Kinetics and mechanism of the uncatalyzed and Ag(I)-catalyzed oxidative decolorization of Sunset Yellow and Ponceau 4R with peroxydisulphate

The kinetics and mechanism of the oxidation of Sunset Yellow (E-110, C.I. 15985), SY, and Ponceau 4R (E-124, C.I. 16255), PR, monoazo dyes with peroxydisulphate have been investigated. The oxidation reaction of SY and PR was very slow and followed a zero-order kinetics for [dye] and a first-order kinetics for [S2O82−]. The reaction showed an activation energy of 102.3 kJ/mol and 96.2 kJ/mol for SY and PR, respectively. The rate of the Ag(I)-catalyzed oxidation reaction was higher with an activation energy of 46 kJ/mol and 45 kJ/mol for SY and PR, respectively. The activation parameters, ΔH#, ΔG≠ and ΔS≠ were also deduced. A reaction mechanism was proposed for the oxidation reaction of SY and PR in the absence and in the presence of Ag(I).