Bulletin of the Chemical Society of Japan
Online ISSN : 1348-0634
Print ISSN : 0009-2673
ISSN-L : 0009-2673
A Fast Kinetic Study of Formation and Decay of 2,2′-Azinobis(3-ethylbenzothiazole-6-sulfonate) Radical Cation in Aqueous Solution
Pichai MaruthamuthuLakshmanan VenkatasubramanianPeriasamy Dharmalingam
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1987 Volume 60 Issue 3 Pages 1113-1117

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Abstract

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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