Kinetics and mechanism of Ru(III) catalysed oxidation of some polyhydric alcohols by N-bromosuccinimide in acidic media

Kinetics of oxidation of ethylene glycol, glycerol, erythritol and dulcitol by acidic solution of N-bromosuccinimide (NBS) in presence of ruthenium(III) chloride as a homogeneous catalyst and mercuric acetate as scavenger in the temperature range of 30–50°C have been reported. The reactions follow identical kinetics, being first order in each NBS, substate and Ru(III). Zero effect of [H⁺], [mercuric acetate] and ionic strength has been observed. A negative effect of succinimide and acetic acid is observed while [Cl^-] shows the positive effect on reaction velocity. Various activation parameters have been computed. The products of the reaction were identified as the coresponding acids. A suitable mechanism consistent with the experimental results has been proposed.     

Efficient oxidation of secondary alcohols to Ketones by NaOCl catalyzed by Salen-Mn(III)/NBS

An efficient catalytic system salen-Mn(III)/NBS for oxidation of secondary alcohols to ketones by inexpensive and readily available oxidizing agent NaOCl has been developed. The process resulted in good to excellent yields under the action of 2 mol % of salen-Mn(III) and 13 mol % of NBS at room temperature. However, such system was not efficient in oxidation of secondary benzyl alcohols with a strong electronicdonating substituent attached to the benzene ring due to bromination of the alcohols.     

Ru(VI)‐catalyzed oxidation of alcohols by hexacyano‐ferrate(III): Computational analysis of mixed kinetic order

The title reaction shows a mixed kinetic order with respect to hexacyanoferrate(III). The reaction tends to be single zero order at high [Fe(CN)] and single first order at low [Fe(CN)]. For this reason, the decay of the absorbance of hexacyanoferrate(III) at 420 nm changes from linear to exponential as the reaction proceeds. This change of order has also been observed in the initial moments of the reaction. The dependence of the reaction rate on [Fe(CN)] has been obtained, by computational methods, at t = 0 and at any subsequent time during the course of the reaction. The coincidence of both equations would indicate that none of the substances produced in the reaction acts as an activator or inhibitor. The mixed order is due to the comparable rates of complex decomposition and catalyst regeneration steps. © 2006 Wiley Periodicals, Inc. Int J Chem Kinet 38: 153–158, 2006     

Ru(III)-catalyzed oxidation of pyruvic acid by iodate -A kinetic study

Ru(III) acts as a catalyst in the oxidative decarboxylation of pyruvic acid by iodate. The reaction is found to be first order with respect to [oxidant] and [catalyst] and fractional order in [pyruvic acid]. Increase in the concentration of H₂SO₄ and decrease in the dielectric constant of the medium retard the oxidation process. The product of oxidation is acetic acid. A mechanism involving the formation of a complex between the substrate and the catalyst, which reacts with the oxidant in the slow step is proposed. The formation constant of the complex and the rate constant of the slow step are determined. This revised version was published online in June 2006 with corrections to the Cover Date.     

Ru(III) catalysis in the oxidation of arenes by periodate. A kinetic study

The title reactions are zero order in periodate and first order in Ru(III). All substrates show a first order dependence except for p-xylene and fluorene which follow a Michaelis-Menten behavior. The Hammett plot gives a values of-2.0. A mechanism involving metal arene -interaction is discussed.

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Ru(III). , - , -. =–2,0. . , -- .

     

Enantioselective oxidation of racemic secondary alcohols catalyzed by chiral Mn(III)-salen complexes with N-bromosuccinimide as a powerful oxidant

We demonstrate an efficient enantioselective oxidation of secondary alcohols catalyzed by Mn(III)-salen complex using N-bromosuccinimide (NBS) as the oxidant. The new protocol is very efficient for the oxidative kinetic resolution of a variety of secondary alcohols, including ortho-substituted benzylic alcohols.     

Efficient solvent-free iron (III) catalyzed oxidation of alcohols by hydrogen peroxide

Selective oxidation of secondary and benzylic alcohols was efficiently accomplished by H₂O₂ under solvent-free condition catalyzed by FeBr₃. Secondary alcohols are selectively oxidized even in the presence of primary ones. This method is high yielding, safe and operationally simple.     

Mechanism of oxidation of some aliphatic ketones by N-bromosuccinimide in acidic media

Kinetics of the oxidation of methyl n-propyl ketone and methyl isobutyl ketone by N-bromosuccinimide (NBS) have been studied in perchloric acid media in presence of mercuric acetate. A zero order dependence to N-bromosuccinimide and a first order dependence to both ketones and hydrogen ion concentrations have been observed. Sodium perchlorate, mercuric acetate and succinimide additions have negligible effect while methanol addition has a positive effect on the reaction rate. A solvent isotope effect (k₀D₂O/K₀H₂O = 2.3-2.7 and 2.4-2.8 for MeCOn.pr and MeCoi-Bu, respectively) has been observed at 35°. Kinetic investigations have revealed that the order of reactivity is methyl n-propyl ketone > methyl isobutyl ketone. Various thermodynamic parameters have been computed and corresponding 1,2-diketones were found to be the products. A suitable mechanism in conformity with the above observations has been proposed.     

Oxidation of secondary alcohols byN-methylmorpholine-N-oxide (NMO) catalyzed by Ru(II) halosulfoxide complexes. A kinetic study

RuX₂(DMSO)₄ (X=Cl,cis; Br,trans) undergoes ligand substitution in N,N-dimethylformamide (DMF) to give RuX₂(DMSO)₃DMF, which catalyzes the oxidation of secondary alcohols by NMO to ketones. Kinetics of the reaction catalyzed bytrans-RuBr₂(DMSO)₄ differed from that ofcis-RuCl₂(DMSO)₄. A mechanism is proposed involving the formation of Ru(IV)oxo species as the active intermediate and a rate expression is derived.     

Cocatalysis by ruthenium(III) in hydrogen ions catalyzed oxidation of iodide ions: A kinetic study

RuCl₃ further catalyzes the oxidation of iodide ion by K₃Fe(CN)₆, already catalyzed by hydrogen ions. The rate of reaction, when catalyzed only by hydrogen ions, was separated graphically from the rate when both Ru(III) and H⁺ ions catalyzed the reaction. Reactions studied separately in the presence as well as absence of RuCl₃ under similar conditions were found to follow second‐order kinetics with respect to [I^?], while the rate showed direct proportionality with respect to [Fe(CN)₆]^3?, [RuCl₃], and [H⁺]. External addition of [Fe(CN)₆]^4? ions retards the reaction velocity, while changing the ionic strength of the medium has no effect on the rate. With the help of the intercept of the catalyst graph, the extent of the reaction that takes place without adding Ru(III) was calculated and it was in accordance with the values obtained from the reaction in which only H⁺ ions catalyzed the reaction. It is proposed that ruthenium forms a complex, which slowly disproportionates into the rate‐determining step. Arrhenius parameters at four different temperatures were also calculated. © 2004 Wiley Periodicals, Inc. Int J Chem Kinet 36: 545–553, 2004     

Kinetics of the Ru(III) catalyzed oxidation of formaldehyde and acetaldehyde by alkaline hexacyanoferrate(III)

The kinetics of ruthenium(III) catalyzed oxidation of formaldehyde and acetaldehyde by alkaline hexacyanoferrate(III) has been studied spectrophotometrically. The rate of oxidation of formaldehyde is directly proportional to [Fe(CN) _3– ⁶ ] while that of acetaldehyde is proportional tok[Fe(CN) _3– ⁶ ]/{k +k[Fe(CN) _3– ⁶ ]}, wherek, k andk are rate constants. The order of reaction in acetylaldehyde is unity while that in formaldehyde falls from 1 to 0. The rate of reaction is proportional to [Ru(III)] _T in each case. A suitable mechanism is proposed and discussed.

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Die Kinetik der Ru(III)-katalysierten Oxidation von Formaldehyd und Acetaldehyd mittels alkalischem Hexacyanoferrat(III)

Zusammenfassung Die Untersuchung der Kinetik erfolgte spektrophotometrisch. Die Geschwindigkeitskonstante der Oxidation von Formaldehyd ist direkt proportional zu [Fe(CN) _3– ⁶ ], währenddessen die entsprechende Konstante für Acetaldehyd proportional zuk[Fe(CN) _3– ⁶ ]/{k +k[Fe(CN) _3– ⁶ ]} ist, wobeik,k undk Geschwindigkeitskonstanten sind. Die Reaktionsordnung für Acetaldehyd ist eine erste, die für Formaldehyd fällt von erster bis zu nullter Ordnung. Die Geschwindigkeitskonstante ist in jedem Fall proportional zu [Ru(III)] _T . Es wird ein passender Mechanismus vorgeschlagen.

     

Kinetics and mechanism of Ru(III)-catalyzed oxidation of aliphatic alcohols by trichloroisocyanuric acid in HClO4 medium

The kinetics and mechanism of Ru(III)-catalyzed oxidation of some aliphatic alcohols by trichloroisocyanuric acid (TCICA) has been studied in aqueous HOAc-HClO₄ medium. The reaction is zero order in [TCICA], fractional order in [alcohol] and first order in [Ru(III)]. The reaction is insensitive towards changes in acid concentration. The rate is not affected by an increase in [Cl⁻]. The polar reaction constant (ρ*) was found to be −1.27 at 308 K. A mechanism involving complex formation between the substrate and catalyst in the fast equilibrium step followed by its decomposition in a slow step is proposed.     

Kinetic study of Ru(VI)-catalyzed oxidation of cyclic alcohols by hexacyanoferrate(III) in aqueous alkaline medium

The kinetics of the oxidation of cyclopentanol, cyclohexanol, 2? methylcyclohexanol, and cycloheptanol by hexacyanoferrate(III) ions in mild alkaline medium has been studied in the presence of traces of ruthenium(VI) ≈ 10^?7M at constant ionic strength (0.26M). The results suggest that the oxidation of the studied cyclic alcohols proceeds via the formation of a complex between Ru(VI) and the substrate which slowly decomposes, giving the reduced form of ruthenium which was reoxidized to Ru(VI) in a fast step by alkaline hexacyanoferrate(III) ions. The product study shows the production of the corresponding ketone.     

Effective oxidation of benzylic and aliphatic alcohols with hydrogen peroxide catalyzed by a manganese(III) Schiff-base complex under solvent-free conditions

A variety of alcohols were oxidized efficiently into the corresponding ketones and carboxylic acids in excellent yields with hydrogen peroxide using a manganese(III) Schiff-base complex as a catalyst under solvent-free and mild conditions. The oxidation procedure is very simple and the products are easily isolated in excellent yields.     

TI(III) oxidation of alkenes and alkynes and Ru(III) catalysis in the oxidation of alkenes: A kinetic and mechanistic study

The oxidation of trans-stilbene, phenylacetylene, and diphenylacetylene by Tl(OAc)₃ in aqueous acetic acid medium in the presence of HClO₄ follows the rate law in [H⁺] of 0.1–1.0M, the [H⁺] dependence below 0.1M being marginal. The reactions are strongly dielectric dependent. The order of reactivity among the substrates is styrene > phenylacetylene and trans-stilbene > diphenylacetylene. A mechanism involving the oxythallation adduct by the Tl⁺(OAc)₂ species has been discussed. The use of Ru(III) as a homogeneous catalyst brings a change in the kinetic orders for trans-stilbene, the rate law being The formation constants K for the Ru(III)–alkene π complex at 40, 50, and 60°C are 90.14M^?1, 105.2M^?1, and 127.7M^?1, respectively. Interestingly the oxidation of phenylacetylene and diphenylacetylene does not undergo catalysis by Ru(III). The mechanism involving the metal–arene π complex is discussed.     

Ru(III)‐catalyzed oxidation of cysteine hydrochloride by methylene blue in acidic medium; synergetic effect of Cu(II): A kinetic study

Cysteine hydrochloride and methylene blue (MB) interact in a molar ratio of 2:1 in acidic medium forming cystine and dihydromethylene blue, and the reaction is catalyzed by Ru(III). At low concentrations (ca. 2.0 × 10^?8 M), Cu(II) does not catalyze the reaction significantly but at this concentration level the catalytic activity of Ru(III) is found to be augmented by the addition of Cu(II) and the kinetics of Ru(III)‐catalyzed reaction has been studied in the absence and in the presence of externally added Cu(II). The reaction follows a half‐order kinetics in MB that increases to ¾ on increasing [MB] beyond 1.5 × 10^?5 M in the Ru‐catalyzed reaction. In the Ru–Cu catalyzed reaction; the order in MB is ¾ even at lower concentrations of MB. The order in cysteine is unity. The rate decreases on increasing [MB] in both cases but attains a limiting value at higher concentrations of MB (ca. >2.0 × 10^?5 M) in the presence of Ru(III) alone. The rate increases on increasing [H⁺] and in Ru‐catalyzed reaction, an optimum is noticed. The rate increases linearly with increasing [Ru(III)], but equilibration of the catalyst with other ingredients of the reaction system decreases the rate. The FTIR spectra of the reaction system exhibit time‐dependent changes in the stretching as well as bending modes of –SH group. The synergetic effect of Cu(II) has been attributed to its ligation with cysteine and its subsequent interaction with Ru(II) produced in situ in the system. © 2008 Wiley Periodicals, Inc. Int J Chem Kinet 40: 145–150, 2008     

Ruthenium (III)-Schiff base complex catalyzed oxidation of secondary alcohols by N-methylmorpholine-N-oxide or thallium (III) acetate

The Ru(III) Schiff base complex [Ru(L)Cl₂]Cl; L = bis(picolinaldehyde) o-phenylenediimine, catalyzes the oxidation of secondary alcohols by N-methylmorpholine-N-oxide(NMO) or thallium(III) acetate as oxidant. Kinetic studies showed the formation of Ru(V) species as the active intermediate. © 1996 John Wiley & Sons, Inc.     

Kinetics and mechanism of oxidation of some aliphatic amines by ditelluratocuprate(III)

The kinetics of oxidation of some primary, secondary and tertiary aliphatic amines by ditelluratocuprate(III) was studied in alkaline medium. The order in both substrate and oxidant was found to be unity each. The reaction rate decreased with increase in ionic strength. The order of reactivity of amines was found to be secondary > primary > tertiary. A mechanism was proposed involving an adduct formation between amine and monotelluratocuprate(III), which dissociates further in a slow step followed by fast steps to give required products. TheTaft linear free energy relationship was shown to be applicable which also supports the proposed mechanism.

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Kinetik und Mechanismus der Oxidation einiger aliphatischer Amine mit Kupfer(III)-ditellurat

Zusammenfassung Die Kinetik der Oxidation einiger primärer, sekundärer und tertiärer aliphatischer Amine mit Kupfer(III)-ditellurat wurde in alkalischem Medium untersucht. Die Reaktion war jeweils erster Ordnung bezüglich Substrat und Oxidationsmittel. Die Reaktionsgeschwindigkeit nahm mit zunehmender Ionenstärke ab. Die Reaktivität stieg in der Reihenfolge sekundäre > primäre > tertiäre Amine an. Ein Mechanismus, der die Bildung eines Adduktes zwischen Amin und Kupfer(III)-monotellurat beinhaltet, wird vorgeschlagen. Dieses Addukt dissoziiert in einem langsamen Schritt, gefolgt von schnellen Schritten, in denen die gefundenen Produkte gebildet werden. Die Anwendbarkeit derTaft-Beziehung wurde getestet und unterstützt den vorgeschlagenen Mechanismus.

     

Kinetic studies of the oxidation of chromium(III) by N-bromosuccinimide

Summary A 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[Cr^VI]/dt = {k ₄ K _h K ₂[NBS][Cr^III]_T}/[₊]{1 + K _h/[H⁺] + (K ₁ + K _h K ₂/[H⁺][NBS])} where K _h, K ₁ and K ₂ are the hydrolysis constant of [Cr^III(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. Abstracted from the Ph.D. Thesis (Ain Shams University) of A. E.-D. M. Abdel-Hady.     

Ru(III)-EDTA catalyzed oxidation of ascorbic acid by hydrogen peroxide in aqueous solution

The kinetics of oxidation of ascorbic acid to dehydroascorbic acid by hydrogen peroxide catalyzed by ethylenediaminetetraacetatoruthenate(III) has been studied over the pH range 1.50 – 2.50, at 30°C and μ = 0.1 M KNO₃. The reaction has a first-order dependence on ascorbic acid and Ru(III)-EDTA concentrations, an inverse first-order dependence on hydrogen ion concentration, and is independent of hydrogen peroxide concentration in the pH range studied. A mechanism has been proposed in which ascorbate anion forms a kinetic intermediate with the catalyst in a pre-equilibrium step. Ruthenium(III) is reduced to ruthenium(II) in a rate-determining step and is reoxidized with hydrogen peroxide back to the Ru(III) complex in a fast step.