V. R. S. Rao

Determination of the protonation constant of chloramine-B

The protonation constant of chloramine-B has been determined at pH < 3.3 by an ionexchange method. The value found is 61 +/- 5.

Stability characteristics of aqueous chloramine-T solutions

Aqueous chloramine-T solutions in strongly alkaline medium are quite stable even up to 60 degrees . In 0.2-2 M sulphuric or perchloric acid at 25-30 degrees , there is no loss in titre, but in hydrochloric acid solutions > 0-5M, there is a loss in titre which increases with increase in hydrochloric acid concentration. This is ascribed to oxidation of chloride to chlorine. In the pH range 2.65-5.65 there is a small but reproducible loss in oxidative titre which is maximal at pH 4.7. This is ascribed to side-reactions occurring during partial disproportionation of monochloramine-T to dichloramine-T and p-toluenesulphonamide.

The gamma-ray induced chemisorption of oxygen on perovskite type catalysts: Determination by reduction with hydrazine sulphate/hydroxylamine hydrochloride

Chemisorbed oxygen can be determined quantitatively by the measurement of gaseous N2/N2O liberated by treatment with hydrazine sulphate/hydroxylamine hydrochloride. The amount of chemisorbed oxygen depends on the degree of dispersion during irradiation and also the γ-dose. The chemisorption is enhanced in the presence of moisture. The partial reduction of the transition metal ion favours the formation of chemisorbed oxygen.

Oxidimetric determination of triphenylphosphine.

A method for the determination of triphenylphosphine based on its oxidation to phosphine oxide by iodine or chloramine-T in acid medium in presence of benzene or carbon tetrachloride is described. The oxidation is completed within 2 min and the analytical values are accurate to within 0.5%. The method is applicable to determination of triphenylphosphine in its metal complexes.

Preparation of radioactive chloramine-B by isotopic exchange with radioactive chlorine

The exchange between chloramine-B and radioactive chlorine has been carried out in various media. The exchange is slow in strong acid and very weak acid media. Its maximum is at pH 3.3. There is no exchange in alkaline media. Optimum conditions for the preparation of radiochloramine-B with high specific activity are reported.

Iron(II)-chloramine-T reaction.

When a large excess of the oxidant is used in the iron(II)-chloramine-T reaction at pH 2.56-5.6 the amount of oxidant consumed is well above the stoichiometric amount required to oxidize iron(II) to iron(III). This has been attributed to the formation and subsequent behaviour of free radicals during the reaction. The formation of free radicals has been experimentally demonstrated. They apparently dimerize to give products of the type R-NCl-NCl-R (R = CH(3)C(6)H(4)SO(2)), which are further oxidized by chloramine-T. The dimerized species liberate iodine very slowly from acidified potassium iodide. This explanation satisfactorily accounts for the observed extent and rate of destruction of excess of chloramine-T in presence of small amounts of Fe(II) or bromide at pH 2.65-4.70. The storage of chloramine-T in metal containers might cause extensive destruction of the oxidant by a similar free radical mechanism and should be avoided.

Physico-chemical and catalytic properties of gamma-irradiated lanthanum nickelate (LaNiO3)

Electronspin resonance (ESR) studies of γ-irradiated LaNiO3 revealed the formation of chemisorbed superoxide ion (O2−) and F centers (electrons trapped in anion vacancies). X-ray photoelectron spectroscopy (XPS) showed that the γ-irradiation of LaNiO3 in the presence of moisture leads to the reduction of the transition metal (Ni3+ to Ni2+) which in turn facilitates the formation of O2− and surface carbonate species (CO32−). A qualitative molecular orbital model has been proposed for the chemisorption of O2− on the reduced transition metal centers (Ni2+). The hydrated electron generated by the radiolysis of moisture reduces the transition metal. Gamma-irradiated LaNiO3 shows enhanced catalytic activity for the decomposition of hydrogen peroxide (H2O2) and the increase in catalytic activity is attributed to the reduced metal content. The formation of chemisorbed oxygen decreases the electrical conductivity by trapping the charge carriers.

XPS characterization of gamma-ray induced chemisorption of oxygen in lanthanum manganate (LaMnO3)

Catalysis of mixed oxide LaMnO3 was studied for the decomposition of hydrogen peroxide (H2O2). The catalyst was γ-irradiated in open petri dishes, vacuum, dry oxygen and moist oxygen. LaMnO3 irradiated in moist oxygen showed highest catalytic activity. X-ray photoelectron spectroscopic (XPS) studies were carried out to investigate the surface modifications occurred during γ-irradiaiton of LaMnO3. No significant change in the surface was noticed in LaMnO3 irradiated in vacuum and dry oxygen. However, LaMnO3 irradiated in moist oxygen and in open petri dishes showed the reduction of transition metal (MN3+ to Mn2+) which in turn leads to the formation of chemisorbed superoxide ions (O2−) and surface carbonate species (CO32−). The latter processes decreases the electrical conductivity by trapping the charge carriers. The hydrated electron generated by the radiolysis of moisture reduces the transition metal. A qualitative molecular orbital model has been proposed for the chemisorption of O2− on the reduced transition metal centers (Mn2+).

Application of radiochloramine-T for the determination of trace amounts of hydrogen sulphide

Hydrogen sulphide at trace level can be determined by radiorelease technique using radiochloramine-T. The minimum detection level is 0.25 ppm. Zinc acetate is used to fix H2S from air samples. CS2 does not interfere. Interference by SO2 can be eliminated by oxidizing it with H2O2.

Determination of carbon disulphide through xanthate by radiorelease method employing radiochloramine-T

Carbon disulphide can be determined at ppm level by converting it into xanthate and then oxidizing it by radiochloramine-T in acid medium. Interference of sulphide, sulphite and nitrite can be eliminated by extracting CS2 from the mixture into carbon tetrachloride and stripping it into aqueous medium as xanthate by the addition of alcoholic KOH to the organic layer.