Kinetics and mechanism of silver(I) catalysed autoxidation of aqueous sulphur(IV) in acetate buffered medium

The kinetics of the silver(I) catalysed autoxidation of aqueous sulphur(IV) an acetate buffered medium obey the rate law: –d[S^IV]/dt = D[Ag^I][S^IV]²[H⁺]^–1/(B+C[S^IV]). The rate is independent of [O₂] but strongly inhibited by EtOH. A free radical mechanism is proposed.     

Kinetics and mechanism of the complexation between hydroxopentaaquochromium(III) and octacyanomolybdate(IV) ions in acidic medium

Summary The reaction between hydroxopentaaquochromium(III) and octacyanomolybdate(IV) was investigated spectrophotometrically and obeyed a 2:1 reactant stoichiometry with respect to formation of the [Cr(H₂O)₄OH]₂ Mo(CN)₈ complex. Kinetic studies reveal that the reaction is first order with respect to hydroxopentaaquochromium(III) in the presence of an excess of octacyanomolybdate(IV). The reaction rate increased with an increase in the ionic strength and temperature, and decreased with an increase in hydrogen ion concentration. A mechanism has been proposed based upon ion-pair formation. The results are best accounted for by the Eigen-Tamm mechanism. Anation of [Cr(H₂O)₅OH]²⁺ is discussed in terms of an associative interchange (I _a) where bond breaking and bond making are equally important. The activation parameters were calculated using Arrhenius's equation.     

Kinetics and mechanism of oxidation of L-ascorbic acid by platinum(IV) in aqueous acid medium

The oxidation of l-ascorbic acid (H₂A) by platinum(IV) in aqueous acid medium exhibits overall second-order kinetics, being first order with respect to each reactant. Increasing both hydrogen and chloride ion concentrations inhibits the rate. The stoichiometry involves reaction of one platinum(IV) ion with H₂A to give dehydroascorbic acid. A reaction mechanism consistent with all the experimental observations is proposed.     

Kinetics and mechanism of electron transfer reactions. Osmium(VIII) catalyzed oxidation of mannitol by hexacyanoferrate(III) in aqueous alkaline medium

The kinetics of electron transfer from mannitol to hexacyanoferrate(III), catalyzed by osmium(VIII), has been studied in alkaline medium. The substrate order is complex, whereas it is one with respect to the catalyst. The rate is independent of the concentration of oxidant. Also, the rate increases with increasing concentration of hydroxide ion in a complex manner. A kinetic rate law corresponding to the proposed mechanism has been suggested as follows:

Kinetics and mechanism of oxidation of tetrahydrofurfuryl alcohol by dihydroxydiperiodatonickelate (IV) complex in aqueous alkaline medium

The kinetics of oxidation of tetrahydrofurfuryl alcohol by dihydroxydiperiodatonickelate (IV) complex in the temperature range of 20–35°C has been studied by spectrophotometry in aqueous alkaline medium. The reaction order in [Ni(IV)] was found to be unity and that in [alcohol] to be 1.64–1.69. The rate of oxidation increases with increase in [OH^?] and decreases with increase in [IO₄^?], indicating that dihydroxymonoperiodatonickelate (IV) complex is the reactive species of oxidant. Salt effect studies indicated that the reaction is of ion-dipole type. Under the protection of nitrogen the reaction system does not induce polymerization of acrylonitrile or acrylamide, which indicates that a one-step two-electron transfer mechanism without free radical intermediate may be in operation. A mechanism involving a preequilibrium of an adduct formation between Ni(IV) and alcohol has been proposed. All the experimental phenomena can be explained by the equation derived from the mechanism. The activation parameters of the rate-determining step have been calculated. © John Wiley & Sons, Inc.     

Metal localized luminescence in rhodium (III) and iridium (III) sulphur chelates

Emission and absorption spectra (liquid nitrogen temperature) are reported for the tris sulphur chelates of diethyl-dithiophosphate (dtp) and dimethyldithiocarbamate (dmtc) with rhodium(III) and iridium(III) ions. The emission for all complexes is broad, structureless and occurs in the near infrared. Emission lifetimes are all ≈μsec magnitude. The emission is assigned as a metal localized ³T₁ → ¹A₁ emission.     

水相法合成双(环戊二烯基)钛氨基酸配合物的研究

以N-(取代苯基)氨基乙酸及盐与双(环戊二烯基)二氯化钛在水相及有机相反应,得到了五个双(环戊二烯基)钛氨基酸配合物,对配合物进行了熔点、元素分析、IR及^1HNMR的表征,确定了它们的结构。这些配合物在空气中稳定。经比较,水相中的合成反应速度快,操作简便,产物较易分离,产率高。     

Kinetics and mechanism of the reactions ofcis-tetraaminediaqua-cobalt(III) with nitrite,azide and salicylate ions in aqueous acidic media

Summary Kinetic studies of the anation of the title complex by NO ₂ ^– show that it occurs in a stepwise manner leading to thecis-dinitro-complex both steps having a common rate equation:-d[complex]/dt = a[NO ₂ ^– ]/{[NO ₂ ^– ] + b}. The variation ofpseudo-first-order rate constant (k_obs) with [NO ₂ ^– ] indicates that the reaction proceeds through ion-pair interchange path. Activation parameters calculated by the Eyring equation are: H ₁ = (65±7) kJ mol^–1 and S ₁ = (–82±11) JK^–1 mol^–1 for the formation of [Co(NH₃)₄(NO₂)(H₂O)]²⁺, and H ₂ = (97±1) kJ mol^–1 and S ₂ = (6±2) JK^–1 mol^–1 for the formation of [Co(NH₃)₄(NO₂)₂]⁺. Anation of the title complex by N ₃ ^– at pH 4.1 also occurs in a stepwise manner ultimately producing thecis-diazido species. At a fixed pH the reaction shows a first-order dependence on [N ₃ ^– ] for each step. pH-variation studies at a fixed [N ₃ ^– ] show that the hydroxoaqua-form of the complex reactsca. 16 times faster than the diaqua form. Evidence is presented for an ion-pair preequilibrium at high ionic strength (I = 2.0 mol dm^–3). Activation parameters obtained from temperature variation studies are: H ₁ = (121±1) kJ mol^–1 and S ₁ = (104±3) JK^–1 mol^–1 (for the first step anation), and H ₂ = (111±2) kJ mol^–1 and S ₂ = (74±9) JK^–1 mol^–1 (for the second step anation). The reaction ofcis-tetraaminediaquacobalt(III) ion with salicylate (HSal^–) has been studied in aqueous acidic medium in the temperature range 39.8–58.2°C. The reaction is biphasic corresponding to the anation of two salicylate ions. The kinetic results for the first phase reaction are compatible with the equation: k_obs = k_IPQ[HSal^–]/(1 + Q[HSal^–]) where Q denotes ion-pair formation constant and k_IP is the first-order rate constant for the interchange reaction. The activation parameters obtained from the temperature dependence of rate are: H = (138±3) kJ mol^–1 and S = (135±4) JK^–1 mol^–1. The reaction seems to take place by a dissociative interchange mechanism.     

Kinetics and mechanism of the reaction oftrans-cyclohexane-1,2-diamine-N N N' N'-tetra-acetatomanganate(III) with substituted thioureas in aqueous medium

Summary The kinetics of reduction of [Mn^III(cydta)]^– (where H₄cydta=trans-cyclohexane-1,2-diamine-N N N' N'-tetraacetic acid) by some thiourea reductants have been studied in aqueous solution by stopped-flow techniques in the pH ranges 2.5–4.5 and 9.2–10.2. An initial increase in absorbance followed by a steady decrease indicated the formation of a precursor complex prior to the electron transfer step. The reactions are first order in both oxidant and reductant. The observed increase in rate in going from low to high pH is attributed to the difference in reactivities of the aqua and hydroxo species of the Mn^III complex; the higher reactivity of the latter is consistent with the formation of a ligand-bridged activated species prior to electron transfer. The reactivity order for the thiourea derivatives follows the order of their reported substituent effects.     

Kinetics and mechanism of the iron(III)-catalyzed autoxidation of sulfur(IV) oxides in aqueous solution. The influence of pH,medium and aging

The influence of pH on the oxygen-dependent step observed during the iron(III)-catalyzed autoxidation of sulfur(IV)-oxides was studied over the pH range 1.5 pH 4. A maximum decomposition rate of the iron(III)-sulfito complexes is observed around pH 2.3. The pH- time profile for the iron(III)-catalyzed autoxidation of sulfur(IV)- oxides exhibited no dependence on the initial [O2] when the reaction is initiated at pH 6.1, but shows an oxygen dependence when the reaction is initiated at pH 2.5. pH-shift experiments clearly demonstrate the reduced catalytic activity of dimeric and polymeric iron(III) hydroxo species. A decrease in the catalytic activity of the iron(III) solutions with time was observed, which depended on the initial pH. This decrease was ascribed to the formation of dimeric and polymeric iron(III) hydroxo species as a result of slow hydrolysis processes during aging. The employed iron(III) salt had no effect on the decrease in the catalytic activity due to aging.     

Kinetics and mechanism of the interaction of hexaaquochromium(III) with octacyanomolybdate(IV) ions

The kinetics of the interaction of hexaaquochromium(III) ion with potassium octacyanomolybdate(IV) have been studied using conductance and spectrophotometric data. The mechanism of the reaction is discussed and the effect of H⁺ ion and the ionic strength on the rate of the reaction determined. The reaction is found to be pseudo-first order with respect to potassium octacyanomolybdate(IV) and inverse first order with [H₃O⁺]. The rate of the reaction increases with increase in ionic strength and temperature. Activation parameters have been calculated using the Arrhenius equation and have the values ΔE^* = 1.3 × 10² kJ mol^?1, ΔH^* = 129 kJ mol^?1, ΔS^* = ?315 e.u., ΔF^* = 2.3 × 10² kJ and A = 1.5 × 10^?3. The mechanism proposed is based on ion-pair formation and the rate equation obtained is given by: k_obs=$\text{[}{}_{\mathrm{kK}}{}_{\mathrm{<mtext>E</mtext>}}\text{[H}{}_3\text{O}{}^{\mathrm{+}}\text{]+}\text{k′K′k}{}_{\mathrm{E}}\text{k}{}_{\mathrm{h}}\text{][Mo(CN)}{}_8{}^{\mathrm{4?}}\text{]}\text{[H}{}_3\text{O}{}^{\mathrm{+}}\text{]+}\text{k}{}_{\mathrm{<mtext>h</mtext>}}\text{+[}\text{K}{}_{\mathrm{<mtext>E</mtext>}}\text{[H}{}_3\text{O}{}^{\mathrm{+}}\text{]+}\text{K′}{}_{\mathrm{E}}\text{k}{}_{\mathrm{h}}\text{][Mo(CN)}{}_8{}^{\mathrm{4?}}\text{]}$     

Kinetics and mechanism of oxidation of benzohydrazide by bromate catalyzed by vanadium(IV) in aqueous acidic medium

The reaction between benzohydrazide and potassium bromate catalyzed by vanadium(IV) was studied under pseudo‐first‐order condition keeping large excess of hydrazide concentration over that of the oxidant. The initiation of the reaction occurs through oxidation of the catalyst vanadium(IV), VO²⁺, to vanadium(V), VO, which then reacts with hydrazide to give N,N′‐diacylhydrazine and benzoic acid as the products. The order in [H⁺] is found to be two, and its effect is due to protonation and hydrolysis of oxidized form of the catalyst to form HVO₃. The oxidized form of the catalyst, VO, forms a complex with the protonated hydrazide as evidenced by the occurrence of absorption maxima at 390 nm. The rate of the reaction remains unaffected by the increase in the ionic strength. The activation parameters were determined, and data support the mechanism. The detailed mechanism and the rate equation are proposed for the reaction. © 2008 Wiley Periodicals, Inc. Int J Chem Kinet 40: 151–159, 2008     

Kinetics and mechanism of oxidation of xylitol and galactitol by hexacyanoferrate(III) ion in aqueous alkaline medium

Kinetics of oxidation of xylitol and galactitol by hexacyanoferrate(III) ion in aqueous alkaline medium is reported. The reaction rate is of first order with respect to hexacyanoferrate(III) in each substrate. The reaction is first order at lower concentrations of xylitol and galactitol and tends towards zero order as the concentration increases. Similarly first order kinetics was obtained with respect to hydroxide ion at lower concentrations and tends to lower order at higher concentration in the oxidation of xylitol; in the oxidation of galactitol the reaction is first order with respect to hydroxide ion even up to manyfold variation. The course of reaction has been considered to proceed through the formation of an activated complex between [K Fe(CN)₆]^2– and substrate anion which decomposes slowly into radical and [K Fe(CN)₆]^3–. A probable reaction mechanism is proposed.

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Kinetik und Mechanismus der Oxidation von Xylit und Galaktit mit Hexacyanoferrat(III) in wäßriger, alkalischer Lösung

Zusammenfassung Das Geschwindigkeitsgesetz der Titelreaktion ist in beiden Fällen erster Ordnung bezüglich Hexacyanoferrat(III). Die Oxidation ist erster Ordnung bei niedrigen Konzentrationen von Xylit und Galaktit und geht bei Erhöhung der Konzentration gegen null. In gleicher Weise wurde eine Kinetik erster Ordnung bezüglich Hydroxyl bei niedrigen Konzentrationen und eine erniedrigte Ordnung bei höheren Konzentrationen für die Oxidation von Xylit beobachtet; bei Galaktit bleibt die Oxidation auch bei höheren Hydroxyl-Konzentrationen erster Ordnung. Es wird angenommen, daß die Reaktion über einen aktivierten Komplex zwischen [KFe(CN)₆]^2– und dem Substrat-Anion verläuft; dieser Komplex zerfällt in [KFe(CN)₆]^3– und ein Substrat-Radikal. Ein möglicher Reaktionsmechanismus wird vorgeschlagen.

     

Kinetics and mechanism of distribution of Am(III) and Eu(III) between thenoyltrifluoroacetone-triphenylarsine oxide mixture in chloroform and aqueous nitrate medium

The kinetics of distribution of Am(III) and Eu(III) between thenoyltrifluoroacetone (HTTA) and triphenylarsine oxide (Ph₃AsO) mixture in chloroform and aqueous nitrate medium has been investigated using a stirred Lewis cell at ionic strength of 0.1M. The effect of the concentration of HTTA, Ph₃AsO, H⁺ and NO ₃ ^– on the rate of distribution of Am(III) and Eu(III) was studied. The results were interpreted by reaction mechanisms where the rate-determining steps are the parallel reactions of Am(OH)²⁺ or Eu(OH)²⁺ with one HTTA molecule and one Ph₃AsO molecule in the aqueous medium. The values at 25 °C of the rate constantk _HLL (HL=HTTA andL=Ph₃AsO) are 1.6±0.3·10⁶M^–2·s^–1 and 2.3±±0.3·10⁸M^–2·s^–1 for Am(III) and Eu(III), respectively.     

Cationic methyl complexes of rhodium(III): synthesis, structure, and some reactions

Cationic methyl complex of rhodium(III), trans-[Rh(Acac)(PPh₃)₂(CH₃)(CH₃CN)][BPh₄] (1) is prepared by interaction of trans-[Rh(Acac)(PPh₃)₂(CH₃)I] with AgBPh₄ in acetonitrile. Cationic methyl complexes of rhodium(III), cis-[Rh(Acac)(PPh₃)₂ (CH₃)(CH₃CN)][BPh₄] (2) and cis-[Rh(BA)(PPh₃)₂(CH₃)(CH₃CN)][BPh₄] (3) (Acac, BA are acetylacetonate and benzoylacetonate, respectively), are obtained by CH₃I oxidative addition to rhodium(I) complexes [Rh(Acac)(PPh₃)₂] and [Rh(BA)(PPh₃)₂] in acetonitrile in the presence of NaBPh₄. Complexes 2 and 3 react readily with NH₃ at room temperature to form cis-[Rh(Acac)(PPh₃)₂(CH₃)(NH₃)][BPh₄] (4) and cis-[Rh(BA)(PPh₃)₂(CH₃)(NH₃)][BPh₄] (5), respectively. Complexes 1-5 were characterized by elemental analysis, ¹H and ³¹P{¹H} NMR spectra. Complexes 1, 2, 3 and 4 were characterized by X-ray diffraction analysis. Complexes 2 and 3 in solutions (CH₂Cl₂, CHCl₃) are presented as mixtures of cis-(PPh₃)₂ isomers involved into a fluxional process. Complex 2 on heating in acetonitrile is converted into trans-isomer 1. In parallel with that isomerization, reductive elimination of methyl group with formation of [CH₃PPh₃][BPh₄] takes place. Replacement of CH₃CN in complexes 1 and 2 by anion I⁻ yields in both cases the neutral complex trans-[Rh(Acac)(PPh₃)₂(CH₃)I]. Strong trans influence of CH₃ ligand manifests itself in the elongation (in solid) and labilization (in solution) of rhodium-acetonitrile nitrogen bond.     

Kinetics and mechanism of interactions of some monofunctional Au(III) complexes with sulphur nucleophiles

Kinetics of the substitution reactions between monofunctional Au(III) complexes, [Au(dien)Cl]²⁺, [Au(bpma)Cl]²⁺ and [Au(terpy)Cl]²⁺ (dien?=?3-azapentane-1,5-diamine, bpma?=?di-(2-picolyl) amine, terpy?=?2,2′;6′,2″-terpyridine), and biologically relevant sulphur ligands, namely glutathione (GSH), l-methionine (l-Met) and l-cysteine (l-Cys), were studied in 0.1 M HCl (pH?=?1.0). The reactions were followed under pseudo-first-order conditions as a function of ligand concentration and temperature using stopped-flow spectrophotometry. The [Au(terpy)Cl]²⁺ complex proved to be more reactive than the [Au(bpma)Cl]²⁺ and [Au(dien)Cl]²⁺ complexes. The reactivities of the nucleophiles follow the same order for all three complexes, viz. l-Met?>?GSH?>?l-Cys. Values of the activation parameters of the reactions support an associative substitution mechanism. In order to confirm that these monofunctional Au(III) complexes undergo a single substitution process in strongly acidic medium, the reaction between [Au(terpy)Cl]²⁺ and l-Met was studied by HPLC. At pH?=?1.0, only one reaction product was detected.     

Electron transfer reactions of nickel(III) and nickel(IV) complexes

This review narrates the electron transfer reactions of various nickel(III) and nickel(IV) complexes reported during the period 1981 until today. The reactions have been categorized mainly with respect to the type of nickel complexes. The reactivity of nickel(III) complexes of macrocycles, 2,2′-bipyridyl and 1,10-phenanthroline, peptides and oxime–imine, and of nickel(IV) complexes derived from oxime–imine, oxime and miscellaneous ligands with various organic and inorganic electron donors have been included. Kinetic and mechanistic features associated with such interactions have been duly analyzed. The relevance of Marcus cross-relation equations in the delineation of the electron transfer paths has also been critically discussed.