Iodine monochloride end point in the oxidation of thiocyanate by permanganate. Determination of cerium

Summary A new volumetric method for cerium determination based on the quantitative reduction of Ce(SO₄)₂ by excess potassium thiocyanate and titration of the excess with standard KMnO₄ to the ICl end point has been described.Sincere thanks of the authors are due to Professor S. S. Joshi for facilities and kind interest in the work. The award of a U. P. Scientific Research Committee Scholarship to one of us (M.K.J.) is also gratefully acknowledged.     

Salt effect in the oxidation of iodide by permanganate

The rate of the reaction between permanganate and iodide ions had been measured in several concentrated salt solutions. There is a salt effect, which is dependent on the hydration heat of the salt present in the reaction medium.

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Lewis acid-activated oxidation of alcohols by permanganate

The oxidation of alcohols by KMnO(4) is greatly accelerated by various Lewis acids. Notably the rate is increased by 4 orders of magnitude in the presence of Ca(2+). The mechanisms of the oxidation of CH(3)OH and PhCH(OH)CH(3) by MnO(4)(-) and BF(3)·MnO(4)(-) have also been studied computationally by the DFT method.     

Kinetics and mechanisms of the oxidation by permanganate of L-Phenylalanine

The oxidation of L-Phenylalanine by permanganate ion in aqueous phosphate buffers is autocatalized by the inorganic reaction product, which is stabilized in solution by adsorption of phosphate ions on its surface. This product is a soluble form of colloidal manganese dioxide. The rate of the noncatalytic reaction pathway is first-order in both the oxidizing and reducing agent. It is not affected by potassium chloride addition to the solution, but by phosphate addition. The rate increases with the pH of the medium. The autocatalytic pathway is first-order in both permanganate ion and colloidal manganese dioxide, (the permanganate ion according to the Langmuir isotherm). The autocatalytic rate increases with reductant concentration (follows the Langmuir adsorption isotherm). It is not affected by potassium chloride addition to the solution, whereas an increase in the phosphate concentration results in an increase in the rate with the same pH of the medium. Mechanisms consistent with the experimental data are proposed.     

Mechanism of the oxidation of organic sulphides by permanganate ion

The kinetics of the oxidation of number of aryl methyl, alkyl phenyl, dialkyl and diphenyl sulphides by permanganate ion to yield the sulphoxides, have been studied. The reaction is first order with respect to the sulphide and permanganate and is independent of hydrogen ion concentration. The reaction exhibited negative polar reaction constants and a small degree of steric hindrance. The lack of solvent isotope effect and the observed solvent effect ( m = 0.39 for McSPh) are explained by an electrophilic attack of permanganate-oxygen on the sulphide yielding a polar transition state. A moderate anchimeric assistance was observed in the oxidation ofo-C00Me ando-C00H substituted methyl phenyl sulphide. A mechanism involving a one-step electrophilic oxygen transfer from permanganate ion to the sulphide and a polar product-like transition state, has been proposed.     

Kinetic study of the oxidation of alcohols by cetyltrimethylammonium permanganate

Kinetics of the oxidation of 2-propanol, 1-butanol, 2-butanol and 1-pentanol by cetyltrimethylammonium permangenate oxidant have been investigated. The reactions are autocatalytic, colloidal manganese dioxide as one of the reaction products has been identified as the auto-catalyst.

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A kinetic study of the permanganate oxidation of triethylamine. Catalysis by soluble colloids

The kinetics of the reaction between permanganate ion and triethylamine in aqueous phosphate buffers (pH 6–8) has been studied. The reaction is autocatalytic, a soluble form of colloidal manganese dioxide temporarily stabilized in solution by adsorption of phosphate ions on its surface having been identified as the autocatalyst. The reaction is also catalyzed by gum arabic. Mechanisms in agreement with the kinetic data are proposed for the reaction pathways taking place in the bulk solution (for both triethylamine and triethylammonium ion as reductants) and on both the gum arabic and manganese dioxide colloidal particles.     

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.     

Determination of thiocyanate by potassium bromate

Summary Estimation of thiocyanate, based on its titration with standard KBrO₃ solution in presence of 1.5–3.0 N hydrochloric acid, is described. The end point is determined either potentiometrically or with methyl orange as indicator.Sincere thanks of the author are due to Professor S. S. Joshi for research facilities.     

The determination of organic substances by the oxidation with permanganate: XVIII. The oxidation of malonic acid

The oxidation of malonic acid with permanganate was studied under various acidity conditions. Analytical procedures, based on oxidation with excess reagent in a sodium carbonate medium and titration of the oxalate or manganese dioxide formed or of unconsumed permanganate, are proposed. On the basis of successive oxidation in sodium carbonate and sulfuric acid media, a titration determination, involving complete oxidation of malonic acid to carbon dioxide and water, was developed.     

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     

Mechanism and kinetics of hypophosphite oxidation by permanganate ion

The kinetics of the permanganate‐hypophosphite redox reaction has been studied over a wide range of pH by using a stopped‐flow technique. It has been found that the reaction leads to the formation of phosphite and orthophosphate, and that the molar ratio of the final products depends on pH. The proposed mechanism of the process was based on the assumption that the first step in the oxidation of hypophosphite is a fast reversible reaction in which an intermediate complex (O₃MnOH₂PO₂)²⁻ is formed. The observed dependence of the reaction rate on pH was attributed to the influence of hydrogen and hydroxyl ions on the decomposition of this complex. The rate constants and the equilibrium constants of elementary reactions are given. © 1999 John Wiley & Sons, Inc. Int J Chem Kinet 31: 737–743, 1999     

Homogeneous permanganate oxidation in non-aqueous organic soution. A stable organomanganese intermediate in the oxidation of endo-dicyclopentadiene

The absorption spectrum of a stable organomanganese intermediate in the homogeneously catalyzed permanganate oxidation of endo-dicyclopentadiene in a non-aqueous system was directly determined. The formation and the decomposition of the intermediate were monitored by following the changes of absorbances.     

Kinetic study of the oxidation of L-phenylalanine by potassium permanganate in acid medium

The kinetics of permanganate oxidation of L-phenylalanine in acid medium at a constant ionic strength has been investigated spectrophotometrically. An autocatalytic reaction was observed being autocatalyzed by a soluble form of Mn(IV). The reaction appears to involve a parallel consecutive reaction process in which Mn(IV) is formed as an intermediate and Mn(II) as a reaction product. A tentative mechanism consistent with the kinetics is discussed. © 1995 John Wiley & Sons, Inc.     

顺序注射分光光度法测定硫氰酸盐

根据硫氰酸盐、K2S2O8和3,5-二溴-吡啶偶氮-二乙基氨基苯酚反应形成紫红色产物的现象,建立了顺序注射分光光度测定硫氰酸盐的新方法,其线性范围为0．70～24．39μg/mL、检出限为0．25μg／mL。已用于工业废水和饮用水中硫氰酸盐的测定,回收率为96．0％-100．8％。     

Determination of thiocyanate in human saliva and urine by ion chromatography.

A simple ion-chromatographic method has been developed for the determination of trace amounts of thiocyanate in human saliva and urine. Thiocyanate separation and detection were carried out on an ODS column coated with cetyldimethylamine and by an ultraviolet detector, respectively. Citrate solution (1 mmol l-1) was used as the mobile phase. Thiocyanate was clearly separated from many organic and inorganic anions found in saliva and urine samples. The analytical results obtained by the proposed method agreed with those of the Fe(3+)-thiocyanate spectrophotometric method. Thiocyanate concentrations in the saliva and urine of smokers were found to be significantly higher than those of non-smokers.