Estimation of cyanide ion in metal salts and complexes by means of chloramine-T and dichloramine-T

A simple and accurate method for the estimation of cyanide in salts and complexes is based on oxidation with chloramine-T (in pH 4 buffer) or dichloramine-T (in presence of acetic anhydride). The oxidation involves a two-electron change. Halides interfere with the estimation of KCN, but the interference can be eliminated by precipitating and determining zinc cyanide. A method for estimating KCN and KCNS in mixtures is also described.     

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.     

Analysis of metal thiourea complexes by chloramine-T oxidation

Summary A rapid method is described for the analysis of metal thiourea complexes of Zn, Cd, Hg and Cu by adding excess of chloramine-T and determining the excess iodometrically. Colloidal suspensions of metal sulphides (Cu, Hg, Zn, Cd) have been found to undergo rapid oxidation to sulphate quantitatively in acid medium by chloramine-T.

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Zusammenfassung Thioharnstoffkomplexe von Zn, Cd, Hg und Cu lassen sich durch Zugabe von überschüssigem Chloramin-T und jodometrischer Titration des Überschusses analysieren. Kolloidale Suspensionen der entsprechenden Metallsulfide werden mit Chloramin-T in saurem Medium rasch und vollständig zu Sulfat oxydiert.

     

Kinetics and mechanism of oxidation of thiocarbohydrazide in the free state and in its metal complex and thiocarbohydrazone by chloramine-T and dichloramine-T

Kinetics of oxidation of thiocarbohydrazide (TCH) in the free state and as its metal complex, and as a hydrazone by chloramine-T (CAT) in aqueous HClO₄ medium, and by dichloramine-T (DCT) in 1:1 (v/v) water-methanol medium in the presence of HClO₄ have been studied. Rates of oxidation of TCH in the free state and in metal complex by CAT were determined. The rate law for the oxidation of TCH at high [H⁺ ] and for complex oxidations were identical to that for CAT oxidations. The conversion of TCH into its hydrazone changed the order in [H⁺] from a positive to a negative value, probably signalling the change of reaction site. The rate law for oxidation under these conditions was determined. Addition of the reduced product of the oxidants had no effect on the rate of oxidations. Variation in ionic strength of the medium had little positive effect, while decrease in dielectric constant of the medium decreased the rate in both the oxidations. Oxidation processes generally follow a Michaelis-Menten type of mechanism. Constants of the rate limiting steps have been calculated at different temperatures and these constants have been used to calculate the activation parameters from the Arrhenius plots. The proposed mechanisms are supported by investigations with HOC1 under identical reaction conditions. Metal complexation of the substrate decreased the reactivity, while conversion of TCH into its hydrazone changed the rate dependence on [H⁺].     

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.     

Oxidimetric determination of methionine and its metal complexes with chloramine-B and dichloramine-B

Simple, rapid, and reproducible methods for the determination of methionine (HMt) and its metal complexes, [NiMt]ClO₄₊ and Na[AgMt₂], in aqueous solutions have been developed, based on their oxidation with chloramine-B and dichloramine-B at room temperature. The direct titration, with a visual or potentiometric endpoint, involves a two-electron change corresponding to the formation of methionine sulfoxide. Several amino acids and common anions and cations do not interfere under these conditions. In the back-titration procedure methionine and its complexes are oxidized by excess CAB in 0.1 N NaOH medium with a four-electron change corresponding to the formation of methionine sulfone. The amino acid and its complexes are, however, oxidized to the respective nitrile, with excess DCB with an eight-electron change.     

Mechanism of oxidations in partially aqueous media: Kinetics of oxidation of thiosemicarbazide and thiosemicarbazone by chloramine-T and dichloramine-T in aqueous methanol

Kinetics of oxidation of thiosemicarbazide (TSC) and its hydrazone (Benzaldehyde thiosemicarbazone) by chloramine-T (CAT) and dichloramine-T (DCT) in aqueous methanol medium in the presence of perchloric acid has been studied. Oxidation of TSC by both the oxidants showed first order dependences in [oxidant], fractional order in [TSC] and nearly inverse first order in [H⁺]. The conversion of TSC into its benzaldehyde hydrazone changed the rate dependence in [CAT] from first to second order, while the dependence in [DCT] remained unchanged. The dependence in [TSC] changes from fractional order to zero order in both CAT and DCT oxidations. The rate followed inverse fractional order kinetics in [H⁺] in both the cases. Increase in ionic strength of the medium slightly decreased the rate, while the decrease in dielectric constant of the medium increased the rates of oxidations for both the oxidants. But the addition of reaction products, p-toluenesulphonamide and chloride had no effect on the rate. Oxidation of TSC with both the oxidants has been shown to follow Michaelis-Menten type mechanism. In hydrazone oxidations oxidants have been shown to disproportionate in slow steps to HOCl, which in turn attacks the substrate in fast steps to give the final products. [TSC] was varied at different temperatures and the constants of rate limiting steps were calculated at each temperature. Using the latter constants the activation parameters have been computed from the Arrhenius plots. The rate constants have been predicted from the rate law for the variation of [H⁺] at constant [TSC] and [oxidant]. The predicted values are in reasonable agreement with the experimental rate constants, providing additional support to the suggested mechanisms.     

Determination of thioacetamide by oxidation with chloramine-T

Chloramine-T oxidises thioacetamide quantitatively in an alkaline medium in the hot, converting the entire sulphur into sulphate. A back-titration method, making use of this oxidation reaction, has been suggested for the determination of thioacetamide.     

Estimation of xylenes with chloramine-T

The reaction between xylenes and chloramine-T has been found to proceed quantitatively over a wide range of experimental conditions. A back-titration procedure in which xylenes are reacted with excess of chloramine-T in 1M perchloric acid-0.03M sodium chloride medium has been developed. Inorganic ions other than chloride do not interfere. The method can be used for estimating xylenes in the presence of some other petrochemicals.     

Estimation of thiosemicarbazide with chloramine-T

A rapid and accurate method for the estimation of thiosemicarbazide in aqueous solution has been developed based on its oxidation with chloramine-T at room temperature and pH 4. The effect of such variables as pH, mode of addition of reagents and concentration of chloride ion on the extent of oxidation has been studied.     

Estimation of dimethylsulphoxide with chloramine-T

A rapid and accurate method for the estimation of dimethyl-sulphoxide has been developed based on its oxidation to dimethyl-sulphone at room temperature by chloramine-T at pH 4-4.5. The effect of variables such as the pH, the mode of addition of reagents and the concentration of chloride ion on the extent and nature of oxidation has been studied and optimal conditons for analytical determination of dimethylsulphoxide derived.     

Estimation of allyl alcohol by chloramine-T

A simple but rapid and accurate method for the estimation of allyl in aqueous solution has been developed, based on its oxidation with chloramine-T at room temperature, in 0.5-1.0M hydrochloric acid medium. The reaction involves a two-electron change. The effect of such variables such as pH of the medium, presence of foreign ions and perchloric or sulphuric acid on the rate of oxidation is discussed.     

Mechanism of the oxidation of cycloheptanone by chloramine-T

The oxidation kinetics of cycloheptanone by chloramine-T in alkaline media has been investigated. A mechanism involving the formation of an intermediate by the interaction between the enolic anion of cycloheptanone and chloramine-T in a slow step followed by its interaction with another molecule of chloramine-T in a fast step leading to products has been proposed. The scheme satisfactorily accords with the observed stoichiometry, negligible influence of ionic strength and a positive dielectric effect. Various rate parameters have been computed and 1.2-cycloheptanedione identified as the end product.With 2 Figures     

Mechanism of retardation of oxidation reactions by metal complexes

Russian Chemical Bulletin -     

Advances in value-added aromatics by oxidation of lignin with transition metal complexes

Transition Metal Chemistry - Lignin is the second most abundant component in biomass, considered as the most abundant and available renewable source of aromatics in Nature. The depolymerization of...