data collected in the wavelength range 318–390 nm – the region characteristic for the cerium(IV) sulphato complexes. The data fit very well to a pseudo-first order dependence under a large molar excess of the reductant. The rate law of the form –d[Ce^IV]/dt = k[Ce^IV][Br^–]² has been obtained at constant H₂SO₄ concentration and ionic strength I = 2 m. The pseudo-first order rate constant decreases with an [H₂SO₄] increase from 0.1 to ca. 0.4 m range, then increases for higher [H₂SO₄]. The apparent activation parameters have been calculated from the third order rate constants k for different [H₂SO₄].     

Kinetics of nucleophilic attack upon coordinated organic moieties.: XXIII. Attack by cyclohexylamine upon the diene ligands in [MX2(1,5-cyclooctadiene)] (M = Pd,Pt; X = Cl,Br) complexes

Kinetic and spectroscopic studies of the reactions of cyclohexylamine with the complexes [MX₂(1,5-cyclooctadiene)] (I) (M = Pd; X = Cl, Br; M = Pt, X = Br) in acetone reveal the rate law, k_obs = K₁k₂[amine]², for the rapid sequence

For X = Br, the palladium(II) complex is ca. 70 times more reactive than its platinum(II) analogue. This is the first quantitative comparison reported to date for nucleophilic attack upon olefins coordinated to Pd^II and Pt^II centres. The reactivity order Pd^II ⪢ Pt^II may arise from the higher ionization potential of Pd²⁺ compared to Pt²⁺, which makes Pd^II a less effective back-π-bonder. Replacing the bromo ligands in [PdBr₂(1,5-COD)] by chloro ligands lowers the rate of formation of III by a factor of 8.     

Ruthenium(III), osmium(VIII) and ruthenium(III) + osmium(VIII) catalysed oxidations ofi-propanol by N-bromosuccinimide in basic solution

Summary The oxidation ofi-propanol (IPA) by N-bromosuccinimide (NBS) in basic solution was investigated separately in the presence of Ru^III, Os^VIII and Ru^III + Os^VIII ions. The order in [IPA] was found to be 0.7, 0.5 and 0.3 respectively in the above three cases in the concentration range studied. The order in [NBS] was unity in the presence of Ru^III chloride but was found to be zero in the case of Os^VIII and Ru^III+Os^VIII catalysis. The order in [metalion] was found to be nearly unity in all the three catalysed reactions. Increase in [^–OH] increased the rate of reaction while addition of succinimide retarded the rate of reaction. Decrease in dielectric constantsof the medium decreased the rate of oxidation. The pseudo first order rate constants (k), zero order rate constants (k₀) and the formation constants (k_f) of the substrate-catalyst complexes and the thermodynamic parameters have been evaluated. Suitable mechanisms in conformity with the experimental observations have been proposed for the three catalysed reactions.     

Osmium(VIII) mediated oxidation of mercury(I) by cerium(IV) in aqueous sulphuric acid – a kinetic and mechanistic study

The oxidation of Hg^I by Ce^IV has been studied in aqueous H₂SO₄. A minute amount (10^–6 mol dm^–3) of Os^VIII is sufficient to catalyse the reaction. The active catalyst, substrate and oxidant species are H₂OsO₅, [Hg₂(SO₄)HSO₄]^– and H₃Ce(SO₄)^– ₄, respectively. Possible mechanisms are proposed and the reaction constants involved have been determined.     

Kinetics and mechanism of ruthenium(III) catalyzed oxidation of tetrahydrofurfuryl alcohol by cerium(IV) in sulfuric acid media

The kinetics and mechanism of ruthenium(III) catalyzed oxidation of tetrahydrofurfuryl alcohol (THFA) by cerium(IV) in sulfuric acid media have been investigated spectrophotometrically in the temperature range 298–313 K. It is found that the reaction is first-order with respect to Ce^IV, and exhibits a positive fractional order with respect to THFA and Ru^III. The pseudo first-order ([THFA]≫[Ce^IV]≫[Ru^III]) rate constant k _obs decreases with the increase of [HSO ₄ ⁻ ]. Under the protection of nitrogen, the reaction system can initiate polymerization of acrylonitrile, indicating the generation of free radicals. On the basis of the experimental results, a reasonable mechanism has been proposed and the rate equations derived from the mechanism can explain all the experimental results. From the dependence of k _obs on the concentration of HSO ₄ ⁻ , has been found as the kinetically active species. Furthermore, the rate constants of the rate determining step together with the activation parameters were evaluated.     

Osmium dimethyl sulfoxide complexes: Synthesis and properties of [H(dmso)2][OsIII(dmso)2Br4]

The reaction of H₂[OsBr₆] with DMSO in ethanol solution resulted in DMSO complex [H(dmso-O)₂][Os^III(dmso-S)₂Br₄] (1) described previously as an intermediate product in the reaction of K₂[OsBr₆] with DMSO and characterized by EAS and ESR spectra. The coordination of DMSO molecules was established by IR and ¹H and ¹³C NMR spectroscopy. The oxidation state of osmium and trans arrangement of DMSO molecules in the anion were established by ESR. The behavior of complex 1 in solutions was studied by EAS, ESR, and mass-spectrometry: a displacement of Br^? ions accompanied by the reduction of osmium to oxidation state +2 occurs in DMSO, a solvation with displacement of DMSO molecules is observed at the first stage in water and methanol (rate constants 2.3 × 10^?4 and 1.7 × 10^?3 s^?1, respectively), the sequential substitution of DMSO molecules and osmium oxidation to form [Os^IVBr₆]_2? ions takes place in 4 mol/L HBr.     

Kinetics of oxidation of hypophosphite ion by platinum(IV) in an alkaline medium

Summary The kinetics of the oxidation of hypophosphite ion by platinum(IV) have been studied spectrophotometrically in alkaline medium at different temperatures. The rate increases as the pH increases and the empirical rate law applicable to the reaction is given by:-d[Pt^IV]/dt = k₃[Pt^IV][H₂PO^2–][OH^–]The rate constant is 2.17×10^–3 (l² mo^–2s^–1) at 40.5°. The energy and entropy of activation for the reaction are 104.2 kJ mol^–1 and 28.5 JK^–1mol^–1 respectively.     

Kinetics and mechanism of osmium(VIII)-catalyzed oxidation of 1,4-thioxane by alkaline hexacyanoferrate(III)

The kinetics of oxidation of 1,4-thioxane (1,4-oxathiane) by alkaline K₃Fe(CN)₆ have been studied in the presence of Os^VIII as catalyst. The reaction is first order in hexacyanoferrate(III) and Os^VIII. The order in thioxane and OH^– is zero. While added salts and ethanol have a negligible effect on the oxidation rate, K₄Fe(CN)₆ retards it. On the basis of kinetic evidence, a mechanism has been proposed.     

Effect of the degree of sulfoethylation of polyethylenimine on the selectivity of sorption of palladium(ii) from binary solutions

Poly(N-2-sulfoethylethylenimine) (SEPEI) with a degree of modification equal to 0.30, 0.58, and 0.74, cross-linked with diethylene glycol diglycidyl ether, demonstrates efficient sorption properties with respect to Pt^IV, Pd^II, and Au^III ions. The selectivity coefficient K_Pd/Au in a HCl solution with pH 0.8 decreases from 90 to 61, and the selectivity coefficient K_Pd/Pt in a HCl solution with pH 3.9 increases from 0.94 to 480 with an increasing degree of modification. A thiourea hydrochloric acid solution effectively removes metal ions; the desorption of Pt^IV, Pd^II, and Au^III from the SEPEI surface reaches 100, 96.9, and 83.8%, respectively.

     

Kinetics of interaction and complexation of the palladium(II) ion with new para-substituted-phenylazo-R-acid chromophores

The kinetics of complex formation between the Pd^II ion and the new phenylazo-R-acid chromophore [HL] and it is para-substituted derivatives {X = H, Cl, CO₂H, and SO₂NH₂}, [p-X-HL], have been studied at various temperatures. The observed rate constant is given by:k_obs=/k₁ K₁/K[H⁺]+k₂ K₂}[p-X-HL]A mechanism involving initial formation of a 1:1 complex between the Pd^II ion and [p-X-HL], followed by aquation as the rate-determining step, is proposed. The activation enthalpy and entropy for the aquation were determined. The rate of formation is greatly effected by electron-withdrawing substitutents in the para position of the phenylazo-R-acid ligand. The solid complex of p-SO₂NH₂-phenylazo-R-acid has been prepared and characterized by elemental analysis, and FT-IR spectra. The p-substituted-phenylazo-R-acid ligands are very active against C. albicans fungi, so that these compounds can be used for the chemotherapy of candidiasis and other fungal skin diseases.     

Kinetics and mechanism of oxidation of uric acid with thallium(III) in acetate buffers

The kinetics of oxidation of uric acid by thallium(III) has been studied in acetate buffers; the oxidation products are alloxan and urea. Deprotonated uric acid, UaH⁻, and T1(OAc)₃ are the reacting species. A probable reaction mechanism has been proposed conforming with rate law (1)-d[T1^III]/dt=(k′₁K′₁+k′₂K′₂K₁/[H⁺]) [T1^III][UaH₂]/1+K₄[OAc⁻] A comparative analysis with other soft acids Hg^II and Pb^IV has been attempted.     

Solvent extraction and spectrophotometric determination of uranium (VI)

Summary Solvent extraction of uranium-sodium diethyldithiocarbamate with ethylmethyl ketone and separation from titanium, zirconium, thorium, lanthanum and cerium has been described. It has been found that 11.75 to 47.00 mg of uranium can be extracted from a binary mixture containing 4.78 to 19.04 mg of titanium, 9.12 to 36.48 mg of zirconium, 116.0 to 460.0 mg of thorium, 6.95 to 27.8 mg of lanthanum or 7.06 to 28.24 mg of cerium at pH 3.0. The pH range between which the separations may be carried out successfully is 2.0 to 3.5. The following cations interfere in the separations: Cu^II, Fe^III, Co^II, Bi^III, Ni^II, Cr^VI, Te^IV, Se^IV, Ag^I, Hg^II, As^III, Sn^IV, Pb^IV, Cd^II, Mo^VI, Mn^II, V^V, Zn^II, In^III, Tl^I, W^VI, Os^VIII and Nb^V.

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Zusammenfassung Uran kann durch Extraktion als Diäthyldithiocarbamidat mit Methyläthylketon von Ti, Zr, Th, La oder Ce getrennt werden. Der günstigste pH-Bereich liegt zwischen 2,0 und 3,5. Die Trennungen wurden mit folgenden Mengen durchgeführt: U (11,75–47,00 mg); Ti (4,78 bis 19,04 mg), Zr (9,12–36,48 mg) Th (116,0–460,0 mg), La (6,95–27,8 mg), Ce (7,06–28,24 mg). Folgende Ionen verursachen Störungen: Cu^II, Fe^III, Co^II, Bi^III, Ni^II, Cr^VI, Te^IV, Se^IV, Ag^I, Hg^II, As^III, Sn^IV, Pb^IV, Cd^II, Mo^VI, Mn^II, V^VI, Zn^II, In^III, Tl^I, W^VI, Os^VIII sowie Nb^V.

     

Mixed-ligand complexes of osmium(III/IV)8-quinolinolates with one ketoximate ligand

Summary A group of mixed-tris chelates of type [OsAQ₂] [A = isonitrosoacetophenonate (A¹) and isonitroso-propiophenonate (A²); Q = deprotonated 8-quinolinol (Q¹) and 2-methyl-8-quinolinol (Q²)] have been prepared by two distinct synthetic approaches. [OsAQ₂]⁺, obtained by Ce^IV oxidation of [OsAQ₂], can be regenerated by hydrazine hydrate reduction of the former. The complexes, characterized by physico-chemical, magnetic and spectroscopic methods, exhibit several spin-allowed and spin-forbidden charge transfer transitions in their electronic spectra. In MeCN solution the OsN₃O₃ unit displays a nearly-reversible Os^IV-Os^III change and an Os^III-Os^II couple in the ca. -1.0– + 0.3V range versus s.c.e. The stability of the metal oxidation levels is discussed in terms of the chemical and electrochemical results.