Kinetic and mechanistic studies on the oxidation of Norfloxacin by Chloramine‐B and N‐Chlorobenzotriazole in acidic medium

The kinetics of oxidation of Norfloxacin [1‐ethyl‐6‐fluoro‐1,4‐dihydro‐4‐oxo‐7‐(l‐piperazinyl)‐3‐quinoline carboxylic acid] by chloramine‐B and N‐chlorobenzotriazole has been studied in aqueous acetic acid medium (25% v/v) in the presence of perchloric acid at 323 K. For both the oxidants, the reaction follows a first‐order dependence on [oxidant], a fractional‐order on [Norfloxacin], and an inverse‐fractional order on [H⁺]. Dependence of reaction rate on ionic strength, reaction product, dielectric constant, solvent isotope, and temperature is studied. Kinetic parameters are evaluated. The reaction products are identified. The proposed reaction mechanism and the derived rate equation are consistent with the observed kinetic data. Formation and decomposition constants for substrate–oxidant complexes are evaluated. ©1999 John Wiley & Sons, Inc. Int J Chem Kinet 31: 153–158, 1999     

Mn(III) oxidation of peptides: A mechanistic investigation of kinetic variations in hydrophobic‐induced oxidation of tetrapeptides of elastin sequences

Four tetrapeptide analogues of elastin sequences, glycyl‐glycyl‐alanyl‐proline (GGAP), glycyl‐glycyl‐valyl‐proline (GGVP), glycyl‐glycyl‐isoleucyl‐proline (GGIP), and glycyl‐glycyl‐phenylalanyl‐proline (GGFP) were synthesized, based on their increasing order of hydrophobicity, by a classical solution phase method and were characterized. These tetrapeptides (TETPs) were oxidized using Mn(OAc)₃ in 25% acetic acid at 298 K, and the kinetics of the reaction was monitored spectrophotometrically at λ_max = 400 nm. A first‐order dependence of rate on each of [Mn(OAc)₃], [OAc^?], and substrate [TETP], an inverse order dependence on [H⁺], has been observed. The rate is independent of [Mn(II)]. However, an inverse order dependence on varying the dielectric constant using various percentages (v/v) of acetic acid has also been observed, and but addition of anions such as Cl^? and ClO₄^? has insignificant effect on the rate. Activation parameters have been evaluated using the Arrhenius and Erying plots. The oxidation products were isolated and characterized. Based on the results obtained, a plausible mechanism involving [Mn(OAc)₄]^? has been proposed. An apparent correlation was noted between the rate of oxidation of these TETPs by Mn(III) in the presence of sulfate ions in sulfuric acid medium and Mn(OAc)₃ in the acetic acid medium. The rate of oxidation with Mn(OAc)₃ was observed to be slower than with the former. The rate of oxidation of GGFP was found to be higher than GGIP, GGVP, and GGAP. This may be due to the presence of an aromatic side chain and/or because of the increased hydrophobicity. The overall order of rate of oxidation of TETPs is GGFP > GGIP > GGVP > GGAP, which also represents an increasing order of their hydrophobicity. © 2005 Wiley Periodicals, Inc. Int J Chem Kinet 38: 115–123, 2006     

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     

Oxidation of 3‐(3,4‐dihydroxy phenyl)‐l‐alanine (levodopa) and 3‐(3,4‐dihydroxy phenyl)‐2‐methyl‐l‐alanine (methyl dopa) by manganese(III) in pyrophosphate media: Kinetic and mechanistic study

Manganese(III) (Mn(III)) has been stabilized in weakly acidic solution by means of pyrophosphate and the nature of the complex was elucidated spectrophotometrically. Stoichiometry of Mn(III)‐oxidation of levodopa and methyl dopa in pyrophosphate medium was established in the pH range 2.5–4.0 by iodometric and spectrophotometric methods. The reaction shows a distinct variation in kinetic order with respect to [Mn(III)], a first‐order dependence in the pH range 1.9–2.6, decreasing to fractional order above pH 3. Other common features include first‐order dependence on [dopa], positive fractional order dependence on [H⁺], and inverse first‐order dependence on [Mn(III)] in the pH range studied. The effects of varying ionic strength and solvent composition were studied. Added ions such as SO₄^2? and ClO₄^? alter the reaction rate, probably due to the change in the formal redox potential of Mn(III)–Mn(II) couple because of the changes in coordination environment of the oxidizing species. Evidence for the transient existence of the free radical intermediate is given. Cyclic voltametric sensing of levodopa and methyl dopa has ruled out the formation of dopaquinones as oxidation products in the pH range studied. Activation parameters have been evaluated using the Arrhenius and Erying plots. Mechanisms consistent with the kinetic data have been proposed and discussed. These studies are expected to throw some light on dopa metabolism. © 2001 John Wiley & Sons, Inc. Int J Chem Kinet 33: 449–457, 2001     

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.     

Effect of Anionic Surfactant on the Oxidation of DL-Aspartic Acid by N-Bromophthalimide: A Kinetic Study

The kinetics of oxidation of DL-Aspartic acid (Asp) by N-bromophthalimide (NBP) was studied in the presence of sodium dodecyl sulfate (SDS) in acidic medium at 308 K. The rate of reaction was found to have first-order dependence on [NBP], fractional order dependence on [Asp] and inverse fractional order dependence on [H⁺]. The addition of reduced product of the oxidant, that is, [Phthalimide] has decreased the rate of reaction. The rate of reaction increased with increase in inorganic salts concentration, whereas a change in [Cl^?], ionic strength of the medium and [Hg(OAc)₂] had no effect on the oxidation velocity. The rate of reaction decreased with a decrease in dielectric constant of the medium. COOH-CH₂-CN was identified as the main oxidation product of the reactions. The various activation parameters have been computed. A suitable reaction mechanism consistent with the experimental findings has been proposed. The micelle-binding constant has been calculated.     

Kinetic Study of Oxidation of DL-Serine by N-Bromophthalimide in the Presence of Sodium Dodecyl Sulfate

The kinetics of oxidation of DL-serine (Ser) by N-bromophthalimide (NBP) was studied in the presence of an anionic surfactant, sodium dodecyl sulfate, in acidic medium at 308 K. The rate of reaction was found to have first-order dependence on [NBP], fractional order dependence on [Ser] and inverse fractional order dependence on [H⁺]. The addition of reduced product of the oxidant [Phthalimide] and [Hg(OAc)₂] has no effect on the rate of reaction. The change in ionic strength of the medium had no effect on oxidation velocity. The rate of reaction increased with increasing [Br^?] and decreased with increasing [Cl^?]. The rate of reaction decreased with decrease in dielectric constant of the medium. OHCH₂CN was identified as the main oxidation product of the reactions. The various activation parameters have been computed. A suitable mechanism consistent with the experimental findings has been proposed. The micelle-binding constant has been calculated.     

Kinetic study of 2‐propanol and benzyl alcohol oxidation by alkaline hexacyanoferrate(III) catalyzed by a terpyridyl ruthenium complex

The complex (Trpy)RuCl₃ (Trpy = 2,2′:6′,2″‐terpyridine) reacts with alkaline hexacyanoferrate(III) to form a terpyridyl ruthenium(IV)‐oxo complex that catalyzes the oxidation of 2‐propanol and benzyl alcohol by alkaline hexacyanoferrate(III). The reaction kinetics of this catalytic oxidation have been studied photometrically. The reaction rate shows a first‐order dependence on [RU(IV)], a zero‐order dependence on [hexacyanoferrate(III)], a fractional order in [substrate], and a fractional inverse order in [HO⁻]. The kinetic data suggest a reaction mechanism in which the catalytic species and its protonated form oxidize the uncoordinated alcohol in parallel slow steps. Isotope effects, substituent effects, and product studies suggest that both species oxidize alcohol through similar pericyclic processes. The reduced catalytic intermediates react rapidly with hexacyanoferrate(III) and hydroxide to reform the unprotonated catalytic species. © 2000 John Wiley & Sons, Inc. Int J Chem Kinet 32: 760–770, 2000     

Oxidation of L-aspartic acid and L-glutamic acid by manganese(III) ions in aqueous sulphuric acid,acetic acid,and pyrophosphate media: A kinetic study

Kinetics of oxidation of L-aspartic acid and L-glutamic acid by manganese(III) ions have been studied in aqueous sulphuric acid, acetic acid, and pyrophosphate media. Manganese(III) solutions were prepared by known electrolytic/chemical methods in the three media. The nature of the oxidizing species present in manganese(III) solutions was determined by spectrophotometric and redox potential measurements. The reaction shows a variable order in [manganese(III)]_o: the order changes from two to one as the reactive oxidizing species changes from an aquo ionic form to a complex form. There is a first-order dependence of the rate on [amino acid]_o in all the three media while the other common features include an inverse dependence each on [H⁺] and on [manganese(II)]. Effects of varying ionic strength and solvent composition were studied. Added anions such as pyrophosphate, fluoride, or chloride alter the reaction rate and mechanism by changing the formal redox potential of Mn(III)-Mn(II) couple. Activation parameters have been evaluated using the Arrhenius and Eyring plots. Mechanisms consistent with the kinetic data have been proposed and discussed. © 1995 John Wiley & Sons, Inc.     

Kinetics of oxidation of pyridoxine by anodically generated manganese(III) in aqueous acetic acid medium

Summary Manganese(III) acetate was prepared by the electrolytic oxidation of Mn(OAc)₂ in aqueous AcOH. The electro-generated manganese(III) species was characterised by spectroscopic and redox potential studies. The kinetics of oxidation of pyridoxine (PRX) by manganese(III) in aqueous AcOH were investigated and is first order with respect to [Mn^III]. The effects of varying [Mn^III], [PRX], added manganese(II), pH and added anions such as AcO⁻, F⁻, Cl⁻ and ClO _inf4 ^sup− and SO _inf4 ^sup2− were studied. The rate decreased slowly with increasing [H⁺] up to 0.2 mol dm⁻³ and increased steeply thereafter. The orders in [PRX] and [Mn^II] were unity and inverse fractional, respectively, in both low and high [H⁺] ranges. The dependence of reaction rate on temperature was studied and activation parameters were computed from Arrhenius and Eyring plots. A mechanism consistent with the observed results is proposed and discussed.     

Kinetics and mechanism of the reaction between dimethylformamide and chromium(VI)

The kinetics of oxidation of N,N‐dimethylformamide by chromium(VI) has been studied spectrophotometrically in aqueous perchloric acid media at 20°C. The rate showed a first‐order dependence on both [Cr(VI)] and [DMF], and increased markedly with increasing [H⁺]. The order with respect to [HClO₄] was found to lie between 1 and 2. The rate was found to be independent of ionic strength as well as of any inhibition effect of Mn(II). The formation of superoxochromium(III) ion was detected in an aerated solution of chromium(VI), DMF and HClO₄. The proposed mechanism, involving two reaction pathways, leads to the rate law, rate = K_a1 [HCrO₄⁻] [DMF] (k_I K_a2 [H⁺]²+k_II[H⁺]). The first pathway, with rate constant k_I, involves the formation of chromium(V) and a free radical. The second pathway, with rate constant k_II, involves the formation of Cr(IV), CO₂ and dimethylamine. © 1999 John Wiley & Sons, Inc. Int J Chem Kinet 31: 409–415, 1999     

Cooxidation of anilides and oxalic acid by chromic acid: A one‐step,three‐electron oxidation

The chromic acid oxidation of a mixture of oxalic acid and anilides proceeds much faster than that of either of the two substrates alone. The oxidation kinetics of acetanilide, p‐methyl‐, p‐chloro‐, and p‐nitroacetanilides by Cr(VI) in the presence of oxalic acid in aqueous acetic acid medium follows first‐order, zero‐order, and second‐order dependence in [oxidant], [substrate], and in [oxalic acid], respectively, while the oxidation kinetics of benzanilide, p‐methyl‐, p‐chloro‐, and p‐nitrobenzanilides follow first order in [oxidant] and fractional order each in [substrate] and [oxalic acid] and yields corresponding azobenzenes and benzaldehydes in the case of benzanilide and substituted benzanilides as the main products of oxidation. Aluminium ions suppress the reaction. The intermediate is believed to be formed from the anilide and a chromic acid‐oxalic acid complex. In the proposed mechanism, the rate‐limiting step involves the direct reduction of Cr(VI) to Cr(III). © 2000 John Wiley & Sons, Inc. Int J Chem Kinet 33: 21–28, 2001     

Kinetics and mechanistic aspects on electron‐transfer process for permanganate oxidation of poly(ethylene glycol) in aqueous acidic solutions in the presence and absence of Ru(III) catalyst

The kinetics and mechanism of oxidation of poly(ethylene glycol) (PEG) by the permanganate ion as a multiequivalent oxidant in aqueous perchlorate solutions at an ionic strength of 2.0 mol dm⁻³ has been investigated spectrophotometrically. The reaction kinetics was found to be of complex in nature. The pseudo–first‐order plots showed curves of inverted S‐shape, consisting of two distinct stages throughout the entire course of reaction. The first stage was relatively slow, followed by a fast reaction rate at longer time periods. The first‐order dependence in [MnO₄⁻], fractional first‐order dependence in [H⁺], and fractional first‐order kinetics in the PEG concentration for the first stage have been revealed in the absence of the Ru(III) catalyst. The influence of the Ru(III) catalyst on the oxidation kinetics has been examined. The oxidation was found to be catalyzed by the added Ru(III) catalyst. The First‐order dependence on the catalyst and zero order with respect to the oxidant concentrations have been observed. The kinetic parameters have been evaluated, and a tentative reaction mechanism consistent with the kinetic results is suggested and discussed.     

The oxidation of organic substances by compounds of trivalent manganese: XIV. Oxidation of malonic acid by manganese(III) sulfate in sulfuric acid medium and with hexaquomanganese(III) ions in noncomplexing perchloric acid medium

The oxidation of malonic acid by manganese(III) sulfate in a medium of sulfuric acid and by hexaquomanganese(III) ions in a noncomplexing perchloric acid medium was studied.The reaction stoichiometry was found and the effect of the concentrations of H⁺, Mn²⁺, and HSO₄^? ions and of the initial reactant concentrations on the course and rate of the reaction was studied.The optimum conditions have been found for analytical use of the reaction, procedures have been proposed for the determination of malonic acid using the two reagents, and the accuracy and reproducibility of the determinations have been found.     

Kinetics and mechanism of oxidation of aspirin by bromamine-T,N-bromosuccinimide,and N-bromophthalimide

The kinetics of the oxidation of aspirin (ASP) by bromamine-T (BAT), N-bromosuccinimide (NBS), and N-bromophthalimide (NBP) has been studied in aqueous perchloric acid at 303 K. The oxidation reaction follows identical kinetics with first-order in [oxidant], fractional-order in [ASP], and inverse fractional-order in [H⁺]. Under identical experimental conditions the extent of oxidation with different oxidizing agents is in the order: NBS>BAT>NBP. The rate decreased with decreasing dielectric constant of the medium. The variation of ionic strength and the addition of the reaction products and halide ions had no significant effect on the reaction rate. The solvent isotope effect was studied using D₂O. Kinetic parameters were evaluated by studying the reaction at different temperatures. The reaction products were identified by GC–MS. The proposed reaction mechanism and the derived rate law are consistent with the observed kinetic data. Formation and decomposition constants for ASP-oxidant complexes have been evaluated. Decarboxylation, bromination, and loss of acetic acid gave 2,4,6-tribromophenol. © 1998 John Wiley & Sons, Inc. Int J Chem Kinet: 30: 407–414, 1998     

A kinetic study of oxidation of 1,4‐dioxane by diperiodatonickelate(IV) in aqueous alkaline medium

The kinetics of oxidation of 1,4‐Dioxane (Dio) by Diperiodatonickelate (IV) (DPN) in aqueous alkaline medium at a constant ionic strength of 1.5 mol dm⁻³ was studied spectrophotometrically. The reaction shows first‐order kinetics in [DPN] and less than unit order dependence each in [Dio] and [OH⁻]. Addition of products, Ni(II) and periodate have no significant effect on the reaction rate. An increase in ionic strength and decrease in dielectric constant of the medium increases the rate. A mechanism based on experimental results, involving two paths, one [Dio] dependent and the other [Dio] independent is proposed. The constants involved in the mechanism are evaluated. There is a good agreement between the observed and calculated rate constants at varying conditions of experiments. © 1999 John Wiley & Sons, Inc. Int J Chem Kinet 31: 789–796, 1999     

Kinetics and mechanism of oxidation of L-Alanine by <Emphasis Type="Italic">N</Emphasis>-bromophthalimide in the presence of sodium dodecyl sulfate

The kinetics of oxidation of L-Alanine (Ala) by N-bromophthalimide (NBP) was studied in the presence of an anionic surfactant, sodium dodecyl sulfate, in acidic medium at 308 K. The rate of reaction was found to have first-order dependence on [NBP], fractional order dependence on [Ala] and inverse fractional order dependence on [H⁺]. The addition of reduced product of the oxidant [Phthalimide] has decreased the rate of reaction. The rate of reaction increased with increase in inorganic salts concentration i.e., [Cl⁻] and [Br⁻], whereas a change in ionic strength of the medium and [Hg(OAc)₂] had no effect on oxidation velocity. The rate of reaction decreased with a decrease in dielectric constant of the medium. CH₃CN was identified as the main oxidation product of the reaction. The various activation parameters have been computed and suitable mechanism consistent with the experimental findings has also been proposed. The micelle-binding constant has been calculated. Published in Russian in Kinetika i Kataliz, 2009, Vol. 50, No. 3, pp. 386–396. The article is published in the original.     

Kinetic study of the Ce(III)‐, Mn(II)‐ or Fe(phen)32+‐catalyzed Belousov‐Zhabotinsky reaction with 2‐ketoglutaric acid

The Belousov‐Zhabotinsky (BZ) reaction of bromate ion with 2‐ketoglutaric acid (KGA) in aqueous sulfuric acid catalyzed by Ce(III), Mn(II), or Fe(phen)₃²⁺ ion exhibits sustained barely damped oscillations under aerobic conditions. In general, the reaction oscillates without an induction period. Fe(phen)₃²⁺ ion behaves differently from Ce(III) and Mn(II) ions in catalyzing this oscillating system. The gem‐diol form of KGA exhibits different behavior from that of the keto form of KGA in the BZ reaction. The kinetics and mechanism of the reaction of KGA with Ce(IV), Mn(III), or Fe(phen)₃³⁺ ion was investigated. The order of relative reactivities of metal ions toward reaction with KGA is Mn(III) > Ce(IV) ≫ Fe(phen)₃³⁺. Experimental results are rationalized. © 2001 John Wiley & Sons, Inc. Int J Chem Kinet 33: 101–107, 2001     

Cu(II) catalyzed oxidation of mercaptoacetic acid by methylene blue in acidic medium: Influence of solvent and morphology

Kinetic studies on the Cu(II) catalyzed oxidation of mercaptoacetic acid (thioglycolic acid, TGA) by the model electron receptor methylene blue in acidic medium show that the reaction follows a second order kinetics in TGA. The order in methylene blue is unity but at higher [TGA], the order is 3/4. The rate shows an inverse relationship with [H⁺] and a second order dependence on [Cu(II)]. The reaction conforms to Arrhenius behavior in aqueous medium but resorts to anti-Arrhenius behavior in aqueous methanol and in aqueous acetone media. The reaction involves the in situ participation of nanoparticles which has been confirmed by SEM, XRD, and FTIR techniques. In aqueous medium, cauliflower shaped nanoparticles (44.21–74.33 nm) are obtained but in the presence of acetone and methanol, nanogranules (38.96–70.73 nm) and nanodisks (47.30–72.16 nm), respectively, are produced at 35°C as revealed by SEM images and XRD data. The reaction is characterized by the participation of two transition states in aqueous acetone medium and the kinetics of the reaction, especially the temperature dependence, is governed by the adsorption of methylene blue on copper nanoparticles as influenced by morphology inter alia dielectric constant of the reaction medium.