Kinetics and mechanism of silver(I)-catalysed oxidation of malonic acid by peroxodiphosphate in acetate buffers

Summary The kinetics of the silver(I)-catalysed oxidation of malonic acid by peroxodiphosphate (pdp) was studied in acetate buffers. The rate law as represented by-d[pdp]/dt = {(k ₁ K _inf2 ^sup-1 [H⁺]² + k ₂[H⁺] + k ₃ K ₃)/ ([H⁺]²/K ₂ + [H⁺] + K ₃)}[pdp][Ag(I)] conforms to the proposed mechanism. The rate is independent of malonic acid concentrations. Acetate ions do not affect the rate; however, the rate decreases as the ionic strength increases. A probable portrait of reaction events is suggested. A comparative analysis of the reactivity pattern of malonic acid towards peroxodiphosphate and peroxodisulphate in presence of silver(I) has been made.     

Evidence of protonation during the oxidation of some aryl alcohols by permanganate in perchloric acid medium and mechanism of the oxidation processes

The oxidation of benzyl alcohol and methoxy-, chloro-, and nitro- substituted benzyl alcohols by permanganate has been studied in aqueous and acetic acid medium in presence of perchloric acid. The reaction is first-order in [MnO₄^?] and [XC₆H₄CH₂OH], but the order is complex with respect to [H⁺]. Different thermodynamic parameters have been evaluated. The reaction occurs through the protonation of alcohol in a fast preequilibrium followed by a slow rate-determining oxidation step. A two-electron transfer oxidation step has been suggested for benzyl alcohol and chloro- and nitro- substituted alcohols, while the oxidation of methoxy compounds involves a one-electron transfer via a free-radical mechanism. © 1995 John Wiley & Sons, Inc.     

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.     

Formic acid as a reagent for alkaline permanganate : Potentiometric determination of formate

Oxidation of formate with permanganate in alkaline solutions yields a mixture of MnO₄^-2 and MnO₂. The reaction occurs slowly without an abrupt change in potential at the end-point. In 0.1N NaOH, at 80° C in the presence ofAg⁺ions or NaCl,the reaction is accelerated and yields MnO₂. The concentrations of formic acid obtained by oxidation with permanganate are comparable with those obtained by neutralization down to 2.295·10^-2N.Reduction of permanganate in the presence of Ba⁺² ions (alkalinity = 0.5 — 1.5N) or in the absence of Ba⁺ ions (alkalinity = 0.5 — 2.5N), gave accurate results for the permanganate concentration comparable with the results of the acid oxalate method.Formic acid is preferred to sodium formate on account of the greater stability of its solutions.     

Kinetics of reactions of N1-phenylbiguanidine with CeIV and [MnO4]− in aqueous sulphuric acid media

Summary In the title reaction each mole of N¹-phenylbiguanidine, R–HNC(=X)NHC(=NH)NH₂ (R=Ph, X=NH), consumes 4 moles of Ce^IV and produces guanylurea (R=H, X=O), 1,4-benzoquinone and ammonia. On the other hand, the reaction of N¹-phenylbiguanidine (pbg) with [MnO₄]^– proceeds with variable stoicheiometry which depends on reaction conditions. In the case of [MnO₄]^– no benzoquinone is detected among the reaction products; instead, carbon dioxide, guanylurea, and ammonia were identified. Pbg itself in acid solution slowly hydrolyses to aniline which rapidly reacts with Ce^IV and [MnO₄]^–. The kinetics for the reactions of pbg with the oxidants is consistent with the rate law –d[oxidant]/dt=k[pbg].The k values and the corresponding activation enthalpies and entropies for the reaction of bpg with Ce^IV, [MnO₄]^–, and Cr^VI lie within a narrow range. These results are interpreted in terms of rate-determining hydrolysis of pbg in all the three cases.     

Kinetics of oxidation of acidic amino acids by sodium N-bromobenzenesulphonamide in acid medium: A mechanistic approach

Kinetics of oxidation of acidic amino acids (glutamic acid (Glu) and aspartic acid (Asp)) by sodium N-bromobenzenesulphonamide (bromamine-B or BAB) has been carried out in aqueous HClO₄ medium at 30°C. The rate shows first-order dependence each on [BAB]_o and [amino acid]_o and inverse first-order on [H⁺]. At [H⁺] > 0·60 mol dm⁻³, the rate levelled off indicating zero-order dependence on [H⁺] and, under these conditions, the rate has fractional order dependence on [amino acid]. Succinic and malonic acids have been identified as the products. Variation of ionic strength and addition of the reaction product benzenesulphonamide or halide ions had no significant effect on the reaction rate. There is positive effect of dielectric constant of the solvent. Proton inventory studies in H₂O-D₂O mixtures showed the involvement of a single exchangeable proton of the OH⁻ ion in the transition state. Kinetic investigations have revealed that the order of reactivity is Asp > Glu. The rate laws proposed and derived in agreement with experimental results are discussed.     

A kinetic study of the oxidation of <Emphasis Type="SmallCaps">l</Emphasis>-methionine by water soluble colloidal MnO<Subscript>2</Subscript>

Aqueous solution of water soluble colloidal MnO₂ was prepared by Perez-Benito method. Kinetics of l-methionine oxidation by colloidal MnO₂ in perchloric acid (0.93 × 10⁻⁴ to 3.72 × 10⁻⁴ mol dm⁻³) has been studied spectrophotometrically. The reaction follows first-order kinetics with respect to [H⁺]. The first-order kinetics with respect to l-methionine at low concentration shifts to zero order at higher concentration. The effects of [Mn(II)] and [F⁻] on the reaction rate were also determined. Manganese (II) has sigmoidal effect on the rate reaction and act as auto catalyst. The exact dependence on [Mn(II)] cannot be explained due to its oxidation by colloidal MnO₂. Methionine sulfoxide was formed as the oxidation product of l-methionine. Ammonia and carbon dioxide have not been identified as the reaction products. The mechanism with the observed kinetics has been proposed and discussed.     

Formic acid as a reagent for alkaline permanganate : Potentiometrrc determination of quadrivalent selenium

Se⁺⁴ can be determined by mixing with KMn0₄ in l N NaOH, stirring the mixture at room temperature and measuring the potential until equilibrium, which needs ~10–15 min. Excess KmnO₄ is then determined with formate.In the direct oxidation of Se⁺⁴ with MnO₄^- in the cold, and in the presence of 2.5 N NaOH and 10% NaCl, MnO₄^- → MnO₄^-2. At 90°C, and in the presence of 0.1 N NaOH 10% NaCl and 2— 3 ml of 0.5% AuCl₃, MnO₄^- → MnO₂. The reaction which is rather slow is accelerated by the above reagents.Reduction of MnO₄^- with Se⁺⁴ in l— 3 N NaOH yields MnO₄^-2.Like the indirect method, the direct potentiometric procedures yield good results.     

A kinetic study of the permanganate—oxalate reaction and kinetic determination of manganese(II) and oxalic acid by the stopped-flow technique

The reduction of permanganate by oxalate in the presence of manganese(II) ion in acidic media is described. All reactions were run at 525 nm and constant ionic strength 1.0 M. The reaction was found to obey the rate expression —$\text{d[MnO}{}_4{}^{\mathrm{-}}\text{]}\text{d}\text{t}$ = k [Mn²⁺] [C₂O₄^2-]² [MnO₄^-] [H⁺]^-2 = k' [MnC₂O₄] [MnO₄^-]. The values of k and k' were shown to be 5.4 × 10⁴ M^-1 s^-1 and 8.2 × 10⁴ M^-1 s^-1, respectively. Reaction rate methods for the determination of manganese(II) and oxalic acid are reported. The rate of disappearance of permanganate was monitored automatically and related directly to manganese-(II) and oxalic acid concentrations. Manganese(II) in the ranges 1–10 × 10^-4 M and 1–10 × 10^-3 M and oxalic acid in the range 0–20 μg ml^-1 can be determined very rapidly with a precision of 1–2%.     

Oxidation with alkaline permanganate using formic acid for the back-titration : Potentiometric determination of chromium

Determination of chromium by oxidation of chromite with permanganate does not give accurate results. KmnO₄ is reduced to MnO₂. Titration of KmnO₄ with Cr⁺³ solution in the presence of 0.8–1.5N NaOH and Ba⁺² ions yields manganate and gives good results. In the absence of Ba⁺² ions and in the presence of 0.5–2N NaOH reduction of KmnO₄ passes quantitatively to MnO₂.Cr⁺³ can be determined by adding the chromic solution to KmnO₄ while stirring in presence of 1N NaOH and Ba⁺² ions, or a. 2.5N NaOH in the absence ofBa⁺² ions. The excess KmnO₄ is then back-titrated with formic acid.     

Oxidations with alkaline permanganate using monovalent thallium for the back titration: Estimation of hydrazine

Oxidation of liydrazine in alkaline solutions with KmnO₄, gives inaccurate results both in the presence of absence of telluric acid. The titration curve is characterized by two inflections.Titration of KmnO₄ with hydrazine gives good results in the presence of Ba⁺² ions and 0.75–1NNaOH (when MnO₄^- gives MnO₂^-) or in the presence of 0.5–2.5N NaOH only (when MnO₄ gives MnO₂).Hydrazine could be estimated by oxidation with KMn0₄ either in the presence of Ba⁺² ions or telluric acid, after which the excess permanganate is back titrated with monovalent thallium. The alkalinity is Kept at 1N NaOH.     

Kinetic Study of the Isotope Exchange Reactions of Malonic Acid and Malonate Ion Using 1H NMR Spectroscopy. Inhibition of Acid and Base

The isotope exchange reactions of malonic acid and a malonate ion were investigated in acidic and basic D₂O solutions, respectively, using ¹H NMR spectroscopy. The isotope exchange reaction of malonic acid is inhibited by the presence of DNO₃ (0–3 M) and DSO₄^? ion (0–0.1 M), whereas it is catalyzed by the presence of DSO₄^? ion (> 0.2 M), D₃PO₄, D₂PO₄^? ion or DPO₄^2– ion. The order of relative reactivity for catalyzing the isotope reaction of malonic acid in D₂O is DPO₄^2– > D₂PO₄^? > D₃PO₄ > DSO₄^? > DNO₃. The rate of the isotope exchange reaction of malonate ion in D₂O decreases to a minimum and then increases with increased [NaOD]₀. The mechanism of the isotope exchange reaction of malonic acid in acidic D₂O is different from the general acid-catalyzed mechanism generally observed for organic acids like acetic and dichloroacetic acids. The bimalonate ion plays an important role in the isotope exchange reactions of this system.     

Oxidation of some monosaccharides by hexavalent manganese in aqueous alkaline medium: A kinetic and mechanistic study

The kinetics of oxidation of some monosaccharides viz., D-ribose, D-xylose, and D-arabinose, D-glucose, D-fructose, D-galactose, 2-deoxyglucose, and α-methyl glucopyranoside by MnO₄^2? in aqueous alkaline medium have been studied. The rate of oxidation has been found to be first-order both with respect to [oxidant] and [sugar]. The rate is independent of [OH^?] under experimental conditions of [OH^?] > 0.5 M where the oxidant is stable. The effect of ionic strength is negligible on the rate. A mechanism involving the formation of a 5-membered cyclic intermediate complex between MnO₄^2? and 1,2-enediol form of the sugar is proposed. The intermediate complex decomposes to give products in the subsequent slow step. The involvement of 1,2-enediol form receives support from the reaction of α-methyl glucopyranoside, which exists in ring structure in alkaline solution reacting much slower than glucose with MnO₄^2? under similar conditions. Second-order rate constant k″ and activation parameters have been evaluated. The series of reactions exhibits a clear demonstration of applicability of isokinetic phenomenon where Arrhenius plots for all the reactions are found to intersect at a common point (295 K). © 1995 John Wiley & Sons, Inc.     

The oxidation of chlorine ions under the joint action of ozone and permanganate ions

The oxidation of chlorine ions in the system O₃ + MnO ₄ ^? + H⁺ + Cl^? with the formation of Cl₂ in the gas phase was studied. The phenomenon of transfer catalysis of the reaction between O₃ and Cl^? by the MnO ₄ ^? ion was observed (the products of the reduction of MnO ₄ ^? by the chlorine ion are oxidized by ozone to recover MnO ₄ ^? ). The rate of the formation of Cl₂ in the O₃ + MnO ₄ ^? + H⁺ + Cl^? system was higher than the sum of the corresponding rates in the oxidation of Cl^? by O₃ and MnO ₄ ^? separately. A scheme explaining the trends observed experimentally for the formation of Cl₂ and changes in MnO ₄ ^? concentration was suggested. The formation of MnO ₄ ^? in the oxidation of Mn³⁺ with ozone in acid media was studied.     

Kinetics of the permanganate oxidation of formic acid in aqueous solution

The kinetics of the permanganate oxidation of formic acid in aqueous perchloric acid at 30°C were examined by the spectrophotometric method. The chemical reaction 2MnO + 3HCOOH + 2H⁺ → 2MnO₂ + 3CO₂ + 4H₂O, appears to proceed via several parallel reactions. The overall rate equation has been obtained by using statistical multilinear regression analysis of the 660 cases studied, and the presence in the rate equation of two new terms in relation to previous studies shows that both permanganate autocatalytic effects and acid media inhibition must be taken into account when the reaction proceeds at constant ionic strength.     

The kinetics of reaction between permanganate and chlorine ions in acid solutions

The reaction between MnO ₄ ^? and Cl^? was studied in acid media at room temperature and ionic strength 1 M. The stoichiometric equation of the reaction has the form MnO ₄ ^? + 8H⁺ + 4Cl^? = Mn³⁺ + 2Cl₂ + 4H₂O. The reaction proceeds in two stages. At the first stage, permanganate ions are consumed to produce one Cl₂ molecule per MnO ₄ ^? ion. At the second stage, the second Cl₂ molecule and the final MnO ₄ ^? reduction product (trivalent manganese) are formed. The first stage is a reaction first-order in MnO ₄ ^? and second-order in H⁺ and Cl^?; its rate constant is (9.8 ± 0.6) × 10^?2l⁴/(mol⁴ min). An analysis of the literature data leads to a value of 18–20 kcal/mol for its activation energy.     

The Kinetics of Oxidation of L-Tryptophan by Water-Soluble Colloidal Manganese Dioxide

The kinetics of the oxidation of L-tryptophan by water-soluble colloidal MnO₂ (prepared from potassium permanganate and sodium thiosulfate solutions) has been carried out in aqueous perchloric acid medium at different temperatures. Monitoring the disappearance of the MnO₂ spectrophotometrically at 390 nm was used to follow the kinetics. The first-order kinetics with respect to [L-tryptophan] at low concentrations shifted to zero-order at higher concentrations. The reaction followed first-order with respect to [MnO₂] but fractional-order with respect to [HClO₄]. Adding trapping agents enhanced the rate of the reaction. The Arrhenius and Eyring equations were found valid for the reaction between 35°C and 55°C and different activation parameters (E_a, ΔH^#, ΔS^#) have been evaluated. On the basis of various observations and product characterization a plausible mechanism has been envisaged for the reaction taking place at the colloid surface. The results suggest formation of an adsorption complex between L-tryptophan and MnO₂. The complex decomposes in a rate-determining step, leading to the formation of free radical, which again reacts with the colloidal MnO₂ in a subsequent fast step to yield products. Freundlich isotherm is used to explain the adsorption of L-tryptophan on the colloidal MnO₂.     

Effect of ionic and non-ionic surfactants on the reduction of water soluble colloidal MnO<Subscript>2</Subscript> by glycolic acid

Kinetics of the redox reaction between colloidal MnO₂ and glycolic acid have been studied spectrophotometrically by monitoring the decay in the absorbance of colloidal MnO₂ in absence and presence of surfactants. Anionic sodium dodecyl sulfate has no effect, non-ionic Triton X-100 catalyzed the reaction and experiments were not possible in presence of cationic cetyltrimethylammonium bromide due to the precipitation of MnO₂.The reaction followed the same type of kinetic behavior, i.e., fractional-, first- and fractional-order dependencies, respectively, in [glycolic acid], [MnO₂] and [H⁺ ] in both the media. Effects of gum arabic and manganese(II) have also been studied and discussed. Mechanisms in accordance with the experimental data are proposed for the reaction.     

Study of the base-catalysed oxidation of the anti-bacterial and anti-protozoal agent metronidazole by permanganate ion in alkaline medium

The mechanism of dismutation of MnO₄ ^2? via the complex [MTZ–MnO₄·OH]^2?, formed during the oxidation of metronidazole (MTZ), has been investigated spectrophotometrically at different temperatures. The stoichiometry of the reaction is 1:1, i.e. 1 mol MTZ reacts with 1 mol Mn(VII).The reaction is first order in permanganate, less than first order in [MTZ] and [alkali]. The effects of added products and the dielectric constant and ionic strength of the reaction medium were investigated. The main products were identified by spot test and FT-IR. A mechanism involving a free radical has been proposed. In the equilibrium step MTZ binds to the MnO₄ ^? species to form a complex (C). Investigation of the reaction at different temperatures enabled determination of the activation data for the slow step of proposed mechanism. The proposed mechanism and the derived rate laws are consistent with the observed kinetics.     

Gram scale,metal-free and selective aerobic oxidation of alcohol and alkyl benzenes using homogeneous recyclable TAIm[MnO4] oxidative ionic liquid under mild conditions: Microwave/ ultrasonic-assisted to carboxylic acid

A homogeneous catalyst-free system has been developed for the selective oxidation of alcohols and alkyl benzenes to the corresponding carbonyl compounds using a recyclable TAIm[MnO₄] oxidative ionic liquid. The reactions were performed in the presence of previously reported TAIm[MnO₄]/ TAIm[OH] ionic liquids and KMnO₄ at ambient temperature under solvent-free conditions. Benzyl alcohols were selectively transferred to benzaldehydes, while under ultrasonic or microwave irradiation, they oxidized to benzoic acid selectively and directly. Scalability of the process also studied at high scale. Also, the ionic liquid could be readily recycled from the aqueous mixture and reused for several consecutive times without any pre-treatment and loss of catalytic activity. In this work, the highly active and toxic KMnO₄ salt has been transformed into a mild recyclable oxidant reagent with high selectivity towards alcohol oxidation.