S. B. Jonnalagadda

Studies on toluidine blue reaction with sulfite in aqueous solution and role of Cu(II) as promoter

The kinetic and mechanistic details of the reaction between toluidine blue and sulfite were studied spectrophotometrically by monitoring the depletion of toluidine blue at 633 nm. The reaction had first-order dependence on both the reactants, a stoichiometric ratio of 1:1 and a negative salt effect indicating the participation of TB+ and SO32− ions in the rate-limiting step. The reaction products were leuco base of toluidine blue and sulfate. The reaction was pH dependent and hence studied at its optimum pH 7.2. Cu(II) acted as promoter by facilitating the formation of a ternary complex with the reactants. The protonation and stability constants of the reactants were determined and used in validating the mechanism. The activation parameters for the reactions in absence and presence of Cu(II) were determined and compared with other systems.

KINETICS AND MECHANISM OF REACTION OF TOLUIDINE BLUE WITH ACIDIC BROMATE

The detailed kinetics of the reaction of toluidine blue {phenothiazine-5-ium, 3-amino-7(dimethylamino)-2-methyl chloride, tolonium chloride, TB+Cl−} with potassium bromate and with aqueous bromine reaction were studied. In most of the experiments, the kinetics were monitored by following the rate of consumption of TB+ at 590 nm with excess acid and bromate. The reaction exhibited complex kinetic behavior. Initial reaction was slow and after an induction time, the TB+ concentration decreased fast. It had first-order dependence on both TB+ and bromate, and second-order dependence on H+. Under excess bromate conditions, the stoichiometric ratio of TB+ to bromate was 1:1. Demethylated sulfoxides were found at the reaction products. Sharp increase in the overall potential synchronized with the increase in bromine levels and the fast depletion of [TB+]. The role of bromide ion and bromine in the reaction was established. A multi-step reaction mechanism is proposed consistent with the experimental results.

A kinetic study of the oxidation of indigo carmine with acidic bromate

The oxidation kinetics of indigo carmine (disodium 3,3′-dioxobi-indolin-2,2′-ylidene-5,5′-disulphonate) with potassium bromate have been studied in aqueous sulphuric acid, by monitoring the absorbance of indigo carmine (IC) at 610 nm. The reaction involves competitive and consecutive reaction steps—an initial slow step followed by a rapid one for depletion of IC. For the initial stages the reaction order is four- first-order with respect to IC and bromate ion and second order with H+ ion. For the fast reaction step the studies are limited to qualitative treatment due to the complex nature of the reaction. The rate of depletion of IC increased with time and with the increase in HOBr concentration. Hypobromous acid, the reaction intermediate, may possibly compete with bromate ion for IC to give an intermediate, which is further oxidised to yield the final product, isatin-5-monosulphonic acid. The stoicheiometric ratio of IC to bromate is 3:2. The dual role of bromine ion as an inhibitor and autocatalyst in the reaction mechanism is discussed. Computer simulations were performed using the proposed mechanism. The results of the computer simulations are similar to the experimental observations.

Kinetics and mechanism of the oxidation of aliphatic diamines by peroxodisulphate

The kinetics of the oxidation of two aliphatic diamines (1,2-diaminoethane and 1,3-diaminopropane) with potassium peroxodisulphate in aqueous medium were investigated under identical conditions. The rates of the uncatalysed reactions were not influenced by changing the ionic strength or by the presence of allyl acetate. An analysis of the dependence of the rates of oxidation shows that the reactions are second order, being first order in both diamine and peroxodisulphate ion. Activation parameters for uncatalysed reactions were reported. The catalytic effect of the cations Cu2+ and Ag+ on the rate of oxidation of diamines is compared. On the basis of kinetic studies and product analysis the rate laws and reaction mechanisms for both uncatalysed and silver-ion catalysed reactions are proposed.

A kinetic study of the oxidation of 2,4-dinitrophenylhydrazine with acidic bromate

The kinetics of the reaction of 2,4-dinitrophenylhydrazine with bromate ion in sulphuric acid solution have been studied by spectrophotometric techniques. In the fast initial step, 2,4-dinitrophenylhydrazine (dnph) is oxidised to the diazonium ion (dnp [graphic omitted]2). The reaction is of first-order with respect to dnph, bromate, and H+. The stoicheiometric ratio of dnph to bromate ion is 1 : 1. The intermediate diazonium ion gives the final products, including 1,3-dinitrobenzene, in a slow reaction.