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     

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

 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.     

Oxidation kinetics of crystal violet by potassium permanganate in acidic medium

The oxidation kinetics of crystal violet (a triphenylmethane dye) by potassium permanganate was focused in an acidic medium by the spectrophotometric method at 584 nm. The oxidation reaction of crystal violet by potassium permanganate is carried out in an acidic medium at different temperatures ranging within 298–318 K. The kinetic study was carried out to investigate the effect of the concentration, ionic strength and temperature. The reaction followed first order kinetics with respect to potassium permanganate and crystal violet and the overall rate of the reaction was found to be second order. Thermodynamic activation parameters like the activation energy (E_a), enthalpy change (ΔH*), free energy change (ΔG*), and entropy change (ΔS*) have also been evaluated.     

Kinetics and Mechanism of Oxidation of l‐Histidine by Permanganate Ions in Sulfuric Acid Medium

The reaction kinetics for the oxidation of l ‐histidine by permanganate ions have been investigated spectrophotometrically in sulfuric acid medium at constant ionic strength and temperature. The order with respect to permanganate ions was found to be unity and second in acid concentration, whereas a fractional order is observed with respect to histidine. The reaction was observed to proceed through formation of a 1:1 intermediate complex between oxidant and substrate. The effect of the acid concentration suggests that the reaction is acid catalyzed. Increasing the ionic strength has no significant effect on the rate. The influence of temperature on the rate of reaction was studied. The presence of metal ion catalysts was found to accelerate the oxidation rate, and the order of effectiveness of the ions was Cu²⁺ > Ni²⁺ > Zn²⁺. The final oxidation products were identified as aldehyde (2‐imidazole acetaldehyde), ammonium ion, manganese(II), and carbon dioxide. Based on the kinetic results, a plausible reaction mechanism is proposed. The activation parameters were determined and discussed with respect to a slow reaction step.     

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.     

Ruthenium(III) Catalyzed Oxidative Degradation of Amitriptyline-A Tricyclic Antidepressant Drug by Permanganate in Aqueous Acidic Medium

The oxidation of amitriptyline by potassium permanganate has been investigated spectrophotometrically in the presence of ruthenium(III) as catalyst in aqueous acidic medium at a constant ionic strength of 0.20 mol⋅dm⁻³. The stoichiometry was found to be 1:1 in terms of the mole ratio of amitriptyline and permanganate ions consumed. The order of the reaction with respect to manganese(VII) and ruthenium(III) concentration was unity while the order with respect to amitriptyline was less than unity over the concentration range studied. The rate increased with an increase in acid concentration. The reaction rates revealed that the Ru(III) catalyzed reaction was about eight-fold faster than the uncatalyzed reaction. The oxidation products were identified by spectral analysis. A tentative mechanism consistent with the kinetics has been proposed. The reaction constants involved in the different steps of the reaction mechanism were calculated. Kinetic experiments suggest that HMnO₄ is the reactive permanganate species and [Ru(H₂O)₆]³⁺ is the reactive Ru(III) species.     

Autocatalytic Oxidation of Thiamine Hydrochloride (Vitamin B1) by Permanganate in Aqueous Sulfuric Acid Medium: A Kinetic and Mechanistic Study

The reaction kinetics of autocatalytic oxidation of thiamine hydrochloride (vitamin B₁) by the permanganate ion in aqueous sulfuric acid medium has been investigated spectrophotometrically under the pseudo–first‐order condition at 25°C. The observed stoichiometry is 6:5 in terms of the mole ratio of permanganate ions and thiamine hydrochloride. Formation of products was confirmed by UV–vis, IR, GC‐MS, and NMR spectral data. Usually in the permanganate oxidation–reduction reactions, one of the products, Mn²⁺ autocatalyzes the reaction, but in the present investigation the autocatalytic effect is due to the (4‐methyl–thiazol‐5‐yl) acetic acid, a product formed from the oxidation of vitamin B₁, which is a rare case. The added Mn²⁺ does not have any significant effect on the rate of reaction. The reaction is first order with respect to both permanganate and thiamine hydrochloride concentrations. An increase in the sulfuric acid concentration decreases the rate of reaction. A composite scheme and rate laws were proposed. The activation parameters with respect to the slow step and reaction constants involved in the mechanism were determined and discussed.     

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.     

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.     

Oxidation of Carbamazepine by Lipopathic Mn(VII), Cetyltrimethylammonium Permanganate: A Mechanistic Study

In this contribution, we report the oxidation of an established anticonvulsant and antiepileptic drug, carbamazepine, by a lipopathic oxidant, cetyltrimethylammonium permanganate (CTAP), in a nonpolar medium. 1H‐Dibenzo[b,f]azepine‐4,5‐dione is found to be the major product of the oxidation reaction. The kinetics of the reaction is studied in organic media spectrophotometrically by monitoring the disappearance of Mn(VII) at 530 nm. The reaction is found to be fractional order with respect to carbamazepine and first order with respect to CTAP. Based on the experimental findings, a suitable ionic mechanism is proposed where carbamazepine reacts with CTAP in a slow rate‐determining step to form a hypomanganate ester intermediate through a nonpolar cyclic transition state. Subsequently, the intermediate decomposes and hydrolyzes in fast steps to the dicarbonyl product. The proposed reaction mechanism is also supported by the effect of solvent and temperature on the rate of the reaction. The addition of ionic surfactants increases the rate of reaction, and the catalyzing effect is explained through the possible formation of mixed reverse micellar aggregates where carbamazepine is partitioned more to the interfacial region in the vicinity of the permanganate anion.     

Oxidative transformation of ciprofloxacin by alkaline permanganate – A kinetic and mechanistic study

This spectroscopic study presents the kinetics and degradation pathways of oxidation of ciprofloxacin by permanganate in alkaline medium at constant ionic strength of 0.04 mol⁻³. Orders with respect to substrate, oxidant and alkali concentrations were determined. Effect of ionic strength and solvent polarity of the medium on the rate of the reaction was studied. The oxidation products were identified by LC-ESI-MS technique. Product characterization of ciprofloxacin reaction mixtures indicates the formation of three major products corresponding to m/z 263, 306, and 348 (corresponding to full or partial dealkylation of the piperazine ring). The piperazine moiety of ciprofloxacin is the predominant oxidative site to KMnO₄. Product analyses showed that oxidation by permanganate results in dealkylation at the piperazine moiety of ciprofloxacin, with the quinolone ring essentially intact. The reaction kinetics and product characterization point to a reaction mechanism that likely begins with formation of a complex between ciprofloxacin and the KMnO₄, followed by oxidation at the aromatic N1 atom of piperazine moiety to generate an anilinyl radical intermediate. The radical intermediates subsequently undergo N-dealkylation. Investigations of the reaction at different temperatures allowed the determination of the activation parameters with respect to the slow step of proposed mechanism. The proposed mechanism and the derived rate laws are consistent with the observed kinetics.     

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 the Autocatalyzed Oxidation of Theophylline by Permanganate in Aqueous Perchloric Acid Medium

The reaction kinetics for the oxidation of theophylline by permanganate ions have been investigated in perchloric acid medium using spectrophotometric techniques at 25?^°C, and at constant ionic strength 1.60 mol?dm^?3, under pseudo first order conditions. An autocatalyzed reaction is observed due to one of the products formed is Mn(II). The orders with respect to theophylline and Mn(VII) were both found to be unity, whereas fractional order is observed with respect to the autocatalyst, Mn(II). The rate of the reaction increases as the concentration of acid increases, but the order with respect to acid concentration is less than unity. The influence of temperature on the rate of reaction was studied. Based on the experimental results a suitable mechanism is proposed. The activation and thermodynamic parameters were determined with respect to slow reaction step.     

Kinetics of Ir (III)-catalyzed Oxidation of D-glucose by Potassium Iodate in Aqueous Alkaline Medium

The kinetics of Ir (III) chloride-catalyzed oxidation of D-glucose by iodate in aqueous alkaline medium was investigated at 45°C. The reaction follows first-order kinetics with respect to potassium iodate in its low concentration range but tends to zero order at its higher concentration. Zero-order kinetics with respect to [D-glucose] was observed. In the lower concentration range of Ir (III) chloride, the reaction follows first kinetics, while the order shifts from first to zero at its higher concentration range. The reaction follows first-order kinetics with respect to [OH^?] at its low concentration but tends towards zero order at higher concentration. Variation in [Cl^?] and ionic strength of the medium did not bring about any significant change in the rate of reaction. The first-order rate constant increased with a decrease in the dielectric constant of the medium. The values of rate constants observed at four different temperatures were utilized to calculate the activation parameters. Sodium salt of formic acid and arabinonic acid have been identified as the main oxidation products of the reaction. A plausible mechanism from the results of kinetic studies, reaction stoichiometry, and product analysis has been proposed.     

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.     

Oxidation of sodium (2-14C) acetate with alkaline permanganate

The mechanism and kinetics of the oxidation of sodium acetate with permanganate in alkaline and neutral media, has been investigated using (2-¹⁴C) acetate. The reaction is first order both with respect to permanganate and acetate ions. The initial second order rate constants depend linearly on the square of the hydroxide ion concentration. Arrhenius acitvation energy of the oxidation reaction carried out in 12M NaOH is 24.0 kcal/mole in the temperature interval 50–100°C. The mechanism of the principal path leading to the oxalate formation and the mechanism of the side reaction resulting in the carbon dioxide production has been proposed and discussed.     

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.     

Studies on the oxidation of red phosphorus by potassium permanganate in an acid medium

Summary Oxidation of red phosphorus by an acid solution of potassium permanganate has been studied and applied in the volumetric determination of red phosphorus. The kinetics of the oxidation-reduction process show that the reaction is of the bimolecular order. Influence of temperature on the velocity coefficient (K) as also the variation of (K) for different concentrations of the oxidant, observed, have been made use of in evaluating the activation energy of the reaction. Further the utilisability of this simple procedure for the volumetric determination of red phosphorus is emphasized.The nature of the above oxidation reaction in an alkaline medium is being investigated.Sincere thanks of the authors are due to Prof. S S. Joshi, for facilities and kind interest in the work.     

Kinetics and mechanism of permanganate oxidation of pectin polysaccharide in acid perchlorate media

The kinetics of oxidation of pectin polysaccharide as a natural polymer by permanganate ion in aqueous perchloric acid at a constant ionic strength of 2.0 mol dm⁻³ has been investigated spectrophotometrically. The reaction time curves showed two distinct stages, the initial stage was relatively slow, followed by an increase in the rate of oxidation at longer times. The results of the initial rates reveal first-order kinetics in permanganate ion and fractional-order with respect to pectin concentration. Kinetic evidence for the formation of an intermediate complex between the polysaccharide and the oxidant is presented. The results obtained at various hydrogen ion concentrations showed that the reaction is acid catalyzed. The added salts lead to the prediction that Mn⁴⁺ and/or Mn³⁺ play an important role in the autoaccleration period kinetics. A tentative reaction mechanism consistent with the kinetic results is discussed.     

Kinetics of the Oxidation of Tartrazine with Peroxydisulfate in the Presence and Absence of Catalysts

Summary.  The food dye tartrazine is oxidized with peroxydisulfate in the absence and in the presence of Ag(I) and Fe(III) catalysts. In the absence of these metal ions, the reaction shows second-order kinetics, first-order in each of the reacting species. With the Ag(I) ion in the medium the reaction proceeds considerably faster, but still follows second-order kinetics. The reaction rate depends on the concentration of Ag(I) and S₂O₈ ²⁻, but is independent of the concentration of the substrate. When Fe(III) acts as the catalyst, a marked enhancement in the reaction rate is observed, and the reaction proceeds through two parallel pathways, the catalyzed and the noncatalyzed. The catalyzed path follows third order kinetics, being first-order in substrate, oxidant, and catalyst concentration. Mechanisms of the noncatalyzed as well as the Ag(I) and Fe(III) catalyzed reaction systems are proposed. Received June 28, 1999. Accepted (revised) September 27, 1999