Kinetic and Mechanistic Study of the Oxidative Deamination and Decarboxylation of L-Valine by Alkaline Permanganate

Summary.  The kinetics of the oxidation of L-valine, (L-Val) by permanganate in aqueous alkaline medium at a constant ionic strength of 0.50 molċdm⁻³ was studied spectrophotometrically. The reaction is of first order in [permanganate ion] and of fractional order in both [L-Val] and [alkali]. Addition of products has no significant effect on the reaction rate. However, increasing ionic strength and decreasing dielectric constant of the medium increase the rate. The oxidation process in alkaline medium has been shown to proceed via two paths, one involving the interaction of L-valine with permanganate ion in a slow step to yield the products, and the other path the interaction of alkali with permanganate ion to give manganate. Some reaction constants involved in the mechanism were determined; calculated and observed rate constants agree excellently. The activation parameters were computed with respect to the slow step of the mechanism. Received December 30, 1999. Accepted (revised) March 6, 2000     

Mechanistic and spectroscopic investigations of oxidative degradation of aspirin by aqueous alkaline permanganate

The kinetics of oxidation of aspirin (ASP) by permanganate in alkaline medium at a constant ionic strength of 0.06 mol dm⁻³ was studied spectrophotometrically using a rapid kinetic accessory. The reaction between permanganate and aspirin in alkaline medium exhibited 1:4 stoichiometry (aspirin: permanganate). The reaction was of first order in [permanganate ion] and had less than unit order in both [ASP] and [alkali]. A decrease in the dielectric constant of the medium decreased the rate of reaction. The effect of added products and ionic strength of the reaction medium have been investigated. The oxidation reaction in alkaline medium has been shown to proceed via a permanganate–aspirin complex, which decomposes slowly in a rate determining step followed by other fast steps to give the products. The main products were identified by spot test and spectroscopic studies. A suitable mechanism is proposed. The reaction constants involved in the different steps of the mechanism were derived. The activation parameters with respect to the slow step of the mechanism were computed and discussed and thermodynamic quantities were also determined.     

Kinetics of the Oxidative Degradation of rac-Serine by Aqueous Alkaline Permanganate

Summary.  The kinetics of the oxidation of rac-serine by permanganate in aqueous alkaline medium was studied spectrophotometrically. The reaction showed first order kinetics in permanganate ion concentration and an order less than unity in rac-serine and alkali concentration. Increasing ionic strength and decreasing dielectric constant of the medium increase the rate. The oxidation reaction proceeds via an alkali-permanganate species which forms a complex with rac-serine. The latter decomposes slowly, followed by a fast reaction between a free radical of rac-serine and another molecule of permanganate to give the products. There is a good agreement between the observed and the 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. Received October 15, 1999. Accepted (revised) December 15, 1999     

Oxidative Deamination and Decarboxylation of L-Asparagine by the Aqueous Alkaline Diperiodatonickelate(IV) Complex

The kinetics of the oxidation of L-asparagine, (L-asp) by diperiodatonickelate(IV), (DPN) in aqueous alkaline medium at a constant ionic strength of 0.5 mol⋅dm⁻³, was studied spectrophotometrically. The reaction is first order in [DPN] and of fractional order in both [L-asp] and [alkali]. Addition of the products has no significant effect on the reaction rate. However, increasing the ionic strength or decreasing the dielectric constant of the medium increases the reaction rate. The oxidation process in alkaline medium is shown to proceed via two paths, one involving the interaction of L-asparagine with diperiodatonickelate(IV) ion in a slow step to yield the products, and the other path involving the interaction of alkali with the diperiodatonickelate(IV) ion to give nickel(II). Some reaction constants involved in the mechanism were determined, and calculated and observed rate constants are in excellent agreement. The activation parameters were computed for the slow step of the mechanism.     

Deamination and decarboxylation in the chromium(III)-catalysed oxidation of L-valine by alkaline permanganate and analysis of chromium(III) in microscopic amounts by a kinetic method

The kinetics of Cr^III-catalysed oxidation of L-valine by permanganate in alkaline medium at a constant ionic strength has been studied spectrophotometrically. The reaction between permanganate and L-valine in alkaline medium exhibits 2:1 stoichiometry (KMnO₄:l-valine). The reaction shows first order dependence on [permanganate] and [chromium(III)], and less than unit order dependence each in [L-valine] and alkali concentrations under the experimental conditions. However the order in [L-valine] and [alkali] changes from first order to zero order as the concentrations change from lower to higher respectively. The results suggest the formation of a complex between L-valine and the hydroxylated species of Cr^III. The complex reacts further with 1 mol of alkaline permanganate species in a rate-determining step, resulting in the formation of a free radical, which again reacts with 1 mol of alkaline permanganate species in a subsequent fast step to yield the products. The reaction constants involved in the mechanism were evaluated. The activation parameters with respect to the slow step of the mechanism were obtained and discussed. The title reaction has been utilised to analyse chromium(III) in the 26.0 ng cm^–3–1.0 g cm^–3 range.     

Palladium(II) Catalysed Oxidation of l-proline by Heptavalent Manganese in Aqueous Alkaline Medium: A Free Radical Intervention and Decarboxylation

The kinetics of palladium(II) catalysed oxidation of l-proline by permanganate in alkaline medium was studied spectrophotometrically. The reaction between permanganate and l-proline in alkaline medium exhibits 2:1 stoichiometry (KMnO₄: l-proline). The reaction is first order with respect to [MnO₄⁻] and [Pd(II)], an apparent less than unit order in [alkali] and zero order in [l-proline] under the experimental conditions. Reaction rate increases with increase in ionic strength and decrease in solvent polarity of the medium. Addition of reaction products did not affect the rate significantly. A mechanism involving the intervention of a free radical generated by l-proline has been proposed. The reaction constants involved in the mechanism were evaluated. The activation parameters with respect to the slow step of the Scheme were evaluated and are discussed.     

Kinetics and mechanism of <Emphasis Type="Italic">L</Emphasis>-isoleucine oxidation by alkaline diperiodatoargentate(III)

The oxidation of L-isoleucine by alkaline diperiodatoargentate(III) (DPA) at 298 K and a constant ionic strength of 0.80 mol dm⁻³ was studied spectrophotometrically. The stoichiometry is [L-isoleucine]: [DPA] = 1:2. The reaction is first order in [DPA] and has less than unit order in both [L-isoleucine] and [alkali] and retarding effect in The oxidation reaction in alkaline medium has been shown to proceed via a L-isoleucine–DPA complex, which further reacts with one molecule of DPA in a rate determining step followed by other fast steps to give the products. Spot test and IR were used to identify the main products. The reaction constants involved in the different steps of the mechanism are calculated. The activation parameters with respect to the slow step of the mechanism are computed and discussed, and thermodynamic quantities are also determined. The probable active species of oxidant have been identified. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Kinetic, mechanistic and spectral investigation of ruthenium (III)-catalysed oxidation of atenolol by alkaline permanganate (stopped-flow technique)

Kinetics of ruthenium (III) catalyzed oxidation of atenolol by permanganate in alkaline medium at constant ionic strength of 0.30 mol dm³ has been studied spectrophotometrically using a rapid kinetic accessory. Reaction between permanganate and atenolol in alkaline medium exhibits 1 : 8 stoichiometry (atenolol : KMnO₄). The reaction shows first-order dependence on [permanganate] and [ruthenium (III)] and apparently less than unit order on both atenolol and alkali concentrations. Reaction rate decreases with increase in ionic strength and increases with decreasing dielectric constant of the medium. Initial addition of reaction products does not affect the rate significantly. A mechanism involving the formation of a complex between catalyst and substrate has been proposed. The active species of ruthenium (III) is understood as [Ru(H₂O)₅OH]₂₊. The reaction constants involved in the different steps of mechanism are calculated. Activation parameters with respect to the slow step of the mechanism are computed and discussed and thermodynamic quantities are also calculated.     

Kinetics and mechanism of chromium(III) catalyzed oxidation of 1,10-phenanthroline by alkaline permanganate

The kinetics of chromium(III) catalyzed oxidation of 1,10-phenanthroline by permanganate in alkaline medium at a constant ionic strength has been studied spectrophotometrically. The reaction between permanganate and 1,10-phenanthroline in alkaline medium exhibits 4:1 stoichiometry (KMnO₄:1,10-phenanthroline). The reaction shows first order dependence on [permanganate] and [chromium(III)] and less than unit order dependence in 1,10-phenanthroline, zero order in alkali concentrations. The results suggest the formation of a complex between the 1,10-phenanthroline and the chromium(III) which reacts further with one mole of permanganate species in the rate-determining step, resulting in the formation of a free radical, which again reacts with three moles of permangante species in a subsequent fast step to yield the products. The reaction constants involved in the mechanism were evaluated. The activation parameters were computed with respect to the slow step of the mechanism.This revised version was published online in December 2005 with corrections to the Cover Date.     

Free radical intervention,deamination and decarboxylation in the ruthenium(III)-catalysed oxidation of L-arginine by alkaline permanganate – a kinetic study

The kinetics of the Ru^III catalysed oxidation of L-arginine by alkaline permanganate was studied spectrophotometrically using a rapid kinetic accessory. The reaction follows a two stage process. In both the stages the reaction is first order with respect to [oxidant] and [catalyst] with an apparent less than unit order in [substrate] and [alkali]. The data suggest that oxidation proceeds via formation of a complex between the active Ru^III species and L-arginine, which then reacts with one mole of permanganate in a slow step to yield a L-arginine free radical, followed by a fast step to form the products. The reaction constants involved in the mechanism were evaluated. There is a good agreement between observed and calculated rate constants under different experimental conditions for both stages of reaction. The activation parameters for the slow step were calculated and are discussed.     

Thermodynamic Quantities for the Different Steps Involved in the Oxidation of the Drug Ketorolac by Copper(III) Periodate Complex in Aqueous Alkaline Medium: A Mechanistic Approach

The oxidation of ketorolac (KET) by diperiodatocuprate(III) (DPC) in aqueous alkaline medium at a constant ionic strength of 0.10 mol⋅dm⁻³ was studied spectrophotometrically at 298 K. The reaction is of first order in [DPC] and has less than unit order in both [KET] and [alkali], and negative fractional order in [periodate]. The oxidation reaction in alkaline medium has been shown to proceed via a DPC-ketorolac complex, which decomposes slowly in a rate determining step followed by other fast steps to give the products. The main products were identified by spot test, IR and GC-MS spectral studies. The reaction constants involved in the different steps of the mechanism were calculated at different temperatures, which yielded thermodynamic quantities for different steps of the reaction scheme. The activation parameters with respect to the slow step of the mechanism were computed and discussed; thermodynamic quantities were also determined.     

Kinetic and mechanistic investigation of the oxidation of the antibacterial agent levofloxacin by permanganate in alkaline medium

The kinetics and mechanism of oxidation of levofloxacin (LF) by manganese(VII) in alkaline medium at constant ionic strength was studied spectrophotometrically. The reaction exhibits 2:1 Mn:LF stoichiometry and is first order in permanganate but fractional order in both LF and alkali. Decrease in the dielectric constant of the medium results in a decrease in the rate of reaction. The effects of added products and ionic strength have also been investigated. The main products identified were hydroxylated LF and Mn(VI). A mechanism involving free radicals is proposed. In a composite equilibrium step, levofloxacin binds to MnO₄ ⁻ to form a complex that subsequently decomposes to the products. Investigations of the reaction at different temperatures allowed the determination of the activation parameters with respect to the slow step of the proposed mechanism.     

Spectral and Mechanistic Investigation of the Osmium(VIII) Catalyzed Oxidation of Diclofenac Sodium by the Copper(III) Periodate Complex in Aqueous Alkaline Medium

The kinetics of the osmium(VIII) (Os(VIII)) catalyzed oxidation of diclofenac sodium (DFS) by diperiodatocuprate(III) (DPC) in aqueous alkaline medium has been studied spectrophotometrically at a constant ionic strength of 1.0 mol⋅dm⁻³. The reaction showed first order kinetics in [Os(VIII)] and [DPC] and less than unit order with respect to [DFS] and [alkali]. The rate decreased with increase in [periodate]. The reaction between DFS and DPC in alkaline medium exhibits 1:2 [DFS]:[DPC] stoichiometry. However, the order in [DFS] and [OH⁻] changes from first order to zero order as their concentration increases. Changes in the ionic strength and dielectric constant did not affect the rate of reaction. The oxidation products were identified by LC-ESI-MS, NMR, and IR spectroscopic studies. A possible mechanism is proposed. The reaction constants involved in the different steps of the mechanism were calculated. The catalytic constant (K _C) was also calculated for Os(VIII) catalysis at the studied temperatures. From plots of log ₁₀ K _C versus 1/T, values of activation parameters have been evaluated with respect to the catalytic reaction. The activation parameters with respect to the slow step of the mechanism were computed and discussed, and thermodynamic quantities were also determined. The active osmium(VIII) and copper(III) periodate species have been identified.     

Kinetics and Mechanism of Oxidation of L-Leucine by Alkaline Diperiodatonickelate(IV) – A Free Radical Intervention, Deamination, and Decarboxylation

The kinetics of oxidation of L-leucine by alkaline diperiodatonickelate(IV) was studied spectrophotometrically using a rapid kinetic accessory. The reaction is first order with respect to [DPN] and apparently less than unit order, each in [L-leucine] and [alkali] under the experimental conditions. However, the order in [L-leucine] and [alkali] changes from first order to zero order as the concentrations change from lower to higher values. Addition of periodate has no effect on the reaction rate. A mechanism involving the deprotonated diperiodatonickelate(IV) (DPN) as the reactive oxidant is proposed. The reaction constants involved in the mechanism were evaluated. There is a good agreement between the observed and calculated rate constants under varying experimental conditions. The isokinetic temperature was determined and the activation parameters with respect to the slow step of the reaction scheme were evaluated and discussed.     

Oxidative degradation and deamination of atenolol by diperiodatocuprate(III) in aqueous alkaline medium: A mechanistic study

The kinetics of oxidation of atenolol (ATN) by diperiodatocuprate(III) (DPC) in aqueous alkaline medium at a constant ionic strength of 0.10 mol dm⁻³ was studied spectrophotometrically. The reaction between DPC and ATN in alkaline medium exhibits 1:2 stoichiometry (ATN:DPC). The reaction is of first order in [DPC] and has less than unit order in both [ATN] and [alkali]. However, the order in [ATN] and [alkali] changes from first order to zero order as their concentration increase. Intervention of free radicals was observed in the reaction. Increase in periodate concentration decreases the rate. The oxidation reaction in alkaline medium has been shown to proceed via a monoperiodatocuprate(III)–ATN complex, which decomposes slowly in a rate-determining step followed by other fast steps to give the products. The main oxidative products were identified by spot test, IR, NMR and LC–ESI-MS studies. The reaction constants involved in the different steps of the mechanism are calculated. The activation parameters with respect to slow step of the mechanism are computed and discussed, and thermodynamic quantities are also determined.     

A comparative study of ruthenium(III) catalysed oxidation of L-leucine and L-isoleucine by alkaline permanganate. A kinetic and mechanistic approach

The kinetics of the Ru^III-catalysed oxidation of L-leucine and L-isoleucine by alkaline permanganate were studied and compared, spectrophotometrically using a rapid kinetic accessory. The reaction is first order with respect to [oxidant] and [catalyst] with an apparently less than unit order in [substrate] and [alkali] respectively. The results suggest the formation of a complex between the amino acid and the hydroxylated species of ruthenium(III). The complex reacts further with the alkaline permanganate species in a rate-determining step, resulting in the formation of a free radical, which again reacts with the alkaline permanganate species in a subsequent fast step to yield the products. The reaction constants involved in the mechanism were calculated. There is a good agreement between observed and calculated rate constants under different experimental conditions. The activation parameters with respect to the slow step of the mechanism for both the amino acids were calculated and discussed. Of the two amino acids, leucine is oxidised at a faster rate than isoleucine.     

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.     

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.     

A study of the kinetics and mechanism of oxidation of L-tryptophan by diperiodatonickelate(IV) in aqueous alkaline medium

The kinetics of oxidation of L-tryptophan by diperiodatonickelate(IV) (DPN) in an aqueous alkaline medium at a constant ionic strength of 0.30 mol dm⁻³ was studied spectrophotometrically. The reaction was first order in diperiodatonickelate(IV) and less than first order in tryptophan and the OH⁻ ion. The addition of periodate had no effect on the reaction, and nickel(II) produced did not influence the reaction rate significantly. An increase in ionic strength and decrease in medium permittivity did not affect the reaction rate. A mechanism involving the formation of a complex between L-tryptophan and reactive DPN species was proposed. The constants characterizing the mechanism were evaluated. The activation parameters for the slow reaction step were computed and discussed. The text was submitted by the authors in English.     

Kinetics and Mechanism of Oxidation of <Emphasis Type="Italic">L</Emphasis>-Leucine by Alkaline Diperiodatonickelate(IV) – A Free Radical Intervention,Deamination, and Decarboxylation

Summary. The kinetics of oxidation of L-leucine by alkaline diperiodatonickelate(IV) was studied spectrophotometrically using a rapid kinetic accessory. The reaction is first order with respect to [DPN] and apparently less than unit order, each in [L-leucine] and [alkali] under the experimental conditions. However, the order in [L-leucine] and [alkali] changes from first order to zero order as the concentrations change from lower to higher values. Addition of periodate has no effect on the reaction rate. A mechanism involving the deprotonated diperiodatonickelate(IV) (DPN) as the reactive oxidant is proposed. The reaction constants involved in the mechanism were evaluated. There is a good agreement between the observed and calculated rate constants under varying experimental conditions. The isokinetic temperature was determined and the activation parameters with respect to the slow step of the reaction scheme were evaluated and discussed.Received September 19, 2002; accepted (revised) January 1, 2003 Published online september 11,2003