D. S. Mahadevappa

Bromamine-B as a new oxidimetric titrant.

A new oxidimetric titrant, bromamine-B (sodium salt of N-bromobenzenesulphonamide) is introduced for use in aqueous medium. Direct potentiometric and visual end-point titrations and back-titration procedures have been developed for the determination of typical reductants.

Estimation of glutathione with chloramine-T and dichloramine-T

A simple but accurate method for the estimation of glutathione in aqueous solution has been developed, based on its oxidation with chloramine-T and dichloramine-T at room temperature. The direct titration with a visual or potentiometric end-point involves a one-electron change, corresponding to the oxidation of the thiol group to disulphide. Most amino-acids do not interfere, but cysteine, methionine and thiourea are oxidized under these conditions. A back-titration procedure in which glutathione is oxidized by excess of chloramine-T with a 10-electron change at pH 5 has also been developed.

Oxidation of dimethylsulphoxide by sodium m-bromobenzene- sulphonamide: A kinetic and mechanistic study

Abstract The kinetics of oxidation of dimethylsulphoxide (DMSO) by sodium N-bromobenzenesulphonamide or bromamine-B (BAB) has been studied in HClO4, HCl and NaOH media, at 35°C, with OsO4 as a catalyst in the latter medium. In acid medium, the rate shows a first order dependence on [BAB] and second order in [H+], but Is Independent of substrate concentration. Alkali retards the reaction (Inverse first order) and the rate is independent of oxidant concentration, but shows fractional order in [DMSO] and depends on (0sO4]2. The solvent isotope effect was studied by using D2O. Activation parameters have also been determined. Mechanisms proposed and the derived rate laws are consistent with the observed kinetics.

Determination of thiocyanate with aromatic halosulphonamides in acid and alkaline media

Ten organic aromatic halosulphonamides, both mono and dihalo compounds, ranging from chlorosulphonamides to iodosulphonamides, have been prepared and characterized by their infrared and NMR spectra and successfully used for determining thiocyanate in its metal salts and complexes. The proposed procedures are simple, rapid and reproducible, with an error of about +/-0.8%. These procedures are also useful for computing the number of thiocyanate ligands present in the complexes. Comparison of the present results with those from the argentometric method shows excellent agreement. The oxidation involves an 8-electron change per thiocyanate ion with the chloro and bromosulphonamides and a 6-electron change with iodosulphonamides.

Dichloramine-B as redox titrant in non-aqueous or partially aqueous media.

Dichloramine-B is proposed as a redox titrant in glacial acetic acid medium. The general conditions for its use and the procedures for estimating hydrazine, ascorbic acid, ferrocyanide, hydroquinone, oxine, antimony(III) and thallium(I) potentiometrically and allyl, crotyl and cinnamyl alcohols by a back-titration procedure are described.

Oxidation of some aldopentoses by chloramine-B in alkaline medium : a kinetic and mechanistic study

The oxidation kinetics of d-xylose, d-ribose, and l-arabinose by chloramine-B (CAB) in alkaline medium at 35° obey the rate law, rate = [CAB][HO−l[Pentose]. Based on the results, a mechanism is suggested involving the anion of the β anomer of the pentose. The addition of reaction products, benzenesulphonamide and NaCl, had no effect on the rate of reaction whereas increase in the ionic strength and dielectric constant of the medium increased the rate. Proton-inventory studies were made in H2OD2O mixtures. The rate of oxidation of pentoses follows the order1: d-xylose >d-ribose >l-arabinose. Kinetic and thermodynamic parameters for the reaction were computed from the Arrhenius plots. The isokinetic temperature β = 416 K, which is much above the experimental temperature, suggests enthalpy-controlled reactions.

Kinetics and mechanism of oxidation of erythro-series pentoses and hexoses by N-chloro-p-toluenesulfonamide

The kinetics and mechanism of oxidation of D-glucose, D-mannose, D-fructose, D-arabinose, and D-ribose with chloramine-T in alkaline medium were studied. The rate law, rate = k [Chloramine-T] [Sugar] [HO-]2, was observed. The rate of the reaction was influenced by a change in ionic strength of the medium, and the dielectric effect was found to be negative. The latter enabled the computation of dAB, the size of the activated complex. The reaction rate was almost doubled in deuterium oxide. Activation energies were calculated from the Arrhenius plots. HPLC and GLC-MS analyses of the products indicated that the sugars were oxidized to a mixture of aldonic acids, consisting of arabinonic, ribonic, erythronic, and glyceric acids. Based on these data, a plausible mechanism involving the aldo-enolic anions of pentoses and keto-enolic anions of hexoses is suggested.

OSMIUM(VIII) CATALYZED KINETICS AND MECHANISM OF INDOLES OXIDATION WITH ARYL-N-HALOAMINES IN ALKALINE MEDIUM

The kinetics of oxidation of the title substrates by sodium N-haloarylsulfonamides (or ary-N-haloamines), chloramine-T (CAT), bromamine-T (BAT), chloramine-B (CAB), and bromamine-B (BAB), catalyzed by osmium(VIII) in alkaline medium has been studied at 30°C. The corresponding oxindoles and arylsulfonamides have been characterized as reaction products. The reaction rate shows a first-order dependence each on |indole|0 and |oxidant|0, a fractional-order on |Os(VIII)|, and an inverse first-order on |OH−|. Addition of arylsulfon-amide, chloride and bromide, and variation of ionic strength of the medium have no effect on the reaction rate. There is a negative effect of dielectric constant of the solvent. Activation parameters have been calculated from the Arrhenius and Eyring plots. Hammett correlation of substituent effects indicates an LFE relationship with ρ = −1.0, showing the formation of an electron deficient transition state. From enthalpy-entropy relationships and Exner correlations, the isokinetic temperatures (333 K and 326 K) have been determined for the reactions of CAT and BAT, respectively. Proton inventory studies in H2O-D2O mixtures have shown the involvement of a single exchangeable proton of OH− ion in the transition state. A mechanism consistent with the observed kinetics has been proposed.

Estimation of methionine and its metal complexes by oxidation with chloramine-T and dichloramine-T

A simple method for the estimation of methionine (HMt) in aqueous solution has been developed, based on its oxidation with chloramine-T and dichloramine-T at room temperature. The direct titration, with visual or potentiometric end-point involves a two-electron change, corresponding to the formation of methionine sulphoxide. Most amino-acids do not interfere, but cysteine, glutathione and thiourea are oxidized under these conditions. A back-titration procedure in which methionine is oxidized in 0.1M sodium hydroxide by excess of chloramine-T with a four-electron change corresponding to the formation of methionine sulphone has also been developed. Methionine is oxidized to the respective nitrile, however, with excess of dichloramine-T. The methods have also been employed in estimating methionine in two of its soluble complexes, [NiMt]ClO(4) and Na[AgMt(2)].

A direct method of estimating cyanide ion in metal salts and complexes by means of chloramine-T, dichloramine-T and lead tetra-acetate

A simple and rapid method of determining cyanide in metal salts and complexes with chloramine-T, dichloramine-T and lead tetra-acetate, in presence of KBr and acetic acid, has been developed.