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.     

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 formic acid for back-titration: Determination of lead and thallium

Pb⁺² (~37-0.6mg) and Tl⁺ (45-0.9 mg) can bc estimated by mixing with KmnO₄ in presence of Ba⁺² ions and I_NNaOH. The excess KmnO₄ is then titrated with formic acid.A mixture of Pb⁺² and Tl⁺ is oxidized simultaneously with KMn0₄ in 0.1N NaOH. Pb⁺² interferes also when precipitated as sulphate or tellurate. In presence of SO₄^-2 and telluric acid, thallium can be titrated only when its concentration is not less than 30 mg, below which lead seriously interferes. Tl⁺ can be accurately determined in the filtrate from the PbS0₄ precipitate.     

Oxidations with alkaline permanganate using monovalent thallium for the back-titration: Determination of iodate,iodide and ferrocyanide

Iodate, iodide, iodine and ferrocyanide can be estimated by oxidation with KmnO₄ in alkaline media; the excess is back-titrated with TI⁷. I^- and I₂ are oxidized to IO₄^- in the presence of Ba⁺² ions but only to IO₃^- in absence of such ions. The direct titration of IO₃^-, I^- with KmnO₄ proved valueless.Ferrocyanide is oxidized by KmnO₄ in alkaline solutions and MnO₂ is formed. In the presence of telluric acid and 0.025–0.1 N NaOH satisfactory results are obtained. Reduction of MnO₄^- with ferrocyanide gives MnO₄^-2 and the results are variable, depending on the rate of adding the ferrocyanide.     

Oxidations with alkaline permanganate using monovalent thallium for the back-titration: Estimation of trivalent arsenic

In absence of Ba⁺² ions arsenite reduces KMnO₄ in alkaline medium to MnO₂ without the appearance of an inflection at the manganate state. Reduction could be checked at the manganate in presence of 1N NaOH and Ba⁺² equal to 3 times that equivalent to MnO₄^-2 and arsenate, and when dilute arsenite solutions are applied viz.0.02N In absence of Ba⁺² ions the end-points are attained later than the MnO₂ stage except in 2–3N NaOH. In presence of telluric acid good results are obtained at all alkalinities whence reduction is checked at Mn⁺⁴.As⁺³ could be estimated also by mixing with KMnO₄ either in the presence of Ba⁺² ions + 1N NaOH or in absence of Ba⁺² ions + I.5–3N NaOH and back-titrating the excess oxidant with monovalent thallium.     

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.     

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.     

Quadrivalent uranium as a reducing agent in potentiometric titrations: Estimation of dichromate,permanganate, bromate and tellurate

Quadrivalent uranium can further be used for the estimation of K₂Cr₂O₇ KmnO₄ (in acid or alkali), H₂TeO₄ and KbrO₃ either alone or in conjunction with Fe⁺³, Ce⁺⁴ and V⁺⁵ The reaction proceeds rapidly in dilute acid solutions and especially when Fe⁺³ iron is used as a catalyst. Reduction of aqueous KmnO₄ gives MnO₂ which then dissolves in the acid of the reagent and undergoes reduction to Mn⁺². In acid solutions no MnO₂ separates. In alkaline medium (1.5–3N NaOH) KmnO₄ is reduced absolutely to MnO₂.     

Oxidations with alkaline permanganate using monovalent thallium for the back titration: Estimation of lead. selenium,tellurium and chromium

Monovalent-thallium can be successfully used for the back titration of KMnO₄ in the course of estimating Pb⁺², Sc⁺⁴, Te⁺⁴ and Cr⁺³.Reduction of KMnO4 with Tl+ in alkaline solution yields MnO₄^-2 which then passes to MnO₂. he end-points are attained late, but in presence of telluric acid the end-point at MnO₂ stage corresonds to the theoretical value. Reduction at the MnO₄^-2 stage can be checked in presence of Ba⁺² ns and good results obtained with 1–1.5N NaOH.     

Photometric and Gas-Chromatographic Determination of Hydrogen Peroxide and Peroxybutanoic Acid in Oxidized Butanoic Acid

Procedures were developed for determining hydrogen peroxide and peroxy acids mixed with peroxide compounds of other classes in the oxidation products of butanoic acid with atmospheric oxygen and hydrogen peroxide. Conditions were found for the selective decomposition of hydrogen peroxide with catalase in the presence of an excess of the carboxylic acid deactivating the enzyme. The errors introduced by the acylation of hydrogen peroxide with the carboxylic acid in the course of sample treatment with the enzyme were eliminated by adding diphenyl sulfide or dimethyl sulfoxide, which selectively reduced the peroxy acids. The concentrations of hydrogen peroxide and the peroxy acid were found from the difference between the total concentration of the peroxide compounds before and after treating a sample with catalase and a sulfur-containing reagent by the photometric method using a reagent containing Fe²⁺ ions and N, N-dimethyl-p-phenylenediamine. Peroxy acids were determined by GLC from the yields of the oxidation products of diphenyl sulfide with the peroxy acid (diphenyl sulfoxide and diphenyl sulfones).     

Oxidation with manganate solutions

Summary The reaction between Tl⁺ solutions and manganate is sluggish. In the titration of Tl⁺ with manganate solution the end points are always attained earlier than the theoretical. When the reaction is accelerated by NaCl and heating to 45–50° C the end points were found to be concordant with the theoretical values. Titration of manganate with Tl⁺ solutions gives accurate results in presence of telluric acid but not in its absence. It is also possible to determine Tl⁺ by oxidation with an excess of K₂MnO₄ using arsenite as a back titrant for excess oxidant.Part III: Issa, I. M., and M. G. E. Allam: Z. analyt. Chem. 175, 103 (1960).     

New water-soluble hydrogen donors for the enzymatic spectrophotometric determination of hydrogen peroxide

Eight N -alkyl-N-V-sulphopropylaniline derivatives have been synthesized and assessed as water-soluble hydrogen donors for the spectrophotometric determination of hydrogen peroxide in the presence of peroxidase. The sodium salts of N-ethyl-N-sulphopropylaniline (ALPS), N-ethyl-N-sulphopropyl-m-toluidine (TOPS) and N -ethyl-N-sulphopropyl-m-anisidine (ADPS) are recommended. They have excellent water solubilities, and the optimum pH range for oxidative condensation with 4-aminoantipyrine in the presence of hydrogen peroxide and peroxidase is 5.5–9.5. The absorbances of the resulting chromogens are 2–3 times higher than that achieved with phenol. The molar absorptivities of the chromogens with 4-aminoantipyrine are 41300 (ALPS, λ_max 561 nm), 37400 (TOPS, λ_max 550 nm) and 27900 (ADPS, λ_max 540 nm). Calibration graphs for the determination of hydrogen peroxide in the presence of a control serum are linear for 7–40 × 10^-6 mol H₂O₂ l^-1.     

Beneficial Effect of Acetic Acid on the Formation of FeIII(OOH) Species and on the Catalytic Activity of Bioinspired Nonheme FeII Complexes.

Three new amine/pyridine Fe^II complexes bearing pentadentate ligand with one, two or three electron enriched 4-methoxy-3,5-dimethylpyridine were used as catalysts for the oxidation of small organic molecules by hydrogen peroxide. The distribution of products formed suggests that these ligands are not enough electron donating to promote the O−O heterolytic cleavage of the oxidant in order to generate selective Fe^V(O) species. Using acetic acid in the reaction mixtures results in a significant increase of the efficiency of these catalytic systems. Our investigations show that the use of AcOH leads to the protonation/dissociation of a pyridyl moiety and the formation of (N₄)Fe^II(OAc)(OH) species. These complexes readily react with excess hydrogen peroxide to yield (N₄)Fe^III(OAc)(OOH) intermediates. These latter intermediates are proposed to evolve into (N₄)Fe^IV(OAc)(O), which are more efficient than the usual (N₄)Fe^IV(O) and (N₅)Fe^IV(O).     

Oxidation with manganate solutions

Summary Manganate solutions prepared by the reduction of permanganate with formic acid in 1 M NaOH are fairly stable in a concentration of 0.015 M in presence of 1 M NaOH. They can be titrated successfuly with arsenite in the presence of telluric acid but not in its absence owing to the sluggishness of the reaction. Titration of arsenite with manganate yields always lower results deviating by 0.77% from the theoretical values in presence of telluric acid and 0.1–0.2 M NaOH. Much earlier end points with errors amounting to – 17 or – 38% are obtained in the absence of telluric acid.This work was started during 1957. Since that time the reactions of manganate with arsenite, tellurite, bivalent manganese and hydrogen peroxide were studied in our laboratory. While this work was prepared for publication den Boef et al. published their first investigation in the same line in 1959.     

A study of the stability of pyrimidine series cytostatics,Ftorafur and 5-fluorouracil: The effect of oxidation on the stability of Ftorafur and 5-fluorouracil

The stability of 1% solutions of cytostatics Ftorafur and 5-fluorouracil was studied during oxidation with hydrogen peroxide in alkaline (0.1 N NaOH), acidic (0.1 N H₂SO₄), and weakly acidic (pH 5) solutions by thin-layer chromatography. The decrease in the cytostatic content was monitored spectrophotometrically in the uv region. The greatest decrease in the cytostatic content occurred in alkaline solutions, where the pyrimidine ring opened between N3 and C4 and between C6 and N1, with formation of urea.     

Diethylenetetra-ammonium sulphatocerate as volumetric reagent: Iodine monochloride method. Indirect determinations

In presence of 4N to N hydrochloric acid, diethylenetetra-ammnonium sulphatocerate was used as a volumetric reagent to determine indirectly potassium iodate, potassium metaperiodate, potassium dichromate, potassium bromate, ceric sulphate, hydrogen peroxide, lead dioxide and chloramine-B by the iodine monochloride method. An excess of potassium iodide added to each of the substances in the acid medium was, titrated back with a standard solution of diethylene-tetra-ammonium suphatocerate. Chloroform was used as an indicator. It was coloured violet owing to the liberation of iodine during the titralion and became very pale yellow at the end-point because of the formation of iodine monochloride.     

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.     

Selective gas-phase oxidation of pyridine derivatives with hydrogen peroxide

The interfering kinetics of the synchronous reactions of hydrogen peroxide decomposition and the oxidation of pyridine derivatives have been studied experimentally. The regions of the selective oxidation of the pyridine derivatives have been found, and the optimal conditions for the production of 4-vinylpyridine, 4-vinylpyridine N-monoxide, 2,2-dipyridyl, and pyridine have been determined. The most probable synchronization mechanism is suggested for hydrogen peroxide decomposition and the free-radical chain oxidation of pyridine derivatives. The HO ₂ ^· radical plays the key role in this mechanism. The activation energies are calculated for the elementary steps of 4-ethylpyridine dehydrogenation.     

Baeyer–Villiger oxidation of <Emphasis Type="Italic">N</Emphasis> <Superscript>1</Superscript>,<Emphasis Type="Italic">N</Emphasis> <Superscript>3</Superscript>,2-triaryl-6-hydroxy-6-methyl-4-oxocyclohexane-1,3-dicarboxamides

Baeyer–Villiger oxidation of N¹,N³,2-triaryl-6-hydroxy-6-methyl-4-oxocyclohexane-1,3-dicarboxamides with 30% hydrogen peroxide in acetic acid afforded 2-(4-aryl-3-carbamoyl-2-methyl-5-oxooxolan-2-yl)acetic acids.     

N,N-Ethylene-bridged flavinium salts derived from l-valinol: synthesis and catalytic activity in H2O2 oxidations

Three chiral N¹,N¹⁰-ethylene-bridged flavinium salts with a stereogenic centre derived from l-valinol are prepared and investigated as oxidation catalysts. These salts efficiently catalyse chemoselective H₂O₂ oxidation of sulfides to sulfoxides and the oxidation of 3-phenylcyclobutanone to the corresponding lactone at room temperature. The flavinium salts react with hydrogen peroxide to form flavin-10a-hydroperoxide, which is the agent responsible for oxidation of the substrate.