Kinetics and mechanism of formation and decay of 2,2′-azinobis-(3-ethylbenzothiazole-6-sulphonate) radical cation in aqueous solution by inorganic peroxides

✍ Scribed by Lakshmanan Venkatasubramanian; Pichai Maruthamuthu

• Publisher: John Wiley and Sons
• Year: 1989
• Tongue: English
• Weight: 930 KB
• Volume: 21
• Category: Article
• ISSN: 0538-8066
• DOI: 10.1002/kin.550210604

✦ Synopsis

The kinetics of oxidation of 2,2'-azinobis-(3-ethylbenzothiazole-6-sulphonate) (ABTS) by the inorganic peroxides, peroxomonosulphate, peroxodisulphate, peroxodiphosphate, and hydrogen peroxide were investigated in aqueous solution. The kinetics of formation of the radical cation, ABTS", on one-electron abstraction by these peroxides and the further reaction of ABTS" with higher concentrations of these peroxides at longer time scale were studied by following the growth and decay of the radical cation, ABTS" at 417 nm. The rate of formation of ABTS" was found to obey a total secondorder, first-order each in [ABTS] and [peroxide], except for H,O,, which reacted through Michaelis-Menten kinetics. All the peroxides investigated were found to react with ABTS"; however peroxodisulphate alone oxidized ABTS'-to the dication (ABTS--), the other peroxides reacted via ionic mechanism, probably forming sulphoxide and sul- phone as products. The kinetics of decay of the radical cation, ABTS", was also found to follow a total second-order, first-order each in [ABTS"] and [peroxidel, except peroxodiphosphate the reaction of which obeyed Michaelis-Menten kinetics. The effect of pH and temperature were also investigated in all the systems and the kinetic and thermodynamic parameters were evaluated and discussed with suitable reaction mechanisms.