The kinetics of oxidation of 2,2′-azinobis(3-ethylbenzothiazole-6-sulfonate) (ABTS) to the radical cation, ABTS·+ by S2O82−, HSO5−, MnO4−, Cr2O72−, Ce(IV), and molecular Cl2, Br2, and I2 and further oxidation to the dication, ABTS2+ by the above oxidants except HSO5−, Br2, and I2 have been carried out by the stoppedflow spectrophotometric technique. The first-stage oxidation was followed by monitoring the absorption of ABTS·+ at 417 nm and the second-stage oxidation, by following the disappearance of ABTS·+ or the appearance of ABTS2+ at 513 nm. Both the reactions, formation and decay of ABTS·+ were found to obey a total second-order kinetics, first-order each with respect to [ABTS] or [ABTS·+] and [oxidant]. With I2, ABTS underwent reversible reaction, the stoichiometry of which being, I2+2ABTS\ightleftarrows2ABTS·++2I− with K=142.8, whereasBr_2generatedonlytheradicalcationandCl_2gaveadecomposedproductviaradicalcationanddicationintermediates.ABTS^2+formedinpresenceofexcessMnO_4^-,Cr_2O_7^2-,andCe(IV)decayedasinthecaseofCl_2reactionbutinpresenceofS_2O_8^2-thedicationwasstableformorethanthreedays.IntheabsenceofexcessS_2O_8^2-,ABTS^2+wentbacktoABTS^·+,possiblyviaoxidationofwater.TheradicalcationwasconvertedbacktotheparentcompoundABTSbyreducingagentssuchasdithioniteandsulfiteions.

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Excitation of Ru(bipy);'ion by visible radiation of wavelength A = 436 nm in aqueous medium in presence of inorganic peroxides, peroxomonosulfate (PMS), peroxodisulfate (PDS), and peroxodiphosphate (PDP) was found to generate Ru(bipy),3'. The kinetics of this photochemical oxidation of Ru(bipy);' by each peroxide was followed spectrophotometrically and found to obey a total second-order, first-order each in [Ru(bipy):+] and [peroxide]. In the absence of light, thermal reaction of PMS and PDS with Ru(bipy);+ occurred but only when a t 1.0 M [H'] and M [peroxide]. The reaction of PMS with the complex is found to be cyclic, ie., Ru(bipy);+ formed oxidizes PMS itself and such a reaction was not observed in the case of PDS and PDP. The effects of pH, [peroxide], and [Ru(bipy);'] on the visible light induced oxidation of Ru(bipy);' by these peroxides are investigated. The results are discussed with suitable reaction mechanisms.

The physical and chemical properties of groundwater in Eloor, an industrial region, have been investigated to evaluate the extent of pollution. The study area was divided into four zones and a total of 40 water samples from different locations were collected, analyzed and correlation analysis has been carried out among the measured parameters. A comparison of the observed parameters with the limits prescribed by BIS revealed that in some area pH values are lower than the prescribed limit. The concentration of the major cations and anions were found to be significant. Magnesium and chloride exceed the desirable limit in some areas but less than the upper limit prescribed by BIS. Significant linear relationship was observed between pH, electrical conductivity, alkalinity, hardness, Ca2+, Mg2+and chloride. The importance of these parameters in predicting the quality characteristics of groundwater is discussed.

The oxidation of benzidine by Ce(IV); the oxoanions MnO4− and Cr2O72−; peroxides, namely potassium peroxomonosulfate (KHSO5), peroxodisulfate (S2O82−) and H2O2; and halogens viz., Cl2, Br2, and I2, to the benzidine mono radical cation (benzidine•+) and further oxidation to the benzidine diradical cation (+•benzidine•+) by the above-mentioned oxidants, except for Br2 and I2, were investigated by a stopped-flow technique. The kinetics of both reactions, the formation and decay of benzidine•+, were monitored by following the absorption of the radical cation at λmax = 603 nm. The reactions were found to follow a total second-order kinetics, first-order each with respect to [benzidine] or [benzidine•+] and the [oxidant]. The effects of the pH and temperature on the formation and decay of benzidine•+ were also investigated. The kinetic and transition-state parameters were evaluated with a suitable reaction mechanism. The radical cation benzidine•+ was converted back to the parent compound, benzidine, by such reducing agents as sulfite (SO32−), thiosulfate (S2O32−), dithionite (S2O42−), and disulfite (S2O52−). The rate constants for these reactions were also estimated. The experimentally determined rate constants for the oxidative electron-transfer reactions were correlated theoretically using Marcus theory; the observed and calculated rate constants show good agreement.