R.R. Merchant

Kinetics of the oxidation of triphenylphosphine with sodium hypochlorite catalysed by aquo-ethylenediaminetetraacetato ruthenate(III) in water-dioxan medium

Abstract The kinetics of oxygenation of aquo-ethylenediaminetetraacetato ruthenate(III) to oxo-ruthenium(V) by NaOCl was studied spectrophotometrically by monitoring the appearance of the characteristic peak of (EDTA)RuV(O)− λmax = 394nm, ϵmax = 8000 ± 20) at pH5.6 and ionic strength 0.2 M (NaClO4). The subsequent oxygen atom transfer from (EDTA)Ruv(O) t to triphenylphosphine was investigated by following the disappearance of (EDTA)Ruv(O) t as a function of substrate concentration and temperature (30–50 °C). Activation parameters for both oxygenation of (EDTA)RuIII(H2O)− to (EDTA)Ruv(O)− and oxygen atom transfer from (EDTA)Ruv(O)− to PPh3 were computed and the experimental results are discussed in reference to the data for the oxygen atom transfer reaction in the oxidation of triphenylphosphine by molecular oxygen catalysed by (EDTA)RuIII(H2O)−.

Kinetics and mechanism of epoxidation of cyclohexene and cyclooctene with potassium hydrogen persulphate catalyzed by aquoethylenediaminetetraacetatoruthenate(III) complex ion in water-dioxane medium

Abstract The kinetics of oxygenation of [(EDTA)Ru III (H 2 O)] − to [(EDTA)Ru v (O)] − by KHSO 5 was studied spectrophotometrically by following the appearance of characteristic peak of [(EDTA)Ru v (O)] − (ϵ 393 max = 8000) at a fixed pH of 6.0 and ionic strength 0.2 M (NaCiO 4 ). The time course of subsequent oxygen transfer from [(EDTA)Ru v (O)] − to cyclohexene and cyclooctene was investigated by following the decrease in the characteristic oxo peak at 393 nm as a function of substrate concentration and temperature (30–50 °C) at a constant pH of 6 and ionic strength 0.2 M (NaC1O 4 ). Activation parameters for both the oxygenation of [(EDTA)Ru III (H 2 O)] − to [(EDTA)Ru v (O)] − and oxygen atom transfer from [(EDTA)Ru v (O)] − to cyclohexene and cyclooctene were determined and probable mechanisms for both reactions proposed.

Kinetics and mechanisms of oxidation of triphenylphosphine with iodosylbenzene catalyzed by N-hydroxyethylethylenediaminetriacetatoruthenate(III) in water—dioxane medium

Abstract The kinetics of oxygenation of [RuIII(HEDTA)(H2O)] complex 1, where HEDTA = N-hydroxyethylethylenediaminetriacetate anion, with iodosylbenzene was studied spectrophotometrically by the stopped flow technique. The rate of formation of [RuV(HEDTA)(O)] complex 2 was monitored at the characteristic peak of the oxo complex 2 at 393 nm. Subsequent oxygen atom transfer from complex 2 to PPh3 was investigated by following the disappearance of the oxo peak at 393 nm. The rate and activation parameters (ΔH≠ and ΔS≠) for both oxygenation of complex 1 with PhIO and oxygen atom transfer from complex 2 to PPh3 were determined and the experimental results are discussed with reference to the data reported for the oxidation of PPh3 catalyzed by the corresponding EDTA—H and PDTA—H complexes.

Synthesis of the complex [RuVO(edta)]− and its application in the oxidation of saturated substrates by oxygen atom transfer reaction

Abstract Oxidation of cyclohexane and cyclohexanol with Ru(edta)(O) − was studied spectrophotometrically by following the disappearance of the oxo peak of the complex Ru V (edta)(O) − at constant pH 5.0. The reaction rate was found to be first order with respect to oxo complex. The rate of oxidation increases with increasing substrate concentration and reaches a limit at high substrate concentration. Rate and activation parameters are in accordance with the mechanism proposed for the oxygen atom transfer reaction from high-valent Ru V (edta)(O) − complexes to saturated hydrocarbons.

Kinetics and mechanism of oxidation of diethylamine and triethylamine by [RuV=O(EDTA)]− in aqueous medium

Abstract The kinetics of oxidation of diethylamine and triethylamine by [Ru V =O(EDTA)] − were studied spectrophotometrically as a function of [Ru V =O(EDTA)] − and [amine] at a fixed pH of 5.0 and ionic strength of 0.2 M NaClO 4 . The reaction rate was followed by observing the disappearance of the characteristic peak at 393 nm of the oxo complex Ru V =O(EDTA) − with time. Oxidative N -dealkylation of tertiary and secondary amines produces secondary and primary amines respectively as oxidation products, the N -alkyl group being oxidized to the corresponding aldehyde. The oxidation reactions were studied at three different temperatures and activation parameters (Δ H ‡ and Δ S ‡) calculated. A mechanism involving a hydride shift from the α-carbon of the substrate to the oxo oxygen is proposed for the oxidation of amines by Ru V =O(EDTA) − . The experimental results are discussed with reference to the oxidation of the corresponding amines with molecular oxygen catalysed by the [Ru III (EDTA)(H 2 O)] − complex.

Epoxidation of cyclohexene, methylcyclohexene and cis-cyclooctene by molecular oxygen using ruthenium(III) aquo ion as catalyst: a kinetic study

Abstract Kinetics of the epoxidation of cyclohexene, methylcyclohexene and cis-cyclooctene by molecular oxygen catalysed by Ru(III) ion, [RuCl2H(2O)4]+ at pH 2.0 in a mixed water-dioxane solvent medium are reported. The reactions were studied manometrically as a function of catalyst, substrate and dioxygen concentrations. For all the substrates studied, the rate of oxidation is first order with respect to catalyst and substrate concentrations and one-half order with respect to dioxygen concentration. The oxidations yielded epoxide as the only product in all cases; these were identified and analysed by GLC technique. Based on the kinetics, a mechanism involving homolytic cleavage of the O-O (peroxo) bond with concerted transfer of the oxygen atom to the substrate was proposed. The presence of methyl group on the cyclohexene ring (reaction 2) and an increase in the number of carbon atoms in the ring for cyclooctene (reaction 3) cause a decrease in the rates of epoxidation. The rate of epoxide formation and the corresponding yields for reactions (1), (2) and (3) decreases in the order: cyclohexene > methylcyclohexene > cyclooctene.

Kinetics and mechanism of the stoichiometric oxidation of toluene and benzyl alcohol by [RuvO(EDTA)]− and [RuvO(PDTA)]− complexes in water—dioxan medium

Abstract Stoichiometric oxidations of toluene to benzyl alcohol and benzyl alcohol to benzaldehyde with LRuvO− (LEDTA, PDTA) were studied spectrophotometrically at constant pH5.0 and ionic strength of 0.1 M (NaClO4). The reaction rate is first order with respect to oxo complex. Increasing the substrate (toluene, benzyl alcohol) concentration increases the reaction rate, and at high substrate concentration the reaction rate is independent of substrate concentration. The rate of oxidation of benzyl alcohol by LRuvO− complexes was found to be five times that of toluene. The oxidations of toluene to benzyl alcohol and benzyl alcohol to benzaldehyde by LRuvO− were studied at three different temperatures and the rate and activation parameters determined. A suitable mechanism consistent with the experimental results has been proposed.

Kinetics and mechanism of oxidation of triphenylphosphine with potassium hydrogen persulfate catalysed by aquapropylenediaminetetraacetatoruthenate(III) in water—dioxane medium

Abstract The kinetics of oxygenation of [(PDTA)Ru III (H 2 O)] − (complex 1 ) to [(PDTA)Ru V (O)] − (complex 2 ) by KHSO 5 was studied spectrophotometrically by monitoring the appearance of the characteristic oxo peak (393 nm, ϵ max 393 = 8200) at a fixed pH 6.0 and ionic strength 0.2 M (NaClO 4 ). The time course of the oxygen atom transfer from complex 2 to PPh 3 was investigated by following the disappearance of characteristic oxo-peak of the oxo-complex 2 as a function of PPh 3 concentration and temperature (30–50 °C) at a fixed pH 6.0 and ionic strength of 0.2 M (NaClO 4 ). Activation parameters for both the oxygenation of complex 1 to complex 2 and oxygen atom transfer from complex 2 to PPh 3 were calculated and probable mechanisms for both reactions proposed.

Kinetics and mechanism of the ligand substitution reaction of aquodiethylenetriaminepentaacetatoruthenate (III) in aqueous solution

The kinetics of ligand substitution reactions of [Ru(H2dtpa) (H2O)] (2) (H2dtpa=diprotonated diethylenetriaminepentaacetic acid) were studied as a function of ligand (L′) concentration, pH (2.5–8.0) and temperature (30–45 °C) at 0.2 M ionic strength. The equilibrium constants for the formation of mixed ligand complex [RuIII(dtpa) (L)] (L=2-mercaptopyrimidine, cysteine) and the distribution of various species in solution in the pH range of 2.5–8.0 were computed from potentiometric results.AbstractКинетику реакций лигандного замещения [Ru(H2dtpa) (H2O)] (где H2dtpa=дипротонированная диэтилтриаминпентауксусная кислота) исследовали в зависимости от концентрации лиганда, pH (2,5–8,0) и температуры (30–45°C) при ионной силе 0,2 M. На основе потенциометрических измерений рассчитаны на ЭВМ константы равновесия образования комплексов смешанных лигандов [RuIII(dtpa) (L)] (где L=2-меркаптопиримидин, цистеин) и распределение различных частиц в растворе при pH=2,5–8,0.

Thermodynamic fitness of an RuIII(EDTA)/RuV = O(EDTA) couple in the oxygen atom transfer reactions

The complex [RuIII(EDTA-H)(H2O)]1 (EDTA-H = protonated ethylenediaminetetraacetic acid) catalyzes the epoxidation of cyclohexene and the oxidation of PPh3 to OPPh3 with molecular oxygen or NaOC1 as the oxidant. In both the cases, the active catalytic species is the [Ruv = O(EDTA)]− ion2 characterized by elemental analyses, UV-vis, infrared spectra and cyclic voltammograms.When oxygen is used as an oxidant in the reaction, oxidation of the substrates proceeds through aμ-peroxo-Ru(IV) intermediate [RusiIV(EDTA)(S)]2O22−3 (S = olefin, PPh3) which undergoes a fast homolytic cleavage of the O-O bond to form [Ruv = O(EDTA)(S)]4 and a rate determining transfer of O atom to S to form SO and1. The cleavage of the O-O bond in 3 and O-atom transfer to S proceed in a concerted step.With NaOCl as an oxidant (excess), oxidation of1 to2 proceeds through a unimolecular decomposition of the [RuIII(EDTA)(OCl)]2− intermediate. The transfer of the O-atom from2 to S proceeds by an associative(Ia) pathway involving a concerted cleavage of the Ru=O bond and formation of an SO bond. The free energy (ΔG) values for various steps are computed and the thermodynamic fitness of2 as an oxidant discussed.