Alginate polyelectrolyte ionotropic gels. XVIII. Oxidation of alginate polysaccharide by potassium permanganate in alkaline solutions: Kinetics of decomposition of intermediate complex

The kinetics of decomposition of [Alg · Mn ^VIO₄^2?] intermediate complex have been investigated spectrophotometrically at a constant ionic strength of 0.5 mol dm^?3. The decomposition reaction was found to be first-order in the intermediate concentration. The results showed that the rate of reaction was base-catalyzed. The kinetic parameters have been evaluated and found to be ΔS^? = ?103.88±6.18 J mol^?1 K^?1, ΔH^? = 51.61 ± 1.02 kJ mol^?1, and ΔG^? = 82.57 ± 2.86 kJ mol^?1, respectively. A reaction mechanism consistent with the results is discussed. © 1993 John Wiley & Sons, Inc.     

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.     

Alginate polyelectrolyte ionotropic gels. XIV. Kinetics and mechanism of formation of intermediate complex during the oxidation of alginate polysaccharide by alkaline permanganate with a spectrophotometric evidence of manganate(VI) transient species

The kinetics and mechanism of the [Alg.Mn ^VIO] intermediate complex formation during the oxidation of alginate polysaccharide at pHs ≥ 12 have been investigated spectrophotometrically. The reaction showed a first-order dependence in permanganate and a fractional order with respect to the alginate concentration (Alg). Kinetic and spectrophotometric evidence revealed the formation of manganate(VI) as transient species. The results obtained indicated the dependence of the rate of formation on the pH of the medium where the complex formation was base catalyzed. A mechanism consistent with the experimental results is discussed. © 1993 John Wiley & Sons, Inc.     

Kinetics and mechanism of oxidation of some simple reducing sugars by permanganate ion in alkaline medium

The kinetics of oxidation of glucose, galactose, fructose, maltose and sucrose by alkaline permanganate anion has been studied. The reactions studied spectrophotometrically over a wide range of experimental conditions show that the rate of the reactions is enhanced by increase in pH, ionic strength, and temperature as well as the reactant concentrations. The mechanism has been proposed to proceed via the formation of enediol intermediate complexes and the order of reactivities of the sugars is fructose > glucose ≈ galactose > maltose > sucrose. The activation parameters were evaluated and lend further support to the proposed mechanism.     

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.     

Kinetics and mechanism of sulfite oxidation by permanganate in basic medium

The kinetics of the permanganate-sulfite redox reaction has been studied in the alkaline medium using a stopped-flow technique. In the pH range 10 to 12 the reaction was found to obey the rate expression: ?½d[MnO₄^?]/dt = (k₁ + k₂[OH^?]) [MnO₄^?] [SO₃^2?]. Mechanisms for the two paths involving the formation of a (O₃MnOSO₃)^3? complex prior to the rate-determining step are consistent with the data. © John Wiley & Sons, Inc.     

Kinetics of oxidation of ethanol by potassium permanganate in perchloric acid medium

The oxidation of ethanol by permanganate has been found to obey the rate law v=k[MeCHO][MnO ₄ ^– ][H⁺]. The results are compared with those found for chromium (VI) oxidation of the same substrate.

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V=k[MeCHO][MnO ₄ ^– ][H⁺]. , (VI).

     

Oxidation of trivalent cerium with potassium permanganate in alkaline solutions

Summary Oxidation of trivalent cerium with KMnO₄ in alkaline carbonate mixture is not possible owing to the instability of the solution and to the sluggishness of the reaction. Reduction of KMnO₄ with Ce³⁺ solution fails to give quantitative results in absence of telluric acid. Good results are obtained in presence of telluric acid provided that the alkalinity of the reaction medium is not less than 1 N, in order to overcome the effect of acid present in the cerous solution.A method depending upon the oxidation of Ce³⁺ solution with KMnO₄ followed by back titrating excess KMnO₄ with monovalent thallium gives accurate results.     

Kinetics and mechanism of the oxidation of acetylacetone by permanganate ion

The kinetics and mechanism of permanganate ion oxidation of acetylacetone (Acac) was studied in acidic and alkaline media. The rate constants for keto, enol, and enolate anions were determined and discussed. Delocalization of the π‐electrons of the double bond by conjugation results in a slower oxidation rate of enol than can be usually observed for unsaturated compounds. In the case of the keto form, the acid‐catalyzed nucleophilic attack of permanganate ion occurs on the carbonyl‐C atom. For enolate anion a mechanism with basis‐catalyzed electron abstraction is suggested. © 2006 Wiley Periodicals, Inc. Int J Chem Kinet 38: 444–450, 2006     

Titrimetric microdetermination of certain sulphur-containing organic compounds by oxidation with alkaline potassium permanganate

A titrimetric procedure is described for the microdetermination of some mercaptans and sulphur-containing amino-acids by oxidation with alkaline potassium permanganate at room temperature in presence of barium ions. The procedure can be applied to 0.002-0.025M solutions with an average deviation of 0.1-0.5%. The effect of variation in the amount of alkali and barium chloride and in the reaction period, on the stoichiometry of the oxidation reactions, has also been studied.     

Kinetics and mechanism of the oxidation of substituted benzylamines by cetyltrimethylammonium permanganate

Oxidation of meta- and para-substituted benzylamines by cetyltrimethylammonium permanganate (CTAP) to the corresponding aldimines is first order with respect to both the amine and CTAP. Oxidation of deuteriated benzylamine (PhCD₂NH₂) exhibited the presence of a substantial kinetic isotope effect (k _H /k _D = 5.60 at 293 K). This confirmed the cleavage of an α-C-H bond in the rate-determining step. Correlation analyses of the rates of oxidation of 19 monosubstituted benzylamines were performed with various single and multiparametric equations. The rates of the oxidation showed excellent correlations in terms of Yukawa—Tsuno and Brown’s equations. The polar reaction constants are negative. The oxidation exhibited an extensive cross-conjugation, in the transition state, between the electron-donating substituents and the reaction centre. A mechanism involving a hydride-ion transfer from the amine to CTAP in the rate-determining step has been proposed.     

Kinetics and mechanism of the permanganate oxidation of trans-crotonic acid

The kinetics and intermediates of the permanganate oxidation of trans-crotonic acid have been investigated in the pH range of 0.5–5.0 using the stoppedflow technique. The formation of manganese(III) as a short-lived intermediate has been established. The reaction is first order with respect to both MnO ₄ ^– and crotonic acid (crotonate). The resolved rate constants at 25°C are 730 and 410 M^–1 sec^–1 for the acid and the anion, respectively. The reaction mechanism is discussed.

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pH=0,5–5,0, . (III) . MnO ₄ ^– , (). 25°C 730 410 M^{–1 –1} , . .

     

Kinetics and mechanism of the oxidation of substituted mandelic acids by acid permanganate

The oxidation of mandelic acid and nine monosubstituted mandelic acids by acid permanganate, in the presence of fluoride ions, have been studied. The reaction is of first order with respect to each the oxidant, the substrate and hydrogen ions. The kinetic isotope effect, k_H/k_D = 3·76 at 25°. The oxidation exhibits a reaction constant ?+= ?2·23 ± 0·07 at 25°. The oxidation does not induce polymerisation of acrylonitrile and does not show any solvent isotope effect. The activation enthalpies entropies are linearly related (r = 0·979). A mechanism involving transfer of a hydride ion to the oxidant is proposed.     

Kinetics and mechanism of the oxidation of selenium(IV) by permanganate

Summary The oxidation of selenium(IV) by permanganate has been studied kinetically in acid, neutral and alkaline media. The reaction exhibits unit-order dependence on selenium(IV) and permanganate in all the three media. Manganese(VI) retards the reaction in alkaline medium. The rate-limiting step is the same in all the three media, but the stoichiometry is different, being 2:1 in alkaline medium, 2:3 in neutral medium and 2:5 in acid medium. Evidence has been obtained for a one electron-transfer in the rate-determining step.     

Kinetics and mechanism of oxidation of 1,2-butanediol by argentate(III) complex in alkaline medium

The kinetics of oxidation of 1,2-butanediol by dihydroxyditellutoargentate(III) (DDA) is studied spectrophotometrically. The reaction rate shows first order dependence in DDA and 1 < n_ap < 2 order in 1,2-butanediol. It is found that the pseudo-first order rate constant k _obs increases with the increase in concentration of OH^? and decreases with the increase in concentration of TeO₄ ^2?. There is a negative salt effect; no free radical is detected. In view of this, the dihydroxymonotelluratoargentate(III) species is assumed to be the active species. A plausible mechanism involving a two-electron transfer is proposed and the rate equations derived from mechanism explains all experimental results. The activation parameters along with the rate constants of the rate-determining step are calculated.     

Kinetics and mechanism of oxidation of leucine by chloramine-T in alkaline media

Alkaline media oxidation of leucine by chloramine-T has been investigated. A first order dependence in chloramine-T and leucine and a near inverse first order dependence in hydroxide ion has been observed. Ionic strength had negligible effect while the effect of methanol addition was slightly negative. The oxidation process has been shown to proceed via two paths, one involving p-toluenesulfochloramide as the main oxidising species and the other involving hypochlorite ion, each interacting in a slow step with a leucine molecule leading to formation of monochloroleucine acid, which subsequently interacts with another molecule of p-toluenesulfochloramide or hypochlorite ion resp., yielding products.     

Kinetics and mechanisms of the permanganate oxidation of L-valine in neutral aqueous solutions

The permanganate oxidation of L-valine has been studied by visible spectrophotometry in neutral aqueous solutions. Under these conditions, both the zwitterionic and anionic forms of the amino acid are oxidized, the reaction being autocatalyzed by soluble colloidal manganese dioxide. Kinetic data for both the uncatalyzed and autocatalytic reaction pathways have been obtained, and reaction sequences consistent with the experimental findings are proposed.     

Kinetics and mechanism of oxidation of secondary alcohols by potassium bromate

The oxidation by Br(V) of propan-2-ol follows the rate law (?d[Br(V)]/dt) = k₄ [alcohol][Br(V)][H⁺]². The initial reaction is complicated by the presence of the product bromide ion. The reaction is composed of two second order reactions—the first, a comparatively slow one and the second stage, a faster reaction which is mainly bromine oxidation. The pure bromate oxidation can be followed by the initial addition of mercuric acetate which prevents the accumulation of bromine in the system under these conditions. The reaction rate does not depend on the nature and structure of the alcohol. A mechanism involving a slow rate-determining formation of an alkyl-bromate ester followed by a fast decomposition to the products is in accord with the observed results.