Ruthenium (III) catalysed and uncatalysed oxidation of torsemide by hexacyanoferrate (III) in aqueous alkaline medium: A kinetic comparative approach

The kinetics approach of oxidation of torsemide (TOR) by hexacyanoferrate (III) [HCF (III)] has been identified spectrophotometrically at 420 ​nm in the alkaline medium in the presence and absence of catalyst ruthenium (III) at 25 ​°C, by keeping ionic strength (1 ​× ​10⁻² ​mol ​dm⁻³) constant. The reaction exhibits at the stoichiometry ratio 1:2 of TOR and HCF (III), for uncatalysed and catalysed reactions. In the absence and presence of the catalyst, the order of the reactions obtained for TOR and HCF (III) was unity. However, the rate of the reactions enhanced by the increase in the concentration of catalyst, as well as the rate increases with an increase in alkaline concentration. The activation parameters for the reaction at the slow step were identified, and the effect of temperature on the rate of the reaction was analysed. A suitable mechanism has been demonstrated by considering the obtained results. The derived rate laws are reliable with analysed experimental kinetics.     

Oxidation of Ciprofloxacin by Hexacyanoferrate(III) in the Presence of Cu(II) as a Catalyst: A Kinetic Study

The Cu(II)‐catalyzed oxidation of ciprofloxacin (CIP) by hexacyanoferrate(III) (HCF) has been investigated spectrophotometrically in an aqueous alkaline medium at 40°C. The stoichiometry for the reaction indicates that the oxidation of 1 mol of CIP requires 2 mol of HCF. The reaction exhibited first‐order kinetics with respect to [HCF] and less than unit order with respect to [CIP] and [OH⁻]. The products were also identified on the basis of stoichiometric results and confirmed by the characterization results of LC‐MS and FT‐IR analysis. All the possible reactive species of the reactants have been discussed, and a most probable kinetic model has been envisaged. The activation parameters with respect to the slow step of the mechanism were computed, and thermodynamic quantities were also determined.     

Kinetic, mechanistic and spectral studies for the oxidation of sulfanilic acid by alkaline hexacyanoferrate(III)

The kinetics of oxidation of sulfanilic acid (p-aminobenzenesulfonic acid) by hexacyanoferrate(III) in alkaline medium was studied spectrophotometrically. The reaction showed first order kinetics in hexacyanoferrate(III) and alkali concentrations and an order of less than unity in sulfanilic acid concentration (SAA). The rate of reaction increases with increase in alkali concentration. Increasing ionic strength increases the rate but the dielectric constant of the medium has no significant effect on the rate of the reaction. A retarding effect was observed by one of the products i.e. hexacyanoferrate(II) (HCF(II)). A mechanism involving the formation of a complex between sulfanilic acid and hexacyanoferrate(III) has been proposed. The reaction constants involved in the mechanism are evaluated. There is a good agreement between the observed and calculated rate constants under different experimental conditions. Investigations at different temperatures allowed the determination of the activation parameters with respect to the slow step of the proposed mechanism.     

Kinetic study of ruthenium(III)-catalyzed oxidation of <Emphasis Type="SmallCaps">l</Emphasis>-alanine by diperiodatoargentate(III) in aqueous alkaline medium

The kinetics of Ru(III)-catalyzed oxidation of l-alanine (Ala) by diperiodatoargentate(III) (DPA) in alkaline medium at 25 °C and a constant ionic strength of 0.90 mol dm⁻³ was studied spectrophotometrically. The products are acetaldehyde, Ag(I), ammonia and bicarbonate. The [Ala] to [DPA] stoichiometry is 1:1. The reaction is first order in both [Ru(III)] and [DPA] and has less than unit order in both [Ala] and [alkali]. Addition of periodate has a retarding effect on the reaction. The effects of added products, ionic strength and dielectric constant of the reaction medium have been investigated. The reaction proceeds via a Ru(III)–Ala complex, which further reacts with one molecule of monoperiodatoargentate(III) in the rate-determining step. The reaction constants were calculated at different temperatures and the activation parameters have been evaluated.     

A kinetic and mechanistic study of oxidation of <Emphasis Type="SmallCaps">l</Emphasis>-lysine by the analytical reagent diperiodatoargentate(III) in aqueous alkaline medium

The kinetics of oxidation of l-lysine by diperiodatoargentate(III) (DPA) in aqueous alkaline medium at a constant ionic strength of 0.50 mol dm⁻³ was studied spectrophotometrically. The oxidation products are aldehyde, 5-aminopentanal and Ag(I). The main products were identified by spot test, IR and GC-MS. The stoichiometry is [l-lysine]:[DPA] = 1:1. The reaction is first order with respect to diperiodatoargentate(III) concentrations, whereas the order with respect to l-lysine and alkali concentrations changes from first order to zero order as the l-lysine and alkali concentrations are increased. The effects of added products, periodate, ionic strength, and dielectric constant of the reaction medium were investigated. Based on the experimental results, a mechanism involving complex formation between DPA species and l-lysine is proposed. The reaction constants involved in the mechanism were evaluated. The activation parameters with respect to the slow step of the mechanism were determined and discussed.     

Kinetics and mechanism of uncatalysed and ruthenium(III)-catalysed oxidation of <Emphasis Type="SmallCaps">d</Emphasis>-panthenol by alkaline permanganate

The oxidation of d-panthenol by MnO₄ ⁻ was studied in the absence and in the presence of ruthenium(III) catalyst in alkaline medium at 298 K and at constant ionic strength of 0.50 mol dm⁻³ by spectrophotometry. The stoichiometry in both the cases was [panthenol]: [MnO₄ ⁻] = 1:4. The oxidation products were identified by IR and GC–MS. The reaction was first-order with respect to both MnO₄ ⁻ and ruthenium(III), while the orders with respect to both panthenol and alkali varied from first order to zero order as the concentrations increased. The effects of added products, ionic strength and dielectric constant were studied. The reaction constants, activation parameters and thermodynamic quantities were calculated for both the uncatalysed and catalysed reactions.     

Rhodium(III) catalyzed oxidation of cyclic ketones by alkaline hexacyanoferrate(III)

The kinetics of the oxidation of 2-methyl cyclohexanone and cycloheptanone with Fe(CN)₆ ³⁻ catalyzed by RhCl₃ in alkaline medium was investigated at four temperatures. The rate follows direct proportionality with respect to lower concentrations of hexacyanoferrate(III) ion, but tends to become zero order at higher concentrations of the oxidant, while the reaction shows first-order kinetics with respect to hydroxide ion and cyclic ketone concentrations. The rate shows a peculiar nature with respect to RhCl₃ concentrations in that it increases with increase in catalyst at low catalyst concentrations but after reaching a maximum, further increase in concentration retards the rate. An increase in the ionic strength of the medium increases the rate, while increase in the Fe(CN)₆ ⁴⁻ concentration decreases the rate.     

Investigation of the mechanism of oxidation of <Emphasis Type="SmallCaps">l</Emphasis>-cystine by diperiodatoargentate(III) in aqueous alkaline medium by stopped flow technique

The kinetics of oxidation of l-cystine by diperiodatoargentate(III) (DPA) in alkaline medium at a constant ionic strength of 0.10 mol dm⁻³ was studied spectrophotometrically. The reaction exhibits a 1:2 stoichiometry (l-cys:DPA) and is first order in [DPA]. The order in both [l-cystine] and [alkali] changes from first to zero order as their concentrations increase. Added periodate retards the rate of reaction. The effects of added products have been investigated. The active species of silver(III) is identified as monoperiodatoargentate(III) (MPA). The oxidation is thought to proceed via an MPA–l-cystine complex, which decomposes in a rate-determining step to give a free radical followed by a fast step to give the products. The products were identified by spot test, IR and GC–MS. The reaction constants involved in different steps of the mechanism were evaluated. The activation parameters with respect to the slow step of the mechanism were computed and discussed.     

Kinetic study of the ruthenium(III)-catalyzed oxidation of glycine by <Emphasis Type="Italic">N</Emphasis>-bromophthalimide in acidic medium

The kinetics of ruthenium(III) chloride-catalyzed oxidation of glycine by N–bromophthalimide (NBP) was studied in aqueous perchloric acid at 35 °C. The results showed first- and zero-order behavior with respect to NBP and Gly, respectively. Ru(III) showed a catalytic effect on the reaction which followed first-order kinetics with respect to [Ru(III)] at a low concentration range and tended to zero order at high concentration range. The rates decreased with increase in the proton concentration, while chloride positively influenced the rate of the reaction. Two moles of NBP were required to oxidize one mole of Gly, and the products were identified as phthalimide (NHP), HCN, CO₂, and Br⁻. Neither added NHP nor Br⁻ influenced the reaction rate. Ionic strength and dielectric constant of the medium had no significant effect on the rate. Activation parameters were determined by studying the reaction at different temperatures. A reaction scheme of the catalytic oxidation is proposed.     

Kinetic study of ruthenium(VI) -- catalyzed oxidation of 2-methoxy- ethanol by aqueous alkaline hexacyanoferrate(III)

The kinetics of ruthenium(VI) catalyzed oxidation of 2-methoxyethanol by hexacyanoferrate(III) ion in an aqueous alkaline medium at constant ionic strength shows zero order dependence on hexacyanoferrate(III) and first order dependence on Ru(VI). Dependence of substrate concentration shows a Michaelis – Menten type behaviour. The rate increases with the decrease in alkali concentration. A reaction mechanism involves the formation of an intermediate complex between the substrate and ruthenium(VI). This complex decomposes slowly, producing ruthenium(IV), which is reoxidized by hexacyanoferrate(III) in subsequent steps. The theoretical rate law obtained is in complete agreement with the experimental observations.     

Kinetics and mechanism of palladium (II) chloride catalyzed oxidation of allyl alcohol by potassium hexacyanoferrate (III)

A kinetic study of the oxidation of allyl alcohol by potassium hexacyanoferrate (III) in the presence of palladium (II) chloride is reported. The reaction was observed by measuring the disappearance of the potassium hexacyanoferrate (III) spectrophotometrically. The reaction is first order with respect to allyl alcohol and palladium (II) chloride, inverse second order with respect to [Cl^?], and zero order with respect to potassium hexacyanoferrate (III). The rate is found to increase linearly with hydroxyl ion concentration.     

Kinetics and Mechanism of Oxidation of Captopril by Hexacyanoferrate(III) in Aqueous Acidic Medium

Captopril (Capt, 1-[2(s)-3-mercapto-2-methyl-1-oxopropyl]-l-proline) was oxidized by hexacyanoferrate(III) (HCF). The kinetics of the oxidation was studied spectrophotometrically at 420 nm. The reaction was found to be first order in [HCF] and [Capt] and to have a negative fractional order in [H⁺]. Oxidation was followed by generation of a free radical from captopril, and the oxidative product of catpotpril was identified as captopril disulfide. It was characterized by IR, GCMS and ESI–MS spectra. Initially added product, hexacyanoferrate(II), retarded the rate of reaction with an order of ?0.5. The retarding effect of added [H⁺] indicated that unprotonated hexacyanoferrate(III) is the active species. A suitable free radical mechanism was proposed. The rate law was derived and verified.     

Ruthenium(VI)-catalysed oxidation of diols by alkaline hexacyanoferrate(III) ion. A kinetic study

The kinetics of Ru^VI-catalysed oxidation of ethane-1,2-diol, propane-1,3-diol, butane-1,3-diol, butane-1,4-diol and 2-butoxyethanol by hexacyanoferrate(III) ion in an aqueous alkaline medium at constant ionic strength shows zeroth order dependence on hexacyanoferrate(III) and first order dependence on Ru^VI and substrate. The results suggest that a complex is formed, between Ru^VI and the diol, which slowly decomposes to a reduced form of ruthenium, which is reoxidized to Ru^VI in a fast step by alkaline hexacyanoferrate(III). A plausible reaction mechanism is proposed.     

Ruthenium(III)‐mediated oxidation of D‐mannitol by cerium(IV) in aqueous sulfuric acid medium: A kinetic and mechanistic approach

The oxidation of D ‐mannitol by cerium(IV) has been studied spectrophotometrically in aqueous sulfuric acid medium at 25°C at constant ionic strength of 1.60 mol dm^?3. A microamount of ruthenium(III) (10^?6 mol dm^?3) is sufficient to enhance the slow reaction between D ‐mannitol and cerium(IV). The oxidation products were identified by spot test, IR and GC‐MS spectra. The stoichiometry is 1:4, i.e., [D ‐mannitol]: [Ce(IV)] = 1:4. The reaction is first order in both cerium(IV) and ruthenium(III) concentrations. The order with respect to D ‐mannitol concentration varies from first order to zero order as the D ‐mannitol concentration increases. Increase in the sulfuric acid concentration decreases the reaction rate. The added sulfate and bisulfate decreases the rate of reaction. The active species of oxidant and catalyst are Ce(SO₄)₂ and [Ru(H₂O)₆]³⁺, respectively. A possible mechanism is proposed. The activation parameters are determined with respect to a slow step and reaction constants involved have been determined. © 2010 Wiley Periodicals, Inc. Int J Chem Kinet 42: 440–452, 2010     

Mechanistic investigations of ruthenium(III) catalyzed oxidation of pentoxifylline by copper(III) periodate complex in aqueous alkaline medium

Abstract  

The kinetics of the oxidation of ruthenium(III)-catalyzed oxidation of pentoxifylline (PTX) by diperiodatocuprate(III) (DPC) in aqueous alkaline medium at a constant ionic strength of 0.30 mol dm⁻³ was studied spectrophotometrically. The reaction between PTX and DPC in alkaline medium in the presence of Ru(III) exhibits 1:2 stoichiometry (PTX:DPC). The reaction was of first order in DPC, less than the unit order in [PTX] and [OH⁻] and negative fractional order in [IO₄ ⁻]. The order in [Ru(III)] was unity. Intervention of free radicals was observed in the reaction. The main products were identified by TLC and spectral studies including LC-MS. The oxidation reaction in alkaline medium has been shown to proceed via a Ru(III)-PTX complex, which reacts with monoperiodatocuprate(III) to decompose in a rate determining step followed by a fast step to give the products. The reaction constants involved in different steps of the mechanism were calculated. The activation parameters with respect to the slow step of the mechanism were computed and discussed, and thermodynamic quantities were also determined. The active species of catalyst and oxidant have been identified.     

Kinetics and mechanism of oxidation of phenylhydrazine and P-bromophenylhydrazine by hexacyanoferrate(III) in acidic medium

Kietics of oxidation of phenylhydrazine and p-bromophenylhydrazine by hexacyanoferrate(III) in acidic medium have been studied. The reactions follow similar kinetics, being first order with respect to both hydrazine and exacyanoferrate(III) and inverse first order with respect to the hydrogen ion. Addition of hexacyanoferrate(II) has no retarding effect on the rate of oxidation. The effects of varying ionic strength, dielectric constant, and temperature on the reaction rates have been investigated. A plausible mechanism has been proposed to account for the experimental results. Benzene and bromobenzene have been identified as the oxidation products.     

Oxidation of Acyclovir by a Cuprate(III) Periodate Complex in Aqueous Alkaline Media: A Kinetic and Mechanistic Approach

The oxidation of acyclovir by diperiodatocuprate(III) in aqueous alkaline media, at a constant ionic strength of 0.01 mol?dm^?3, was studied spectrophotometrically at 25?°C. The reaction between acyclovir and DPC in alkaline media exhibits 1:4 stoichiometry (acyclovir:diperiodatocuprate(III)). The main oxidation products were identified by a spot test, along with infrared and liquid chromatography mass spectral studies. The oxidation reaction is first order with regard to the diperiodatocuprate(III) concentration, but has less than unit order in the acyclovir concentration and negative fractional orders in the periodate and alkali concentrations. Intervention of free radicals was observed in the reaction. The oxidation reaction in alkaline media was shown to proceed via a diperiodatocuprate(III)?Cacyclovir complex, which decomposes slowly in a rate determining step followed by subsequent fast steps to give the products. A suitable mechanism is proposed for these observations. The reaction constants involved in the different steps of the mechanism were calculated. The activation parameters with respect to the slow step of the mechanism, along with the thermodynamic quantities, were determined and discussed.     

A kinetic and mechanistic study of the oxidation of tyrosine by chromium(VI) in aqueous perchloric acid medium

The oxidation of tyrosine by chromium(VI) in aqueous perchloric acid medium has been studied spectrophotometrically at 30 °C and at a constant ionic strength I = 3.10 mol dm⁻³. The main reaction products were identified as chromium(III) and 4-hydroxyphenylacetaldehyde. The stoichiometry is 2:3, i.e., two moles of chromium(VI) react with three moles of tyrosine. The reaction is first order with respect to both chromium(VI) and tyrosine. Increase in perchloric acid concentration increased the rate of reaction. The order with respect to acid concentration was found to be two. Added products, ionic strength and dielectric constant of the medium did not have any significant effect on the reaction rate. A suitable mechanism is proposed. The activation parameters were determined with respect to the slow step of the mechanism. The thermodynamic quantities were also determined and discussed.     

Determination of hexacyanoferrate based on its catalytic influence on the oxidation of p-phenylenediamines by iron(III)

Summary Both hexacyanoferrate(III) and hexacyanoferrate(II) catalyze the oxidation of p-phenylenediamines by iron(III)_aq. The rate of this reaction in the presence of a sample with an unknown amount of hexacyanoferrate is compared with the reaction rate of solutions containing well defined concentrations of this substance. In this way, hexacyanoferrate can be determined photometrically down to <10^–9 mol/l. Although this procedure is very sensitive, the analysis can be performed with a simple photometer. Absorbance changes >0.2 can easily be obtained in 1 cm cuvettes, even at extremely small concentrations of hexacyanoferrate, because it is not an absorbance proportional to the concentration of hexacyanoferrate but rather the formation rate of p-semiquinonediimine which enables the quantitative determination of hexacyanoferrate.     

Mechanistic aspects of the reduction of ruthenium(III) catalyzed

The kinetics of Ru_III catalyzed reduction of hexacyanoferrate(III) [Fe(CN)₆]^3–, by atenolol in alkaline medium at constant ionic strength (0.80 mol dm^–3) has been studied spectrophotometrically, using a rapid kinetic accessory. The reaction between atenolol and [Fe(CN)₆]^3– in alkaline medium exhibits 1:2 stoichiometry [atenolol:Fe(CN)₆ ^3–]. The reaction showed first order kinetics in [Fe(CN)₆]^3– concentration and apparent less than unit order dependence, each in atenolol and alkali concentrations. Effect of added products, ionic strength and dielectric constant of the reaction medium have been investigated. A retarding effect was observed by one of the products i.e., hexacyanoferrate(II). The main products were identified by i.r., n.m.r., fluorimetric and mass spectral studies. A mechanism involving the formation of a complex between the atenolol and the hydroxylated species of ruthenium(III) has been proposed. The active species of oxidant and catalyst were [Fe(CN)₆]^3–and [Ru (H₂O)₅OH]²⁺, respectively. The reaction constants involved in the mechanism were evaluated. The activation parameters were computed with respect to the slow step of the mechanism, and discussed.